move pdf generation code from command to separate package

README.md

@@ -1,80 +1,175 @@
 # opentimestamps
 
-Interact with calendar servers, create and verify OTS attestations.
+A fork of [github.com/nbd-wtf/opentimestamps](https://github.com/nbd-wtf/opentimestamps) that lets you interact with calendar servers, create and verify OTS attestations.
 
 # How to use
 
-Full documentation at https://pkg.go.dev/github.com/nbd-wtf/opentimestamps. See some commented pseudocode below (you probably should not try to run it as it is).
+Here's an example of how to use the library to create a timestamp, attempt to upgrade it periodically, and display information about it:
 
 ```go
 package main
 
-import "github.com/nbd-wtf/opentimestamps"
+import (
+	"context"
+	"crypto/sha256"
+	"fmt"
+	"os"
+	"time"
 
-func main () {
-    // create a timestamp at a specific calendar server
-    hash := sha256.Sum256([]byte{1,2,3,4,5,6})
-    seq, _ := opentimestamps.Stamp(context.Background(), "https://alice.btc.calendar.opentimestamps.org/", hash)
+	"git.intruders.space/public/opentimestamps"
+	"git.intruders.space/public/opentimestamps/ots"
+)
 
-    // you can just call UpgradeSequence() to get the upgraded sequence (or an error if not yet available)
-    upgradedSeq, err := opentimestamps.UpgradeSequence(context.Background(), seq, hash[:])
-    if err != nil {
-        fmt.Println("wait more")
-    }
+func main() {
+	// Read a file to timestamp
+	fileData, err := os.ReadFile("document.txt")
+	if err != nil {
+		fmt.Println("Error reading file:", err)
+		return
+	}
 
-    // a File is a struct that represents the content of an .ots file, which contains the initial digest and any number of sequences
-    file := File{
-        Digest: hash,
-        Sequences: []Sequence{seq},
-    }
+	// Calculate the digest
+	digest := sha256.Sum256(fileData)
+	fmt.Printf("File digest: %x\n", digest)
 
-    // it can be written to disk
-    os.WriteFile("file.ots", file.SerializeToFile(), 0644)
+	// Define calendar servers
+	calendars := []string{
+		"https://alice.btc.calendar.opentimestamps.org",
+		"https://bob.btc.calendar.opentimestamps.org",
+		"https://finney.calendar.eternitywall.com",
+	}
 
-    // or printed in human-readable format
-    fmt.Println(file.Human())
+	// Create a timestamp using each calendar
+	ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
+	defer cancel()
 
-    // sequences are always composed of a bunch of operation instructions -- these can be, for example, "append", "prepend", "sha256"
-    fmt.Println(seq[0].Operation.Name) // "append"
-    fmt.Println(seq[1].Operation.Name) // "sha256"
-    fmt.Println(seq[2].Operation.Name) // "prepend"
+	var sequences []ots.Sequence
+	for _, calendarURL := range calendars {
+		fmt.Printf("Submitting to %s...\n", calendarURL)
+		seq, err := opentimestamps.Stamp(ctx, calendarURL, digest)
+		if err != nil {
+			fmt.Printf("Failed to submit to %s: %v\n", calendarURL, err)
+			continue
+		}
+		fmt.Printf("Submission to %s successful\n", calendarURL)
+		sequences = append(sequences, seq)
+	}
 
-    // "prepend" and "append" are "binary", i.e. they take an argument
-    fmt.Println(hex.EncodeToString(seq[2].Argument)) // "c40fe258f9b828a0b5a7"
+	if len(sequences) == 0 {
+		fmt.Println("Failed to create any timestamps")
+		return
+	}
 
-    // all these instructions can be executed in order, starting from the initial hash
-    result := seq.Compute(hash) // this is the value we send to the calendar server in order to get the upgraded sequence
-    finalResult := upgradedSeq.Compute(hash) // this should be the merkle root of a bitcoin block if this sequence is upgraded
+	// Create the timestamp file
+	file := &ots.File{
+		Digest:    digest[:],
+		Sequences: sequences,
+	}
 
-    // each sequence always ends in an "attestation"
-    // it can be either a pending attestation, i.e. a reference to a calendar server from which we will upgrade this sequence later
-    fmt.Println(seq[len(seq)-1].Attestation.CalendarServerURL) // "https://alice.btc.calendar.opentimestamps.org/"
-    // or it can be a reference to a bitcoin block, the merkle root of which we will check against the result of Compute() for verifying
-    fmt.Println(upgradedSeq[len(upgradedSeq)-1].Attestation.BitcoinBlockHeight) // 810041
+	// Save the OTS file
+	otsData := file.SerializeToFile()
+	if err := os.WriteFile("document.txt.ots", otsData, 0644); err != nil {
+		fmt.Println("Failed to save OTS file:", err)
+		return
+	}
+	fmt.Println("Timestamp file created successfully")
 
-    // speaking of verifying, this is how we do it:
-    // first we need some source of bitcoin blocks,
-    var bitcoin opentimestamps.Bitcoin
-    if useLocallyRunningBitcoindNode {
-        // it can be either a locally running bitcoind node
-        bitcoin, _ = opentimestamps.NewBitcoindInterface(rpcclient.ConnConfig{
-            User:         "nakamoto",
-            Pass:         "mumbojumbo",
-            HTTPPostMode: true,
-        })
-    } else {
-        // or an esplora HTTP endpoint
-        bitcoin = opentimestamps.NewEsploraClient("https://blockstream.info/api")
-    }
+	// Display initial timestamp info
+	fmt.Println("\nInitial timestamp info:")
+	fmt.Println(file.Human(false))
 
-    // then we pass that to a sequence
-    if err := upgradedSeq.Verify(bitcoin, hash); err == nil {
-        fmt.Println("it works!")
-    }
+	// Attempt to upgrade the timestamp every 20 minutes
+	fmt.Println("\nWill check for upgrades every 20 minutes...")
+
+	maxAttempts := 12 // Try for about 4 hours (12 * 20 minutes)
+	for attempt := 0; attempt < maxAttempts; attempt++ {
+		if attempt > 0 {
+			fmt.Printf("\nWaiting 20 minutes before next upgrade attempt (%d/%d)...\n", attempt+1, maxAttempts)
+			time.Sleep(20 * time.Minute)
+		}
+
+		upgraded := false
+		pendingSequences := file.GetPendingSequences()
+		if len(pendingSequences) == 0 {
+			fmt.Println("No pending sequences to upgrade")
+			break
+		}
+
+		fmt.Printf("Attempting to upgrade %d pending sequences...\n", len(pendingSequences))
+
+		upgradeCtx, upgradeCancel := context.WithTimeout(context.Background(), 30*time.Second)
+		for _, seq := range pendingSequences {
+			att := seq.GetAttestation()
+			fmt.Printf("Trying to upgrade sequence from %s...\n", att.CalendarServerURL)
+
+			upgradedSeq, err := opentimestamps.UpgradeSequence(upgradeCtx, seq, digest[:])
+			if err != nil {
+				fmt.Printf("Failed to upgrade sequence from %s: %v\n", att.CalendarServerURL, err)
+				continue
+			}
+
+			// Replace the sequence in the file
+			for i, origSeq := range file.Sequences {
+				origAtt := origSeq.GetAttestation()
+				if origAtt.CalendarServerURL == att.CalendarServerURL {
+					file.Sequences[i] = upgradedSeq
+					upgraded = true
+
+					newAtt := upgradedSeq.GetAttestation()
+					if newAtt.BitcoinBlockHeight > 0 {
+						fmt.Printf("Sequence upgraded! Confirmed in Bitcoin block %d\n", newAtt.BitcoinBlockHeight)
+					} else {
+						fmt.Println("Sequence updated but still pending")
+					}
+					break
+				}
+			}
+		}
+		upgradeCancel()
+
+		if upgraded {
+			// Save the upgraded file
+			otsData = file.SerializeToFile()
+			if err := os.WriteFile("document.txt.ots", otsData, 0644); err != nil {
+				fmt.Println("Failed to save upgraded OTS file:", err)
+			} else {
+				fmt.Println("Upgraded timestamp file saved")
+			}
+		}
+
+		// If all sequences are confirmed, we're done
+		if len(file.GetPendingSequences()) == 0 {
+			fmt.Println("All sequences are now confirmed in the Bitcoin blockchain!")
+			break
+		}
+	}
+
+	// Final report
+	fmt.Println("\nFinal timestamp status:")
+
+	confirmedSeqs := file.GetBitcoinAttestedSequences()
+	pendingSeqs := file.GetPendingSequences()
+
+	fmt.Printf("Confirmed attestations: %d\n", len(confirmedSeqs))
+	for _, seq := range confirmedSeqs {
+		att := seq.GetAttestation()
+		fmt.Printf("- Confirmed in Bitcoin block %d\n", att.BitcoinBlockHeight)
+	}
+
+	fmt.Printf("Pending attestations: %d\n", len(pendingSeqs))
+	for _, seq := range pendingSeqs {
+		att := seq.GetAttestation()
+		fmt.Printf("- Still pending at %s\n", att.CalendarServerURL)
+	}
+
+	fmt.Println("\nDetailed timestamp info:")
+	fmt.Println(file.Human(true))
 }
 ```
 
-You can also take a look at [`ots`](https://github.com/fiatjaf/ots), a simple CLI to OpenTimestamps which is basically a wrapper over this library.
+This repository includes an `ots` command line tool which provides a convenient interface to the core library functionality. Run it without arguments to see usage information.
+
+You can also take a look at the original [`ots`](https://github.com/fiatjaf/ots) CLI which is another implementation based on the same concepts.
 
 # License
 

cmd/example/main.go

@@ -0,0 +1,158 @@
+package main
+
+import (
+	"context"
+	"crypto/sha256"
+	"fmt"
+	"os"
+	"time"
+
+	"git.intruders.space/public/opentimestamps"
+	"git.intruders.space/public/opentimestamps/ots"
+)
+
+func main() {
+	// Read a file to timestamp
+	fileData, err := os.ReadFile("document.txt")
+	if err != nil {
+		fmt.Println("Error reading file:", err)
+		return
+	}
+
+	// Calculate the digest
+	digest := sha256.Sum256(fileData)
+	fmt.Printf("File digest: %x\n", digest)
+
+	// Define calendar servers
+	calendars := []string{
+		"https://alice.btc.calendar.opentimestamps.org",
+		"https://bob.btc.calendar.opentimestamps.org",
+		"https://finney.calendar.eternitywall.com",
+	}
+
+	// Create a timestamp using each calendar
+	ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
+	defer cancel()
+
+	var sequences []ots.Sequence
+	for _, calendarURL := range calendars {
+		fmt.Printf("Submitting to %s...\n", calendarURL)
+		seq, err := opentimestamps.Stamp(ctx, calendarURL, digest)
+		if err != nil {
+			fmt.Printf("Failed to submit to %s: %v\n", calendarURL, err)
+			continue
+		}
+		fmt.Printf("Submission to %s successful\n", calendarURL)
+		sequences = append(sequences, seq)
+	}
+
+	if len(sequences) == 0 {
+		fmt.Println("Failed to create any timestamps")
+		return
+	}
+
+	// Create the timestamp file
+	file := &ots.File{
+		Digest:    digest[:],
+		Sequences: sequences,
+	}
+
+	// Save the OTS file
+	otsData := file.SerializeToFile()
+	if err := os.WriteFile("document.txt.ots", otsData, 0644); err != nil {
+		fmt.Println("Failed to save OTS file:", err)
+		return
+	}
+	fmt.Println("Timestamp file created successfully")
+
+	// Display initial timestamp info
+	fmt.Println("\nInitial timestamp info:")
+	fmt.Println(file.Human(false))
+
+	// Attempt to upgrade the timestamp every 20 minutes
+	fmt.Println("\nWill check for upgrades every 20 minutes...")
+
+	maxAttempts := 12 // Try for about 4 hours (12 * 20 minutes)
+	for attempt := 0; attempt < maxAttempts; attempt++ {
+		if attempt > 0 {
+			fmt.Printf("\nWaiting 20 minutes before next upgrade attempt (%d/%d)...\n", attempt+1, maxAttempts)
+			time.Sleep(20 * time.Minute)
+		}
+
+		upgraded := false
+		pendingSequences := file.GetPendingSequences()
+		if len(pendingSequences) == 0 {
+			fmt.Println("No pending sequences to upgrade")
+			break
+		}
+
+		fmt.Printf("Attempting to upgrade %d pending sequences...\n", len(pendingSequences))
+
+		upgradeCtx, upgradeCancel := context.WithTimeout(context.Background(), 30*time.Second)
+		for _, seq := range pendingSequences {
+			att := seq.GetAttestation()
+			fmt.Printf("Trying to upgrade sequence from %s...\n", att.CalendarServerURL)
+
+			upgradedSeq, err := opentimestamps.UpgradeSequence(upgradeCtx, seq, digest[:])
+			if err != nil {
+				fmt.Printf("Failed to upgrade sequence from %s: %v\n", att.CalendarServerURL, err)
+				continue
+			}
+
+			// Replace the sequence in the file
+			for i, origSeq := range file.Sequences {
+				origAtt := origSeq.GetAttestation()
+				if origAtt.CalendarServerURL == att.CalendarServerURL {
+					file.Sequences[i] = upgradedSeq
+					upgraded = true
+
+					newAtt := upgradedSeq.GetAttestation()
+					if newAtt.BitcoinBlockHeight > 0 {
+						fmt.Printf("Sequence upgraded! Confirmed in Bitcoin block %d\n", newAtt.BitcoinBlockHeight)
+					} else {
+						fmt.Println("Sequence updated but still pending")
+					}
+					break
+				}
+			}
+		}
+		upgradeCancel()
+
+		if upgraded {
+			// Save the upgraded file
+			otsData = file.SerializeToFile()
+			if err := os.WriteFile("document.txt.ots", otsData, 0644); err != nil {
+				fmt.Println("Failed to save upgraded OTS file:", err)
+			} else {
+				fmt.Println("Upgraded timestamp file saved")
+			}
+		}
+
+		// If all sequences are confirmed, we're done
+		if len(file.GetPendingSequences()) == 0 {
+			fmt.Println("All sequences are now confirmed in the Bitcoin blockchain!")
+			break
+		}
+	}
+
+	// Final report
+	fmt.Println("\nFinal timestamp status:")
+
+	confirmedSeqs := file.GetBitcoinAttestedSequences()
+	pendingSeqs := file.GetPendingSequences()
+
+	fmt.Printf("Confirmed attestations: %d\n", len(confirmedSeqs))
+	for _, seq := range confirmedSeqs {
+		att := seq.GetAttestation()
+		fmt.Printf("- Confirmed in Bitcoin block %d\n", att.BitcoinBlockHeight)
+	}
+
+	fmt.Printf("Pending attestations: %d\n", len(pendingSeqs))
+	for _, seq := range pendingSeqs {
+		att := seq.GetAttestation()
+		fmt.Printf("- Still pending at %s\n", att.CalendarServerURL)
+	}
+
+	fmt.Println("\nDetailed timestamp info:")
+	fmt.Println(file.Human(true))
+}

cmd/ots/create.go

@@ -0,0 +1,130 @@
+package main
+
+import (
+	"context"
+	"crypto/sha256"
+	"fmt"
+	"log/slog"
+	"os"
+	"strings"
+	"time"
+
+	"git.intruders.space/public/opentimestamps"
+	"git.intruders.space/public/opentimestamps/ots"
+	"github.com/spf13/cobra"
+)
+
+// Default calendar servers
+var defaultCalendars = []string{
+	"https://alice.btc.calendar.opentimestamps.org",
+	"https://bob.btc.calendar.opentimestamps.org",
+	"https://finney.calendar.eternitywall.com",
+}
+
+var (
+	// Create command flags
+	createOutput       string
+	createCalendarsStr string
+	createTimeout      time.Duration
+)
+
+// createCmd represents the create command
+var createCmd = &cobra.Command{
+	Use:   "create [flags] <file>",
+	Short: "Create a timestamp for a file",
+	Long: `Create a timestamp for a file by submitting its digest to OpenTimestamps calendar servers.
+The resulting timestamp is saved to a .ots file, which can later be verified or upgraded.`,
+	Args: cobra.ExactArgs(1),
+	Run:  runCreateCmd,
+}
+
+func init() {
+	// Local flags for the create command
+	createCmd.Flags().StringVarP(&createOutput, "output", "o", "", "Output filename (default: input filename with .ots extension)")
+	createCmd.Flags().StringVar(&createCalendarsStr, "calendar", strings.Join(defaultCalendars, ","), "Comma-separated list of calendar server URLs")
+	createCmd.Flags().DurationVar(&createTimeout, "timeout", 30*time.Second, "Timeout for calendar server connections")
+}
+
+func runCreateCmd(cmd *cobra.Command, args []string) {
+	inputPath := args[0]
+
+	// Determine output file path
+	outputPath := createOutput
+	if outputPath == "" {
+		outputPath = inputPath + ".ots"
+	}
+
+	// Parse calendar servers
+	calendars := strings.Split(createCalendarsStr, ",")
+	if len(calendars) == 0 {
+		calendars = defaultCalendars
+	}
+
+	// Read the input file
+	fileData, err := os.ReadFile(inputPath)
+	if err != nil {
+		slog.Error("Failed to read input file", "file", inputPath, "error", err)
+		os.Exit(1)
+	}
+
+	// Compute the file digest
+	digest := sha256.Sum256(fileData)
+	slog.Info("Computed file digest", "digest", fmt.Sprintf("%x", digest))
+
+	// Create context with timeout
+	ctx, cancel := context.WithTimeout(context.Background(), createTimeout)
+	defer cancel()
+
+	// Create timestamps using all calendar servers
+	var sequences []ots.Sequence
+	var errors []string
+
+	for _, calendarURL := range calendars {
+		calendarURL = strings.TrimSpace(calendarURL)
+		if calendarURL == "" {
+			continue
+		}
+
+		slog.Info("Submitting to calendar", "url", calendarURL)
+		seq, err := opentimestamps.Stamp(ctx, calendarURL, digest)
+		if err != nil {
+			slog.Warn("Calendar submission failed", "url", calendarURL, "error", err)
+			errors = append(errors, fmt.Sprintf("%s: %v", calendarURL, err))
+			continue
+		}
+
+		sequences = append(sequences, seq)
+		slog.Info("Calendar submission successful", "url", calendarURL)
+	}
+
+	if len(sequences) == 0 {
+		slog.Error("All calendar submissions failed", "errors", errors)
+		os.Exit(1)
+	}
+
+	// Create the timestamp file
+	file := &ots.File{
+		Digest:    digest[:],
+		Sequences: sequences,
+	}
+
+	// Write the OTS file
+	otsData := file.SerializeToFile()
+	err = os.WriteFile(outputPath, otsData, 0644)
+	if err != nil {
+		slog.Error("Failed to write OTS file", "file", outputPath, "error", err)
+		os.Exit(1)
+	}
+
+	slog.Info("Timestamp file created successfully",
+		"file", outputPath,
+		"timestamps", len(sequences),
+		"size", len(otsData))
+
+	// Print human-readable representation
+	slog.Debug("Timestamp details", "info", file.Human(false))
+
+	slog.Info("Timestamp creation complete",
+		"status", "pending",
+		"note", "Use 'ots upgrade' to upgrade this timestamp when it's confirmed in the Bitcoin blockchain")
+}

cmd/ots/info.go

@@ -0,0 +1,108 @@
+package main
+
+import (
+	"encoding/hex"
+	"fmt"
+	"log/slog"
+	"os"
+	"strings"
+
+	"git.intruders.space/public/opentimestamps"
+	"git.intruders.space/public/opentimestamps/ots"
+	"github.com/spf13/cobra"
+)
+
+// infoCmd represents the info command
+var infoCmd = &cobra.Command{
+	Use:   "info [flags] <file.ots>",
+	Short: "Display information about a timestamp",
+	Long: `Display detailed information about a timestamp file in human-readable format.
+Shows the file digest and the sequence of operations and attestations.`,
+	Args: cobra.ExactArgs(1),
+	Run:  runInfoCmd,
+}
+
+func init() {
+	// No specific flags needed for info command
+}
+
+func runInfoCmd(cmd *cobra.Command, args []string) {
+	otsPath := args[0]
+
+	// Read and parse the OTS file
+	otsData, err := os.ReadFile(otsPath)
+	if err != nil {
+		slog.Error("Failed to read OTS file", "file", otsPath, "error", err)
+		os.Exit(1)
+	}
+
+	timestampFile, err := opentimestamps.ReadFromFile(otsData)
+	if err != nil {
+		slog.Error("Failed to parse OTS file", "file", otsPath, "error", err)
+		os.Exit(1)
+	}
+
+	// Print the timestamp information in the requested format
+	fmt.Printf("File sha256 hash: %s\n", hex.EncodeToString(timestampFile.Digest))
+	fmt.Println("Timestamp:")
+
+	// Format and print each sequence
+	for i, seq := range timestampFile.Sequences {
+		if i > 0 {
+			// Add a separator between sequences if needed
+			fmt.Println()
+		}
+		printSequenceInfo(seq, 0, timestampFile.Digest)
+	}
+}
+
+func printSequenceInfo(seq ots.Sequence, depth int, initialDigest []byte) {
+	prefix := strings.Repeat(" ", depth)
+
+	// Track the current result as we apply operations
+	current := initialDigest
+
+	// For the first level (depth 0), don't add the arrow
+	arrowPrefix := ""
+	if depth > 0 {
+		arrowPrefix = " -> "
+	}
+
+	for _, inst := range seq {
+		// Skip attestation for now, we'll handle it at the end
+		if inst.Attestation != nil {
+			continue
+		}
+
+		// Print operation
+		if inst.Operation != nil {
+			line := fmt.Sprintf("%s%s%s", prefix, arrowPrefix, inst.Operation.Name)
+			if inst.Operation.Binary {
+				line += fmt.Sprintf(" %s", hex.EncodeToString(inst.Argument))
+			}
+			fmt.Println(line)
+
+			// Update current result
+			current = inst.Operation.Apply(current, inst.Argument)
+
+			// Only show arrow prefix for the first line
+			arrowPrefix = ""
+		}
+	}
+
+	// Check if there's an attestation at the end
+	if len(seq) > 0 && seq[len(seq)-1].Attestation != nil {
+		att := seq[len(seq)-1].Attestation
+		var attLine string
+
+		if att.BitcoinBlockHeight > 0 {
+			attLine = fmt.Sprintf("verify BitcoinAttestation(block %d)", att.BitcoinBlockHeight)
+		} else if att.CalendarServerURL != "" {
+			attLine = fmt.Sprintf("verify PendingAttestation('%s')", att.CalendarServerURL)
+		}
+
+		if attLine != "" {
+			fmt.Printf("%s%s\n", prefix, attLine)
+		}
+	}
+}

cmd/ots/main.go

@@ -0,0 +1,13 @@
+package main
+
+import (
+	"fmt"
+	"os"
+)
+
+func main() {
+	if err := rootCmd.Execute(); err != nil {
+		fmt.Println(err)
+		os.Exit(1)
+	}
+}

cmd/ots/pdf.go

@@ -0,0 +1,99 @@
+package main
+
+import (
+	"log/slog"
+	"os"
+
+	"git.intruders.space/public/opentimestamps"
+	"git.intruders.space/public/opentimestamps/pdf"
+	"github.com/spf13/cobra"
+)
+
+var (
+	// PDF command flags
+	pdfOutput         string
+	pdfIncludeContent bool
+	pdfTitle          string
+	pdfComment        string
+	pdfEsploraURL     string
+)
+
+// pdfCmd represents the pdf command
+var pdfCmd = &cobra.Command{
+	Use:   "pdf [flags] <file> <file.ots>",
+	Short: "Generate a PDF certificate for a timestamp",
+	Long: `Generate a PDF certificate that explains how to verify the timestamp.
+The PDF includes all necessary information such as hashes, operations,
+and instructions for manual verification.`,
+	Args: cobra.ExactArgs(2),
+	Run:  runPdfCmd,
+}
+
+func init() {
+	// Local flags for the pdf command
+	pdfCmd.Flags().StringVarP(&pdfOutput, "output", "o", "", "Output PDF filename (default: original filename with .pdf extension)")
+	pdfCmd.Flags().BoolVar(&pdfIncludeContent, "include-content", false, "Include the original file content in the PDF (for text files only)")
+	pdfCmd.Flags().StringVar(&pdfTitle, "title", "OpenTimestamps Certificate", "Title for the PDF document")
+	pdfCmd.Flags().StringVar(&pdfComment, "comment", "", "Additional comment to include in the certificate")
+	pdfCmd.Flags().StringVar(&pdfEsploraURL, "esplora", "https://blockstream.info/api", "URL of Esplora API for fetching block information")
+}
+
+func runPdfCmd(cmd *cobra.Command, args []string) {
+	filePath := args[0]
+	otsPath := args[1]
+
+	// Determine output file path
+	outputPath := pdfOutput
+	if outputPath == "" {
+		outputPath = filePath + ".certificate.pdf"
+	}
+
+	// Read the original file
+	fileData, err := os.ReadFile(filePath)
+	if err != nil {
+		slog.Error("Failed to read file", "file", filePath, "error", err)
+		os.Exit(1)
+	}
+
+	// Read and parse the OTS file
+	otsData, err := os.ReadFile(otsPath)
+	if err != nil {
+		slog.Error("Failed to read OTS file", "file", otsPath, "error", err)
+		os.Exit(1)
+	}
+
+	timestampFile, err := opentimestamps.ReadFromFile(otsData)
+	if err != nil {
+		slog.Error("Failed to parse OTS file", "file", otsPath, "error", err)
+		os.Exit(1)
+	}
+
+	// Set up PDF options from command line flags
+	options := pdf.CertificateOptions{
+		Title:          pdfTitle,
+		Comment:        pdfComment,
+		IncludeContent: pdfIncludeContent,
+		EsploraURL:     pdfEsploraURL,
+	}
+
+	// Generate the PDF
+	pdfBuffer, err := pdf.GenerateCertificate(
+		filePath,
+		fileData,
+		timestampFile,
+		options,
+	)
+	if err != nil {
+		slog.Error("Failed to generate PDF", "error", err)
+		os.Exit(1)
+	}
+
+	// Write to file
+	err = pdf.WriteToFile(pdfBuffer, outputPath)
+	if err != nil {
+		slog.Error("Failed to write PDF to file", "file", outputPath, "error", err)
+		os.Exit(1)
+	}
+
+	slog.Info("PDF certificate generated successfully", "file", outputPath)
+}

cmd/ots/root.go

@@ -0,0 +1,65 @@
+package main
+
+import (
+	"log/slog"
+	"os"
+	"strings"
+
+	"github.com/spf13/cobra"
+)
+
+var (
+	// Global flags
+	jsonLog  bool
+	logLevel string
+)
+
+// rootCmd represents the base command when called without any subcommands
+var rootCmd = &cobra.Command{
+	Use:   "ots",
+	Short: "OpenTimestamps CLI tool",
+	Long: `A command-line interface for OpenTimestamps operations.
+It allows creating, verifying and upgrading timestamps for files.`,
+	PersistentPreRun: setupLogging,
+}
+
+func init() {
+	// Global flags for all commands
+	rootCmd.PersistentFlags().BoolVar(&jsonLog, "json", false, "Use JSON format for logging")
+	rootCmd.PersistentFlags().StringVar(&logLevel, "log-level", "info", "Log level: debug, info, warn, error")
+
+	// Add subcommands
+	rootCmd.AddCommand(createCmd)
+	rootCmd.AddCommand(verifyCmd)
+	rootCmd.AddCommand(upgradeCmd)
+	rootCmd.AddCommand(infoCmd)
+	rootCmd.AddCommand(pdfCmd)
+}
+
+// setupLogging configures the global logger based on the flags
+func setupLogging(cmd *cobra.Command, args []string) {
+	loggerOptions := slog.HandlerOptions{}
+
+	switch strings.ToLower(logLevel) {
+	case "debug":
+		loggerOptions.Level = slog.LevelDebug
+	case "info":
+		loggerOptions.Level = slog.LevelInfo
+	case "warn":
+		loggerOptions.Level = slog.LevelWarn
+	case "error":
+		loggerOptions.Level = slog.LevelError
+	default:
+		loggerOptions.Level = slog.LevelInfo
+	}
+
+	var logHandler slog.Handler
+	if jsonLog {
+		logHandler = slog.NewJSONHandler(os.Stdout, &loggerOptions)
+	} else {
+		logHandler = slog.NewTextHandler(os.Stdout, &loggerOptions)
+	}
+
+	logger := slog.New(logHandler)
+	slog.SetDefault(logger)
+}

cmd/ots/upgrade.go

@@ -0,0 +1,138 @@
+package main
+
+import (
+	"context"
+	"log/slog"
+	"os"
+	"time"
+
+	"git.intruders.space/public/opentimestamps"
+	"github.com/spf13/cobra"
+)
+
+var (
+	// Upgrade command flags
+	upgradeOutput  string
+	upgradeTimeout time.Duration
+	upgradeDryRun  bool
+)
+
+// upgradeCmd represents the upgrade command
+var upgradeCmd = &cobra.Command{
+	Use:   "upgrade [flags] <file.ots>",
+	Short: "Upgrade a timestamp",
+	Long: `Upgrade a timestamp by checking if pending attestations have been confirmed in the Bitcoin blockchain.
+If confirmed, the timestamp will be updated with the Bitcoin block information.`,
+	Args: cobra.ExactArgs(1),
+	Run:  runUpgradeCmd,
+}
+
+func init() {
+	// Local flags for the upgrade command
+	upgradeCmd.Flags().StringVarP(&upgradeOutput, "output", "o", "", "Output filename (default: overwrites the input file)")
+	upgradeCmd.Flags().DurationVar(&upgradeTimeout, "timeout", 30*time.Second, "Timeout for calendar server connections")
+	upgradeCmd.Flags().BoolVar(&upgradeDryRun, "dry-run", false, "Don't write output file, just check if upgrade is possible")
+}
+
+func runUpgradeCmd(cmd *cobra.Command, args []string) {
+	inputPath := args[0]
+
+	// Determine output file path
+	outputPath := upgradeOutput
+	if outputPath == "" {
+		outputPath = inputPath
+	}
+
+	// Read and parse the OTS file
+	otsData, err := os.ReadFile(inputPath)
+	if err != nil {
+		slog.Error("Failed to read OTS file", "file", inputPath, "error", err)
+		os.Exit(1)
+	}
+
+	timestampFile, err := opentimestamps.ReadFromFile(otsData)
+	if err != nil {
+		slog.Error("Failed to parse OTS file", "file", inputPath, "error", err)
+		os.Exit(1)
+	}
+
+	// Get pending sequences to upgrade
+	pendingSequences := timestampFile.GetPendingSequences()
+	if len(pendingSequences) == 0 {
+		slog.Info("No pending timestamps found, file is already fully upgraded", "file", inputPath)
+		os.Exit(0)
+	}
+
+	slog.Info("Found pending timestamps", "count", len(pendingSequences))
+
+	// Create context with timeout
+	ctx, cancel := context.WithTimeout(context.Background(), upgradeTimeout)
+	defer cancel()
+
+	// Try to upgrade each pending sequence
+	upgradedCount := 0
+	for i, seq := range pendingSequences {
+		att := seq.GetAttestation()
+		slog.Info("Attempting to upgrade timestamp",
+			"index", i+1,
+			"calendar", att.CalendarServerURL)
+
+		upgraded, err := opentimestamps.UpgradeSequence(ctx, seq, timestampFile.Digest)
+		if err != nil {
+			slog.Warn("Upgrade failed",
+				"calendar", att.CalendarServerURL,
+				"error", err)
+			continue
+		}
+
+		// Replace the pending sequence with the upgraded one
+		for j, origSeq := range timestampFile.Sequences {
+			if origSeq[len(origSeq)-1].Attestation != nil &&
+				origSeq[len(origSeq)-1].Attestation.CalendarServerURL == att.CalendarServerURL {
+				timestampFile.Sequences[j] = upgraded
+				break
+			}
+		}
+
+		upgradedCount++
+
+		newAtt := upgraded.GetAttestation()
+		if newAtt.BitcoinBlockHeight > 0 {
+			slog.Info("Timestamp upgraded successfully",
+				"calendar", att.CalendarServerURL,
+				"block", newAtt.BitcoinBlockHeight)
+		} else {
+			slog.Info("Timestamp replaced but still pending", "calendar", att.CalendarServerURL)
+		}
+	}
+
+	if upgradedCount == 0 {
+		slog.Warn("No timestamps could be upgraded at this time. Try again later.", "file", inputPath)
+		if !upgradeDryRun {
+			os.Exit(1)
+		}
+		os.Exit(0)
+	}
+
+	// In dry run mode, don't write the file
+	if upgradeDryRun {
+		slog.Info("Dry run completed", "upgraded", upgradedCount, "total", len(pendingSequences))
+		os.Exit(0)
+	}
+
+	// Write the updated OTS file
+	newOtsData := timestampFile.SerializeToFile()
+	err = os.WriteFile(outputPath, newOtsData, 0644)
+	if err != nil {
+		slog.Error("Failed to write updated OTS file", "file", outputPath, "error", err)
+		os.Exit(1)
+	}
+
+	slog.Info("Timestamp file upgraded successfully",
+		"file", outputPath,
+		"upgraded", upgradedCount,
+		"total", len(pendingSequences))
+
+	// Print human-readable representation
+	slog.Debug("Updated timestamp details", "info", timestampFile.Human(false))
+}

cmd/ots/verify.go

@@ -0,0 +1,170 @@
+package main
+
+import (
+	"crypto/sha256"
+	"fmt"
+	"log/slog"
+	"os"
+	"strings"
+	"time"
+
+	"git.intruders.space/public/opentimestamps"
+	"git.intruders.space/public/opentimestamps/verifyer"
+	"github.com/btcsuite/btcd/rpcclient"
+	"github.com/spf13/cobra"
+)
+
+var (
+	// Verify command flags
+	verifyEsploraURL   string
+	verifyBitcoindHost string
+	verifyBitcoindUser string
+	verifyBitcoindPass string
+	verifyTimeout      time.Duration
+)
+
+// verifyCmd represents the verify command
+var verifyCmd = &cobra.Command{
+	Use:   "verify [flags] <file> <file.ots>",
+	Short: "Verify a timestamp",
+	Long: `Verify a timestamp against the Bitcoin blockchain.
+It computes the file digest, checks it against the timestamp,
+and verifies the timestamp against Bitcoin using either Esplora API or bitcoind.`,
+	Args: cobra.ExactArgs(2),
+	Run:  runVerifyCmd,
+}
+
+func init() {
+	// Local flags for the verify command
+	verifyCmd.Flags().StringVar(&verifyEsploraURL, "esplora", "https://blockstream.info/api", "URL of Esplora API")
+	verifyCmd.Flags().StringVar(&verifyBitcoindHost, "bitcoind", "", "Host:port of bitcoind RPC (e.g. localhost:8332)")
+	verifyCmd.Flags().StringVar(&verifyBitcoindUser, "rpcuser", "", "Bitcoin RPC username")
+	verifyCmd.Flags().StringVar(&verifyBitcoindPass, "rpcpass", "", "Bitcoin RPC password")
+	verifyCmd.Flags().DurationVar(&verifyTimeout, "timeout", 30*time.Second, "Connection timeout")
+}
+
+func runVerifyCmd(cmd *cobra.Command, args []string) {
+	filePath := args[0]
+	otsPath := args[1]
+
+	// Read the original file
+	fileData, err := os.ReadFile(filePath)
+	if err != nil {
+		slog.Error("Failed to read file", "file", filePath, "error", err)
+		os.Exit(1)
+	}
+
+	// Compute the file digest
+	digest := sha256.Sum256(fileData)
+	slog.Debug("Computed file digest", "digest", digest)
+
+	// Read and parse the OTS file
+	otsData, err := os.ReadFile(otsPath)
+	if err != nil {
+		slog.Error("Failed to read OTS file", "file", otsPath, "error", err)
+		os.Exit(1)
+	}
+
+	timestampFile, err := opentimestamps.ReadFromFile(otsData)
+	if err != nil {
+		slog.Error("Failed to parse OTS file", "file", otsPath, "error", err)
+		os.Exit(1)
+	}
+
+	// Setup Bitcoin connection
+	var bitcoin verifyer.Bitcoin
+	if verifyBitcoindHost != "" {
+		if verifyBitcoindUser == "" || verifyBitcoindPass == "" {
+			slog.Error("Bitcoind RPC credentials required with --bitcoind")
+			os.Exit(1)
+		}
+
+		// Create bitcoind connection config
+		config := rpcclient.ConnConfig{
+			Host:         verifyBitcoindHost,
+			User:         verifyBitcoindUser,
+			Pass:         verifyBitcoindPass,
+			HTTPPostMode: true,
+			DisableTLS:   true,
+		}
+
+		btc, err := verifyer.NewBitcoindInterface(config)
+		if err != nil {
+			slog.Error("Failed to connect to bitcoind", "error", err)
+			os.Exit(1)
+		}
+		bitcoin = btc
+		slog.Info("Using bitcoind", "host", verifyBitcoindHost)
+	} else {
+		// Use Esplora API
+		bitcoin = verifyer.NewEsploraClient(verifyEsploraURL, verifyTimeout)
+		slog.Info("Using Esplora API", "url", verifyEsploraURL)
+	}
+
+	// Check if digests match
+	if string(digest[:]) != string(timestampFile.Digest) {
+		slog.Warn("File digest doesn't match timestamp digest",
+			"file_digest", digest,
+			"timestamp_digest", timestampFile.Digest)
+	}
+
+	// Get Bitcoin-attested sequences
+	bitcoinSequences := timestampFile.GetBitcoinAttestedSequences()
+	if len(bitcoinSequences) == 0 {
+		// If no Bitcoin sequences, check if there are pending sequences
+		pendingSequences := timestampFile.GetPendingSequences()
+		if len(pendingSequences) > 0 {
+			slog.Info("Timestamp is pending confirmation in the Bitcoin blockchain")
+			slog.Info("Use 'ots upgrade <file.ots>' to try upgrading it")
+
+			for _, seq := range pendingSequences {
+				att := seq.GetAttestation()
+				slog.Info("Pending at calendar", "url", att.CalendarServerURL)
+			}
+		} else {
+			slog.Error("No valid attestations found in this timestamp")
+		}
+		os.Exit(1)
+	}
+
+	// Verify each Bitcoin-attested sequence
+	verificationSuccess := false
+	for i, seq := range bitcoinSequences {
+		slog.Info("Verifying sequence", "index", i+1, "total", len(bitcoinSequences))
+
+		tx, err := seq.Verify(bitcoin, timestampFile.Digest)
+		if err != nil {
+			slog.Warn("Verification failed", "error", err)
+			continue
+		}
+
+		att := seq.GetAttestation()
+
+		// Get the block time
+		blockHash, err := bitcoin.GetBlockHash(int64(att.BitcoinBlockHeight))
+		blockTime := ""
+		if err == nil {
+			blockHeader, err := bitcoin.GetBlockHeader(blockHash)
+			if err == nil {
+				// Format the block time
+				blockTime = fmt.Sprintf(" (%s)", blockHeader.Timestamp.Format(time.RFC3339))
+			}
+		}
+
+		slog.Info("Verification successful",
+			"block_height", att.BitcoinBlockHeight,
+			"block_time", strings.TrimPrefix(blockTime, " "))
+
+		if tx != nil {
+			slog.Info("Bitcoin transaction", "txid", tx.TxHash().String())
+		}
+		verificationSuccess = true
+	}
+
+	if !verificationSuccess {
+		slog.Error("All verification attempts failed")
+		os.Exit(1)
+	}
+
+	slog.Info("Timestamp successfully verified")
+}

examples/bad-stamp.txt

@@ -1,2 +0,0 @@
-The timestamp on this file is well-formatted, but will fail Bitcoin block
-header validation.

examples/hello-world.txt

@@ -1 +0,0 @@
-Hello World!

examples/incomplete.txt

@@ -1 +0,0 @@
-The timestamp on this file is incomplete, and can be upgraded.

examples/known-and-unknown-notary.txt

@@ -1,2 +0,0 @@
-This file's timestamp has two attestations, one from a known notary, and one
-from an unknown notary.

examples/merkle1.txt

@@ -1,2 +0,0 @@
-This file is one of three different files that have been timestamped together
-with a single merkle tree. (1/3)

examples/merkle2.txt

@@ -1,2 +0,0 @@
-This file is one of three different files that have been timestamped together
-with a single merkle tree. (2/3)

examples/merkle3.txt

@@ -1,2 +0,0 @@
-This file is one of three different files that have been timestamped together
-with a single merkle tree. (3/3)

examples/two-calendars.txt

@@ -1 +0,0 @@
-This file has an (incomplete) timestamp with two different calendars.

examples/unknown-notary.txt

@@ -1 +0,0 @@
-This file's timestamp has a single attestation from an unknown notary.

fixtures/flatearthers-united.txt

@@ -0,0 +1 @@
+earth is flat

go.mod

@@ -1,21 +1,28 @@
-module github.com/nbd-wtf/opentimestamps
+module git.intruders.space/public/opentimestamps
 
-go 1.21
+go 1.24.2
 
 require (
-	github.com/btcsuite/btcd v0.23.4
-	github.com/btcsuite/btcd/chaincfg/chainhash v1.0.1
-	golang.org/x/crypto v0.13.0
+	github.com/btcsuite/btcd v0.24.2
+	github.com/btcsuite/btcd/chaincfg/chainhash v1.1.0
+	github.com/jung-kurt/gofpdf v1.16.2
+	github.com/spf13/cobra v1.9.1
+	github.com/stretchr/testify v1.10.0
+	golang.org/x/crypto v0.36.0
 )
 
 require (
-	github.com/btcsuite/btcd/btcec/v2 v2.1.3 // indirect
-	github.com/btcsuite/btcd/btcutil v1.1.0 // indirect
-	github.com/btcsuite/btclog v0.0.0-20170628155309-84c8d2346e9f // indirect
+	github.com/btcsuite/btcd/btcec/v2 v2.3.4 // indirect
+	github.com/btcsuite/btcd/btcutil v1.1.6 // indirect
+	github.com/btcsuite/btclog v1.0.0 // indirect
 	github.com/btcsuite/go-socks v0.0.0-20170105172521-4720035b7bfd // indirect
 	github.com/btcsuite/websocket v0.0.0-20150119174127-31079b680792 // indirect
-	github.com/decred/dcrd/crypto/blake256 v1.0.0 // indirect
-	github.com/decred/dcrd/dcrec/secp256k1/v4 v4.0.1 // indirect
-	github.com/stretchr/testify v1.8.4 // indirect
-	golang.org/x/sys v0.12.0 // indirect
+	github.com/davecgh/go-spew v1.1.1 // indirect
+	github.com/decred/dcrd/crypto/blake256 v1.1.0 // indirect
+	github.com/decred/dcrd/dcrec/secp256k1/v4 v4.4.0 // indirect
+	github.com/inconshreveable/mousetrap v1.1.0 // indirect
+	github.com/pmezard/go-difflib v1.0.0 // indirect
+	github.com/spf13/pflag v1.0.6 // indirect
+	golang.org/x/sys v0.32.0 // indirect
+	gopkg.in/yaml.v3 v3.0.1 // indirect
 )

go.sum

@@ -1,18 +1,26 @@
 github.com/aead/siphash v1.0.1/go.mod h1:Nywa3cDsYNNK3gaciGTWPwHt0wlpNV15vwmswBAUSII=
+github.com/boombuler/barcode v1.0.0/go.mod h1:paBWMcWSl3LHKBqUq+rly7CNSldXjb2rDl3JlRe0mD8=
 github.com/btcsuite/btcd v0.20.1-beta/go.mod h1:wVuoA8VJLEcwgqHBwHmzLRazpKxTv13Px/pDuV7OomQ=
 github.com/btcsuite/btcd v0.22.0-beta.0.20220111032746-97732e52810c/go.mod h1:tjmYdS6MLJ5/s0Fj4DbLgSbDHbEqLJrtnHecBFkdz5M=
-github.com/btcsuite/btcd v0.23.4 h1:IzV6qqkfwbItOS/sg/aDfPDsjPP8twrCOE2R93hxMlQ=
-github.com/btcsuite/btcd v0.23.4/go.mod h1:0QJIIN1wwIXF/3G/m87gIwGniDMDQqjVn4SZgnFpsYY=
+github.com/btcsuite/btcd v0.23.5-0.20231215221805-96c9fd8078fd/go.mod h1:nm3Bko6zh6bWP60UxwoT5LzdGJsQJaPo6HjduXq9p6A=
+github.com/btcsuite/btcd v0.24.2 h1:aLmxPguqxza+4ag8R1I2nnJjSu2iFn/kqtHTIImswcY=
+github.com/btcsuite/btcd v0.24.2/go.mod h1:5C8ChTkl5ejr3WHj8tkQSCmydiMEPB0ZhQhehpq7Dgg=
 github.com/btcsuite/btcd/btcec/v2 v2.1.0/go.mod h1:2VzYrv4Gm4apmbVVsSq5bqf1Ec8v56E48Vt0Y/umPgA=
-github.com/btcsuite/btcd/btcec/v2 v2.1.3 h1:xM/n3yIhHAhHy04z4i43C8p4ehixJZMsnrVJkgl+MTE=
 github.com/btcsuite/btcd/btcec/v2 v2.1.3/go.mod h1:ctjw4H1kknNJmRN4iP1R7bTQ+v3GJkZBd6mui8ZsAZE=
+github.com/btcsuite/btcd/btcec/v2 v2.3.4 h1:3EJjcN70HCu/mwqlUsGK8GcNVyLVxFDlWurTXGPFfiQ=
+github.com/btcsuite/btcd/btcec/v2 v2.3.4/go.mod h1:zYzJ8etWJQIv1Ogk7OzpWjowwOdXY1W/17j2MW85J04=
 github.com/btcsuite/btcd/btcutil v1.0.0/go.mod h1:Uoxwv0pqYWhD//tfTiipkxNfdhG9UrLwaeswfjfdF0A=
-github.com/btcsuite/btcd/btcutil v1.1.0 h1:MO4klnGY+EWJdoWF12Wkuf4AWDBPMpZNeN/jRLrklUU=
 github.com/btcsuite/btcd/btcutil v1.1.0/go.mod h1:5OapHB7A2hBBWLm48mmw4MOHNJCcUBTwmWH/0Jn8VHE=
-github.com/btcsuite/btcd/chaincfg/chainhash v1.0.1 h1:q0rUy8C/TYNBQS1+CGKw68tLOFYSNEs0TFnxxnS9+4U=
+github.com/btcsuite/btcd/btcutil v1.1.5/go.mod h1:PSZZ4UitpLBWzxGd5VGOrLnmOjtPP/a6HaFo12zMs00=
+github.com/btcsuite/btcd/btcutil v1.1.6 h1:zFL2+c3Lb9gEgqKNzowKUPQNb8jV7v5Oaodi/AYFd6c=
+github.com/btcsuite/btcd/btcutil v1.1.6/go.mod h1:9dFymx8HpuLqBnsPELrImQeTQfKBQqzqGbbV3jK55aE=
+github.com/btcsuite/btcd/chaincfg/chainhash v1.0.0/go.mod h1:7SFka0XMvUgj3hfZtydOrQY2mwhPclbT2snogU7SQQc=
 github.com/btcsuite/btcd/chaincfg/chainhash v1.0.1/go.mod h1:7SFka0XMvUgj3hfZtydOrQY2mwhPclbT2snogU7SQQc=
-github.com/btcsuite/btclog v0.0.0-20170628155309-84c8d2346e9f h1:bAs4lUbRJpnnkd9VhRV3jjAVU7DJVjMaK+IsvSeZvFo=
+github.com/btcsuite/btcd/chaincfg/chainhash v1.1.0 h1:59Kx4K6lzOW5w6nFlA0v5+lk/6sjybR934QNHSJZPTQ=
+github.com/btcsuite/btcd/chaincfg/chainhash v1.1.0/go.mod h1:7SFka0XMvUgj3hfZtydOrQY2mwhPclbT2snogU7SQQc=
 github.com/btcsuite/btclog v0.0.0-20170628155309-84c8d2346e9f/go.mod h1:TdznJufoqS23FtqVCzL0ZqgP5MqXbb4fg/WgDys70nA=
+github.com/btcsuite/btclog v1.0.0 h1:sEkpKJMmfGiyZjADwEIgB1NSwMyfdD1FB8v6+w1T0Ns=
+github.com/btcsuite/btclog v1.0.0/go.mod h1:w7xnGOhwT3lmrS4H3b/D1XAXxvh+tbhUm8xeHN2y3TQ=
 github.com/btcsuite/btcutil v0.0.0-20190425235716-9e5f4b9a998d/go.mod h1:+5NJ2+qvTyV9exUAL/rxXi3DcLg2Ts+ymUAY5y4NvMg=
 github.com/btcsuite/go-socks v0.0.0-20170105172521-4720035b7bfd h1:R/opQEbFEy9JGkIguV40SvRY1uliPX8ifOvi6ICsFCw=
 github.com/btcsuite/go-socks v0.0.0-20170105172521-4720035b7bfd/go.mod h1:HHNXQzUsZCxOoE+CPiyCTO6x34Zs86zZUiwtpXoGdtg=
@@ -23,13 +31,17 @@ github.com/btcsuite/snappy-go v1.0.0/go.mod h1:8woku9dyThutzjeg+3xrA5iCpBRH8XEEg
 github.com/btcsuite/websocket v0.0.0-20150119174127-31079b680792 h1:R8vQdOQdZ9Y3SkEwmHoWBmX1DNXhXZqlTpq6s4tyJGc=
 github.com/btcsuite/websocket v0.0.0-20150119174127-31079b680792/go.mod h1:ghJtEyQwv5/p4Mg4C0fgbePVuGr935/5ddU9Z3TmDRY=
 github.com/btcsuite/winsvc v1.0.0/go.mod h1:jsenWakMcC0zFBFurPLEAyrnc/teJEM1O46fmI40EZs=
+github.com/cpuguy83/go-md2man/v2 v2.0.6/go.mod h1:oOW0eioCTA6cOiMLiUPZOpcVxMig6NIQQ7OS05n1F4g=
 github.com/davecgh/go-spew v0.0.0-20171005155431-ecdeabc65495/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
-github.com/decred/dcrd/crypto/blake256 v1.0.0 h1:/8DMNYp9SGi5f0w7uCm6d6M4OU2rGFK09Y2A4Xv7EE0=
 github.com/decred/dcrd/crypto/blake256 v1.0.0/go.mod h1:sQl2p6Y26YV+ZOcSTP6thNdn47hh8kt6rqSlvmrXFAc=
-github.com/decred/dcrd/dcrec/secp256k1/v4 v4.0.1 h1:YLtO71vCjJRCBcrPMtQ9nqBsqpA1m5sE92cU+pd5Mcc=
+github.com/decred/dcrd/crypto/blake256 v1.1.0 h1:zPMNGQCm0g4QTY27fOCorQW7EryeQ/U0x++OzVrdms8=
+github.com/decred/dcrd/crypto/blake256 v1.1.0/go.mod h1:2OfgNZ5wDpcsFmHmCK5gZTPcCXqlm2ArzUIkw9czNJo=
 github.com/decred/dcrd/dcrec/secp256k1/v4 v4.0.1/go.mod h1:hyedUtir6IdtD/7lIxGeCxkaw7y45JueMRL4DIyJDKs=
+github.com/decred/dcrd/dcrec/secp256k1/v4 v4.4.0 h1:NMZiJj8QnKe1LgsbDayM4UoHwbvwDRwnI3hwNaAHRnc=
+github.com/decred/dcrd/dcrec/secp256k1/v4 v4.4.0/go.mod h1:ZXNYxsqcloTdSy/rNShjYzMhyjf0LaoftYK0p+A3h40=
 github.com/decred/dcrd/lru v1.0.0/go.mod h1:mxKOwFd7lFjN2GZYsiz/ecgqR6kkYAl+0pz0tEMk218=
 github.com/fsnotify/fsnotify v1.4.7/go.mod h1:jwhsz4b93w/PPRr/qN1Yymfu8t87LnFCMoQvtojpjFo=
 github.com/fsnotify/fsnotify v1.4.9/go.mod h1:znqG4EE+3YCdAaPaxE2ZRY/06pZUdp0tY4IgpuI1SZQ=
@@ -40,13 +52,21 @@ github.com/golang/protobuf v1.4.0-rc.2/go.mod h1:LlEzMj4AhA7rCAGe4KMBDvJI+AwstrU
 github.com/golang/protobuf v1.4.0-rc.4.0.20200313231945-b860323f09d0/go.mod h1:WU3c8KckQ9AFe+yFwt9sWVRKCVIyN9cPHBJSNnbL67w=
 github.com/golang/protobuf v1.4.0/go.mod h1:jodUvKwWbYaEsadDk5Fwe5c77LiNKVO9IDvqG2KuDX0=
 github.com/golang/protobuf v1.4.2/go.mod h1:oDoupMAO8OvCJWAcko0GGGIgR6R6ocIYbsSw735rRwI=
+github.com/golang/snappy v0.0.4/go.mod h1:/XxbfmMg8lxefKM7IXC3fBNl/7bRcc72aCRzEWrmP2Q=
 github.com/google/go-cmp v0.3.0/go.mod h1:8QqcDgzrUqlUb/G2PQTWiueGozuR1884gddMywk6iLU=
 github.com/google/go-cmp v0.3.1/go.mod h1:8QqcDgzrUqlUb/G2PQTWiueGozuR1884gddMywk6iLU=
 github.com/google/go-cmp v0.4.0/go.mod h1:v8dTdLbMG2kIc/vJvl+f65V22dbkXbowE6jgT/gNBxE=
+github.com/gorilla/websocket v1.5.0 h1:PPwGk2jz7EePpoHN/+ClbZu8SPxiqlu12wZP/3sWmnc=
+github.com/gorilla/websocket v1.5.0/go.mod h1:YR8l580nyteQvAITg2hZ9XVh4b55+EU/adAjf1fMHhE=
 github.com/hpcloud/tail v1.0.0/go.mod h1:ab1qPbhIpdTxEkNHXyeSf5vhxWSCs/tWer42PpOxQnU=
+github.com/inconshreveable/mousetrap v1.1.0 h1:wN+x4NVGpMsO7ErUn/mUI3vEoE6Jt13X2s0bqwp9tc8=
+github.com/inconshreveable/mousetrap v1.1.0/go.mod h1:vpF70FUmC8bwa3OWnCshd2FqLfsEA9PFc4w1p2J65bw=
 github.com/jessevdk/go-flags v0.0.0-20141203071132-1679536dcc89/go.mod h1:4FA24M0QyGHXBuZZK/XkWh8h0e1EYbRYJSGM75WSRxI=
 github.com/jessevdk/go-flags v1.4.0/go.mod h1:4FA24M0QyGHXBuZZK/XkWh8h0e1EYbRYJSGM75WSRxI=
 github.com/jrick/logrotate v1.0.0/go.mod h1:LNinyqDIJnpAur+b8yyulnQw/wDuN1+BYKlTRt3OuAQ=
+github.com/jung-kurt/gofpdf v1.0.0/go.mod h1:7Id9E/uU8ce6rXgefFLlgrJj/GYY22cpxn+r32jIOes=
+github.com/jung-kurt/gofpdf v1.16.2 h1:jgbatWHfRlPYiK85qgevsZTHviWXKwB1TTiKdz5PtRc=
+github.com/jung-kurt/gofpdf v1.16.2/go.mod h1:1hl7y57EsiPAkLbOwzpzqgx1A30nQCk/YmFV8S2vmK0=
 github.com/kkdai/bstream v0.0.0-20161212061736-f391b8402d23/go.mod h1:J+Gs4SYgM6CZQHDETBtE9HaSEkGmuNXF86RwHhHUvq4=
 github.com/nxadm/tail v1.4.4/go.mod h1:kenIhsEOeOJmVchQTgglprH7qJGnHDVpk1VPCcaMI8A=
 github.com/onsi/ginkgo v1.6.0/go.mod h1:lLunBs/Ym6LB5Z9jYTR76FiuTmxDTDusOGeTQH+WWjE=
@@ -57,15 +77,33 @@ github.com/onsi/gomega v1.4.1/go.mod h1:C1qb7wdrVGGVU+Z6iS04AVkA3Q65CEZX59MT0QO5
 github.com/onsi/gomega v1.4.3/go.mod h1:ex+gbHU/CVuBBDIJjb2X0qEXbFg53c61hWP/1CpauHY=
 github.com/onsi/gomega v1.7.1/go.mod h1:XdKZgCCFLUoM/7CFJVPcG8C1xQ1AJ0vpAezJrB7JYyY=
 github.com/onsi/gomega v1.10.1/go.mod h1:iN09h71vgCQne3DLsj+A5owkum+a2tYe+TOCB1ybHNo=
+github.com/phpdave11/gofpdi v1.0.7/go.mod h1:vBmVV0Do6hSBHC8uKUQ71JGW+ZGQq74llk/7bXwjDoI=
+github.com/pkg/errors v0.8.1/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINEl0=
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
-github.com/stretchr/testify v1.8.4 h1:CcVxjf3Q8PM0mHUKJCdn+eZZtm5yQwehR5yeSVQQcUk=
+github.com/russross/blackfriday/v2 v2.1.0/go.mod h1:+Rmxgy9KzJVeS9/2gXHxylqXiyQDYRxCVz55jmeOWTM=
+github.com/ruudk/golang-pdf417 v0.0.0-20181029194003-1af4ab5afa58/go.mod h1:6lfFZQK844Gfx8o5WFuvpxWRwnSoipWe/p622j1v06w=
+github.com/spf13/cobra v1.9.1 h1:CXSaggrXdbHK9CF+8ywj8Amf7PBRmPCOJugH954Nnlo=
+github.com/spf13/cobra v1.9.1/go.mod h1:nDyEzZ8ogv936Cinf6g1RU9MRY64Ir93oCnqb9wxYW0=
+github.com/spf13/pflag v1.0.6 h1:jFzHGLGAlb3ruxLB8MhbI6A8+AQX/2eW4qeyNZXNp2o=
+github.com/spf13/pflag v1.0.6/go.mod h1:McXfInJRrz4CZXVZOBLb0bTZqETkiAhM9Iw0y3An2Bg=
+github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
+github.com/stretchr/objx v0.4.0/go.mod h1:YvHI0jy2hoMjB+UWwv71VJQ9isScKT/TqJzVSSt89Yw=
+github.com/stretchr/objx v0.5.0/go.mod h1:Yh+to48EsGEfYuaHDzXPcE3xhTkx73EhmCGUpEOglKo=
+github.com/stretchr/testify v1.2.2/go.mod h1:a8OnRcib4nhh0OaRAV+Yts87kKdq0PP7pXfy6kDkUVs=
+github.com/stretchr/testify v1.7.0/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
+github.com/stretchr/testify v1.7.1/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
+github.com/stretchr/testify v1.8.0/go.mod h1:yNjHg4UonilssWZ8iaSj1OCr/vHnekPRkoO+kdMU+MU=
 github.com/stretchr/testify v1.8.4/go.mod h1:sz/lmYIOXD/1dqDmKjjqLyZ2RngseejIcXlSw2iwfAo=
+github.com/stretchr/testify v1.10.0 h1:Xv5erBjTwe/5IxqUQTdXv5kgmIvbHo3QQyRwhJsOfJA=
+github.com/stretchr/testify v1.10.0/go.mod h1:r2ic/lqez/lEtzL7wO/rwa5dbSLXVDPFyf8C91i36aY=
+github.com/syndtr/goleveldb v1.0.1-0.20210819022825-2ae1ddf74ef7/go.mod h1:q4W45IWZaF22tdD+VEXcAWRA037jwmWEB5VWYORlTpc=
 golang.org/x/crypto v0.0.0-20170930174604-9419663f5a44/go.mod h1:6SG95UA2DQfeDnfUPMdvaQW0Q7yPrPDi9nlGo2tz2b4=
 golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
 golang.org/x/crypto v0.0.0-20200622213623-75b288015ac9/go.mod h1:LzIPMQfyMNhhGPhUkYOs5KpL4U8rLKemX1yGLhDgUto=
-golang.org/x/crypto v0.13.0 h1:mvySKfSWJ+UKUii46M40LOvyWfN0s2U+46/jDd0e6Ck=
-golang.org/x/crypto v0.13.0/go.mod h1:y6Z2r+Rw4iayiXXAIxJIDAJ1zMW4yaTpebo8fPOliYc=
+golang.org/x/crypto v0.36.0 h1:AnAEvhDddvBdpY+uR+MyHmuZzzNqXSe/GvuDeob5L34=
+golang.org/x/crypto v0.36.0/go.mod h1:Y4J0ReaxCR1IMaabaSMugxJES1EpwhBHhv2bDHklZvc=
+golang.org/x/image v0.0.0-20190910094157-69e4b8554b2a/go.mod h1:FeLwcggjj3mMvU+oOTbSwawSJRM1uh48EjtB4UJZlP0=
 golang.org/x/net v0.0.0-20180719180050-a680a1efc54d/go.mod h1:mL1N/T3taQHkDXs73rZJwtUhF3w3ftmwwsq0BUmARs4=
 golang.org/x/net v0.0.0-20180906233101-161cd47e91fd/go.mod h1:mL1N/T3taQHkDXs73rZJwtUhF3w3ftmwwsq0BUmARs4=
 golang.org/x/net v0.0.0-20190404232315-eb5bcb51f2a3/go.mod h1:t9HGtf8HONx5eT2rtn7q6eTqICYqUVnKs3thJo3Qplg=
@@ -81,8 +119,8 @@ golang.org/x/sys v0.0.0-20191120155948-bd437916bb0e/go.mod h1:h1NjWce9XRLGQEsW7w
 golang.org/x/sys v0.0.0-20200323222414-85ca7c5b95cd/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20200519105757-fe76b779f299/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20200814200057-3d37ad5750ed/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
-golang.org/x/sys v0.12.0 h1:CM0HF96J0hcLAwsHPJZjfdNzs0gftsLfgKt57wWHJ0o=
-golang.org/x/sys v0.12.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+golang.org/x/sys v0.32.0 h1:s77OFDvIQeibCmezSnk/q6iAfkdiQaJi4VzroCFrN20=
+golang.org/x/sys v0.32.0/go.mod h1:BJP2sWEmIv4KK5OTEluFJCKSidICx8ciO85XgH3Ak8k=
 golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
 golang.org/x/text v0.3.2/go.mod h1:bEr9sfX3Q8Zfm5fL9x+3itogRgK3+ptLWKqgva+5dAk=
 golang.org/x/text v0.3.3/go.mod h1:5Zoc/QRtKVWzQhOtBMvqHzDpF6irO9z98xDceosuGiQ=
@@ -95,11 +133,13 @@ google.golang.org/protobuf v0.0.0-20200228230310-ab0ca4ff8a60/go.mod h1:cfTl7dwQ
 google.golang.org/protobuf v1.20.1-0.20200309200217-e05f789c0967/go.mod h1:A+miEFZTKqfCUM6K7xSMQL9OKL/b6hQv+e19PK+JZNE=
 google.golang.org/protobuf v1.21.0/go.mod h1:47Nbq4nVaFHyn7ilMalzfO3qCViNmqZ2kzikPIcrTAo=
 google.golang.org/protobuf v1.23.0/go.mod h1:EGpADcykh3NcUnDUJcl1+ZksZNG86OlYog2l/sGQquU=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
 gopkg.in/fsnotify.v1 v1.4.7/go.mod h1:Tz8NjZHkW78fSQdbUxIjBTcgA1z1m8ZHf0WmKUhAMys=
 gopkg.in/tomb.v1 v1.0.0-20141024135613-dd632973f1e7/go.mod h1:dt/ZhP58zS4L8KSrWDmTeBkI65Dw0HsyUHuEVlX15mw=
 gopkg.in/yaml.v2 v2.2.1/go.mod h1:hI93XBmqTisBFMUTm0b8Fm+jr3Dg1NNxqwp+5A1VGuI=
 gopkg.in/yaml.v2 v2.2.4/go.mod h1:hI93XBmqTisBFMUTm0b8Fm+jr3Dg1NNxqwp+5A1VGuI=
 gopkg.in/yaml.v2 v2.3.0/go.mod h1:hI93XBmqTisBFMUTm0b8Fm+jr3Dg1NNxqwp+5A1VGuI=
+gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
 gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
 gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=

ots/attestation.go

@@ -0,0 +1,28 @@
+package ots
+
+import "fmt"
+
+type Attestation struct {
+	BitcoinBlockHeight uint64
+	CalendarServerURL  string
+}
+
+func (att Attestation) Name() string {
+	if att.BitcoinBlockHeight != 0 {
+		return "bitcoin"
+	} else if att.CalendarServerURL != "" {
+		return "pending"
+	} else {
+		return "unknown/broken"
+	}
+}
+
+func (att Attestation) Human() string {
+	if att.BitcoinBlockHeight != 0 {
+		return fmt.Sprintf("bitcoin(%d)", att.BitcoinBlockHeight)
+	} else if att.CalendarServerURL != "" {
+		return fmt.Sprintf("pending(%s)", att.CalendarServerURL)
+	} else {
+		return "unknown/broken"
+	}
+}

ots/crypto.go

@@ -1,4 +1,4 @@
-package opentimestamps
+package ots
 
 import (
 	deprecated_ripemd160 "golang.org/x/crypto/ripemd160"

ots/file.go

@@ -1,59 +1,23 @@
-package opentimestamps
+package ots
 
 import (
-	"bytes"
-	"crypto/sha256"
 	"encoding/hex"
 	"fmt"
 	"slices"
 	"strings"
 
-	"github.com/btcsuite/btcd/wire"
+	"git.intruders.space/public/opentimestamps/varn"
 )
 
-/*
- * Header magic bytes
- * Designed to be give the user some information in a hexdump, while being identified as 'data' by the file utility.
- * \x00OpenTimestamps\x00\x00Proof\x00\xbf\x89\xe2\xe8\x84\xe8\x92\x94
- */
-var headerMagic = []byte{0x00, 0x4f, 0x70, 0x65, 0x6e, 0x54, 0x69, 0x6d, 0x65, 0x73, 0x74, 0x61, 0x6d, 0x70, 0x73, 0x00, 0x00, 0x50, 0x72, 0x6f, 0x6f, 0x66, 0x00, 0xbf, 0x89, 0xe2, 0xe8, 0x84, 0xe8, 0x92, 0x94}
-
+// Header magic bytes
+// Designed to be give the user some information in a hexdump, while being identified as 'data' by the file utility.
+// \x00OpenTimestamps\x00\x00Proof\x00\xbf\x89\xe2\xe8\x84\xe8\x92\x94
 var (
-	pendingMagic = []byte{0x83, 0xdf, 0xe3, 0x0d, 0x2e, 0xf9, 0x0c, 0x8e}
-	bitcoinMagic = []byte{0x05, 0x88, 0x96, 0x0d, 0x73, 0xd7, 0x19, 0x01}
+	HeaderMagic  = []byte{0x00, 0x4f, 0x70, 0x65, 0x6e, 0x54, 0x69, 0x6d, 0x65, 0x73, 0x74, 0x61, 0x6d, 0x70, 0x73, 0x00, 0x00, 0x50, 0x72, 0x6f, 0x6f, 0x66, 0x00, 0xbf, 0x89, 0xe2, 0xe8, 0x84, 0xe8, 0x92, 0x94}
+	PendingMagic = []byte{0x83, 0xdf, 0xe3, 0x0d, 0x2e, 0xf9, 0x0c, 0x8e}
+	BitcoinMagic = []byte{0x05, 0x88, 0x96, 0x0d, 0x73, 0xd7, 0x19, 0x01}
 )
 
-type Operation struct {
-	Name   string
-	Tag    byte
-	Binary bool // it's an operation that takes one argument, otherwise takes none
-	Apply  func(curr []byte, arg []byte) []byte
-}
-
-var tags = map[byte]*Operation{
-	0xf0: {"append", 0xf0, true, func(curr []byte, arg []byte) []byte {
-		result := make([]byte, len(curr)+len(arg))
-		copy(result[0:], curr)
-		copy(result[len(curr):], arg)
-		return result
-	}},
-	0xf1: {"prepend", 0xf1, true, func(curr []byte, arg []byte) []byte {
-		result := make([]byte, len(curr)+len(arg))
-		copy(result[0:], arg)
-		copy(result[len(arg):], curr)
-		return result
-	}},
-	0xf2: {"reverse", 0xf2, false, func(curr []byte, arg []byte) []byte { panic("reverse not implemented") }},
-	0xf3: {"hexlify", 0xf3, false, func(curr []byte, arg []byte) []byte { panic("hexlify not implemented") }},
-	0x02: {"sha1", 0x02, false, func(curr []byte, arg []byte) []byte { panic("sha1 not implemented") }},
-	0x03: {"ripemd160", 0x03, false, ripemd160},
-	0x08: {"sha256", 0x08, false, func(curr []byte, arg []byte) []byte {
-		v := sha256.Sum256(curr)
-		return v[:]
-	}},
-	0x67: {"keccak256", 0x67, false, func(curr []byte, arg []byte) []byte { panic("keccak256 not implemented") }},
-}
-
 // A File represents the parsed content of an .ots file: it has an initial digest and
 // a series of sequences of instructions. Each sequence must be evaluated separately, applying the operations
 // on top of each other, starting with the .Digest until they end on an attestation.
@@ -62,53 +26,6 @@ type File struct {
 	Sequences []Sequence
 }
 
-// a Instruction can be an operation like "append" or "prepend" (this will be the case when .Operation != nil)
-// or an attestation (when .Attestation != nil).
-// It will have a non-nil .Argument whenever the operation requires an argument.
-type Instruction struct {
-	*Operation
-	Argument []byte
-	*Attestation
-}
-
-type Sequence []Instruction
-
-func (seq Sequence) GetAttestation() Attestation {
-	if len(seq) == 0 {
-		return Attestation{}
-	}
-	att := seq[len(seq)-1]
-	if att.Attestation == nil {
-		return Attestation{}
-	}
-	return *att.Attestation
-}
-
-// Compute runs a sequence of operations on top of an initial digest and returns the result, which is often a
-// Bitcoin block merkle root. It also tries to identify the point in the sequence in which an actual Bitcoin
-// transaction is formed and parse that.
-func (seq Sequence) Compute(initial []byte) (merkleRoot []byte, bitcoinTx *wire.MsgTx) {
-	current := initial
-	for i, inst := range seq {
-		if inst.Operation == nil {
-			break
-		}
-
-		// the first time we do a double-sha256 that is likely a bitcoin transaction
-		if bitcoinTx == nil &&
-			inst.Operation.Name == "sha256" &&
-			len(seq) > i+1 && seq[i+1].Operation != nil &&
-			seq[i+1].Operation.Name == "sha256" {
-			tx := &wire.MsgTx{}
-			tx.Deserialize(bytes.NewReader(current))
-			bitcoinTx = tx
-		}
-
-		current = inst.Operation.Apply(current, inst.Argument)
-	}
-	return current, bitcoinTx
-}
-
 func (ts File) GetPendingSequences() []Sequence {
 	bitcoin := ts.GetBitcoinAttestedSequences()
 
@@ -182,8 +99,8 @@ func (ts File) Human(withPartials bool) string {
 
 func (ts File) SerializeToFile() []byte {
 	data := make([]byte, 0, 5050)
-	data = append(data, headerMagic...)
-	data = appendVarUint(data, 1)
+	data = append(data, HeaderMagic...)
+	data = varn.AppendVarUint(data, 1)
 	data = append(data, 0x08) // sha256
 	data = append(data, ts.Digest...)
 	data = append(data, ts.SerializeInstructionSequences()...)
@@ -203,7 +120,7 @@ func (ts File) SerializeInstructionSequences() []byte {
 		// keep an ordered slice of all the checkpoints we will potentially leave during our write journey for this sequence
 		checkpoints := make([]int, 0, len(sequences[s1]))
 		for s2 := s1 + 1; s2 < len(sequences); s2++ {
-			chp := getCommonPrefixIndex(sequences[s1], sequences[s2])
+			chp := GetCommonPrefixIndex(sequences[s1], sequences[s2])
 			if pos, found := slices.BinarySearch(checkpoints, chp); !found {
 				checkpoints = append(checkpoints, -1)        // make room
 				copy(checkpoints[pos+1:], checkpoints[pos:]) // move elements to the right
@@ -236,7 +153,7 @@ func (ts File) SerializeInstructionSequences() []byte {
 				// write normal operation
 				result = append(result, inst.Operation.Tag)
 				if inst.Operation.Binary {
-					result = appendVarBytes(result, inst.Argument)
+					result = varn.AppendVarBytes(result, inst.Argument)
 				}
 			} else if inst.Attestation != nil {
 				// write attestation record
@@ -245,15 +162,15 @@ func (ts File) SerializeInstructionSequences() []byte {
 					// will use a new buffer for the actual attestation result
 					abuf := make([]byte, 0, 100)
 					if inst.BitcoinBlockHeight != 0 {
-						result = append(result, bitcoinMagic...) // this goes in the main result buffer
-						abuf = appendVarUint(abuf, inst.BitcoinBlockHeight)
+						result = append(result, BitcoinMagic...) // this goes in the main result buffer
+						abuf = varn.AppendVarUint(abuf, inst.BitcoinBlockHeight)
 					} else if inst.CalendarServerURL != "" {
-						result = append(result, pendingMagic...) // this goes in the main result buffer
-						abuf = appendVarBytes(abuf, []byte(inst.CalendarServerURL))
+						result = append(result, PendingMagic...) // this goes in the main result buffer
+						abuf = varn.AppendVarBytes(abuf, []byte(inst.CalendarServerURL))
 					} else {
 						panic(fmt.Sprintf("invalid attestation: %v", inst))
 					}
-					result = appendVarBytes(result, abuf) // we append that result as varbytes
+					result = varn.AppendVarBytes(result, abuf) // we append that result as varbytes
 				}
 			} else {
 				panic(fmt.Sprintf("invalid instruction: %v", inst))
@@ -263,27 +180,43 @@ func (ts File) SerializeInstructionSequences() []byte {
 	return result
 }
 
-type Attestation struct {
-	BitcoinBlockHeight uint64
-	CalendarServerURL  string
-}
-
-func (att Attestation) Name() string {
-	if att.BitcoinBlockHeight != 0 {
-		return "bitcoin"
-	} else if att.CalendarServerURL != "" {
-		return "pending"
-	} else {
-		return "unknown/broken"
+func ParseOTSFile(buf varn.Buffer) (*File, error) {
+	// read magic
+	// read version [1 byte]
+	// read crypto operation for file digest [1 byte]
+	// read file digest [32 byte (depends)]
+	if magic, err := buf.ReadBytes(len(HeaderMagic)); err != nil || !slices.Equal(HeaderMagic, magic) {
+		return nil, fmt.Errorf("invalid ots file header '%s': %w", magic, err)
 	}
-}
 
-func (att Attestation) Human() string {
-	if att.BitcoinBlockHeight != 0 {
-		return fmt.Sprintf("bitcoin(%d)", att.BitcoinBlockHeight)
-	} else if att.CalendarServerURL != "" {
-		return fmt.Sprintf("pending(%s)", att.CalendarServerURL)
-	} else {
-		return "unknown/broken"
+	if version, err := buf.ReadVarUint(); err != nil || version != 1 {
+		return nil, fmt.Errorf("invalid ots file version '%v': %w", version, err)
 	}
+
+	tag, err := buf.ReadByte()
+	if err != nil {
+		return nil, fmt.Errorf("failed to read operation byte: %w", err)
+	}
+
+	if op, err := ReadInstruction(buf, tag); err != nil || op.Operation.Name != "sha256" {
+		return nil, fmt.Errorf("invalid crypto operation '%v', only sha256 supported: %w", op, err)
+	}
+
+	// if we got here assume the digest is sha256
+	digest, err := buf.ReadBytes(32)
+	if err != nil {
+		return nil, fmt.Errorf("failed to read 32-byte digest: %w", err)
+	}
+
+	ts := &File{
+		Digest: digest,
+	}
+
+	if seqs, err := ParseTimestamp(buf); err != nil {
+		return nil, err
+	} else {
+		ts.Sequences = seqs
+	}
+
+	return ts, nil
 }

ots/instruction.go

@@ -1,11 +1,32 @@
-package opentimestamps
+package ots
 
 import (
+	"fmt"
+	"slices"
 	"strings"
 
-	"slices"
+	"git.intruders.space/public/opentimestamps/varn"
 )
 
+// a Instruction can be an operation like "append" or "prepend" (this will be the case when .Operation != nil)
+// or an attestation (when .Attestation != nil).
+// It will have a non-nil .Argument whenever the operation requires an argument.
+type Instruction struct {
+	*Operation
+	Argument []byte
+	*Attestation
+}
+
+func GetCommonPrefixIndex(s1 []Instruction, s2 []Instruction) int {
+	n := min(len(s1), len(s2))
+	for i := 0; i < n; i++ {
+		if CompareInstructions(s1[i], s2[i]) != 0 {
+			return i
+		}
+	}
+	return n
+}
+
 // CompareInstructions returns negative if a<b, 0 if a=b and positive if a>b.
 // It considers an operation smaller than an attestation, a pending attestation smaller than a Bitcoin attestation.
 // It orders operations by their tag byte and then by their argument.
@@ -50,3 +71,24 @@ func CompareInstructions(a, b Instruction) int {
 		return 0
 	}
 }
+
+func ReadInstruction(buf varn.Buffer, tag byte) (*Instruction, error) {
+	op, ok := Tags[tag]
+	if !ok {
+		return nil, fmt.Errorf("unknown tag %v", tag)
+	}
+
+	inst := Instruction{
+		Operation: op,
+	}
+
+	if op.Binary {
+		val, err := buf.ReadVarBytes()
+		if err != nil {
+			return nil, fmt.Errorf("error reading argument: %w", err)
+		}
+		inst.Argument = val
+	}
+
+	return &inst, nil
+}

ots/operation.go

@@ -0,0 +1,34 @@
+package ots
+
+import "crypto/sha256"
+
+type Operation struct {
+	Name   string
+	Tag    byte
+	Binary bool // it's an operation that takes one argument, otherwise takes none
+	Apply  func(curr []byte, arg []byte) []byte
+}
+
+var Tags = map[byte]*Operation{
+	0xf0: {"append", 0xf0, true, func(curr []byte, arg []byte) []byte {
+		result := make([]byte, len(curr)+len(arg))
+		copy(result[0:], curr)
+		copy(result[len(curr):], arg)
+		return result
+	}},
+	0xf1: {"prepend", 0xf1, true, func(curr []byte, arg []byte) []byte {
+		result := make([]byte, len(curr)+len(arg))
+		copy(result[0:], arg)
+		copy(result[len(arg):], curr)
+		return result
+	}},
+	0xf2: {"reverse", 0xf2, false, func(curr []byte, arg []byte) []byte { panic("reverse not implemented") }},
+	0xf3: {"hexlify", 0xf3, false, func(curr []byte, arg []byte) []byte { panic("hexlify not implemented") }},
+	0x02: {"sha1", 0x02, false, func(curr []byte, arg []byte) []byte { panic("sha1 not implemented") }},
+	0x03: {"ripemd160", 0x03, false, ripemd160},
+	0x08: {"sha256", 0x08, false, func(curr []byte, arg []byte) []byte {
+		v := sha256.Sum256(curr)
+		return v[:]
+	}},
+	0x67: {"keccak256", 0x67, false, func(curr []byte, arg []byte) []byte { panic("keccak256 not implemented") }},
+}

ots/sequence.go

@@ -1,66 +1,88 @@
-package opentimestamps
+package ots
 
 import (
+	"bytes"
 	"fmt"
 	"io"
-
 	"slices"
+
+	"git.intruders.space/public/opentimestamps/varn"
+	"git.intruders.space/public/opentimestamps/verifyer"
+	"github.com/btcsuite/btcd/wire"
 )
 
-func parseCalendarServerResponse(buf Buffer) (Sequence, error) {
-	seqs, err := parseTimestamp(buf)
-	if err != nil {
-		return nil, err
-	}
-	if len(seqs) != 1 {
-		return nil, fmt.Errorf("invalid number of sequences obtained: %d", len(seqs))
-	}
+type Sequence []Instruction
 
-	return seqs[0], nil
+func (seq Sequence) GetAttestation() Attestation {
+	if len(seq) == 0 {
+		return Attestation{}
+	}
+	att := seq[len(seq)-1]
+	if att.Attestation == nil {
+		return Attestation{}
+	}
+	return *att.Attestation
 }
 
-func parseOTSFile(buf Buffer) (*File, error) {
-	// read magic
-	// read version [1 byte]
-	// read crypto operation for file digest [1 byte]
-	// read file digest [32 byte (depends)]
-	if magic, err := buf.readBytes(len(headerMagic)); err != nil || !slices.Equal(headerMagic, magic) {
-		return nil, fmt.Errorf("invalid ots file header '%s': %w", magic, err)
-	}
+// Compute runs a sequence of operations on top of an initial digest and returns the result, which is often a
+// Bitcoin block merkle root. It also tries to identify the point in the sequence in which an actual Bitcoin
+// transaction is formed and parse that.
+func (seq Sequence) Compute(initial []byte) (merkleRoot []byte, bitcoinTx *wire.MsgTx) {
+	current := initial
+	for i, inst := range seq {
+		if inst.Operation == nil {
+			break
+		}
 
-	if version, err := buf.readVarUint(); err != nil || version != 1 {
-		return nil, fmt.Errorf("invalid ots file version '%v': %w", version, err)
-	}
+		// the first time we do a double-sha256 that is likely a bitcoin transaction
+		if bitcoinTx == nil &&
+			inst.Operation.Name == "sha256" &&
+			len(seq) > i+1 && seq[i+1].Operation != nil &&
+			seq[i+1].Operation.Name == "sha256" {
+			tx := &wire.MsgTx{}
+			tx.Deserialize(bytes.NewReader(current))
+			bitcoinTx = tx
+		}
 
-	tag, err := buf.readByte()
-	if err != nil {
-		return nil, fmt.Errorf("failed to read operation byte: %w", err)
+		current = inst.Operation.Apply(current, inst.Argument)
 	}
-
-	if op, err := readInstruction(buf, tag); err != nil || op.Operation.Name != "sha256" {
-		return nil, fmt.Errorf("invalid crypto operation '%v', only sha256 supported: %w", op, err)
-	}
-
-	// if we got here assume the digest is sha256
-	digest, err := buf.readBytes(32)
-	if err != nil {
-		return nil, fmt.Errorf("failed to read 32-byte digest: %w", err)
-	}
-
-	ts := &File{
-		Digest: digest,
-	}
-
-	if seqs, err := parseTimestamp(buf); err != nil {
-		return nil, err
-	} else {
-		ts.Sequences = seqs
-	}
-
-	return ts, nil
+	return current, bitcoinTx
 }
 
-func parseTimestamp(buf Buffer) ([]Sequence, error) {
+// Verify validates sequence of operations that starts with digest and ends on a Bitcoin attestation against
+// an actual Bitcoin block, as given by the provided Bitcoin interface.
+func (seq Sequence) Verify(bitcoin verifyer.Bitcoin, digest []byte) (*wire.MsgTx, error) {
+	if len(seq) == 0 {
+		return nil, fmt.Errorf("empty sequence")
+	}
+
+	att := seq[len(seq)-1]
+	if att.Attestation == nil || att.BitcoinBlockHeight == 0 {
+		return nil, fmt.Errorf("sequence doesn't include a bitcoin attestation")
+	}
+
+	blockHash, err := bitcoin.GetBlockHash(int64(att.BitcoinBlockHeight))
+	if err != nil {
+		return nil, fmt.Errorf("failed to get block %d hash: %w", att.BitcoinBlockHeight, err)
+	}
+
+	blockHeader, err := bitcoin.GetBlockHeader(blockHash)
+	if err != nil {
+		return nil, fmt.Errorf("failed to get block %s header: %w", blockHash, err)
+	}
+
+	merkleRoot := blockHeader.MerkleRoot[:]
+	result, tx := seq.Compute(digest)
+
+	if !bytes.Equal(result, merkleRoot) {
+		return nil, fmt.Errorf("sequence result '%x' doesn't match the bitcoin merkle root for block %d: %x",
+			result, att.BitcoinBlockHeight, merkleRoot)
+	}
+
+	return tx, nil
+}
+
+func ParseTimestamp(buf varn.Buffer) ([]Sequence, error) {
 	// read instructions
 	//   if operation = push
 	//   if 0x00 = attestation
@@ -83,7 +105,7 @@ func parseTimestamp(buf Buffer) ([]Sequence, error) {
 
 	// go read these tags
 	for {
-		tag, err := buf.readByte()
+		tag, err := buf.ReadByte()
 		if err != nil {
 			if err == io.EOF {
 				return seqs, nil
@@ -93,20 +115,20 @@ func parseTimestamp(buf Buffer) ([]Sequence, error) {
 
 		if tag == 0x00 {
 			// enter an attestation context
-			magic, err := buf.readBytes(8)
+			magic, err := buf.ReadBytes(8)
 			if err != nil {
 				return nil, fmt.Errorf("failed to read attestion magic bytes: %w", err)
 			}
 
-			this, err := buf.readVarBytes()
+			this, err := buf.ReadVarBytes()
 			if err != nil {
 				return nil, fmt.Errorf("failed to read attestation bytes: %w", err)
 			}
-			abuf := newBuffer(this)
+			abuf := varn.NewBuffer(this)
 
 			switch {
-			case slices.Equal(magic, pendingMagic):
-				val, err := abuf.readVarBytes()
+			case slices.Equal(magic, PendingMagic):
+				val, err := abuf.ReadVarBytes()
 				if err != nil {
 					return nil, fmt.Errorf("failed reading calendar server url: %w", err)
 				}
@@ -114,8 +136,8 @@ func parseTimestamp(buf Buffer) ([]Sequence, error) {
 					seqs[currInstructionsBlock],
 					Instruction{Attestation: &Attestation{CalendarServerURL: string(val)}},
 				)
-			case slices.Equal(magic, bitcoinMagic):
-				val, err := abuf.readVarUint()
+			case slices.Equal(magic, BitcoinMagic):
+				val, err := abuf.ReadVarUint()
 				if err != nil {
 					return nil, fmt.Errorf("failed reading bitcoin block number: %w", err)
 				}
@@ -144,7 +166,7 @@ func parseTimestamp(buf Buffer) ([]Sequence, error) {
 			checkpoints = append(checkpoints, chp)
 		} else {
 			// a new operation in this block
-			inst, err := readInstruction(buf, tag)
+			inst, err := ReadInstruction(buf, tag)
 			if err != nil {
 				return nil, fmt.Errorf("failed to read instruction: %w", err)
 			}
@@ -152,24 +174,3 @@ func parseTimestamp(buf Buffer) ([]Sequence, error) {
 		}
 	}
 }
-
-func readInstruction(buf Buffer, tag byte) (*Instruction, error) {
-	op, ok := tags[tag]
-	if !ok {
-		return nil, fmt.Errorf("unknown tag %v", tag)
-	}
-
-	inst := Instruction{
-		Operation: op,
-	}
-
-	if op.Binary {
-		val, err := buf.readVarBytes()
-		if err != nil {
-			return nil, fmt.Errorf("error reading argument: %w", err)
-		}
-		inst.Argument = val
-	}
-
-	return &inst, nil
-}

pdf/certificate.go

@@ -0,0 +1,343 @@
+package pdf
+
+import (
+	"bytes"
+	"crypto/sha256"
+	"encoding/hex"
+	"fmt"
+	"io"
+	"os"
+	"path/filepath"
+	"strings"
+	"time"
+
+	"git.intruders.space/public/opentimestamps/ots"
+	"git.intruders.space/public/opentimestamps/verifyer"
+	"github.com/jung-kurt/gofpdf"
+)
+
+// CertificateOptions contains options for generating a PDF certificate
+type CertificateOptions struct {
+	// Title for the PDF document
+	Title string
+	// Additional comment to include in the certificate
+	Comment string
+	// Whether to include the original file content in the PDF (for text files only)
+	IncludeContent bool
+	// URL of Esplora API for fetching block information
+	EsploraURL string
+}
+
+// DefaultOptions returns the default certificate options
+func DefaultOptions() CertificateOptions {
+	return CertificateOptions{
+		Title:          "OpenTimestamps Certificate",
+		Comment:        "",
+		IncludeContent: false,
+		EsploraURL:     "https://blockstream.info/api",
+	}
+}
+
+// GenerateCertificate generates a PDF certificate for an OpenTimestamps timestamp
+// It returns a bytes.Buffer containing the PDF data
+func GenerateCertificate(
+	filename string,
+	fileData []byte,
+	timestampFile *ots.File,
+	options CertificateOptions,
+) (*bytes.Buffer, error) {
+	// Compute the file digest
+	fileDigest := sha256.Sum256(fileData)
+
+	// Extract Bitcoin attestations
+	bitcoinSeqs := timestampFile.GetBitcoinAttestedSequences()
+
+	// Create Bitcoin interface for block time lookup
+	bitcoin := verifyer.NewEsploraClient(options.EsploraURL, 30*time.Second)
+
+	// Create a buffer to store the PDF
+	var buf bytes.Buffer
+
+	// Generate the PDF into the buffer
+	err := generateVerificationPDF(
+		&buf,
+		filename,
+		fileData,
+		fileDigest[:],
+		timestampFile,
+		bitcoinSeqs,
+		bitcoin,
+		options,
+	)
+	if err != nil {
+		return nil, err
+	}
+
+	return &buf, nil
+}
+
+// WriteToFile writes the certificate buffer to a file
+func WriteToFile(buf *bytes.Buffer, outputPath string) error {
+	return os.WriteFile(outputPath, buf.Bytes(), 0644)
+}
+
+func generateVerificationPDF(
+	output io.Writer,
+	filePath string,
+	fileData []byte,
+	fileDigest []byte,
+	timestamp *ots.File,
+	bitcoinSeqs []ots.Sequence,
+	bitcoin verifyer.Bitcoin,
+	options CertificateOptions,
+) error {
+	// Create a new PDF
+	pdf := gofpdf.New("P", "mm", "A4", "")
+	pdf.SetTitle(options.Title, true)
+	pdf.SetAuthor("OpenTimestamps", true)
+	pdf.SetCreator("OpenTimestamps CLI", true)
+
+	// Set margins
+	pdf.SetMargins(25, 25, 25)
+	pdf.SetAutoPageBreak(true, 25)
+
+	// Add first page - Certificate
+	pdf.AddPage()
+
+	// Title
+	pdf.SetFont("Helvetica", "B", 24)
+	pdf.CellFormat(0, 12, options.Title, "", 1, "C", false, 0, "")
+	pdf.Ln(10)
+
+	// Timestamp information section
+	pdf.SetFont("Helvetica", "B", 18)
+	pdf.CellFormat(0, 10, "Timestamp Information", "", 1, "L", false, 0, "")
+	pdf.Ln(5)
+
+	pdf.SetFont("Helvetica", "B", 12)
+	pdf.CellFormat(0, 8, "Filename:", "", 1, "L", false, 0, "")
+	pdf.SetFont("Helvetica", "", 12)
+	pdf.CellFormat(0, 8, filepath.Base(filePath), "", 1, "L", false, 0, "")
+	pdf.Ln(2)
+
+	// Timestamp date
+	pdf.SetFont("Helvetica", "B", 12)
+	if len(bitcoinSeqs) > 0 {
+		// Find the earliest Bitcoin attestation
+		var earliestHeight uint64
+		var earliestBlockTime time.Time
+
+		for _, seq := range bitcoinSeqs {
+			att := seq.GetAttestation()
+			if earliestHeight == 0 || att.BitcoinBlockHeight < earliestHeight {
+				earliestHeight = att.BitcoinBlockHeight
+
+				// Fetch the block time from the blockchain
+				blockHash, err := bitcoin.GetBlockHash(int64(att.BitcoinBlockHeight))
+				if err == nil {
+					blockHeader, err := bitcoin.GetBlockHeader(blockHash)
+					if err == nil {
+						earliestBlockTime = time.Unix(int64(blockHeader.Timestamp.Unix()), 0)
+					}
+				}
+			}
+		}
+
+		// Show Bitcoin timestamp
+		pdf.CellFormat(0, 8, "Timestamp Created:", "", 1, "L", false, 0, "")
+		pdf.SetFont("Helvetica", "", 12)
+
+		if !earliestBlockTime.IsZero() {
+			// If we successfully retrieved the block time, display it
+			pdf.CellFormat(0, 8, fmt.Sprintf("Bitcoin Block #%d (%s)",
+				earliestHeight, earliestBlockTime.Format("Jan 02, 2006 15:04:05 UTC")),
+				"", 1, "L", false, 0, "")
+		} else {
+			// Fallback to just showing the block height
+			pdf.CellFormat(0, 8, fmt.Sprintf("Bitcoin Block #%d", earliestHeight), "", 1, "L", false, 0, "")
+		}
+	} else {
+		// Pending attestation
+		pdf.CellFormat(0, 8, "Status:", "", 1, "L", false, 0, "")
+		pdf.SetFont("Helvetica", "", 12)
+		pdf.CellFormat(0, 8, "Pending confirmation in the Bitcoin blockchain", "", 1, "L", false, 0, "")
+	}
+	pdf.Ln(2)
+
+	// File hash
+	pdf.SetFont("Helvetica", "B", 12)
+	pdf.CellFormat(0, 8, "File SHA-256 Digest:", "", 1, "L", false, 0, "")
+	pdf.SetFont("Courier", "", 10)
+	pdf.CellFormat(0, 8, hex.EncodeToString(fileDigest), "", 1, "L", false, 0, "")
+	pdf.Ln(5)
+
+	// Include comment if provided
+	if options.Comment != "" {
+		pdf.SetFont("Helvetica", "B", 12)
+		pdf.CellFormat(0, 8, "Comment:", "", 1, "L", false, 0, "")
+		pdf.SetFont("Helvetica", "", 12)
+		pdf.MultiCell(0, 8, options.Comment, "", "L", false)
+		pdf.Ln(5)
+	}
+
+	// Include file content if requested and looks like text
+	if options.IncludeContent && isTextFile(fileData) && len(fileData) < 5000 {
+		pdf.SetFont("Helvetica", "B", 12)
+		pdf.CellFormat(0, 8, "File Content:", "", 1, "L", false, 0, "")
+		pdf.SetFont("Courier", "", 10)
+		content := string(fileData)
+		content = strings.ReplaceAll(content, "\r\n", "\n")
+		pdf.MultiCell(0, 5, content, "", "L", false)
+		pdf.Ln(5)
+	}
+
+	// Add Bitcoin transaction information for each attestation
+	if len(bitcoinSeqs) > 0 {
+		pdf.SetFont("Helvetica", "B", 18)
+		pdf.CellFormat(0, 10, "Bitcoin Attestations", "", 1, "L", false, 0, "")
+		pdf.Ln(5)
+
+		for i, seq := range bitcoinSeqs {
+			att := seq.GetAttestation()
+
+			pdf.SetFont("Helvetica", "B", 14)
+			pdf.CellFormat(0, 8, fmt.Sprintf("Attestation #%d", i+1), "", 1, "L", false, 0, "")
+			pdf.Ln(2)
+
+			// Get block details
+			blockHash, err := bitcoin.GetBlockHash(int64(att.BitcoinBlockHeight))
+			blockTime := "Unknown"
+			if err == nil {
+				blockHeader, err := bitcoin.GetBlockHeader(blockHash)
+				if err == nil {
+					blockTime = blockHeader.Timestamp.Format("Jan 02, 2006 15:04:05 UTC")
+				}
+			}
+
+			pdf.SetFont("Helvetica", "B", 12)
+			pdf.CellFormat(0, 8, "Bitcoin Block Height:", "", 1, "L", false, 0, "")
+			pdf.SetFont("Helvetica", "", 12)
+			pdf.CellFormat(0, 8, fmt.Sprintf("%d", att.BitcoinBlockHeight), "", 1, "L", false, 0, "")
+
+			pdf.SetFont("Helvetica", "B", 12)
+			pdf.CellFormat(0, 8, "Block Time:", "", 1, "L", false, 0, "")
+			pdf.SetFont("Helvetica", "", 12)
+			pdf.CellFormat(0, 8, blockTime, "", 1, "L", false, 0, "")
+
+			pdf.SetFont("Helvetica", "B", 12)
+			pdf.CellFormat(0, 8, "Block Hash:", "", 1, "L", false, 0, "")
+			pdf.SetFont("Courier", "", 10)
+			if blockHash != nil {
+				pdf.CellFormat(0, 8, blockHash.String(), "", 1, "L", false, 0, "")
+			} else {
+				pdf.CellFormat(0, 8, "Unable to retrieve", "", 1, "L", false, 0, "")
+			}
+
+			// Show operations sequence
+			pdf.SetFont("Helvetica", "B", 12)
+			pdf.CellFormat(0, 8, "Verification Operations:", "", 1, "L", false, 0, "")
+			pdf.SetFont("Courier", "", 10)
+
+			// Format the operations
+			var operationsText string
+			merkleRoot, _ := seq.Compute(timestamp.Digest)
+
+			operationsText += fmt.Sprintf("Starting with digest: %s\n", hex.EncodeToString(timestamp.Digest))
+
+			for j, inst := range seq {
+				if inst.Operation != nil {
+					if inst.Operation.Binary {
+						operationsText += fmt.Sprintf("%d. %s %s\n", j+1, inst.Operation.Name, hex.EncodeToString(inst.Argument))
+					} else {
+						operationsText += fmt.Sprintf("%d. %s\n", j+1, inst.Operation.Name)
+					}
+				}
+			}
+
+			operationsText += fmt.Sprintf("\nResulting merkle root: %s\n", hex.EncodeToString(merkleRoot))
+
+			pdf.MultiCell(0, 5, operationsText, "", "L", false)
+			pdf.Ln(5)
+		}
+	}
+
+	// Add second page - Verification Instructions
+	pdf.AddPage()
+	pdf.SetFont("Helvetica", "B", 18)
+	pdf.CellFormat(0, 10, "Verification Instructions", "", 1, "L", false, 0, "")
+	pdf.Ln(5)
+
+	// Instructions
+	addVerificationInstructions(pdf)
+
+	// Save the PDF to the writer
+	return pdf.Output(output)
+}
+
+func addVerificationInstructions(pdf *gofpdf.Fpdf) {
+	pdf.SetFont("Helvetica", "B", 14)
+	pdf.CellFormat(0, 8, "1. Compute the SHA-256 digest of your file", "", 1, "L", false, 0, "")
+	pdf.SetFont("Helvetica", "", 12)
+	pdf.MultiCell(0, 6, `To verify this timestamp, first compute the SHA-256 digest of your original file. You can use various tools for this:
+
+- On Linux/macOS: Use the command "shasum -a 256 filename"
+- On Windows: Use tools like PowerShell's "Get-FileHash" or third-party tools
+- Online: Various websites can calculate file hashes, but only use trusted sources for sensitive files
+
+Verify that the digest matches the one shown in this certificate.`, "", "L", false)
+	pdf.Ln(5)
+
+	pdf.SetFont("Helvetica", "B", 14)
+	pdf.CellFormat(0, 8, "2. Verify the operations sequence", "", 1, "L", false, 0, "")
+	pdf.SetFont("Helvetica", "", 12)
+	pdf.MultiCell(0, 6, `The operations sequence shown in this certificate transforms the file digest into a value that was stored in the Bitcoin blockchain. To verify manually:
+
+- Start with the file's SHA-256 digest
+- Apply each operation in sequence as shown in the certificate
+- For "append" operations, add the shown bytes to the end of the current value
+- For "prepend" operations, add the shown bytes to the beginning of the current value
+- For "sha256" operations, compute the SHA-256 hash of the current value
+- The final result should match the merkle root shown in the certificate`, "", "L", false)
+	pdf.Ln(5)
+
+	pdf.SetFont("Helvetica", "B", 14)
+	pdf.CellFormat(0, 8, "3. Verify the Bitcoin attestation", "", 1, "L", false, 0, "")
+	pdf.SetFont("Helvetica", "", 12)
+	pdf.MultiCell(0, 6, `For full verification, check that the merkle root was recorded in the Bitcoin blockchain:
+
+- Find the Bitcoin block at the height shown in the certificate
+- The block's merkle root or transaction should contain the computed value
+- You can use block explorers like blockstream.info or blockchain.com
+- The timestamp is confirmed when the merkle root appears in the blockchain`, "", "L", false)
+	pdf.Ln(5)
+
+	pdf.SetFont("Helvetica", "B", 14)
+	pdf.CellFormat(0, 8, "4. Use the OpenTimestamps verifier", "", 1, "L", false, 0, "")
+	pdf.SetFont("Helvetica", "", 12)
+	pdf.MultiCell(0, 6, `For easier verification, use the OpenTimestamps verification tools:
+
+- Command line: Use "ots verify <file> <file.ots>"
+- Online: Visit https://opentimestamps.org and upload your file and .ots timestamp
+- The tools will perform all verification steps automatically`, "", "L", false)
+
+	// Add footer with generation time
+	pdf.Ln(10)
+	pdf.SetFont("Helvetica", "I", 10)
+	pdf.CellFormat(0, 6, fmt.Sprintf("Certificate generated at: %s", time.Now().Format(time.RFC3339)), "", 1, "C", false, 0, "")
+	pdf.CellFormat(0, 6, "OpenTimestamps - https://opentimestamps.org", "", 1, "C", false, 0, "")
+}
+
+// isTextFile tries to determine if a file is likely to be text
+func isTextFile(data []byte) bool {
+	// Simple heuristic: if the file doesn't contain too many non-printable characters,
+	// it's probably text
+	nonPrintable := 0
+	for _, b := range data {
+		if (b < 32 || b > 126) && b != 9 && b != 10 && b != 13 {
+			nonPrintable++
+		}
+	}
+
+	// Allow up to 1% non-printable characters
+	return nonPrintable <= len(data)/100
+}

stamp.go

@@ -6,9 +6,15 @@ import (
 	"fmt"
 	"io"
 	"net/http"
+	"strings"
+
+	"git.intruders.space/public/opentimestamps/ots"
+	"git.intruders.space/public/opentimestamps/varn"
 )
 
-func Stamp(ctx context.Context, calendarUrl string, digest [32]byte) (Sequence, error) {
+var httpClient = &http.Client{}
+
+func Stamp(ctx context.Context, calendarUrl string, digest [32]byte) (ots.Sequence, error) {
 	body := bytes.NewBuffer(digest[:])
 	req, err := http.NewRequestWithContext(ctx, "POST", normalizeUrl(calendarUrl)+"/digest", body)
 	if err != nil {
@@ -18,7 +24,8 @@ func Stamp(ctx context.Context, calendarUrl string, digest [32]byte) (Sequence,
 	req.Header.Add("User-Agent", "github.com/fiatjaf/opentimestamps")
 	req.Header.Add("Accept", "application/vnd.opentimestamps.v1")
 	req.Header.Add("Content-Type", "application/x-www-form-urlencoded")
-	resp, err := http.DefaultClient.Do(req)
+
+	resp, err := httpClient.Do(req)
 	if err != nil {
 		return nil, fmt.Errorf("'%s' request failed: %w", calendarUrl, err)
 	}
@@ -29,7 +36,7 @@ func Stamp(ctx context.Context, calendarUrl string, digest [32]byte) (Sequence,
 	}
 	resp.Body.Close()
 
-	seq, err := parseCalendarServerResponse(newBuffer(full))
+	seq, err := parseCalendarServerResponse(varn.NewBuffer(full))
 	if err != nil {
 		return nil, fmt.Errorf("failed to parse response from '%s': %w", calendarUrl, err)
 	}
@@ -37,11 +44,11 @@ func Stamp(ctx context.Context, calendarUrl string, digest [32]byte) (Sequence,
 	return seq, nil
 }
 
-func ReadFromFile(data []byte) (*File, error) {
-	return parseOTSFile(newBuffer(data))
+func ReadFromFile(data []byte) (*ots.File, error) {
+	return ots.ParseOTSFile(varn.NewBuffer(data))
 }
 
-func UpgradeSequence(ctx context.Context, seq Sequence, initial []byte) (Sequence, error) {
+func UpgradeSequence(ctx context.Context, seq ots.Sequence, initial []byte) (ots.Sequence, error) {
 	result, _ := seq.Compute(initial)
 	attestation := seq.GetAttestation()
 
@@ -54,7 +61,8 @@ func UpgradeSequence(ctx context.Context, seq Sequence, initial []byte) (Sequenc
 	req.Header.Add("User-Agent", "github.com/fiatjaf/opentimestamps")
 	req.Header.Add("Accept", "application/vnd.opentimestamps.v1")
 	req.Header.Add("Content-Type", "application/x-www-form-urlencoded")
-	resp, err := http.DefaultClient.Do(req)
+
+	resp, err := httpClient.Do(req)
 	if err != nil {
 		return nil, fmt.Errorf("'%s' request failed: %w", attestation.CalendarServerURL, err)
 	}
@@ -69,14 +77,34 @@ func UpgradeSequence(ctx context.Context, seq Sequence, initial []byte) (Sequenc
 	}
 	resp.Body.Close()
 
-	tail, err := parseCalendarServerResponse(newBuffer(body))
+	tail, err := parseCalendarServerResponse(varn.NewBuffer(body))
 	if err != nil {
 		return nil, fmt.Errorf("failed to parse response from '%s': %w", attestation.CalendarServerURL, err)
 	}
 
-	newSeq := make(Sequence, len(seq)+len(tail)-1)
+	newSeq := make(ots.Sequence, len(seq)+len(tail)-1)
 	copy(newSeq, seq[0:len(seq)-1])
 	copy(newSeq[len(seq)-1:], tail)
 
 	return newSeq, nil
 }
+
+func parseCalendarServerResponse(buf varn.Buffer) (ots.Sequence, error) {
+	seqs, err := ots.ParseTimestamp(buf)
+	if err != nil {
+		return nil, err
+	}
+	if len(seqs) != 1 {
+		return nil, fmt.Errorf("invalid number of sequences obtained: %d", len(seqs))
+	}
+
+	return seqs[0], nil
+}
+
+func normalizeUrl(u string) string {
+	u = strings.TrimSuffix(u, "/")
+	if !strings.HasPrefix(u, "https://") && !strings.HasPrefix(u, "http://") {
+		u = "http://" + u
+	}
+	return u
+}

utils.go

@@ -1,111 +0,0 @@
-package opentimestamps
-
-import (
-	"io"
-	"strings"
-)
-
-func normalizeUrl(u string) string {
-	if strings.HasSuffix(u, "/") {
-		u = u[0 : len(u)-1]
-	}
-	if !strings.HasPrefix(u, "https://") && !strings.HasPrefix(u, "http://") {
-		u = "http://" + u
-	}
-	return u
-}
-
-type Buffer struct {
-	pos *int
-	buf []byte
-}
-
-func newBuffer(buf []byte) Buffer {
-	zero := 0
-	return Buffer{&zero, buf}
-}
-
-func (buf Buffer) readBytes(n int) ([]byte, error) {
-	// fmt.Println("reading", n, "bytes")
-	if *buf.pos >= len(buf.buf) {
-		return nil, io.EOF
-	}
-	res := buf.buf[*buf.pos : *buf.pos+n]
-	*buf.pos = *buf.pos + n
-	// fmt.Println("->", hex.EncodeToString(res))
-	return res, nil
-}
-
-func (buf Buffer) readByte() (byte, error) {
-	b, err := buf.readBytes(1)
-	if err != nil {
-		return 0, err
-	}
-	return b[0], nil
-}
-
-func (buf Buffer) readVarUint() (uint64, error) {
-	var value uint64 = 0
-	var shift uint64 = 0
-
-	for {
-		b, err := buf.readByte()
-		if err != nil {
-			return 0, err
-		}
-		value |= (uint64(b) & 0b01111111) << shift
-		shift += 7
-		if b&0b10000000 == 0 {
-			break
-		}
-	}
-	return value, nil
-}
-
-func (buf Buffer) readVarBytes() ([]byte, error) {
-	v, err := buf.readVarUint()
-	if err != nil {
-		return nil, err
-	}
-	b, err := buf.readBytes(int(v))
-	if err != nil {
-		return nil, err
-	}
-	return b, nil
-}
-
-func appendVarUint(buf []byte, value uint64) []byte {
-	if value == 0 {
-		buf = append(buf, 0)
-	} else {
-		for value != 0 {
-			b := byte(value & 0b01111111)
-			if value > 0b01111111 {
-				b |= 0b10000000
-			}
-			buf = append(buf, b)
-			if value <= 0b01111111 {
-				break
-			}
-			value >>= 7
-		}
-	}
-
-	return buf
-}
-
-func appendVarBytes(buf []byte, value []byte) []byte {
-	buf = appendVarUint(buf, uint64(len(value)))
-	buf = append(buf, value...)
-	return buf
-}
-
-func getCommonPrefixIndex(s1 []Instruction, s2 []Instruction) int {
-	n := min(len(s1), len(s2))
-	for i := 0; i < n; i++ {
-		if CompareInstructions(s1[i], s2[i]) != 0 {
-			return i
-		}
-	}
-	return n
-}

varn/buffer.go

@@ -0,0 +1,81 @@
+package varn
+
+import "io"
+
+// Buffer is a simple buffer reader that allows reading bytes and
+// variable-length integers. It is not thread-safe and should not be used
+// concurrently.
+type Buffer struct {
+	pos *int
+	buf []byte
+}
+
+// NewBuffer creates a new Buffer instance.
+func NewBuffer(buf []byte) Buffer {
+	zero := 0
+	return Buffer{&zero, buf}
+}
+
+// ReadBytes reads n bytes from the buffer.
+func (buf Buffer) ReadBytes(n int) ([]byte, error) {
+	if *buf.pos >= len(buf.buf) {
+		return nil, io.EOF
+	}
+	if *buf.pos+n > len(buf.buf) {
+		return nil, io.ErrUnexpectedEOF
+	}
+
+	res := buf.buf[*buf.pos : *buf.pos+n]
+	*buf.pos = *buf.pos + n
+	return res, nil
+}
+
+func (buf Buffer) ReadByte() (byte, error) {
+	b, err := buf.ReadBytes(1)
+	if err != nil {
+		return 0, err
+	}
+	return b[0], nil
+}
+
+// ReadVarUint reads a variable-length unsigned integer from the buffer.
+// Returns io.EOF if the end of the buffer is reached before a complete integer
+// is read.
+func (buf Buffer) ReadVarUint() (uint64, error) {
+	var value uint64 = 0
+	var shift uint64 = 0
+
+	for {
+		b, err := buf.ReadByte()
+		if err != nil {
+			return 0, err
+		}
+		value |= (uint64(b) & 0b01111111) << shift
+		shift += 7
+		if b&0b10000000 == 0 {
+			break
+		}
+	}
+	return value, nil
+}
+
+// ReadVarBytes reads a variable-length byte array from the buffer.
+// It first reads a variable-length unsigned integer to determine the length
+// of the byte array, and then reads that many bytes from the buffer.
+// Returns the byte array and an error if any occurs during reading.
+// The function will return io.EOF if the end of the buffer is reached before
+// the specified number of bytes is read.
+// If the length of the byte array is 0, it will return an empty byte slice.
+// If the length is greater than the remaining bytes in the buffer, it will
+// return io.EOF.
+func (buf Buffer) ReadVarBytes() ([]byte, error) {
+	v, err := buf.ReadVarUint()
+	if err != nil {
+		return nil, err
+	}
+	b, err := buf.ReadBytes(int(v))
+	if err != nil {
+		return nil, err
+	}
+	return b, nil
+}

varn/buffer_test.go

@@ -0,0 +1,155 @@
+package varn_test
+
+import (
+	"io"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+
+	"git.intruders.space/public/opentimestamps/varn"
+)
+
+func TestNewBuffer(t *testing.T) {
+	data := []byte{0x01, 0x02, 0x03}
+	buf := varn.NewBuffer(data)
+
+	// Test the first byte to verify initialization
+	b, err := buf.ReadByte()
+	assert.NoError(t, err)
+	assert.Equal(t, byte(0x01), b)
+
+	// Test reading the second byte
+	b, err = buf.ReadByte()
+	assert.NoError(t, err)
+	assert.Equal(t, byte(0x02), b)
+
+	// Test reading the third byte
+	b, err = buf.ReadByte()
+	assert.NoError(t, err)
+	assert.Equal(t, byte(0x03), b)
+
+	// Test reading beyond the buffer
+	_, err = buf.ReadByte()
+	assert.ErrorIs(t, err, io.EOF)
+
+	// Test reading from an empty buffer
+	emptyBuf := varn.NewBuffer([]byte{})
+	_, err = emptyBuf.ReadByte()
+	assert.ErrorIs(t, err, io.EOF)
+
+	// Test reading from a nil buffer
+	nilBuf := varn.NewBuffer(nil)
+	_, err = nilBuf.ReadByte()
+	assert.ErrorIs(t, err, io.EOF)
+
+	// Test reading from a buffer with a single byte
+	singleByteBuf := varn.NewBuffer([]byte{0xFF})
+	b, err = singleByteBuf.ReadByte()
+	assert.NoError(t, err)
+	assert.Equal(t, byte(0xFF), b)
+}
+
+func TestReadBytes(t *testing.T) {
+	data := []byte{0x01, 0x02, 0x03, 0x04, 0x05}
+	buf := varn.NewBuffer(data)
+
+	// Read 3 bytes
+	bytes, err := buf.ReadBytes(3)
+	assert.NoError(t, err)
+	assert.Equal(t, []byte{0x01, 0x02, 0x03}, bytes)
+
+	// Read 2 more bytes
+	bytes, err = buf.ReadBytes(2)
+	assert.NoError(t, err)
+	assert.Equal(t, []byte{0x04, 0x05}, bytes)
+
+	// Try to read beyond the buffer
+	_, err = buf.ReadBytes(1)
+	assert.ErrorIs(t, err, io.EOF)
+}
+
+func TestReadByte(t *testing.T) {
+	data := []byte{0x0A, 0x0B}
+	buf := varn.NewBuffer(data)
+
+	// Read first byte
+	b, err := buf.ReadByte()
+	assert.NoError(t, err)
+	assert.Equal(t, byte(0x0A), b)
+
+	// Read second byte
+	b, err = buf.ReadByte()
+	assert.NoError(t, err)
+	assert.Equal(t, byte(0x0B), b)
+
+	// Try to read beyond the buffer
+	_, err = buf.ReadByte()
+	assert.ErrorIs(t, err, io.EOF)
+}
+
+func TestReadVarUint(t *testing.T) {
+	testCases := []struct {
+		name     string
+		input    []byte
+		expected uint64
+	}{
+		{
+			name:     "Single byte",
+			input:    []byte{0x01},
+			expected: 1,
+		},
+		{
+			name:     "Two bytes",
+			input:    []byte{0x81, 0x01}, // 129 in varint encoding
+			expected: 129,
+		},
+		{
+			name:     "Large number",
+			input:    []byte{0xFF, 0xFF, 0xFF, 0xFF, 0x01}, // 536870911 in varint encoding
+			expected: 536870911,
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			buf := varn.NewBuffer(tc.input)
+			val, err := buf.ReadVarUint()
+			assert.NoError(t, err)
+			assert.Equal(t, tc.expected, val)
+		})
+	}
+
+	// Test EOF
+	buf := varn.NewBuffer([]byte{0x81}) // Incomplete varint
+	_, err := buf.ReadVarUint()
+	assert.ErrorIs(t, err, io.EOF)
+}
+
+func TestReadVarBytes(t *testing.T) {
+	// Test normal case: length followed by data
+	data := []byte{0x03, 0x0A, 0x0B, 0x0C, 0x0D}
+	buf := varn.NewBuffer(data)
+
+	bytes, err := buf.ReadVarBytes()
+	assert.NoError(t, err)
+	assert.Equal(t, []byte{0x0A, 0x0B, 0x0C}, bytes)
+
+	// Test empty array
+	data = []byte{0x00, 0x01}
+	buf = varn.NewBuffer(data)
+
+	bytes, err = buf.ReadVarBytes()
+	assert.NoError(t, err)
+	assert.Equal(t, []byte{}, bytes)
+
+	// Test EOF during length read
+	buf = varn.NewBuffer([]byte{})
+	_, err = buf.ReadVarBytes()
+	assert.ErrorIs(t, err, io.EOF)
+
+	// Test error during data read (insufficient bytes)
+	data = []byte{0x03, 0x01}
+	buf = varn.NewBuffer(data)
+	_, err = buf.ReadVarBytes()
+	assert.ErrorIs(t, err, io.ErrUnexpectedEOF)
+}

varn/varn.go

@@ -0,0 +1,38 @@
+// Package varn implements variable-length encoding for unsigned integers and
+// byte slices. It is used in the OpenTimestamps protocol to encode
+// instructions and attestations. The encoding is similar to the one used in
+// Protocol Buffers, but with a different format for the variable-length
+// integers. The encoding is designed to be compact and efficient, while still
+// being easy to decode. The package provides functions to read and write
+// variable-length integers and byte slices, as well as a Buffer type for
+// reading and writing data in a more convenient way. The package is not
+// thread-safe and should not be used concurrently. It is intended for use in
+// the OpenTimestamps protocol and is not a general-purpose encoding library.
+package varn
+
+// AppendVarUint appends a variable-length unsigned integer to the buffer
+func AppendVarUint(buf []byte, value uint64) []byte {
+	if value == 0 {
+		buf = append(buf, 0)
+	} else {
+		for value != 0 {
+			b := byte(value & 0b01111111)
+			if value > 0b01111111 {
+				b |= 0b10000000
+			}
+			buf = append(buf, b)
+			if value <= 0b01111111 {
+				break
+			}
+			value >>= 7
+		}
+	}
+
+	return buf
+}
+
+func AppendVarBytes(buf []byte, value []byte) []byte {
+	buf = AppendVarUint(buf, uint64(len(value)))
+	buf = append(buf, value...)
+	return buf
+}

varn/varn_test.go

@@ -0,0 +1,118 @@
+package varn_test
+
+import (
+	"bytes"
+	"encoding/hex"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	"git.intruders.space/public/opentimestamps/varn"
+)
+
+// Helper functions for decoding (to verify encoding)
+func readVarUint(t *testing.T, data []byte) (uint64, int) {
+	t.Helper()
+	require.NotZero(t, data, "empty buffer")
+
+	if data[0] == 0 {
+		return 0, 1
+	}
+
+	var value uint64
+	var bytesRead int
+
+	for i, b := range data {
+		bytesRead = i + 1
+		value |= uint64(b&0x7F) << uint(7*i)
+		if b&0x80 == 0 {
+			break
+		}
+		require.Less(t, i, 9, "varint too long") // 9 is max bytes needed for uint64
+	}
+
+	return value, bytesRead
+}
+
+func readVarBytes(t *testing.T, data []byte) ([]byte, int) {
+	t.Helper()
+	length, bytesRead := readVarUint(t, data)
+
+	require.GreaterOrEqual(t, uint64(len(data)-bytesRead), length, "buffer too short")
+
+	end := bytesRead + int(length)
+	return data[bytesRead:end], end
+}
+
+func TestAppendVarUint(t *testing.T) {
+	tests := []struct {
+		name     string
+		value    uint64
+		expected string // hex representation of expected bytes
+	}{
+		{"zero", 0, "00"},
+		{"small value", 42, "2a"},
+		{"value below 128", 127, "7f"},
+		{"value requiring 2 bytes", 128, "8001"},
+		{"medium value", 300, "ac02"},
+		{"large value", 1234567890, "d285d8cc04"}, // Updated from "d2a6e58e07" to correct encoding
+		{"max uint64", 18446744073709551615, "ffffffffffffffffff01"},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			var buf []byte
+			result := varn.AppendVarUint(buf, tt.value)
+
+			// Check encoding
+			expected, err := hex.DecodeString(tt.expected)
+			assert.NoError(t, err)
+			assert.Equal(t, expected, result)
+
+			// Verify by decoding
+			decoded, _ := readVarUint(t, result)
+			assert.Equal(t, tt.value, decoded)
+		})
+	}
+}
+
+func TestAppendVarBytes(t *testing.T) {
+	tests := []struct {
+		name  string
+		value []byte
+	}{
+		{"empty", []byte{}},
+		{"small", []byte{0x01, 0x02, 0x03}},
+		{"medium", bytes.Repeat([]byte{0xAA}, 127)},
+		{"large", bytes.Repeat([]byte{0xBB}, 256)},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			var buf []byte
+			result := varn.AppendVarBytes(buf, tt.value)
+
+			// Verify by decoding
+			decoded, _ := readVarBytes(t, result)
+			assert.Equal(t, tt.value, decoded)
+
+			// Check that length is properly encoded
+			lenEncoded, _ := readVarUint(t, result)
+			assert.Equal(t, uint64(len(tt.value)), lenEncoded)
+		})
+	}
+}
+
+func TestAppendingToExistingBuffer(t *testing.T) {
+	existing := []byte{0xFF, 0xFF}
+
+	// Test AppendVarUint
+	result := varn.AppendVarUint(existing, 42)
+	assert.Equal(t, []byte{0xFF, 0xFF, 0x2A}, result)
+
+	// Test AppendVarBytes
+	data := []byte{0x01, 0x02, 0x03}
+	result = varn.AppendVarBytes(existing, data)
+	assert.Equal(t, []byte{0xFF, 0xFF, 0x03, 0x01, 0x02, 0x03}, result)
+}

verifier.go

@@ -1,47 +0,0 @@
-package opentimestamps
-
-import (
-	"bytes"
-	"fmt"
-
-	"github.com/btcsuite/btcd/chaincfg/chainhash"
-	"github.com/btcsuite/btcd/wire"
-)
-
-type Bitcoin interface {
-	GetBlockHash(height int64) (*chainhash.Hash, error)
-	GetBlockHeader(hash *chainhash.Hash) (*wire.BlockHeader, error)
-}
-
-// Verify validates sequence of operations that starts with digest and ends on a Bitcoin attestation against
-// an actual Bitcoin block, as given by the provided Bitcoin interface.
-func (seq Sequence) Verify(bitcoin Bitcoin, digest []byte) (*wire.MsgTx, error) {
-	if len(seq) == 0 {
-		return nil, fmt.Errorf("empty sequence")
-	}
-
-	att := seq[len(seq)-1]
-	if att.Attestation == nil || att.BitcoinBlockHeight == 0 {
-		return nil, fmt.Errorf("sequence doesn't include a bitcoin attestation")
-	}
-
-	blockHash, err := bitcoin.GetBlockHash(int64(att.BitcoinBlockHeight))
-	if err != nil {
-		return nil, fmt.Errorf("failed to get block %d hash: %w", att.BitcoinBlockHeight, err)
-	}
-
-	blockHeader, err := bitcoin.GetBlockHeader(blockHash)
-	if err != nil {
-		return nil, fmt.Errorf("failed to get block %s header: %w", blockHash, err)
-	}
-
-	merkleRoot := blockHeader.MerkleRoot[:]
-	result, tx := seq.Compute(digest)
-
-	if !bytes.Equal(result, merkleRoot) {
-		return nil, fmt.Errorf("sequence result '%x' doesn't match the bitcoin merkle root for block %d: %x",
-			result, att.BitcoinBlockHeight, merkleRoot)
-	}
-
-	return tx, nil
-}

verifyer/bitcoin.go

@@ -0,0 +1,15 @@
+package verifyer
+
+import (
+	"github.com/btcsuite/btcd/chaincfg/chainhash"
+	"github.com/btcsuite/btcd/rpcclient"
+	"github.com/btcsuite/btcd/wire"
+)
+
+type Bitcoin interface {
+	GetBlockHash(height int64) (*chainhash.Hash, error)
+	GetBlockHeader(hash *chainhash.Hash) (*wire.BlockHeader, error)
+}
+
+var _ Bitcoin = (*esplora)(nil)
+var _ Bitcoin = (*rpcclient.Client)(nil)

verifyer/bitcoind.go

@@ -1,4 +1,4 @@
-package opentimestamps
+package verifyer
 
 import "github.com/btcsuite/btcd/rpcclient"
 

verifyer/esplora.go

@@ -1,4 +1,4 @@
-package opentimestamps
+package verifyer
 
 import (
 	"bytes"
@@ -8,6 +8,7 @@ import (
 	"net/http"
 	"strconv"
 	"strings"
+	"time"
 
 	"slices"
 
@@ -15,29 +16,38 @@ import (
 	"github.com/btcsuite/btcd/wire"
 )
 
-func NewEsploraClient(url string) Bitcoin {
-	if strings.HasSuffix(url, "/") {
-		url = url[0 : len(url)-1]
-	}
-	return esplora{url}
+// esplora is a client for the Esplora API, which provides access to Bitcoin
+// blockchain data.
+type esplora struct {
+	httpClient *http.Client
+	baseURL    string
 }
 
-type esplora struct{ baseurl string }
+func NewEsploraClient(url string, timeout time.Duration) Bitcoin {
+	url = strings.TrimSuffix(url, "/")
+
+	h := &http.Client{
+		Timeout: timeout,
+	}
+
+	return esplora{h, url}
+}
 
 func (e esplora) GetBlockHash(height int64) (*chainhash.Hash, error) {
-	resp, err := http.Get(e.baseurl + "/block-height/" + strconv.FormatInt(height, 10))
+	resp, err := e.httpClient.Get(e.baseURL + "/block-height/" + strconv.FormatInt(height, 10))
 	if err != nil {
-		return nil, err
+		return nil, fmt.Errorf("failed to get block hash: %w", err)
 	}
 	defer resp.Body.Close()
+
 	hexb, err := io.ReadAll(resp.Body)
 	if err != nil {
-		return nil, err
+		return nil, fmt.Errorf("failed to read block hash: %w", err)
 	}
 
 	hash, err := hex.DecodeString(string(hexb))
 	if err != nil {
-		return nil, err
+		return nil, fmt.Errorf("failed to decode block hash: %w", err)
 	}
 	if len(hash) != chainhash.HashSize {
 		return nil, fmt.Errorf("got block hash (%x) of invalid size (expected %d)", hash, chainhash.HashSize)
@@ -50,11 +60,12 @@ func (e esplora) GetBlockHash(height int64) (*chainhash.Hash, error) {
 }
 
 func (e esplora) GetBlockHeader(hash *chainhash.Hash) (*wire.BlockHeader, error) {
-	resp, err := http.Get(fmt.Sprintf("%s/block/%s/header", e.baseurl, hash.String()))
+	resp, err := e.httpClient.Get(fmt.Sprintf("%s/block/%s/header", e.baseURL, hash.String()))
 	if err != nil {
 		return nil, err
 	}
 	defer resp.Body.Close()
+
 	hexb, err := io.ReadAll(resp.Body)
 	if err != nil {
 		return nil, err