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2026-01-11 06:53:39 +01:00
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ctfetch

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Copyright 2026, IPng Networks GmbH, Pim van Pelt <pim@ipng.ch>
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# ctfetch
Fetch and dump leaf entries from Certificate Transparency logs.
## Install
```bash
go install
```
## Usage
```bash
ctfetch [--dumpall] <log-url> <leaf-index>
```
### Examples
Dump a specific entry:
```bash
ctfetch https://halloumi2026h1.mon.ct.ipng.ch 629794635
```
Dump all entries in the tile:
```bash
ctfetch --dumpall https://halloumi2026h1.mon.ct.ipng.ch 629794635
```
## Options
- `--dumpall`: Dump all entries in the tile instead of just the specified leaf

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module ctfetch
go 1.24.6
require (
filippo.io/sunlight v0.6.3
golang.org/x/mod v0.32.0
)
require (
filippo.io/torchwood v0.5.1-0.20250713221105-b067ac9d4cf6 // indirect
github.com/google/certificate-transparency-go v1.3.2 // indirect
golang.org/x/crypto v0.39.0 // indirect
golang.org/x/sync v0.15.0 // indirect
)

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filippo.io/sunlight v0.6.3 h1:bxN0JLUoW2rV8jNluRWKpj+9ZpWutBfoiWgM6FGlTMw=
filippo.io/sunlight v0.6.3/go.mod h1:1wUWZmC0tYtzP0PC2rsegshLsLYZ6sgFSe4Utj33Tyg=
filippo.io/torchwood v0.5.1-0.20250713221105-b067ac9d4cf6 h1:feb1i6byodl8n5WEJJ1fafcP3eVBiiVloh3mYvnRmJY=
filippo.io/torchwood v0.5.1-0.20250713221105-b067ac9d4cf6/go.mod h1:Z+iz3Syg0RCaVkL9nBjG2STp/9HpuFl1+SbaNSZ/Ez8=
github.com/google/certificate-transparency-go v1.3.2 h1:9ahSNZF2o7SYMaKaXhAumVEzXB2QaayzII9C8rv7v+A=
github.com/google/certificate-transparency-go v1.3.2/go.mod h1:H5FpMUaGa5Ab2+KCYsxg6sELw3Flkl7pGZzWdBoYLXs=
golang.org/x/crypto v0.39.0 h1:SHs+kF4LP+f+p14esP5jAoDpHU8Gu/v9lFRK6IT5imM=
golang.org/x/crypto v0.39.0/go.mod h1:L+Xg3Wf6HoL4Bn4238Z6ft6KfEpN0tJGo53AAPC632U=
golang.org/x/mod v0.32.0 h1:9F4d3PHLljb6x//jOyokMv3eX+YDeepZSEo3mFJy93c=
golang.org/x/mod v0.32.0/go.mod h1:SgipZ/3h2Ci89DlEtEXWUk/HteuRin+HHhN+WbNhguU=
golang.org/x/sync v0.15.0 h1:KWH3jNZsfyT6xfAfKiz6MRNmd46ByHDYaZ7KSkCtdW8=
golang.org/x/sync v0.15.0/go.mod h1:1dzgHSNfp02xaA81J2MS99Qcpr2w7fw1gpm99rleRqA=

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// Command ctfetch fetches and dumps a specific leaf entry from a given Static CT log.
// It can also dump the whole contents of the tile, if the -dumpall flag is specified.
// (C) Copyright 2026 Pim van Pelt <pim@ipng.ch>
package main
import (
"bytes"
"compress/gzip"
"encoding/json"
"flag"
"fmt"
"io"
"net/http"
"os"
"strconv"
"strings"
"filippo.io/sunlight"
"golang.org/x/mod/sumdb/tlog"
)
func main() {
dumpAll := flag.Bool("dumpall", false, "dump all entries in the tile")
flag.Usage = func() {
fmt.Fprintf(os.Stderr, "Usage: %s [--dumpall] <log-url> <leaf-index>\n", os.Args[0])
fmt.Fprintf(os.Stderr, "Example: %s https://halloumi2026h1.mon.ct.ipng.ch 457683896\n", os.Args[0])
fmt.Fprintf(os.Stderr, "\nFlags:\n")
flag.PrintDefaults()
}
flag.Parse()
if flag.NArg() != 2 {
flag.Usage()
os.Exit(1)
}
logURL := strings.TrimSuffix(flag.Arg(0), "/")
leafIndex, err := strconv.ParseInt(flag.Arg(1), 10, 64)
if err != nil {
fatal("invalid leaf index: %v", err)
}
// Convert leaf index to tile coordinates
tile := tlog.TileForIndex(sunlight.TileHeight, tlog.StoredHashIndex(0, leafIndex))
tile.L = -1 // Data tiles are at level -1
// Get the tile path (both partial and full versions)
partialPath := sunlight.TilePath(tile)
// For full tile path, we need to remove the .p/W suffix if present
fullTile := tile
fullTile.W = sunlight.TileWidth
fullPath := sunlight.TilePath(fullTile)
positionInTile := leafIndex % sunlight.TileWidth
fmt.Fprintf(os.Stderr, "Leaf Index: %d\n", leafIndex)
fmt.Fprintf(os.Stderr, "Position in tile: %d\n", positionInTile)
fmt.Fprintf(os.Stderr, "Partial tile path: %s\n", partialPath)
fmt.Fprintf(os.Stderr, "Full tile path: %s\n", fullPath)
// Try to fetch the tile (partial first, then full)
var tileData []byte
var fetchedPath string
// Try partial tile first
partialURL := logURL + "/" + partialPath
fmt.Fprintf(os.Stderr, "Trying: %s\n", partialURL)
tileData, err = fetchURL(partialURL)
if err == nil {
fetchedPath = partialPath
fmt.Fprintf(os.Stderr, "Successfully fetched partial tile\n")
} else {
// Fall back to full tile
fullURL := logURL + "/" + fullPath
fmt.Fprintf(os.Stderr, "Partial tile failed, trying: %s\n", fullURL)
tileData, err = fetchURL(fullURL)
if err != nil {
fatal("failed to fetch tile: %v", err)
}
fetchedPath = fullPath
fmt.Fprintf(os.Stderr, "Successfully fetched full tile\n")
}
// Decompress if needed
tileData, err = decompress(tileData)
if err != nil {
fatal("failed to decompress tile: %v", err)
}
fmt.Fprintf(os.Stderr, "Tile size: %d bytes\n", len(tileData))
fmt.Fprintf(os.Stderr, "Fetched path: %s\n\n", fetchedPath)
if *dumpAll {
// Dump all entries in the tile
dumpAllEntries(tileData)
} else {
// Dump only the specific entry at the position
dumpEntryAtPosition(tileData, int(positionInTile), leafIndex)
}
}
func fetchURL(url string) ([]byte, error) {
resp, err := http.Get(url)
if err != nil {
return nil, err
}
defer resp.Body.Close()
if resp.StatusCode != http.StatusOK {
return nil, fmt.Errorf("HTTP %d", resp.StatusCode)
}
return io.ReadAll(resp.Body)
}
func dumpAllEntries(tileData []byte) {
entryNum := 0
for len(tileData) > 0 {
e, remaining, err := sunlight.ReadTileLeaf(tileData)
if err != nil {
fatal("failed to read entry %d: %v", entryNum, err)
}
tileData = remaining
dumpEntry(e, entryNum)
fmt.Println()
entryNum++
}
fmt.Printf("Total entries: %d\n", entryNum)
}
func dumpEntryAtPosition(tileData []byte, position int, expectedIndex int64) {
entryNum := 0
for len(tileData) > 0 {
e, remaining, err := sunlight.ReadTileLeaf(tileData)
if err != nil {
fatal("failed to read entry %d: %v", entryNum, err)
}
tileData = remaining
if entryNum == position {
if e.LeafIndex != expectedIndex {
fmt.Fprintf(os.Stderr, "WARNING: Expected leaf index %d but found %d at position %d\n",
expectedIndex, e.LeafIndex, position)
}
dumpEntry(e, entryNum)
return
}
entryNum++
}
fatal("position %d not found in tile (only %d entries)", position, entryNum)
}
func dumpEntry(e *sunlight.LogEntry, entryNum int) {
fmt.Printf("=== Entry %d ===\n", entryNum)
fmt.Printf("Leaf Index: %d\n", e.LeafIndex)
fmt.Printf("Timestamp: %d\n", e.Timestamp)
fmt.Printf("Is Precert: %v\n", e.IsPrecert)
if e.IsPrecert {
fmt.Printf("Issuer Key Hash: %x\n", e.IssuerKeyHash)
}
fmt.Printf("Certificate: %d bytes\n", len(e.Certificate))
if e.PreCertificate != nil {
fmt.Printf("PreCertificate: %d bytes\n", len(e.PreCertificate))
}
fmt.Printf("Chain Fingerprints: %d entries\n", len(e.ChainFingerprints))
for i, fp := range e.ChainFingerprints {
fmt.Printf(" [%d]: %x\n", i, fp)
}
// Try to extract parsed certificate info
if trimmed, err := e.TrimmedEntry(); err == nil {
if data, err := json.MarshalIndent(trimmed, " ", " "); err == nil {
fmt.Printf("Parsed Certificate Info:\n %s\n", data)
}
}
}
const maxCompressRatio = 100
func decompress(data []byte) ([]byte, error) {
r, err := gzip.NewReader(bytes.NewReader(data))
if err != nil {
// Not gzipped, return as-is
return data, nil
}
maxSize := int64(len(data)) * maxCompressRatio
return io.ReadAll(io.LimitReader(r, maxSize))
}
func fatal(format string, args ...any) {
fmt.Fprintf(os.Stderr, "Error: "+format+"\n", args...)
os.Exit(1)
}