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Pim van Pelt
2026-04-06 01:29:38 +02:00
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/ctfetch /ctfetch
/tiledump /ctail

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README.md
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# ctfetch # Certificate Transparency tools
Tools for working with Certificate Transparency log tiles. Tools for working with [Static CT log](https://c2sp.org/static-ct-api) tiles.
## Install ## Install
```bash ```bash
GOPRIVATE=git.ipng.ch go install git.ipng.ch/certificate-transparency/ctfetch/cmd/ctfetch@latest GOPRIVATE=git.ipng.ch go install git.ipng.ch/certificate-transparency/ctfetch/cmd/...@latest
``` ```
The GOPRIVATE environment variable skips _Go checksum database_ and _Go module proxy_ as these do ## Tools
not index modules on `git.ipng.ch`.
## Usage ### ctfetch
`ctfetch` operates in two modes depending on the arguments given. Fetch and decode entries from a Static CT log as structured JSON.
### Leaf-index mode
Fetch a specific entry (or all entries in its tile) by leaf index:
```bash
ctfetch [flags] <log-url> <leaf-index> [+sct] [+issuer] [+ctlog] [+all]
```
**Examples:**
Dump a specific entry:
```bash
ctfetch https://halloumi2026h1.mon.ct.ipng.ch 629794635
```
Dump with SCTs, issuer chain, and CT log details:
```bash ```bash
ctfetch https://halloumi2026h1.mon.ct.ipng.ch 629794635 +all ctfetch https://halloumi2026h1.mon.ct.ipng.ch 629794635 +all
``` ```
### Tile-dump mode → [Full documentation](docs/ctfetch.md)
Fetch all entries from a tile URL or a local file. Automatically detects data tiles (log entries) and hash tiles (Merkle tree hashes). ### ctail
Tail a Static CT log, printing a one-liner per new cert/precert as it arrives.
```bash ```bash
ctfetch [flags] <tile-url-or-file> [+sct] [+issuer] [+ctlog] [+all] ctail https://halloumi2026h1.mon.ct.ipng.ch
``` ```
**Examples:** → [Full documentation](docs/ctail.md)
Data tile from a URL:
```bash
ctfetch https://halloumi2026h1.mon.ct.ipng.ch/tile/data/x002/x460/135
```
Data tile with SCTs and CT log details:
```bash
ctfetch https://halloumi2026h1.mon.ct.ipng.ch/tile/data/x002/x460/135 +sct +ctlog
```
Hash tile from a URL:
```bash
ctfetch https://halloumi2026h1.mon.ct.ipng.ch/tile/0/x100/999
```
Data tile from a local file (with issuer resolution):
```bash
ctfetch --monitoring-url https://halloumi2026h1.mon.ct.ipng.ch tile.bin +issuer
```
## Hash tiles vs data tiles
A Static CT log stores two kinds of tiles:
**Data tiles** (`/tile/data/...`) contain the actual log entries — DER-encoded certificates and precertificates along with their metadata (leaf index, timestamp, chain fingerprints, etc.). These are what `ctfetch` parses into structured JSON. The output modifiers `+sct`, `+issuer`, `+ctlog`, and `+all` all operate on data tiles.
**Hash tiles** (`/tile/N/...`, where N is a tree level ≥ 0) contain the internal nodes of the Merkle tree — rows of raw 32-byte SHA-256 hashes used for inclusion and consistency proofs. There are no certificates in a hash tile; `ctfetch` outputs only the list of hashes. Using `+sct`, `+issuer`, `+ctlog`, or `+all` with a hash tile is an error.
The tree is organised so that level 0 hashes cover individual leaves (each is `SHA-256(0x00 || MerkleTreeLeaf)`), and each higher level hashes pairs of nodes from the level below. The tile URL encodes the level: `/tile/0/...` is level 0, `/tile/1/...` is level 1, and so on.
## Output modifiers
| Modifier | Description |
|---|---|
| `+sct` | Parse and include embedded Signed Certificate Timestamps from final (non-precert) certificates |
| `+issuer` | Fetch and include issuer certificate details from the log's `/issuer/<fp>` endpoint |
| `+ctlog` | Look up each SCT's log ID in the CT log list and include operator/state details |
| `+all` | Enable all of `+sct`, `+issuer`, and `+ctlog` at once |
## Flags
| Flag | Default | Description |
|---|---|---|
| `--logs-list-url` | `https://www.gstatic.com/ct/log_list/v3/all_logs_list.json` | URL of the CT log list JSON used for `+ctlog` lookups |
| `--monitoring-url` | _(none)_ | Log root URL for issuer lookups when input is a local file |
## Notes
- In tile-dump mode with a tile URL, `+issuer` automatically derives the log root by stripping the `/tile/...` path. With a local file, `--monitoring-url` must be provided.
- Partial tiles (`.p/N` suffix) are tried first; on 404 the full tile is fetched automatically.
- The CT log list and issuer certificates are cached in memory, so each unique resource is fetched only once per invocation.

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cmd/ctail/main.go Normal file
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// Command ctail tails a Static CT log, printing a one-liner per new entry.
//
// ctail [flags] <log-url>
//
// (C) Copyright 2026 Pim van Pelt <pim@ipng.ch>
package main
import (
"bufio"
"bytes"
"crypto/x509"
"flag"
"fmt"
"io"
"net/http"
"os"
"strconv"
"strings"
"time"
"filippo.io/sunlight"
"git.ipng.ch/certificate-transparency/ctfetch/internal/utils"
"golang.org/x/mod/sumdb/tlog"
)
const version = "0.1.0"
var (
userAgent string
rateLimit time.Duration
lastRequest time.Time
)
func main() {
interval := flag.Duration("interval", 15*time.Second, "polling interval")
fromLeaf := flag.Int64("from-leaf", -1, "start from this leaf index (-1 = current tree tip)")
rateLimitFlag := flag.Duration("rate-limit", 2*time.Second, "minimum time between HTTP requests")
flag.StringVar(&userAgent, "user-agent", "ctail/"+version+" (https://git.ipng.ch/certificate-transparency/)", "User-Agent header for HTTP requests")
flag.Usage = func() {
fmt.Fprintf(os.Stderr, "Usage: ctail [flags] <log-url>\n")
fmt.Fprintf(os.Stderr, "\nPrints a one-liner per cert/pre-cert as new entries arrive in a Static CT log.\n")
fmt.Fprintf(os.Stderr, "\nExamples:\n")
fmt.Fprintf(os.Stderr, " ctail https://halloumi2026h1.mon.ct.ipng.ch\n")
fmt.Fprintf(os.Stderr, " ctail --from-leaf 0 --interval 10s https://halloumi2026h1.mon.ct.ipng.ch\n")
fmt.Fprintf(os.Stderr, "\nFlags:\n")
flag.PrintDefaults()
}
flag.Parse()
if *interval < time.Second {
fmt.Fprintf(os.Stderr, "Error: --interval must be at least 1s\n")
os.Exit(1)
}
if *rateLimitFlag < 100*time.Millisecond {
fmt.Fprintf(os.Stderr, "Error: --rate-limit must be at least 100ms\n")
os.Exit(1)
}
rateLimit = *rateLimitFlag
if flag.NArg() != 1 {
flag.Usage()
os.Exit(1)
}
logURL := strings.TrimSuffix(flag.Arg(0), "/")
var nextLeaf int64 = -1
for {
checkpointAt := time.Now()
treeSize, err := fetchCheckpointSize(logURL)
if err != nil {
fmt.Fprintf(os.Stderr, "checkpoint error: %v\n", err)
time.Sleep(*interval)
continue
}
if nextLeaf < 0 {
if *fromLeaf >= 0 {
fmt.Fprintf(os.Stderr, "Starting from leaf %d, tree size %d, polling every %s\n", *fromLeaf, treeSize, *interval)
nextLeaf = *fromLeaf
} else {
fmt.Fprintf(os.Stderr, "Starting at tree size %d, polling every %s\n", treeSize, *interval)
nextLeaf = treeSize
}
}
if err := processNewEntries(logURL, &nextLeaf, treeSize); err != nil {
fmt.Fprintf(os.Stderr, "error: %v\n", err)
}
if wait := time.Until(checkpointAt.Add(*interval)); wait > 0 {
time.Sleep(wait)
}
}
}
func processNewEntries(logURL string, nextLeaf *int64, treeSize int64) error {
for *nextLeaf < treeSize {
tileStart := (*nextLeaf / sunlight.TileWidth) * sunlight.TileWidth
if treeSize < tileStart+sunlight.TileWidth {
break // tile not yet complete; wait for next poll
}
tile := tlog.TileForIndex(sunlight.TileHeight, tlog.StoredHashIndex(0, *nextLeaf))
tile.L = -1
tilePath := sunlight.TilePath(tile)
// Always fetch the full tile; strip any .p/N partial suffix.
if idx := strings.Index(tilePath, ".p/"); idx != -1 {
tilePath = tilePath[:idx]
}
tileData, err := fetchURL(logURL + "/" + tilePath)
if err != nil {
return fmt.Errorf("fetch tile at leaf %d: %w", *nextLeaf, err)
}
tileData, err = utils.Decompress(tileData)
if err != nil {
return fmt.Errorf("decompress tile: %w", err)
}
prevNext := *nextLeaf
remaining := tileData
for len(remaining) > 0 {
e, rest, err := sunlight.ReadTileLeaf(remaining)
if err != nil {
return fmt.Errorf("read tile leaf: %w", err)
}
remaining = rest
if e.LeafIndex >= *nextLeaf {
fmt.Println(formatEntry(e))
*nextLeaf = e.LeafIndex + 1
}
}
if *nextLeaf == prevNext {
return fmt.Errorf("no progress reading tile at leaf %d", *nextLeaf)
}
}
return nil
}
func fetchURL(url string) ([]byte, error) {
if wait := time.Until(lastRequest.Add(rateLimit)); wait > 0 {
time.Sleep(wait)
}
lastRequest = time.Now()
req, err := http.NewRequest(http.MethodGet, url, nil)
if err != nil {
return nil, err
}
req.Header.Set("User-Agent", userAgent)
resp, err := http.DefaultClient.Do(req)
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 fetchCheckpointSize(logURL string) (int64, error) {
data, err := fetchURL(logURL + "/checkpoint")
if err != nil {
return 0, err
}
// Checkpoint format (tlog/sunlight):
// line 1: origin
// line 2: tree size (decimal)
// line 3: root hash (base64)
// (blank line + signature lines)
scanner := bufio.NewScanner(bytes.NewReader(data))
for i := 0; scanner.Scan(); i++ {
if i == 1 {
return strconv.ParseInt(scanner.Text(), 10, 64)
}
}
return 0, fmt.Errorf("checkpoint too short")
}
// formatEntry formats a log entry as a single ~100-char line.
func formatEntry(e *sunlight.LogEntry) string {
certType := "cert"
if e.IsPrecert {
certType = "pre "
}
certDER := e.Certificate
if e.IsPrecert && len(e.PreCertificate) > 0 {
certDER = e.PreCertificate
}
name := "(unknown)"
issuer := ""
validRange := ""
// x509.ParseCertificate may return a non-nil cert even on error (e.g. precerts
// with the CT poison critical extension), so we use the cert regardless.
cert, _ := x509.ParseCertificate(certDER)
if cert != nil {
if len(cert.DNSNames) > 0 {
name = cert.DNSNames[0]
} else if cert.Subject.CommonName != "" {
name = cert.Subject.CommonName
}
issuer = issuerLabel(cert)
notBefore := cert.NotBefore.UTC().Format("2006-01-02")
notAfter := cert.NotAfter.UTC().Format("2006-01-02")
validRange = notBefore + ".." + notAfter
}
return fmt.Sprintf("%9d %-4s %-21s %-40s %s",
e.LeafIndex, certType,
validRange, trunc(issuer, 40), name)
}
// issuerLabel builds a human-readable issuer string. When the CN is terse
// (e.g. "R13") and the org name isn't already embedded in it, we prepend the
// org so the result reads as "Let's Encrypt R13" instead of just "R13".
func issuerLabel(cert *x509.Certificate) string {
cn := cert.Issuer.CommonName
if len(cert.Issuer.Organization) == 0 {
return cn
}
org := cert.Issuer.Organization[0]
// Only prepend if the CN doesn't already contain the org's first word.
firstWord := strings.Fields(org)[0]
if strings.Contains(cn, firstWord) {
return cn
}
return org + " " + cn
}
// trunc truncates s to at most n bytes, appending "..." if truncated.
func trunc(s string, n int) string {
if len(s) <= n {
return s
}
return s[:n-3] + "..."
}

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# ctail
Tail a Static CT log, printing a one-liner per new certificate or precertificate as it arrives.
## Install
```bash
GOPRIVATE=git.ipng.ch go install git.ipng.ch/certificate-transparency/ctfetch/cmd/ctail@latest
```
## Usage
```bash
ctail [flags] <log-url>
```
Example:
```bash
ctail https://halloumi2026h1.mon.ct.ipng.ch
```
By default `ctail` starts at the current tree tip and prints new entries as they appear. Use `--from-leaf 0` to replay from the beginning.
## Output format
One line per entry:
```
leaf-index type validity-range issuer (up to 40 chars) subject name
```
Example:
```
1440154358 cert 2026-03-31..2026-06-29 Let's Encrypt R13 bereavementcounselling.uk
1440154359 pre 2026-03-31..2026-06-29 ZeroSSL ECC Domain Secured Ce... alpenglowforeverfilms.com
```
- **type**: `cert` for a final certificate, `pre` for a precertificate
- **issuer**: CommonName, prefixed with the organisation name when the CN alone is terse (e.g. `R13` → `Let's Encrypt R13`)
- **subject name**: first DNS SAN, falling back to the certificate's CommonName
## Flags
| Flag | Default | Description |
|---|---|---|
| `--interval` | `15s` | How often to poll the checkpoint (minimum 1s) |
| `--from-leaf` | `-1` | Start from this leaf index; `-1` means current tree tip |
| `--rate-limit` | `2s` | Minimum time between HTTP requests (minimum 100ms) |
| `--user-agent` | `ctail/VERSION (https://git.ipng.ch/certificate-transparency/)` | User-Agent header sent with every request |
## Notes
- The interval timer starts when the checkpoint is fetched, so tile-fetch time counts against the interval and the next poll stays on schedule.
- A tile is only fetched once the checkpoint confirms it is complete (256 entries). This avoids unnecessary 404s at the tree tip.
- Status and error messages go to stderr; the entry one-liners go to stdout.

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# ctfetch
Fetch and decode entries from a Static CT log, outputting structured JSON.
## Install
```bash
GOPRIVATE=git.ipng.ch go install git.ipng.ch/certificate-transparency/ctfetch/cmd/ctfetch@latest
```
The `GOPRIVATE` variable skips the Go checksum database and module proxy, which do not index modules on `git.ipng.ch`.
## Modes
`ctfetch` operates in two modes depending on the arguments given.
### Leaf-index mode
Fetch the entry at a specific leaf index:
```bash
ctfetch [flags] <log-url> <leaf-index> [+sct] [+issuer] [+ctlog] [+all]
```
Examples:
```bash
ctfetch https://halloumi2026h1.mon.ct.ipng.ch 629794635
ctfetch https://halloumi2026h1.mon.ct.ipng.ch 629794635 +all
```
### Tile-dump mode
Fetch all entries from a tile URL or local file. Automatically detects data tiles (log entries) and hash tiles (Merkle tree hashes).
```bash
ctfetch [flags] <tile-url-or-file> [+sct] [+issuer] [+ctlog] [+all]
```
Examples:
```bash
ctfetch https://halloumi2026h1.mon.ct.ipng.ch/tile/data/x002/x460/135
ctfetch https://halloumi2026h1.mon.ct.ipng.ch/tile/data/x002/x460/135 +sct +ctlog
ctfetch https://halloumi2026h1.mon.ct.ipng.ch/tile/0/x100/999
ctfetch --monitoring-url https://halloumi2026h1.mon.ct.ipng.ch tile.bin +issuer
```
## Output modifiers
| Modifier | Description |
|---|---|
| `+sct` | Parse embedded Signed Certificate Timestamps from final (non-precert) certificates |
| `+issuer` | Fetch issuer certificate details from the log's `/issuer/<fp>` endpoint |
| `+ctlog` | Look up each SCT's log ID in the CT log list and include operator/state details |
| `+all` | Enable all of `+sct`, `+issuer`, and `+ctlog` |
## Flags
| Flag | Default | Description |
|---|---|---|
| `--logs-list-url` | `https://www.gstatic.com/ct/log_list/v3/all_logs_list.json` | CT log list URL for `+ctlog` lookups |
| `--monitoring-url` | _(none)_ | Log root URL for issuer lookups when input is a local file |
## Hash tiles vs data tiles
**Data tiles** (`/tile/data/...`) contain DER-encoded certificates and precertificates with metadata (leaf index, timestamp, chain fingerprints). Output modifiers `+sct`, `+issuer`, `+ctlog`, and `+all` only apply here.
**Hash tiles** (`/tile/N/...`, N ≥ 0) contain raw 32-byte SHA-256 hashes — the internal nodes of the Merkle tree used for inclusion and consistency proofs. `ctfetch` outputs only the list of hashes; using output modifiers with a hash tile is an error.
## Notes
- With a tile URL, `+issuer` derives the log root by stripping the `/tile/...` path. With a local file, `--monitoring-url` must be provided.
- Partial tiles (`.p/N` suffix) are tried first; on 404 the full tile is fetched automatically.
- The CT log list and issuer certificates are cached in memory per invocation.