julienboudry/elephstamp repository overview

⁠ElephStamp

Prove that a file existed at a given time, anchored forever in the Bitcoin blockchain. No account, no fee, no trusted third party: just a small .ots proof next to your file, which anyone can check independently.

elephstamp is a friendly command-line tool for OpenTimestamps⁠, the open standard for blockchain timestamping. Stamp a contract, a source release, a dataset or a photo today; collect the Bitcoin confirmation a few hours later; verify it whenever you need to, years from now. Its proofs are byte-for-byte interoperable with the reference ots client, so you are never locked in.

⁠Why ElephStamp

• Your own Bitcoin node is optional. Verify against it, pruned or not, for a check that trusts nobody else; or, when you do not run one, against public explorers (mempool.space, blockstream.info). Their block headers' proof of work is checked locally and several can be cross-checked, which bounds the trust you put in them.
• Safer than the reference client. Every answer a calendar server sends back is checked against the blockchain before it goes into your proof: a buggy or hostile calendar cannot leave you with a proof that fails verification.
• Reports you can read. See what every calendar did, which block and transaction carry your proof, and why a proof is still pending, instead of a raw dump.
• Made for automation. Stamp many files in one go, poll pending proofs from cron, and script everything with documented exit codes and a stable --json output.
• Hardened. An .ots file is treated as untrusted input: only whitelisted calendars are ever contacted, over HTTPS, with strict size and time limits.

⁠Quick start

Define the alias once, in your shell's profile:

alias elephstamp='docker run --rm -v "$PWD:/data" --user "$(id -u):$(id -g)" julienboudry/elephstamp'

The volume shows your current directory to the container; --user makes the proofs it writes belong to you. Then:

elephstamp stamp contract.pdf          # → contract.pdf.ots, pending
elephstamp upgrade contract.pdf.ots    # a few hours later: collect the Bitcoin attestation
elephstamp verify contract.pdf.ots     # check it against the blockchain

 VERIFIED

 contract.pdf existed before 2026-09-18 15:27:58 UTC (Bitcoin block 967571).

  Original         contract.pdf — digest matches the proof
  Proof            sha256 digest 065470e2…, 3 Bitcoin attestations recomputed offline
  Block headers    mempool.space — trusted for block headers only
  Required depth   6 confirmations

elephstamp info explains a proof in plain words, elephstamp tree shows every hash for checking by hand, and elephstamp help <command> lists every option.

⁠The image

• Tags: an exact version (X.Y.Z), X.Y and X for the newest release in that line, and latest.
• Platforms: linux/amd64, linux/arm64, linux/riscv64.
• Contents: the release's elephstamp.phar on the official Debian-based PHP image, nothing else.
• Provenance: every image carries a signed build attestation, checkable with gh attestation verify oci://docker.io/julienboudry/elephstamp:latest --repo CondorcetVote/Elephstamp.

⁠Learn more

• Docker usage in detail⁠: paths, networking, reaching a Bitcoin node, building the image yourself.
• Command-line guide⁠: every command, option, JSON output and exit code.
• ElephStamp on GitHub⁠: also a PHP library, with other installation methods and the changelog. MIT licensed.