Try to break a receipt -- Treeship

Two minutes, five commands. Sign something, change one character, and watch verification fail.

The fastest way to see what a receipt is: make one, tamper with it, and check it again. Everything runs on your machine. No account, and no network after the install.

Needs Node.js and npm. macOS or Linux; Windows via WSL.

Install and initialize

npm install -g treeship && treeship init

init generates an Ed25519 keypair, the ship key. The private key stays on this machine.

Sign something

treeship wrap -- echo hello

The command runs as normal, then Treeship seals a signed receipt for it. The no active session warning is expected: this receipt stands on its own.

Verify it

treeship verify last

✓ verified  (1 artifact . chain intact)

Break it

Open the receipt in any editor. It is the art_….json file in:

ls ~/.treeship/artifacts/

Find the long "payload" value under "envelope". That is the signed record of what ran: the command, its exit code and output hash, the time and the actor. Change any single character inside it, or inside "sig", and save the file.

The fields at the top of the file (signed_at, key_id, digest, artifact_id) are a local index for listing receipts. Verification ignores them and reads only the signed envelope, so editing them changes nothing that is checked: verify still passes and still shows the signed time, not the edited one.

Verify again

treeship verify last

✗ verification failed
  outcome: fail
  passed: 0
  failed: 1
  …
       reason: invalid signature for key: key_…

The command exits 1, so a script or CI job can gate on it.

What just happened

A receipt is an Ed25519 signature over the exact bytes of its signed payload, and its id is derived from those same bytes. Change one of them and the signature no longer matches. Nothing was asked of a server: the check ran on your machine, against a public key.

Take it further

Check a receipt with no Treeship code at all. treeship receipt export <id> --format json prints the signed message, the signature and the public key for any Ed25519 library.
Tampering matters most on someone else's machine. Verify a session package walks through checking a package you were handed.
Know the limits before you rely on it: What a receipt proves.

Try to break a receipt