attest-receipts 0.8.0

Own what you buy. The seller signs a receipt, you hold the file, anyone can verify it offline — even after the store is gone.

You don't own your movies. Not your games, your music or your ebooks either. You clicked "buy", you paid real money, and what you got is a permission slip that lives on someone else's server and can be revoked at any moment. The store folds, an algorithm flags your account, a licensing deal expires — and a library you spent years paying for evaporates. Nobody broke into your house. One click on a machine you'll never see, and it's gone.

None of this was ever a secret: it's in the terms of service nobody reads. But with physical media all but gone, the fine print is starting to bite. Sony spelled it out this August: your PlayStation purchases are a "license, not owned". Users across Europe and the UK had already been told what that means in practice: on September 1st, 551 movies they had bought — Terminator 2, Paddington, Apocalypse Now — disappear from their libraries, because a licensing deal expired. No refunds. Who gives me back the money I paid for those movies? Who decides whether I keep watching what I legitimately bought? Today the answer is: they do. And Sony is no exception. Weeks earlier, Xbox had pulled three games not just from the store but from the libraries of everyone who'd bought them. Microsoft shut its ebook store in 2019: refunds went out, and every book it had ever sold stopped opening anyway. Amazon once deleted 1984, of all titles, straight off people's Kindles. When Yahoo closed its music store in 2008 it switched off the DRM servers, and songs people had paid for stopped working on any new device. Different store, different medium, same click.

Digital was supposed to set content free. A handful of stores sell honest, DRM-free files; everywhere else it got rebuilt into an instrument of control. attest is the counterattack. It can't win back the libraries already lost; nothing can. But it's built so the next purchase doesn't end the same way: every future purchase gets the one thing every physical purchase always had, a piece that's yours — on your own disk, cryptographically provable, out of reach of anyone's click. Here's how:

What attest is

When you buy something digital, the seller signs a receipt and hands it to you. That's the whole mechanism. The receipt is a small file: keep it on a disk, in cloud storage, even printed as a QR code. Anyone can check it's genuine with free tools, offline, no account needed. If the store closes tomorrow, the receipt still verifies twenty years from now. It's the part of your purchase nobody can take away.

This works today wherever files are sold without DRM: GOG-style stores, itch.io, independent publishers selling directly. A seller could start signing this afternoon, without asking anyone's permission. Buy there, download, and keep the file next to the receipt: content plus proof, both in your hands. No store does it yet. The standard, two implementations and the conformance suite exist; the first pilot doesn't.

Closed platforms are the second track. In the EU they're already required to confirm every purchase on a durable medium; today that's the receipt email in your inbox. attest is that same confirmation in a form a machine can verify and you can take with you, still valid when the seller is no longer around to ask. That gives regulators a concrete format to point to, and the standard is built for exactly that.

Where this goes: receipts you can pass on to someone else where the rights holder allows it; transfer authority that can outlive the original seller, the hardest open problem on the roadmap; records witnessed by independent parties, so nobody can quietly rewrite them; and publishers signing a pledge, today, that if they ever shut down, their content becomes redistributable and your receipt proves you'd bought it. Owning digital things the way you own physical ones. That's the destination. The receipt is the first brick.

One thing a receipt is not, and this matters: it is not a backup. If a store dies and you never downloaded the DRM-free file, no signature can conjure it back off a dead server. What survives is the proof — see the FAQ for exactly what that's worth in each case.

attest-receipts on PyPI (issue and verify) and attest-verifier on npm (verify only) are independent Python and TypeScript implementations that agree on all 158 conformance vector leaves. Try it in your browser: https://bernalli.github.io/attest/ — drop a .attest bundle (or the built-in sample) and watch it verify entirely client-side. Be clear about the status: no store issues attest receipts in production yet, and there are no external reviews. The package version and the wire format are different things — receipts declare attest_version 0.1 or 0.2, and old receipts keep verifying under every later release, by design.

If you sell digital files, this is the part that concerns you: signing receipts costs one small self-hosted service next to your existing checkout, and it gives your customers something no competitor offers — proof of purchase that outlives your shop. Start with bridge/, or tell me what would stop you: GitHub Discussions or bernalli@proton.me. A first seller is worth more to this project than another feature.

Start here

Depending on why you landed on this page:

• You want to see whether it actually works. Open the verifier and drop the built-in sample on it. It takes about thirty seconds, installs nothing, and you can disconnect from the network first — that is the whole point of the thing.
• You want to know whether any of this concerns you. Read the FAQ. It answers the questions a sceptical person asks first, including the ones where the answer is no.
• You want the standard. docs/spec/attest-v0.1.md is the normative specification, attest-v0.2.md the additive delta, and docs/spec/vectors/ the conformance corpus every implementation is measured against.
• You might be the person this was built for — an archive, a successor, an escrow, anyone who could end up deciding who is entitled to something after the seller is gone. The question at the top of this page is a real one, and Discussions is where to answer it.

How it works, for humans

At checkout, the store signs a receipt and hands the buyer an .attest bundle — a small file the buyer keeps anywhere: disk, cloud, USB, wherever. There is no account to keep alive and nothing to sync. Later, anyone with a verifier — a friend, a marketplace, the buyer themself — can check that bundle's signature offline against the issuer's published key material and confirm it is genuine; whether it has since been revoked is only as good as the status material that verifier has, and with none it reports revocation as unknown rather than guessing. If the buyer needs to prove the receipt is specifically theirs (not just a copy that has floated around), they can do so by disclosing a salt or answering a key challenge, without exposing their identity to the verifier. Nothing in this loop requires a server: there is no central attest authority, no registry that must exist, and no phone-home — a verifier needs only the receipt bytes, the issuer's key material, and, optionally, a revocation feed.

What it is / is not

attest is a normative specification for a signed receipt envelope, a restricted JSON canonicalization profile, a pinned Ed25519 signing/verification ruleset, issuer key/artifact manifests with rotation and compromise handling, a layered offline verification algorithm, revocation-by-class semantics, and buyer-binding proof — plus a Python reference implementation and an independent TypeScript verifier.

It is not a DRM-stripping tool, a content host, an index of content, a marketplace, a general resale right (v0.1 defines no transfer at all; v0.2 §17 adds it only where the issuer mediates it), a blockchain or NFT product, or a payment instrument. A receipt is evidence of a license grant, not the artifact itself and not the transaction that paid for it.

None of this bypasses an unwilling seller: a receipt is issuer-signed, and attest cannot conjure a valid one out of a store that refuses to sign. A seller that never issues receipts leaves nothing for a later gate to check, and no amount of protocol fixes that.

Status

Spec v0.1 is complete and v0.2 is specified and implemented on main, with two independent implementations — a Python reference implementation and a TypeScript verifier — that agree on all 158 conformance vector leaves across 40 groups: 52 of them the v0.1 corpus, the rest exercising v0.2's hybrid signature profile, transparency/anchoring behaviour, the upgrade-policy hardening (mixed-keyset prohibition, artifact-manifest currency, anchor profile v2, logged revocation deadlines), and Stage 3 issuer-mediated transfer. (A v0.1-only verifier is required to reject v0.2 envelopes, so it is measured against the 51-leaf subset.) There is also an end-to-end demo that deletes a store's entire infrastructure mid-lifecycle and proves the receipt still verifies.

The published packages ship all of v0.2 — Stages 1 and 2 (hybrid signatures; transparency and anchoring) and Stage 3, issuer-mediated transfer, this document's own §17.

Seven pieces of work go beyond what a test suite can show. All of them are on main, and they are linked here rather than left invisible:

• Formal verification. A Tamarin model of the wire protocol: machine-checked theorems that acceptance implies an issuer signature, that a rotation is accepted only when the previous active key signed it or it carries an explicit compromise flag, and that the reason a revoked key is rejected cannot itself be forged — soundness, not liveness — plus attack exhibits proved reachable rather than argued in prose, plus negative controls that must falsify. Each theorem states its own scope in the theory file; nothing is claimed more broadly there than the prover checked, and a CI checker pins those statements so the claims cannot drift from the proofs.
• Threat model. 67 attacks catalogued across the whole receipt lifecycle, each either mitigated or recorded as out of scope with a reason, a traceability matrix, and the protocol gaps the exercise found left tracked in the open instead of quietly fixed.
• Privacy considerations. Every field classified by what it reveals to which observer, twenty testable privacy claims, and a GDPR annex covering what a receipt deliberately does not record.
• Transfer economics (non-normative). The market and legal context behind Stage 3's transfer profile — resale velocity, the issuer-royalty incentive, and the CJEU case law (UsedSoft, Tom Kabinet) that makes transfer issuer-mediated rather than a general resale right.
• Internet-Draft. A snapshot-profile mirror of this specification was submitted to the IETF Datatracker on 2026-08-06 and accepted as an individual submission (Informational, expires 2027-02-07) — it declares that it mirrors v0.1 revision 5 and v0.2 revision 6, so the specification in this repository, not the draft, remains normative. The XML source lives here and builds clean to txt/html in CI; the next revision will go out under the name it now carries, and will be submitted declaring the first as the document it replaces. Being an I-D means the document exists and can be cited as work in progress, nothing more: it is not endorsed by the IETF and has no formal standing in the standards process.
• Standards-relationship annex. Documents attest's boundary against every adjacent standard people compare it to — W3C Verifiable Credentials, eIDAS 2.0/the EUDI Wallet, JOSE/JWS and COSE, RFC 8785 (JCS), C2PA, SCITT/RFC 9943, and RATS (RFC 9334) — so each comparison is answered once instead of re-argued per issue.
• Conformance program. One documented command, run with a third party's own adapter against the vector corpus, produces a pass/fail report and a self-certification claim; both in-repo verifiers pass 130/130 through that exact path.

Quickstart

Install the reference implementation from PyPI (the distribution is named attest-receipts; the import package and the CLI are both attest):

pip install attest-receipts
attest --help

The TypeScript verifier is on npm as attest-verifier:

npm install attest-verifier

Or work from a checkout of this repo:

uv venv --python 3.12 .venv && uv pip install --python .venv -e '.[dev]'
# or: pip install -e .

.venv/bin/attest --help

.venv/bin/python demo/store_dies.py

.venv/bin/pytest --cov=attest --cov-report=term-missing

and a TypeScript verifier quickstart:

cd verifiers/ts && npm install && npm test

See demo/README.md for what each step of the demo proves, and docs/spec/attest-v0.1.md plus its companion JSON Schema for the normative specification. docs/spec/vectors/ holds the conformance corpus every implementation is checked against.

For merchants who'd rather not hand-sign anything, see bridge/README.md.

For anyone wanting to run a witness — the component that cosigns a log's checkpoints so a verifier can tell that somebody else saw the same tree — see witness/README.md. Like the bridge, it is a reference implementation for operators and is not published to any package registry.

docs/spec/attest-v0.2.md is an additive delta specification defining the v0.2 hybrid Ed25519+ML-DSA-65 signature profile (post-quantum-resistant receipts, attest_version: "0.2"); v0.1 receipts remain valid and verifiable forever. That profile was Stage 1; Stage 2 — issuer key transparency and timestamp anchoring, where a log corroborates a receipt's existence without ever being able to make an unsigned receipt look authentic — is specified in the same document. Stage 3 — issuer-mediated transfer, giving license.transferable its first real meaning, layered on top of the Stage 2 log — is specified there too (§17); business economics around resale are deliberately out of protocol and live in the non-normative transfer-economics annex.

docs/spec/attest-versioning.md is the normative upgrade policy governing both specifications above: the additive pattern new extensions must follow, the eternal-verifiability guarantee, the three-state algorithm lifecycle (active / deprecated / unsafe), the amendment procedure, and the signature-suite, payload-field, revocation-class, log-entry-type, and transfer-type registries.

docs/spec/attest-threat-model.md is the maintained threat model behind the two specifications above — a living normative companion that analyzes their mechanisms rather than imposing requirements of its own — and docs/spec/attest-privacy.md is its privacy-considerations sibling.

The core protocol properties are machine-checked in Tamarin: formal/ holds the model, the property↔lemma↔spec map, and the honest scope of what is and is not proved, gated in CI by a statement-pinning checker.

docs/spec/attest-standards-relationship.md (non-normative) is the boundary annex: in terms an expert in each standard would accept, it states attest's relationship to W3C Verifiable Credentials, eIDAS 2.0/the EUDI Wallet, JOSE/JWS and COSE, RFC 8785 (JCS), C2PA, SCITT (RFC 9943), and RATS (RFC 9334) — including what a future bridge to one of them could look like, where one exists.

Roadmap / north star

Non-normative, and deliberately undated — these are directions, not commitments:

The authorized preservation escrow described at the top of this page is not listed here: it is the case this project is aimed at, not a future direction. What follows is genuinely speculative.

• Evidence capture for non-cooperating stores. A research track into TLS-session-proof techniques (the zkTLS/TLSNotary class) that could let a buyer capture their own evidence of a purchase from a store that never signs anything, at weaker-than-issuer-signed trust. Legal review is required before any of this is built.
• Registry / replication layer. An optional layer for replicating verification material, with optional Merkle-root transparency anchoring — separate from the shipped §17.5 chain-of-title audit surface, and still strictly optional.

Licensing, contributing, contact

License. Code is licensed Apache-2.0; the specification and other documentation are licensed CC BY 4.0 — reuse and derivatives of the spec must credit the original author, since attribution is a condition of that license, not a courtesy. NOTICE and AUTHORS carry the required attribution.

Naming. The name attest identifies this project and implementations that actually conform to it; forks are welcome to use the technology but not the name for a divergent derivative. This paragraph is a naming norm, not a trademark registration — real trademark enforcement would require actually registering the mark, which has not happened. Conformance claims follow the self-certification process in docs/conformance.md.

Contributing. See CONTRIBUTING.md. Implementation pull requests must pass all 158 conformance vector leaves and keep both the Python and TypeScript suites green.

Contact. Use GitHub Issues for technical bugs, GitHub Discussions for everything else, or email bernalli@proton.me. Security issues follow a different path — see SECURITY.md, and do not open a public issue for a vulnerability.

Skeptical about any of this? docs/faq.md answers the first questions a reasonable person asks.