datumesh

Verify Datumesh receipts in Python. A receipt is a signed answer for one addressable data cell; this library checks its canonical form (RFC 8785 JSON) and its Ed25519 signature against the signer's published keys, and optionally the recomputation checks (function descriptor, input receipts and slice manifests, and a value you computed) and the content of a blob value, as the Datumesh specification (revision spec-0.4.0) defines. It also checks a mesh's response envelope and resolves the unit of a cell's value.

pip install datumesh
git clone --depth 1 --branch spec-0.4.0 https://github.com/datumesh-com/datumesh-spec && cd datumesh-spec

import json
from datumesh import keys_from_response, verify

vector = json.load(open("vectors/receipt/stored-number.json"))
key_doc = vector["keys"]["rates.example.org"]["https"]["body"]  # served at https://rates.example.org/.well-known/datumesh.json
keys = keys_from_response("rates.example.org", 200, key_doc)
result = verify(vector["input"], keys)
print(result.ok, result.level, result.key)  # True signed rates.example.org#d712b32a2cc5cb7c

Website: https://datumesh.com · Specification: https://github.com/datumesh-com/datumesh-spec

API

• verify(receipt, keys, recompute=None, blob=None) -> VerifyResult: runs the verification procedure of SPEC 10.1. Never raises for an invalid receipt or bad key material; the result has ok, code ("OK" or an error code), level ("signed" or "recomputed"), hash, key, detail and path. Two codes come with success, at level signed (SPEC 10.1 step 7.6): "E_EVAL_UNAVAILABLE" when you pass recompute without a value because you could not evaluate the function (the other recomputation checks still run first), and "E_INPUT_SUPERSEDED" when your value differs but the evaluation's lineage shows that an input was replaced by a later version (the receipt is historical, not wrong). It uses no network: keys are an argument (a key document, a KeysResult, a {key id: public key} mapping, or a list of these). recompute takes the descriptor (leave it out if you have none; None is a JSON null and fails the hash check), the input receipts (slice members included), the manifests of slice entries (slice:<slice id>:<members hash>), the value you computed and optionally the evaluation's lineage (the library does not evaluate functions, formulas included); blob takes the content bytes of a blob value, whose length and SHA-256 are then checked (step 7.7, reported as blob_checked).
• check_envelope(status, body, keys, request) -> EnvelopeResult: checks a mesh's response to https://<mesh>/cell/... (SPEC 5.5), verifies the receipt inside it, and checks that it answers your request (request is {"cell_id": ..., "asof": ...}, asof only if you asked for one; the receipt's asof must be at or before it, for ok and stale alike). A not_covered envelope may carry a formula evaluation fault (exposed as fault). The envelope itself is unsigned: stale, superseded_by, a verified label and the currency ok asserts remain the mesh's claims.
• resolved_unit(descriptor, cell) -> str | None: the unit of a cell's value, such as USD/EUR (SPEC 7.1, units.md).
• keys_from_response(host, status, body) -> KeysResult: interprets a response for https://<host>/.well-known/datumesh.json (SPEC 9.3).
• fetch_keys(host, timeout=10.0) -> KeysResult: the only function that uses the network. One GET, TLS verified, redirects not followed.
• canonicalize(obj, kind=None) -> bytes, cell_hash, function_hash, receipt_hash, receipt_payload, jcs: validation, RFC 8785 canonical bytes and SHA-256 hashes. Kinds "slice" and "manifest", with slice_id, members_hash and slice_entry, cover slice objects and manifests (SPEC 4.4, 15.13).
• parse_uri(uri, signature), format_uri(ref), uri_to_https(uri, mesh): cell URIs (SPEC 5).
• DatumeshError (with .code and .path), ERROR_CODES, SUCCESS_CODES, FAULT_CODES, SPEC_VERSION, UNITS, CURRENCIES.

Requires Python 3.10 or later and PyNaCl. String rules use Unicode 15.1 tables shipped with the package, so results do not depend on the Python version's own Unicode database; the unit list is copied from the specification's units.md. Choosing which publishers to trust is up to you: a valid signature only means the key holder made the statement.

Licence: Apache-2.0.