Crypto
Signature verification and key parsing. This package exists so that a service can check that a request really came from the account that claims to have sent it: you resolve the issuer’s signing key from its DID document, and verify the signature against it.
You need it directly only when you are handling raw signatures. Verifying an inbound service-auth JWT, the common case, goes through Server, which uses this package underneath. See Building a feed generator.
Verifying a signature
verify_signature takes the public key as a did:key string, the bytes that were signed, and the signature:
from atproto import verify_signature
is_valid = verify_signature(did_key, signing_input, signature)
It returns a bool. A key whose algorithm is not supported raises UnsupportedSignatureAlgorithmError; a malformed did:key raises one of the DidKeyError subclasses.
did:key and multikeys
A did:key is did:key: followed by a multikey: the compressed public key, prefixed with a multicodec identifying its curve, encoded as base58btc multibase. parse_did_key unwraps both layers and decompresses the key:
from atproto_crypto.did import parse_did_key
multikey = parse_did_key(did_key) # 'did:key:zQ3s...' or 'did:key:zDna...'
print(multikey.jwt_alg) # ES256K or ES256
print(len(multikey.key_bytes)) # 65: the decompressed public key
Multikey is that pair, jwt_alg and key_bytes, with from_str and to_str for the multikey form without the did:key: prefix.
Going the other way:
- format_did_key
Compress a public key and format it as
did:key:....- format_multikey
The same without the
did:key:prefix.- format_did_key_multikey
Prefix a multikey that is already compressed.
- get_multikey_alg
Read the algorithm out of a multikey without decompressing the key.
- get_did_key
Convert a DID document verification method, its
typeandpublicKeyMultibase, into adid:key. This is what DidDocument.get_did_key calls, and it accepts the three types the protocol uses:EcdsaSecp256r1VerificationKey2019,EcdsaSecp256k1VerificationKey2019andMultikey. It returnsNonefor anything else.
Multibase has the raw base58btc encode and decode, if you need the layer below.
Supported algorithms
Curve |
JWT alg |
Multicodec prefix |
|---|---|---|
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Both are ECDSA over SHA-256, and both are verify-only here: this package does not generate keys or sign. Signatures must be in the compact 64-byte form, and only the low-S variant is accepted; a high-S signature over otherwise valid data verifies as False, per the cryptography spec.