A signature lets anyone verify a blob's author without a server. The private key behind the blob's signer produces it, and it covers every other byte of the blob.

This page defines the signature value type, an alias of bytes used for the sig field of the blob envelope. Its formal schema is attached as the schemaDefinition in this document's metadata, so the app can show it.

The signed message is the blob itself with sig set to 64 zero bytes, encoded as canonical DAG-CBOR. The real signature then replaces the zeros and the blob is encoded again. Verification checks the length first (64 bytes for both Ed25519 and P-256), zeroes the field, re-encodes and verifies. An implementation that signs the blob with the field omitted produces a signature the daemon rejects. Ed25519 signatures are deterministic, which is why the home document's genesis Change is the same bytes on every device of an account. See Signed Blobs.

See also

Signed Blobs: the signing rule and encoding.

blob: the envelope that carries sig.

principal: the public key that verifies it.

Integrity: what a signature proves.