The ed25519sha256_single signature scheme

Tutorial

Application

This scheme computes a single ed25519 digital signature over the input message. Its output is a ~sig object with the following contents:

{
    "@type": "https://didcomm.org/signature/1.0/ed25519Sha512_single",
    "sig_data": "base64URL(64bit_integer_from_unix_epoch|msg)",
    "signature": "base64URL(ed25519 signature)",
    "signer": "base64URL(inlined_ed25519_signing_verkey)"
}

• @type MUST be https://didcomm.org/signature/1.0/ed25519Sha512_single
• sig_data MUST be the base64URL encoding of a 64-bit integer prepended to the message
• signature MUST be the base64URL encoding of the resulting ed25519 digital signature over sig_data
• signer MUST be the base64URL encoding of the corresponding ed25519 public key used to sign sig_data

Verification

The successful outcome of this scheme is the plaintext.

1. base64URL-decode signer
2. base64URL-decode signature
3. Verify the ed25519 signature over sig_data with the key provided in signer
4. Further processing is halted if verification fails and an "authentication failure" error is returned
5. base64URL-decode the sig_data
6. Strip out the first 8 bytes
7. Return the remaining bytes