{
  "v": "atsp.receipt/1",
  "alg": "Ed25519",
  "public_key_b64": "5CcVos+PxwS2/xNUjhaUW2oEyUk7Cu3WeXZZu30B5pI=",
  "key_id": "ed25519:5CcVos+PxwS2/xNU",
  "signed_message": "atsp.receipt/1|<hash>",
  "hash": "sha256(canonical JSON {v,seq,t,type,actor,body_sha256,prev})"
}