Cryptography

// 1. Canonicalize receipt data
canonical = json_canonicalize(receipt_data)

// 2. Compute SHA-256 hash
digest = SHA256(canonical)

// 3. Sign with organization's Ed25519 private key
signature = Ed25519.sign(digest, org_private_key)

// 4. Store signature and public key reference
verity_receipt = {
  hash: "0x" + digest.hex(),
  proof: {
    signedBy: org_public_key,
    signature: base64(signature),
    algorithm: "Ed25519+SHA-256"
  }
}

// 5. Verification (any party with the public key)
valid = Ed25519.verify(digest, signature, org_public_key)

// Each negotiation event is hashed with the previous hash
event_0_hash = SHA256(serialize(event_0))
event_1_hash = SHA256(serialize(event_1) + event_0_hash)
event_n_hash = SHA256(serialize(event_n) + event_n-1_hash)

// The chain is broken if any event is modified or reordered
// Verification: replay from event_0 and compare final hash