Zero-Key Roundtrip Failure in Sealed Event Encryption

[ryanleecode]

Summary

When using an all-zero 32-byte key for both sealEvent() and unsealEvent(), the seal operation succeeds but unseal fails. This affects both Ed25519 private keys and symmetric channel keys.

Expected Behavior

Any 32-byte value should roundtrip successfully:

• Ed25519 internally clamps keys (masks bits, handles edge cases)
• Zero is a valid scalar on the curve (produces identity point as public key)
• Symmetric keys have no mathematical constraints

Actual Behavior

Counterexample from PBT:

{
  channelKey: Uint8Array(32).fill(0),  // all zeros
  senderPrivateKey: Uint8Array(32).fill(0)  // all zeros
}

Flow:

1. sealEvent(params) → Right({ data: Uint8Array, messageId: string }) ✅ succeeds
2. unsealEvent(data, channelKey) → Left(SealedEventError) ❌ fails

Reproduction

import { sealEvent, unsealEvent } from './sealed-event.fn.js'
import { SealedEventParams } from './sealed-event.schema.js'

const zeroKey = new Uint8Array(32)  // all zeros
const params = new SealedEventParams({
  content: 'test',
  channelKey: zeroKey,
  senderPrivateKey: zeroKey,
})

const sealed = sealEvent(params)
// sealed is Right

const unsealed = unsealEvent(sealed.right.data, zeroKey)
// unsealed is Left - decryption/signature verification fails

Code Path

sealEvent:

const ed25519Key = BctsEd25519PrivateKey.from(senderPrivateKey)  // zero key
const derivedPublicKey = ed25519Key.publicKey().toData()  // identity point
const privKey = SigningPrivateKey.newEd25519(ed25519Key)
const signed = envelope.sign(privKey)  // succeeds
const salted = signed.addSalt()
const symmetricKey = SymmetricKey.fromData(channelKey)  // zero key
const encrypted = salted.encrypt(symmetricKey)  // succeeds

unsealEvent:

const encrypted = EnvelopeDecoder.tryFromCborData(data)
const symmetricKey = SymmetricKey.fromData(channelKey)  // same zero key
const decrypted = encrypted.decrypt(symmetricKey)  // likely fails here
const unwrapped = decrypted.unwrap()  // or fails here on signature

Hypothesis

Either:

1. SymmetricKey decryption with zero key fails (AES/ChaCha edge case)
2. Signature verification fails because zero-derived public key (identity point) doesn't verify signatures correctly

The library may have assertions or checks that reject zero keys internally, even though they're mathematically valid.

Environment

• Library: @bcts/components (Blockchain Commons Gordian Envelope)
• Ed25519 + X25519 + ECIES encryption
• Symmetric encryption (likely AES-256-GCM or ChaCha20-Poly1305)

Suggested Fix

Either:

1. Accept zero keys and handle edge case correctly (preferred)
2. Reject zero keys explicitly at from() with clear error message (documented limitation)

[leonardocustodio]

Nice, I need to check how they handle that at https://github.com/blockchainCommons/bc-components-rust
This repo is supposed to be an exact copy as we want everything to behave exactly the same and be 100% compatible. Will queue over here to see how they handle if it could have been a mistake when porting it.