Expose spend-auth signing and verification accessors - #193
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Add two public methods needed for non-transaction signatures (such as
UFVK binding signatures in zcash_keys):
- SpendAuthorizingKey::sign signs a message with the unrandomized key,
delegating to the inner redjubjub::SigningKey.
- SpendValidatingKey::to_verification_key returns the unrandomized
redjubjub::VerificationKey, enabling verification of non-spend signatures.
Also moves the rand_core::{CryptoRng, RngCore} import from a cfg(test) gate
to unconditional, since the new sign method needs it in production code.
Co-Authored-By: Claude <noreply@anthropic.com>
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Won't do. |
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Motivation
Downstream consumers (notably
zcash_keysin librustzcash) need to sign and verify non-transaction messages with spend-authorizing keys. For example, the proposed UFVK binding signature inzcash_keyssigns a UFVK's canonical encoding with the account'sUnifiedSpendingKeyto detect tampering of the stored UFVK in a wallet database (audit finding COR-1649).Currently, the signing and verification primitives are only accessible through the
randomizepath, which applies a per-spend randomizer. For non-transaction signatures, no randomizer is needed, but there is no public way to sign with the unrandomized key or to obtain the unrandomized verification key.Changes
SpendAuthorizingKey::signsigns a message with the unrandomized spend-authorizing key, delegating to the innerredjubjub::SigningKey.SpendValidatingKey::to_verification_keyreturns the unrandomizedredjubjub::VerificationKey, enabling verification of non-spend signatures.Both are pure delegation methods with no new logic. The existing
randomizepath is unchanged.COR-1649
Co-Authored-By: Claude noreply@anthropic.com