SigningNonces not zeroized (upstream frost-secp256k1-tr)

[kwsantiago]

Problem

SigningNonces from frost-secp256k1-tr doesn't implement Zeroize. FROST nonces are critical—if leaked or reused, the private key can be recovered.

Affected Locations

• keep-core/src/frost/signing.rs:49-61 - NonceWrapper has empty zeroize() impl
• keep-core/src/frost/coordinator.rs:16-24 - our_nonces: Option<SigningNonces>

Mitigation Options

1. File upstream issue with frost-secp256k1-tr maintainers
2. Consider process isolation for signing sessions
3. Explicit memory clearing after signing completes

[kwsantiago]

Made an issue here: ZcashFoundation/frost#986

[kwsantiago]

Merged in ZcashFoundation/frost#987

Waiting on their new release with the fixes included.