TransactionSigner

Transaction signer using Schnorr BIP-340 signatures via JNI to Rust midnight-ledger.

This class bridges Kotlin → JNI → Rust FFI → midnight-ledger for cryptographic signing.

Architecture:

Kotlin: TransactionSigner.signData(privateKey, data)
  ↓
JNI (C): kuira_crypto_jni.c - Extract bytes, call Rust
  ↓
Rust FFI: transaction_ffi.rs - create_signing_key, sign_data
  ↓
midnight-ledger: Schnorr BIP-340 signing over secp256k1

Security Notes:

• Private keys are copied to native memory and zeroized immediately after use

• Transaction data is zeroized after signing (prevents memory dump recovery)

• SigningKey pointers must be freed to prevent memory leaks

• Uses OS-level RNG for signature nonces (secure by default)

Thread Safety:

• Each signing operation creates an independent SigningKey

• SigningKey pointers are NOT shared across threads

• Safe to call signData() from multiple threads concurrently with different keys

• DO NOT manually share SigningKey pointers between threads (use-after-free risk)

• The useSigningKey() helper ensures automatic cleanup and prevents pointer misuse

Memory Management:

• Native library loads once on first use

• Each signData() call creates a new SigningKey, uses it, and frees it automatically

• Manual management with nativeCreateSigningKey() requires calling nativeFreeSigningKey()

• Use useSigningKey() for automatic cleanup (recommended pattern)

See also