DustKeyDeriver

JNI bridge to Midnight's Rust cryptography for deriving dust keys.

Architecture:

Kotlin (Android) → JNI → Rust FFI → Midnight Ledger (Rust)

What is Dust? Dust is Midnight's fee payment mechanism. Night UTXOs can be registered for dust generation, which produces dust tokens over time. These dust tokens are consumed to pay transaction fees.

Dust Key Derivation Path: Dust keys are derived at BIP-44 path: m/44'/2400'/account'/2/index

• Role 2 = Dust (defined in MidnightKeyRole.DUST)

• Typically index 0 for primary dust key

Native Library: This class loads libkuira_crypto_ffi.so (Android) which is compiled from:

• Location: kuira-crypto-ffi/

• Dependencies: midnight-ledger (version-abstract FFI — see Cargo.toml)

Thread Safety: This object is thread-safe. The underlying Rust functions are pure and stateless.

Memory Safety:

• The JNI bridge allocates C strings for results

• Native memory is freed automatically after copying to Kotlin strings

• The seed ByteArray is NOT cleared by this function - caller must wipe it

Usage:

val seed = deriveSeedFromBIP32()  // 32 bytes at m/44'/2400'/0'/2/0
try {
    val dustPublicKey = DustKeyDeriver.derivePublicKey(seed)
    println("Dust PK: ${dustPublicKey}")
} finally {
    MemoryUtils.wipe(seed)  // CRITICAL: Always wipe seed
}

Error Handling:

• Returns null if FFI call fails (invalid seed, native library error, etc.)

• Logs error details to stderr in the native library

• On Android, check Logcat for native error messages

References:

• Rust FFI: kuira-crypto-ffi/src/lib.rs

• Dust Spec: midnight-libraries/midnight-ledger/spec/dust.md