Function derive_symmetric_key

pub fn derive_symmetric_key(
    input: &Bytes,
    gas_limit: u64,
) -> Result<PrecompileOutput, PrecompileErrors>

Derive Symmetric Key (ECDH + HKDF-AES)

Accepts 65 bytes of input:

• 0..32: sk_bytes (secp256k1 secret key)
• 32..65: pk_bytes (compressed public key)

Steps:

1. Compute ECDH shared secret using pk * sk.
2. Derive a 32-byte AES key from the shared secret via seismic_enclave::derive_aes_key, which internally runs HKDF-SHA256 (see separate doc for gas breakdown).

Returns the 32-byte AES key if successful, or an error otherwise.

Gas:

We apply a constant DERIVE_SYM_KEY_COST (3,800), ensuring we overestimate in comparison to ECRecover and simpler HKDF ops.

If gas_limit < DERIVE_SYM_KEY_COST, we revert with OutOfGas.