pub fn encode(key: &Sm2PrivateKey) -> Vec<u8>Expand description
Encode an SM2 private key as a DER-encoded unencrypted
PKCS#8 OneAsymmetricKey.
The inner ECPrivateKey carries the scalar plus the optional
publicKey field (uncompressed 04 || X || Y); the outer
privateKeyAlgorithm is id-ecPublicKey with sm2p256v1.
The intermediate ECPrivateKey body is zeroized before return.
The returned Vec<u8> contains the raw scalar bytes —
caller is responsible for wiping it before letting it leave
their stack frame.