@Override
    protected byte[] engineSign() throws SignatureException {
        if (privateKey == null) {
            // This should not happen.
            throw new SignatureException("No privateKey provided");
        }
        byte[] sig = NativeCrypto.SLHDSA_SHA2_128S_sign(
                buffer.array(), buffer.size(), privateKey.getRaw());
        buffer.reset();
        return sig;
    }
Buffer to hold value to be signed or verified.
common/src/main/java/org/conscrypt/OpenSslSignatureSlhDsa.java