@Override
  public byte[] sign(final byte[] data) throws GeneralSecurityException {
    byte[] signature;
    if (messageSuffix.length == 0) {
      signature = noPrefixSign(data);
    } else {
      signature = noPrefixSign(Bytes.concat(data, messageSuffix));
    }
    if (outputPrefix.length == 0) {
      return signature;
    } else {
      return Bytes.concat(outputPrefix, signature);
    }
  }
RsaSsaPkcs1 (i.e. RSA Signature Schemes with Appendix (SSA) with PKCS1-v1_5 encoding) signing
with JCE.
java_src/src/main/java/com/google/crypto/tink/subtle/RsaSsaPkcs1SignJce.java