encodePrivateKeyToPem method

dynamic encodePrivateKeyToPem(RSAPrivateKey privateKey)

Implementation

encodePrivateKeyToPem(RSAPrivateKey privateKey) {
  var version = ASN1Integer(BigInt.from(0));

  var algorithmSeq = new ASN1Sequence();
  var algorithmAsn1Obj = new ASN1Object.fromBytes(Uint8List.fromList(
      [0x6, 0x9, 0x2a, 0x86, 0x48, 0x86, 0xf7, 0xd, 0x1, 0x1, 0x1]));
  var paramsAsn1Obj =
      new ASN1Object.fromBytes(Uint8List.fromList([0x5, 0x0]));
  algorithmSeq.add(algorithmAsn1Obj);
  algorithmSeq.add(paramsAsn1Obj);

  var privateKeySeq = new ASN1Sequence();
  var modulus = ASN1Integer(privateKey.n!);
  var publicExponent = ASN1Integer(BigInt.parse('65537'));
  var privateExponent = ASN1Integer(privateKey.d!);
  var p = ASN1Integer(privateKey.p!);
  var q = ASN1Integer(privateKey.q!);
  var dP = privateKey.d! % (privateKey.p! - BigInt.from(1));
  var exp1 = ASN1Integer(dP);
  var dQ = privateKey.d! % (BigInt.from(1) - privateKey.q!);
  var exp2 = ASN1Integer(dQ);
  var iQ = privateKey.q!.modInverse(privateKey.p!);
  var co = ASN1Integer(iQ);

  privateKeySeq.add(version);
  privateKeySeq.add(modulus);
  privateKeySeq.add(publicExponent);
  privateKeySeq.add(privateExponent);
  privateKeySeq.add(p);
  privateKeySeq.add(q);
  privateKeySeq.add(exp1);
  privateKeySeq.add(exp2);
  privateKeySeq.add(co);
  var publicKeySeqOctetString =
      new ASN1OctetString(Uint8List.fromList(privateKeySeq.encodedBytes));

  var topLevelSeq = new ASN1Sequence();
  topLevelSeq.add(version);
  topLevelSeq.add(algorithmSeq);
  topLevelSeq.add(publicKeySeqOctetString);
  var dataBase64 =
      _castToPrintableEncodingPem(base64.encode(topLevelSeq.encodedBytes));

  return """-----BEGIN PRIVATE KEY-----\r\n$dataBase64\r\n-----END PRIVATE KEY-----""";
}