encodeRSAPrivateKeyToPemPkcs1 static method

String encodeRSAPrivateKeyToPemPkcs1(RSAPrivateKey rsaPrivateKey)

Enode the given rsaPrivateKey to PEM format using the PKCS#1 standard.

The ASN1 structure is decripted at tools.ietf.org/html/rfc8017#page-54.

RSAPrivateKey ::= SEQUENCE {
  version           Version,
  modulus           INTEGER,  -- n
  publicExponent    INTEGER,  -- e
  privateExponent   INTEGER,  -- d
  prime1            INTEGER,  -- p
  prime2            INTEGER,  -- q
  exponent1         INTEGER,  -- d mod (p-1)
  exponent2         INTEGER,  -- d mod (q-1)
  coefficient       INTEGER,  -- (inverse of q) mod p
  otherPrimeInfos   OtherPrimeInfos OPTIONAL
}

Implementation

static String encodeRSAPrivateKeyToPemPkcs1(RSAPrivateKey rsaPrivateKey) {
  var version = ASN1Integer(BigInt.from(0));
  var modulus = ASN1Integer(rsaPrivateKey.n);
  var publicExponent = ASN1Integer(BigInt.parse('65537'));
  var privateExponent = ASN1Integer(rsaPrivateKey.privateExponent);

  var p = ASN1Integer(rsaPrivateKey.p);
  var q = ASN1Integer(rsaPrivateKey.q);
  var dP =
      rsaPrivateKey.privateExponent! % (rsaPrivateKey.p! - BigInt.from(1));
  var exp1 = ASN1Integer(dP);
  var dQ =
      rsaPrivateKey.privateExponent! % (rsaPrivateKey.q! - BigInt.from(1));
  var exp2 = ASN1Integer(dQ);
  var iQ = rsaPrivateKey.q!.modInverse(rsaPrivateKey.p!);
  var co = ASN1Integer(iQ);

  var topLevelSeq = ASN1Sequence();
  topLevelSeq.add(version);
  topLevelSeq.add(modulus);
  topLevelSeq.add(publicExponent);
  topLevelSeq.add(privateExponent);
  topLevelSeq.add(p);
  topLevelSeq.add(q);
  topLevelSeq.add(exp1);
  topLevelSeq.add(exp2);
  topLevelSeq.add(co);
  var dataBase64 = base64.encode(topLevelSeq.encode());
  var chunks = _chunk(dataBase64, 64);
  return '$BEGIN_RSA_PRIVATE_KEY\n${chunks.join('\n')}\n$END_RSA_PRIVATE_KEY';
}