Decrypting with private key from .pem file in c# with .NET crypto library

Question

I know this is a similar question to this one but before I head down the Bouncey Castle route, does anyone know if its possible to load an RSA KeyPair from a .pem file (-----BEGIN RSA PRIVATE KEY-----) directly with the .NET 3.5 crypto library without having to go to a 3rd party or roll my own?

Answer 1

http://www.jensign.com/opensslkey/index.html

with source at http://www.jensign.com/opensslkey/opensslkey.cs

edit: excerpted relevant code:

first, extract the text between the ---- BEGIN ---- and ---- END ---- sections, and base64-decode it into a byte array (see link above for details), then pass it to:

//------- Parses binary ans.1 RSA private key; returns RSACryptoServiceProvider  ---
public static RSACryptoServiceProvider DecodeRSAPrivateKey(byte[] privkey)
{
 byte[] MODULUS, E, D, P, Q, DP, DQ, IQ ;

// ---------  Set up stream to decode the asn.1 encoded RSA private key  ------
 MemoryStream  mem = new MemoryStream(privkey) ;
 BinaryReader binr = new BinaryReader(mem) ;    //wrap Memory Stream with BinaryReader for easy reading
 byte bt = 0;
 ushort twobytes = 0;
 int elems = 0;
 try {
  twobytes = binr.ReadUInt16();
  if (twobytes == 0x8130) //data read as little endian order (actual data order for Sequence is 30 81)
   binr.ReadByte(); //advance 1 byte
  else if (twobytes == 0x8230)
   binr.ReadInt16(); //advance 2 bytes
  else
   return null;

  twobytes = binr.ReadUInt16();
  if (twobytes != 0x0102) //version number
   return null;
  bt = binr.ReadByte();
  if (bt !=0x00)
   return null;


//------  all private key components are Integer sequences ----
  elems = GetIntegerSize(binr);
  MODULUS = binr.ReadBytes(elems);

  elems = GetIntegerSize(binr);
  E = binr.ReadBytes(elems) ;

  elems = GetIntegerSize(binr);
  D = binr.ReadBytes(elems) ;

  elems = GetIntegerSize(binr);
  P = binr.ReadBytes(elems) ;

  elems = GetIntegerSize(binr);
  Q = binr.ReadBytes(elems) ;

  elems = GetIntegerSize(binr);
  DP = binr.ReadBytes(elems) ;

  elems = GetIntegerSize(binr);
  DQ = binr.ReadBytes(elems) ;

  elems = GetIntegerSize(binr);
  IQ = binr.ReadBytes(elems) ;

  Console.WriteLine("showing components ..");
  if (verbose) {
   showBytes("\nModulus", MODULUS) ;
   showBytes("\nExponent", E);
   showBytes("\nD", D);
   showBytes("\nP", P);
   showBytes("\nQ", Q);
   showBytes("\nDP", DP);
   showBytes("\nDQ", DQ);
   showBytes("\nIQ", IQ);
  }

// ------- create RSACryptoServiceProvider instance and initialize with public key -----
  RSACryptoServiceProvider RSA = new RSACryptoServiceProvider();
  RSAParameters RSAparams = new RSAParameters();
  RSAparams.Modulus =MODULUS;
  RSAparams.Exponent = E;
  RSAparams.D = D;
  RSAparams.P = P;
  RSAparams.Q = Q;
  RSAparams.DP = DP;
  RSAparams.DQ = DQ;
  RSAparams.InverseQ = IQ;
  RSA.ImportParameters(RSAparams);
  return RSA;
 }
 catch (Exception) {
  return null;
 }
 finally {
  binr.Close();
 }
}