Decryption using private key from .pem file in C # with .NET crypto library

Question

I know this is a similar question to this , but before I hit the Bouncey Castle path, does anyone know if RSA KeyPair can be downloaded from .pem, for example:

-----BEGIN RSA PRIVATE KEY----- MIIBOgIBAAJBALKzy66nRuof8Fg0ItatyHS9RiDIKH0m5lorKzKn4y5wR6BXpVUv ZwnevrAJWBd6EPr/lcV3hjObxD6+q9vmN8ECAwEAAQJAGNcxWwfZrbXe3QPyS9FA aindU7U/G5aKssIJcTMxO0UYpGU+WArJbboKeEIE7bpNfhDOKTL7ZL6kWBR1Svlh WQIhAOhtx+xXuSrIot59tmXZaypBDjA4n+Xare0ObFLQxWuvAiEAxNMwm6w33bVr FHS9slkOh59Le2mgs0uNT6perHaRP48CIGMyRzrlDY/m5SvTtz6slgIIlceawxNU Sxp7J1wI4djdAiA6+BchHNjkCP2a9Fr9OydaRMSFpiDqduFQk/enbiKYSwIhANO3 SQ51oLFtWN9gX3tfKTXflyO6BV8rgPo980d9CEsb -----END RSA PRIVATE KEY----- 

directly using the .NET 3.5 cryptographic data library without having to go to a third party or roll back my own?

Answer 1

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

with source at http://www.jensign.com/opensslkey/opensslkey.cs Update: Source code is no longer available at this link. It can be found at https://gist.github.com/stormwild/7887264 or https://web.archive.org/web/20170731015547/http://www.jensign.com/opensslkey/opensslkey.cs .

edit: fragment of the corresponding code:

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

 //------- 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(); } } 

Answer 2

I created a small NuGet helper package to create an X509 certificate based on a public key and a private key (rsa).

See NuGet and the Github-project for functionality and sample code based on opensslkey .