How to decrypt RSA content in .NET?

Question

I am generating RSA private & public keys using OpenSSL, sending public key into HTML page to encrypt username & password (with JSEncrypt).The encrypted content sends to

Answer 1

The RSA format generate by OpenSSL is different with .NET,you should convert OpenSSL RSA xmlPrivateKey to XML format so it could be recognized by RSACryptoServiceProvider.

        private static RSACryptoServiceProvider DecodeRsaPrivateKey(string priKey)
        {
            var privkey = Convert.FromBase64String(priKey);
            byte[] MODULUS, E, D, P, Q, DP, DQ, IQ;

            // ---------  Set up stream to decode the asn.1 encoded RSA private key  ------
            var mem = new MemoryStream(privkey);
            var binr = new BinaryReader(mem);    //wrap Memory Stream with BinaryReader for easy reading
            try
            {
                var 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;
                var bt = binr.ReadByte();
                if (bt != 0x00)
                    return null;

                //------  all private key components are Integer sequences ----
                var 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);

                // ------- create RSACryptoServiceProvider instance and initialize with public key -----
                var rsa = new RSACryptoServiceProvider();
                var rsAparams = new RSAParameters
                {
                    Modulus = MODULUS,
                    Exponent = E,
                    D = D,
                    P = P,
                    Q = Q,
                    DP = DP,
                    DQ = DQ,
                    InverseQ = IQ
                };
                rsa.ImportParameters(rsAparams);
                return rsa;
            }
            catch (Exception e)
            {
                LogHelper.Logger.Error("DecodeRsaPrivateKey failed", e);
                return null;
            }
            finally
            {
                binr.Close();
            }
        }



        private static int GetIntegerSize(BinaryReader binary)
        {
            byte binaryReadByte = 0;
            var count = 0;
            binaryReadByte = binary.ReadByte();
            if (binaryReadByte != 0x02)        //expect integer
                return 0;
            binaryReadByte = binary.ReadByte();
            if (binaryReadByte == 0x81)
            {
                count = binary.ReadByte(); // data size in next byte
            }
            else
            {
                if (binaryReadByte == 0x82)
                {
                    var highbyte = binary.ReadByte();
                    var lowbyte = binary.ReadByte();
                    byte[] modint = { lowbyte, highbyte, 0x00, 0x00 };
                    count = BitConverter.ToInt32(modint, 0);
                }
                else
                {
                    count = binaryReadByte; // we already have the data size
                }
            }
            while (binary.ReadByte() == 0x00)
            {    //remove high order zeros in data
                count -= 1;
            }
            binary.BaseStream.Seek(-1, SeekOrigin.Current);        //last ReadByte wasn't a removed zero, so back up a byte
            return count;
        }

So the RSACryptoServiceProvider can decrypt the original context.