一个完整的类用来读取OpenSSL生成的pem格式的x509证书（C#）

     internal static class CcbRsaHelper
     {
         private const string Begin = "-----BEGIN ";
         private const string End = "-----END ";
         private const string Private = "PRIVATE KEY";

         /// <summary>Imports PEM formatted key or certificate into crypto provider</summary>
         /// <param name="data">Content of PEM-formatted object.</param>
         /// <returns>Crypto provider, defined by given argument.</returns>
         internal static RSACryptoServiceProvider FromPem(string data)
         {
             return FromPem(data, null);
         }

         /// <summary>Imports PEM formatted key or certificate into crypto provider</summary>
         /// <param name="data">Content of PEM-formatted object.</param>
         /// <param name="passKey">Passkey for PEM-formatted object.</param>
         /// <returns>Crypto provider, defined by given argument.</returns>
         internal static RSACryptoServiceProvider FromPem(string data, string passKey)
         {
             using (var reader = new StringReader(data))
             {
                 var line = reader.ReadLine();
                 if (line.IsEmpty() || !line.StartsWith(Begin))
                 {
                     throw new ArgumentException("This is not valid PEM format", "data", new FormatException("PEM start identifier is invalid or not found."));
                 }
                 line = line.Substring(Begin.Length);
                 var idx = line.IndexOf('-');
                 if (idx <= )
                 {
                     throw new ArgumentException("This is not valid PEM format", "data", new FormatException("PEM start identifier is invalid or not found."));
                 }
                 var type = line.Before(idx);
                 return LoadPem(reader, type, passKey);
             }
         }

         internal static RSAParameters FromPemPublicKey(string pemFileConent)
         {
             if (string.IsNullOrEmpty(pemFileConent))
             {
                 throw new ArgumentNullException("pemFileConent", "This arg cann't be empty.");
             }

             pemFileConent = pemFileConent.Replace("-----BEGIN PUBLIC KEY-----", "").Replace("-----END PUBLIC KEY-----", "").Replace("\n", "").Replace("\r", "");
             var keyData = Convert.FromBase64String(pemFileConent);
             var keySize1024 = (keyData.Length == );
             var keySize2048 = (keyData.Length == );
             if (!(keySize1024 || keySize2048))
             {
                 throw new ArgumentException("pem file content is incorrect, Only support the key size is 1024 or 2048");
             }

             var pemModulus = (keySize1024 ? new byte[] : new byte[]);
             var pemPublicExponent = new byte[];
             Array.Copy(keyData, (keySize1024 ?  : ), pemModulus, , (keySize1024 ?  : ));
             Array.Copy(keyData, (keySize1024 ?  : ), pemPublicExponent, , );
             var para = new RSAParameters {Modulus = pemModulus, Exponent = pemPublicExponent};
             return para;
         }

         private static RSACryptoServiceProvider LoadPem(TextReader reader, string type, string passkey)
         {
             var end = End + type;
             var headers = new PemHeaders();
             string line;
             var body = new StringBuilder();
             while ((line = reader.ReadLine()) != null && line.IndexOf(end, StringComparison.Ordinal) == -)
             {
                 var d = line.IndexOf(':');
                 if (d >= )
                 {
                     // header
                     var n = line.Substring(, d).Trim();
                     if (n.StartsWith("X-")) n = n.Substring();
                     var v = line.After(d).Trim();
                     if (!headers.ContainsKey(n))
                     {
                         headers.Add(n, v);
                     }
                     else
                     {
                         throw new FormatException("Duplicate header {0} in PEM data.".Substitute(n));
                     }
                 }
                 else
                 {
                     // body
                     body.Append(line);
                 }
             }
             if (body.Length% != )
             {
                 throw new FormatException("PEM data is invalid or truncated.");
             }

             return CreatePem(type, headers, Convert.FromBase64String(body.ToString()), passkey);
         }

         private static RSACryptoServiceProvider CreatePem(string type, PemHeaders headers, byte[] body, string passkey)
         {
             if (type.EndsWith(Private))
             {
                 return FromPrivateKey(type, headers, body, passkey);
             }
             throw new NotSupportedException("Import of {0} is not supported. Only RSA private key import is supported.".Substitute(type));
         }

         private static RSACryptoServiceProvider FromPrivateKey(string type, PemHeaders headers, byte[] body, string passkey)
         {
             if (type == null) throw new ArgumentNullException("type");
             var pType = headers.TryGet("Proc-Type");
             if (pType != "4,ENCRYPTED") return null;
             if (passkey.IsEmpty())
             {
                 throw new ArgumentException("Passkey is mandatory for encrypted PEM object");
             }

             var dek = headers.TryGet("DEK-Info");
             var tkz = dek.Split(',');
             if (tkz.Length > )
             {
                 var alg = new Alg(tkz[]);
                 var saltLen = tkz[].Length;
                 var salt = new byte[saltLen/];
                 for (var i = ; i < saltLen/; i++)
                 {
                     var pair = tkz[].Substring(*i, );
                     salt[i] = Byte.Parse(pair, NumberStyles.AllowHexSpecifier);
                 }

                 body = DecodePem(body, passkey, alg, salt);
                 if (body != null)
                 {
                     return DecodeRsaPrivateKey(body);
                 }
             }
             else
             {
                 throw new FormatException("DEK information is invalid or truncated.");
             }

             return null;
         }

         private static RSACryptoServiceProvider DecodeRsaPrivateKey(byte[] body)
         {
             using (var ms = new MemoryStream(body))
             {
                 using (var reader = new BinaryReader(ms))
                 {
                     try
                     {
                         var tb = reader.ReadUInt16(); // LE: x30 x81
                         switch (tb)
                         {
                             case 0x8130:
                                 reader.ReadByte(); // fw 1
                                 break;
                             case 0x8230:
                                 reader.ReadInt16(); // fw 2
                                 break;
                             default:
                                 return null;
                         }

                         tb = reader.ReadUInt16(); // version
                         if (tb != 0x0102)
                         {
                             return null;
                         }
                         if (reader.ReadByte() != 0x00)
                         {
                             return null;
                         }

                         var modulus = ReadInt(reader);
                         var e = ReadInt(reader);
                         var d = ReadInt(reader);
                         var p = ReadInt(reader);
                         var q = ReadInt(reader);
                         var dp = ReadInt(reader);
                         var dq = ReadInt(reader);
                         var iq = ReadInt(reader);

                         var result = new RSACryptoServiceProvider();
                         var param = new RSAParameters
                         {
                             Modulus = modulus,
                             Exponent = e,
                             D = d,
                             P = p,
                             Q = q,
                             DP = dp,
                             DQ = dq,
                             InverseQ = iq
                         };
                         result.ImportParameters(param);
                         return result;
                     }
                     finally
                     {
                         reader.Close();
                     }
                 }
             }
         }

         private static readonly Func<BinaryReader, byte[]> ReadInt = r =>
         {
             var s = GetIntSize(r);
             return r.ReadBytes(s);
         };

         private static readonly Func<BinaryReader, int> GetIntSize = r =>
         {
             int c;
             var b = r.ReadByte();
             if (b != 0x02)
             {
                 //int
                 return ;
             }
             b = r.ReadByte();

             switch (b)
             {
                 case 0x81:
                     c = r.ReadByte(); //size
                     break;
                 case 0x82:
                     var hb = r.ReadByte();
                     var lb = r.ReadByte();
                     byte[] m = {lb, hb, 0x00, 0x00};
                     c = BitConverter.ToInt32(m, );
                     break;
                 default:
                     c = b; //got size
                     break;
             }

             while (r.ReadByte() == 0x00)
             {
                 //remove high zero
                 c -= ;
             }
             r.BaseStream.Seek(-, SeekOrigin.Current); // last byte is not zero, go back;
             return c;
         };

         private static byte[] DecodePem(byte[] body, string passkey, Alg alg, byte[] salt)
         {
             if (alg == null) throw new ArgumentNullException("alg");
             if (alg.AlgBase != Alg.BaseAlg.DES_EDE3 && alg.AlgMode != Alg.Mode.CBC)
             {
                 throw new NotSupportedException("Only 3DES-CBC keys are supported.");
             }
             var des = Get3DesKey(salt, passkey);
             if (des == null)
             {
                 throw new ApplicationException("Unable to calculate 3DES key for decryption.");
             }
             var rsa = DecryptRsaKey(body, des, salt);
             if (rsa == null)
             {
                 throw new ApplicationException("Unable to decrypt RSA private key.");
             }
             return rsa;
         }

         private static byte[] DecryptRsaKey(byte[] body, byte[] desKey, byte[] iv)
         {
             byte[] result;
             using (var stream = new MemoryStream())
             {
                 var alg = TripleDES.Create();
                 alg.Key = desKey;
                 alg.IV = iv;
                 using (var cs = new CryptoStream(stream, alg.CreateDecryptor(), CryptoStreamMode.Write))
                 {
                     cs.Write(body, , body.Length);
                     cs.Close();
                 }
                 result = stream.ToArray();
             }
             return result;
         }

         private static byte[] Get3DesKey(byte[] salt, string passkey)
         {
             const int hashlength = ;
             const int m = ; // 2 iterations for at least 24 bytes
             const int c = ; // 1 hash for Open SSL
             var k = new byte[hashlength*m];

             var pk = Encoding.ASCII.GetBytes(passkey);
             var data = new byte[salt.Length + pk.Length];
             Array.Copy(pk, data, pk.Length);
             Array.Copy(salt, , data, pk.Length, salt.Length);
             var md5 = new MD5CryptoServiceProvider();
             byte[] result = null;
             var hash = new byte[hashlength + data.Length];

             for (var i = ; i < m; i++)
             {
                 if (i == )
                 {
                     result = data;
                 }
                 else
                 {
                     Array.Copy(result, hash, result.Length);
                     Array.Copy(data, , hash, result.Length, data.Length);
                     result = hash;
                 }

                 for (var j = ; j < c; j++)
                 {
                     result = md5.ComputeHash(result);
                 }
                 Array.Copy(result, , k, i*hashlength, result.Length);
             }
             var dk = new byte[]; //final key
             Array.Copy(k, dk, dk.Length);
             return dk;
         }

         private class PemHeaders : Dictionary<string, string>
         {
         }

         private sealed class Alg
         {
             public Alg(string alg)
             {
                 AlgMode = Mode.ECB;
                 switch (alg.Trim())
                 {
                     //TK: DES-EDE based algorithms come only with ECB mode.
                     case "DES-EDE":
                         AlgBase = BaseAlg.DES_EDE;
                         return;
                     case "DES-EDE3":
                         AlgBase = BaseAlg.DES_EDE3;
                         return;
                     default:
                         var p = alg.LastIndexOf('-');
                         if (p >= )
                         {
                             AlgBase = (BaseAlg) _parseVal(typeof (BaseAlg), alg.Before(p));
                             AlgMode = (Mode) _parseVal(typeof (Mode), alg.After(p));
                             return;
                         }
                         break;
                 }
                 throw new ArgumentException("Unknown DEK algorithm '{0}'", alg);
             }

             public BaseAlg AlgBase { get; private set; }

             public Mode AlgMode { get; private set; }

             private readonly Func<Type, string, Enum> _parseVal = (t, s) =>
             {
                 s = s.Replace('-', '_');
                 return (Enum) Enum.Parse(t, s);
             };

             public enum BaseAlg
             {
                 DES_EDE,
                 DES_EDE3
             };

             public enum Mode
             {
                 CBC,
                 ECB
             };
         }
     }

     internal static class Helper
     {
         public static bool IsEmpty(this string value)
         {
             return String.IsNullOrWhiteSpace(value);
         }

         public static string Before(this string value, int end)
         {
             return (end ==  ? String.Empty : value.Between(, end - ));
         }

         public static string After(this string value, int start)
         {
             return value.Between(start + , Int32.MaxValue);
         }

         public static string Between(this string value, int start, int end)
         {
             var len = (String.IsNullOrEmpty(value) ?  : value.Length);
             if (start < ) start += len;
             if (end < ) end += len;
             if (len ==  || start > len -  || end < start)
             {
                 return String.Empty;
             }
             if (start < ) start = ;
             if (end >= len) end = len - ;
             return value.Substring(start, end - start + );
         }

         public static string Substitute(this string format, params object[] args)
         {
             var value = String.Empty;
             if (String.IsNullOrEmpty(format)) return value;
             if (args.Length == ) return format;
             try
             {
                 return String.Format(format, args);
             }
             catch (FormatException)
             {
                 return format;
             }
             catch
             {
                 return "***";
             }
         }

         public static TV TryGet<TK, TV>(this Dictionary<TK, TV> dictionary, TK key)
         {
             return dictionary.TryGet(key, default(TV));
         }

         public static TV TryGet<TK, TV>(this Dictionary<TK, TV> dictionary, TK key, TV defaultValue)
         {
             if (dictionary != null && dictionary.ContainsKey(key))
             {
                 return dictionary[key];
             }
             return defaultValue;
         }
     }