/// <summary>  
    /// 類名：RSACrypt  
    /// 功能：RSA加密、解密、簽名、驗籤  
    /// </summary>  
    public sealed class RSACrypt
    {
        /// <summary>  
        /// 簽名  
        /// </summary>  
        /// <param name="content">待簽名字串</param>  
        /// <param name="privateKey">私鑰</param>  
        /// <param name="input_charset">編碼格式</param>  
        /// <returns>簽名後字串</returns>  
        public static string sign(string content, string privateKey, string input_charset)
        {
            byte[] Data = Encoding.GetEncoding(input_charset).GetBytes(content);
            RSACryptoServiceProvider rsa = DecodePemPrivateKey(privateKey);
            SHA1 sh = new SHA1CryptoServiceProvider();
            byte[] signData = rsa.SignData(Data, sh);
            return Convert.ToBase64String(signData);
        }
 
        /// <summary>  
        /// 驗籤  
        /// </summary>  
        /// <param name="content">待驗簽字符串</param>  
        /// <param name="signedString">簽名</param>  
        /// <param name="publicKey">公鑰</param>  
        /// <param name="input_charset">編碼格式</param>  
        /// <returns>true(通過)，false(不通過)</returns>  
        public static bool verify(string content, string signedString, string publicKey, string input_charset)
        {
            bool result = false;
            byte[] Data = Encoding.GetEncoding(input_charset).GetBytes(content);
            byte[] data = Convert.FromBase64String(signedString);
            RSAParameters paraPub = ConvertFromPublicKey(publicKey);
            RSACryptoServiceProvider rsaPub = new RSACryptoServiceProvider();
            rsaPub.ImportParameters(paraPub);
            SHA1 sh = new SHA1CryptoServiceProvider();
            result = rsaPub.VerifyData(Data, sh, data);
            return result;
        }
 
        /// <summary>  
        /// 加密  
        /// </summary>  
        /// <param name="resData">需要加密的字串</param>  
        /// <param name="publicKey">公鑰</param>  
        /// <param name="input_charset">編碼格式</param>  
        /// <returns>明文</returns>  
        public static string encryptData(string resData, string publicKey, string input_charset)
        {
            byte[] DataToEncrypt = Encoding.ASCII.GetBytes(resData);
            string result = encrypt(DataToEncrypt, publicKey, input_charset);
            return result;
        }
 
 
        /// <summary>  
        /// 解密  
        /// </summary>  
        /// <param name="resData">加密字串</param>  
        /// <param name="privateKey">私鑰</param>  
        /// <param name="input_charset">編碼格式</param>  
        /// <returns>明文</returns>  
        public static string decryptData(string resData, string privateKey, string input_charset)
        {
            byte[] DataToDecrypt = Convert.FromBase64String(resData);
            string result = "";
            for (int j = 0; j < DataToDecrypt.Length / 128; j++)
            {
                byte[] buf = new byte[128];
                for (int i = 0; i < 128; i++)
                {
 
                    buf[i] = DataToDecrypt[i + 128 * j];
                }
                result += decrypt(buf, privateKey, input_charset);
            }
            return result;
        }
 
        private static string encrypt(byte[] data, string publicKey, string input_charset)
        {
            RSACryptoServiceProvider rsa = DecodePemPublicKey(publicKey);
            SHA1 sh = new SHA1CryptoServiceProvider();
            byte[] result = rsa.Encrypt(data, false);
 
            return Convert.ToBase64String(result);
        }
 
        private static string decrypt(byte[] data, string privateKey, string input_charset)
        {
            string result = "";
            RSACryptoServiceProvider rsa = DecodePemPrivateKey(privateKey);
            SHA1 sh = new SHA1CryptoServiceProvider();
            byte[] source = rsa.Decrypt(data, false);
            char[] asciiChars = new char[Encoding.GetEncoding(input_charset).GetCharCount(source, 0, source.Length)];
            Encoding.GetEncoding(input_charset).GetChars(source, 0, source.Length, asciiChars, 0);
            result = new string(asciiChars);
            return result;
        }
 
        private static RSACryptoServiceProvider DecodePemPublicKey(String pemstr)
        {
            byte[] pkcs8publickkey;
            pkcs8publickkey = Convert.FromBase64String(pemstr);
            if (pkcs8publickkey != null)
            {
                RSACryptoServiceProvider rsa = DecodeRSAPublicKey(pkcs8publickkey);
                return rsa;
            }
            else
                return null;
        }
 
        private static RSACryptoServiceProvider DecodePemPrivateKey(String pemstr)
        {
            byte[] pkcs8privatekey;
            pkcs8privatekey = Convert.FromBase64String(pemstr);
            if (pkcs8privatekey != null)
            {
                RSACryptoServiceProvider rsa = DecodePrivateKeyInfo(pkcs8privatekey);
                return rsa;
            }
            else
                return null;
        }
 
        private static RSACryptoServiceProvider DecodePrivateKeyInfo(byte[] pkcs8)
        {
            byte[] SeqOID = { 0x30, 0x0D, 0x06, 0x09, 0x2A, 0x86, 0x48, 0x86, 0xF7, 0x0D, 0x01, 0x01, 0x01, 0x05, 0x00 };
            byte[] seq = new byte[15];
 
            MemoryStream mem = new MemoryStream(pkcs8);
            int lenstream = (int)mem.Length;
            BinaryReader binr = new BinaryReader(mem);   
            byte bt = 0;
            ushort twobytes = 0;
 
            try
            {
                twobytes = binr.ReadUInt16();
                if (twobytes == 0x8130)   
                    binr.ReadByte();   
                else if (twobytes == 0x8230)
                    binr.ReadInt16(); 
                else
                    return null;
 
                bt = binr.ReadByte();
                if (bt != 0x02)
                    return null;
 
                twobytes = binr.ReadUInt16();
 
                if (twobytes != 0x0001)
                    return null;
 
                seq = binr.ReadBytes(15); 
                if (!CompareBytearrays(seq, SeqOID)) 
                    return null;
 
                bt = binr.ReadByte();
                if (bt != 0x04) 
                    return null;
 
                bt = binr.ReadByte();
                if (bt == 0x81)
                    binr.ReadByte();
                else
                    if (bt == 0x82)
                        binr.ReadUInt16();
 
                byte[] rsaprivkey = binr.ReadBytes((int)(lenstream - mem.Position));
                RSACryptoServiceProvider rsacsp = DecodeRSAPrivateKey(rsaprivkey);
                return rsacsp;
            }
 
            catch (Exception)
            {
                return null;
            }
 
            finally { binr.Close(); }
        }
 
        private static bool CompareBytearrays(byte[] a, byte[] b)
        {
            if (a.Length != b.Length)
                return false;
            int i = 0;
            foreach (byte c in a)
            {
                if (c != b[i])
                    return false;
                i++;
            }
            return true;
        }
 
        private static RSACryptoServiceProvider DecodeRSAPublicKey(byte[] publickey)
        {
            byte[] SeqOID = { 0x30, 0x0D, 0x06, 0x09, 0x2A, 0x86, 0x48, 0x86, 0xF7, 0x0D, 0x01, 0x01, 0x01, 0x05, 0x00 };
            byte[] seq = new byte[15];
            MemoryStream mem = new MemoryStream(publickey);
            BinaryReader binr = new BinaryReader(mem); 
            byte bt = 0;
            ushort twobytes = 0;
 
            try
            {
 
                twobytes = binr.ReadUInt16();
                if (twobytes == 0x8130) 
                    binr.ReadByte(); 
                else if (twobytes == 0x8230)
                    binr.ReadInt16(); 
                else
                    return null;
 
                seq = binr.ReadBytes(15); 
                if (!CompareBytearrays(seq, SeqOID)) 
                    return null;
 
                twobytes = binr.ReadUInt16();
                if (twobytes == 0x8103) 
                    binr.ReadByte(); 
                else if (twobytes == 0x8203)
                    binr.ReadInt16(); 
                else
                    return null;
 
                bt = binr.ReadByte();
                if (bt != 0x00) 
                    return null;
 
                twobytes = binr.ReadUInt16();
                if (twobytes == 0x8130) 
                    binr.ReadByte();
                else if (twobytes == 0x8230)
                    binr.ReadInt16();
                else
                    return null;
 
                twobytes = binr.ReadUInt16();
                byte lowbyte = 0x00;
                byte highbyte = 0x00;
 
                if (twobytes == 0x8102) 
                    lowbyte = binr.ReadByte();
                else if (twobytes == 0x8202)
                {
                    highbyte = binr.ReadByte();
                    lowbyte = binr.ReadByte();
                }
                else
                    return null;
                byte[] modint = { lowbyte, highbyte, 0x00, 0x00 }; 
                int modsize = BitConverter.ToInt32(modint, 0);
 
                byte firstbyte = binr.ReadByte();
                binr.BaseStream.Seek(-1, SeekOrigin.Current);
 
                if (firstbyte == 0x00)
                {   
                    binr.ReadByte();   
                    modsize -= 1;  
                }
 
                byte[] modulus = binr.ReadBytes(modsize);  
 
                if (binr.ReadByte() != 0x02)  
                    return null;
                int expbytes = (int)binr.ReadByte();   
                byte[] exponent = binr.ReadBytes(expbytes);
 
                RSACryptoServiceProvider RSA = new RSACryptoServiceProvider();
                RSAParameters RSAKeyInfo = new RSAParameters();
                RSAKeyInfo.Modulus = modulus;
                RSAKeyInfo.Exponent = exponent;
                RSA.ImportParameters(RSAKeyInfo);
                return RSA;
            }
            catch (Exception)
            {
                return null;
            }
 
            finally { binr.Close(); }
        }
 
        private static RSACryptoServiceProvider DecodeRSAPrivateKey(byte[] privkey)
        {
            byte[] MODULUS, E, D, P, Q, DP, DQ, IQ;
 
            MemoryStream mem = new MemoryStream(privkey);
            BinaryReader binr = new BinaryReader(mem); 
            byte bt = 0;
            ushort twobytes = 0;
            int elems = 0;
            try
            {
                twobytes = binr.ReadUInt16();
                if (twobytes == 0x8130)  
                    binr.ReadByte(); 
                else if (twobytes == 0x8230)
                    binr.ReadInt16();  
                else
                    return null;
 
                twobytes = binr.ReadUInt16();
                if (twobytes != 0x0102) 
                    return null;
                bt = binr.ReadByte();
                if (bt != 0x00)
                    return null;
 
                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);
 
                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(); }
        }
 
        private static int GetIntegerSize(BinaryReader binr)
        {
            byte bt = 0;
            byte lowbyte = 0x00;
            byte highbyte = 0x00;
            int count = 0;
            bt = binr.ReadByte();
            if (bt != 0x02) 
                return 0;
            bt = binr.ReadByte();
 
            if (bt == 0x81)
                count = binr.ReadByte(); 
            else
                if (bt == 0x82)
                {
                    highbyte = binr.ReadByte(); 
                    lowbyte = binr.ReadByte();
                    byte[] modint = { lowbyte, highbyte, 0x00, 0x00 };
                    count = BitConverter.ToInt32(modint, 0);
                }
                else
                {
                    count = bt;  
                }
 
            while (binr.ReadByte() == 0x00)
            {  
                count -= 1;
            }
            binr.BaseStream.Seek(-1, SeekOrigin.Current);       
            return count;
        }
 
        private static RSAParameters ConvertFromPublicKey(string pemFileConent)
        {
 
            byte[] keyData = Convert.FromBase64String(pemFileConent);
            if (keyData.Length < 162)
            {
                throw new ArgumentException("pem file content is incorrect.");
            }
            byte[] pemModulus = new byte[128];
            byte[] pemPublicExponent = new byte[3];
            Array.Copy(keyData, 29, pemModulus, 0, 128);
            Array.Copy(keyData, 159, pemPublicExponent, 0, 3);
            RSAParameters para = new RSAParameters();
            para.Modulus = pemModulus;
            para.Exponent = pemPublicExponent;
            return para;
        }
 
        private static RSAParameters ConvertFromPrivateKey(string pemFileConent)
        {
            byte[] keyData = Convert.FromBase64String(pemFileConent);
            if (keyData.Length < 609)
            {
                throw new ArgumentException("pem file content is incorrect.");
            }
 
            int index = 11;
            byte[] pemModulus = new byte[128];
            Array.Copy(keyData, index, pemModulus, 0, 128);
 
            index += 128;
            index += 2;
            byte[] pemPublicExponent = new byte[3];
            Array.Copy(keyData, index, pemPublicExponent, 0, 3);
 
            index += 3;
            index += 4;
            byte[] pemPrivateExponent = new byte[128];
            Array.Copy(keyData, index, pemPrivateExponent, 0, 128);
 
            index += 128;
            index += ((int)keyData[index + 1] == 64 ? 2 : 3);
            byte[] pemPrime1 = new byte[64];
            Array.Copy(keyData, index, pemPrime1, 0, 64);
 
            index += 64;
            index += ((int)keyData[index + 1] == 64 ? 2 : 3);//346  
            byte[] pemPrime2 = new byte[64];
            Array.Copy(keyData, index, pemPrime2, 0, 64);
 
            index += 64;
            index += ((int)keyData[index + 1] == 64 ? 2 : 3);
            byte[] pemExponent1 = new byte[64];
            Array.Copy(keyData, index, pemExponent1, 0, 64);
 
            index += 64;
            index += ((int)keyData[index + 1] == 64 ? 2 : 3);
            byte[] pemExponent2 = new byte[64];
            Array.Copy(keyData, index, pemExponent2, 0, 64);
 
            index += 64;
            index += ((int)keyData[index + 1] == 64 ? 2 : 3);
            byte[] pemCoefficient = new byte[64];
            Array.Copy(keyData, index, pemCoefficient, 0, 64);
 
            RSAParameters para = new RSAParameters();
            para.Modulus = pemModulus;
            para.Exponent = pemPublicExponent;
            para.D = pemPrivateExponent;
            para.P = pemPrime1;
            para.Q = pemPrime2;
            para.DP = pemExponent1;
            para.DQ = pemExponent2;
            para.InverseQ = pemCoefficient;
            return para;
        }
    }

　　測試程式碼如下

    static void Main(string[] args)
        {
            /**RSA加密測試,RSA中的金鑰對通過SSL工具生成，生成命令如下： 
            * 1 生成RSA私鑰： 
            * openssl genrsa -out rsa_private_key.pem 1024 
            *2 生成RSA公鑰 
            * openssl rsa -in rsa_private_key.pem -pubout -out rsa_public_key.pem 
            * 
            * 3 將RSA私鑰轉換成PKCS8格式 
            * openssl pkcs8 -topk8 -inform PEM -in rsa_private_key.pem -outform PEM -nocrypt -out rsa_pub_pk8.pem 
            * 
            * 直接開啟rsa_private_key.pem和rsa_pub_pk8.pem檔案就可以獲取金鑰對內容，獲取金鑰對內容組成字串時，注意將換行符刪除 
            * */
            //rsa_pub_pk8.pem內容
            string privatekey = "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";
            //rsa_public_key.pem內容
            string publickey = "MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDLK6Hw+RE///HKM1zukQTao/ybdm7RpbQ2bvDTHtDWysx46vIC4wosNZwP3bmxEpzq8f6B3jZeqtcoxCWfVNi1S1FNjyKpC55xmjzrCTNUe9mSgKwyoGU/kHpR4FyXTgP02XkuDXXJrODlDQQg0UNrgbkA9BboLxdxkZLsp1tshQIDAQAB";
            //加密字串  
            string data = "yangyoushan";
 
            Console.WriteLine("加密前字串內容：" + data);
            //加密  
            string encrypteddata = RSACrypt.encryptData(data, publickey, "UTF-8");
            Console.WriteLine("加密後的字串為：" + encrypteddata);
            Console.WriteLine("解密後的字串內容：" + RSACrypt.decryptData(encrypteddata, privatekey, "UTF-8"));
 
            Console.WriteLine("*****我是分割線******");
 
            //解密  
            string endata = "VbOtmCuc8+8gKXbDyYHAVG6Hnoa7lCphMZePUmxaM7zQ0XD7oTcRY59xNo9xOpwG5YwjbEiHKcuANuKNBlPLkieX5yGSS8iOd1cki+DujqUtffHQicMegubh4vaPhvhBnOflUejtZH1xi2r2a2t8v9xQO+vmZc7gNJ91+3gtFuc=";
            string datamw = RSACrypt.decryptData(endata, privatekey, "UTF-8");
            Console.WriteLine("靜態加密後的字串為：" + endata);
            Console.WriteLine("解密後的字串內容：" + datamw);
 
            //簽名  
            string signdata = "20180522201658IMFINE";
            Console.WriteLine("簽名前的字串內容：" + signdata);
            string sign = RSACrypt.sign(signdata, privatekey, "UTF-8");
            Console.WriteLine("簽名後的字串：" + sign);
 
            string sourceSign = "VEAgvbHavdbOPYSP8jqxJPYTv/FV/Nl3MClHFBN4qvDRM3ixbOKpUY2P1w99edC29C4Q7qNY99jKYJucRM21mBf8RgEnsBqZVIzqnJYafIQ0AFCL7BpNAORM7uns+NxFj2Zse6Kr61lSpEvie1GCzo+iuYYvzPlMlz+W6nScp2A=";
            Console.WriteLine("生成的簽名:" + sourceSign);
            bool realSign1 = RSACrypt.verify("20180522201658IMFINE", sign, publickey, "UTF-8");
            Console.WriteLine(realSign1);
 
            bool realSign2 = RSACrypt.verify("20180522201658IMFINEHAHA", sign, publickey, "UTF-8");
            Console.WriteLine(realSign2);
            Console.ReadLine();  
        }

　來源：https://blog.csdn.net/yysyangyangyangshan/article/details/80411134