我们在开发系统时对于一些敏感的数据往往要使用加密技术对敏感数据进行加密，C#实现加密的方法有很多，比如MD5加密，RSA加密等加密方式。今天我们主要讲解一下RSA加密算法的使用。

C#RSA加密算法代码如下：

using System;
using System.IO;
using System.Security.Cryptography;
using System.Text;
 
namespace RSAClass
{
    /// <summary>
    /// 堆代码 duidaima.com
    /// RSA加解密 使用OpenSSL的公钥加密/私钥解密
    /// 公私钥请使用openssl生成  ssh-keygen -t rsa 命令生成的公钥私钥是不行的
    /// 
    /// </summary>
    public class RSAHelper
    {
        private readonly RSA _privateKeyRsaProvider;
        private readonly RSA _publicKeyRsaProvider;
        private readonly HashAlgorithmName _hashAlgorithmName;
        private readonly Encoding _encoding;
 
        /// <summary>
        /// 实例化RSAHelper
        /// </summary>
        /// <param name="rsaType">加密算法类型 RSA SHA1;RSA2 SHA256 密钥长度至少为2048</param>
        /// <param name="encoding">编码类型</param>
        /// <param name="privateKey">私钥</param>
        /// <param name="publicKey">公钥</param>
        public RSAHelper(RSAType rsaType, Encoding encoding, string privateKey, string publicKey = null)
        {
            _encoding = encoding;
            if (!string.IsNullOrEmpty(privateKey))
            {
                _privateKeyRsaProvider = CreateRsaProviderFromPrivateKey(privateKey);
            }
 
            if (!string.IsNullOrEmpty(publicKey))
            {
                _publicKeyRsaProvider = CreateRsaProviderFromPublicKey(publicKey);
            }
 
            _hashAlgorithmName = rsaType == RSAType.RSA ? HashAlgorithmName.SHA1 : HashAlgorithmName.SHA256;
        }
 
        #region 使用私钥签名
 
        /// <summary>
        /// 使用私钥签名
        /// </summary>
        /// <param name="data">原始数据</param>
        /// <returns></returns>
        public string Sign(string data)
        {
            byte[] dataBytes = _encoding.GetBytes(data);
 
            var signatureBytes = _privateKeyRsaProvider.SignData(dataBytes, _hashAlgorithmName, RSASignaturePadding.Pkcs1);
 
            return Convert.ToBase64String(signatureBytes);
        }
 
        #endregion
 
        #region 使用公钥验证签名
 
        /// <summary>
        /// 使用公钥验证签名
        /// </summary>
        /// <param name="data">原始数据</param>
        /// <param name="sign">签名</param>
        /// <returns></returns>
        public bool Verify(string data,string sign)
        {
            byte[] dataBytes = _encoding.GetBytes(data);
            byte[] signBytes = Convert.FromBase64String(sign);
 
            var verify = _publicKeyRsaProvider.VerifyData(dataBytes, signBytes, _hashAlgorithmName, RSASignaturePadding.Pkcs1);
 
            return verify;
        }
 
        #endregion
 
        #region 解密
 
        public string Decrypt(string cipherText)
        {
            if (_privateKeyRsaProvider == null)
            {
                throw new Exception("_privateKeyRsaProvider is null");
            }
            return Encoding.UTF8.GetString(_privateKeyRsaProvider.Decrypt(Convert.FromBase64String(cipherText), RSAEncryptionPadding.Pkcs1));
        }
 
        #endregion
 
        #region 加密
 
        public string Encrypt(string text)
        {
            if (_publicKeyRsaProvider == null)
            {
                throw new Exception("_publicKeyRsaProvider is null");
            }
            return Convert.ToBase64String(_publicKeyRsaProvider.Encrypt(Encoding.UTF8.GetBytes(text), RSAEncryptionPadding.Pkcs1));
        }
 
        #endregion
 
        #region 使用私钥创建RSA实例
 
        public RSA CreateRsaProviderFromPrivateKey(string privateKey)
        {
            var privateKeyBits = Convert.FromBase64String(privateKey);
 
            var rsa = RSA.Create();
            var rsaParameters = new RSAParameters();
 
            using (BinaryReader binr = new BinaryReader(new MemoryStream(privateKeyBits)))
            {
                byte bt = 0;
                ushort twobytes = 0;
                twobytes = binr.ReadUInt16();
                if (twobytes == 0x8130)
                    binr.ReadByte();
                else if (twobytes == 0x8230)
                    binr.ReadInt16();
                else
                    throw new Exception("Unexpected value read binr.ReadUInt16()");
 
                twobytes = binr.ReadUInt16();
                if (twobytes != 0x0102)
                    throw new Exception("Unexpected version");
 
                bt = binr.ReadByte();
                if (bt != 0x00)
                    throw new Exception("Unexpected value read binr.ReadByte()");
 
                rsaParameters.Modulus = binr.ReadBytes(GetIntegerSize(binr));
                rsaParameters.Exponent = binr.ReadBytes(GetIntegerSize(binr));
                rsaParameters.D = binr.ReadBytes(GetIntegerSize(binr));
                rsaParameters.P = binr.ReadBytes(GetIntegerSize(binr));
                rsaParameters.Q = binr.ReadBytes(GetIntegerSize(binr));
                rsaParameters.DP = binr.ReadBytes(GetIntegerSize(binr));
                rsaParameters.DQ = binr.ReadBytes(GetIntegerSize(binr));
                rsaParameters.InverseQ = binr.ReadBytes(GetIntegerSize(binr));
            }
 
            rsa.ImportParameters(rsaParameters);
            return rsa;
        }
 
        #endregion
 
        #region 使用公钥创建RSA实例
 
        public RSA CreateRsaProviderFromPublicKey(string publicKeyString)
        {
            // encoded OID sequence for  PKCS #1 rsaEncryption szOID_RSA_RSA = "1.2.840.113549.1.1.1"
            byte[] seqOid = { 0x30, 0x0D, 0x06, 0x09, 0x2A, 0x86, 0x48, 0x86, 0xF7, 0x0D, 0x01, 0x01, 0x01, 0x05, 0x00 };
            byte[] seq = new byte[15];
 
            var x509Key = Convert.FromBase64String(publicKeyString);
 
            // ---------  Set up stream to read the asn.1 encoded SubjectPublicKeyInfo blob  ------
            using (MemoryStream mem = new MemoryStream(x509Key))
            {
                using (BinaryReader binr = new BinaryReader(mem))  //wrap Memory Stream with BinaryReader for easy reading
                {
                    byte bt = 0;
                    ushort twobytes = 0;
 
                    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;
 
                    seq = binr.ReadBytes(15);       //read the Sequence OID
                    if (!CompareBytearrays(seq, seqOid))    //make sure Sequence for OID is correct
                        return null;
 
                    twobytes = binr.ReadUInt16();
                    if (twobytes == 0x8103) //data read as little endian order (actual data order for Bit String is 03 81)
                        binr.ReadByte();    //advance 1 byte
                    else if (twobytes == 0x8203)
                        binr.ReadInt16();   //advance 2 bytes
                    else
                        return null;
 
                    bt = binr.ReadByte();
                    if (bt != 0x00)     //expect null byte next
                        return null;
 
                    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();
                    byte lowbyte = 0x00;
                    byte highbyte = 0x00;
 
                    if (twobytes == 0x8102) //data read as little endian order (actual data order for Integer is 02 81)
                        lowbyte = binr.ReadByte();  // read next bytes which is bytes in modulus
                    else if (twobytes == 0x8202)
                    {
                        highbyte = binr.ReadByte(); //advance 2 bytes
                        lowbyte = binr.ReadByte();
                    }
                    else
                        return null;
                    byte[] modint = { lowbyte, highbyte, 0x00, 0x00 };   //reverse byte order since asn.1 key uses big endian order
                    int modsize = BitConverter.ToInt32(modint, 0);
 
                    int firstbyte = binr.PeekChar();
                    if (firstbyte == 0x00)
                    {   //if first byte (highest order) of modulus is zero, don't include it
                        binr.ReadByte();    //skip this null byte
                        modsize -= 1;   //reduce modulus buffer size by 1
                    }
 
                    byte[] modulus = binr.ReadBytes(modsize);   //read the modulus bytes
 
                    if (binr.ReadByte() != 0x02)            //expect an Integer for the exponent data
                        return null;
                    int expbytes = (int)binr.ReadByte();        // should only need one byte for actual exponent data (for all useful values)
                    byte[] exponent = binr.ReadBytes(expbytes);
 
                    // ------- create RSACryptoServiceProvider instance and initialize with public key -----
                    var rsa = RSA.Create();
                    RSAParameters rsaKeyInfo = new RSAParameters
                    {
                        Modulus = modulus,
                        Exponent = exponent
                    };
                    rsa.ImportParameters(rsaKeyInfo);
 
                    return rsa;
                }
 
            }
        }
 
        #endregion
 
        #region 导入密钥算法
 
        private int GetIntegerSize(BinaryReader binr)
        {
            byte bt = 0;
            int count = 0;
            bt = binr.ReadByte();
            if (bt != 0x02)
                return 0;
            bt = binr.ReadByte();
 
            if (bt == 0x81)
                count = binr.ReadByte();
            else
            if (bt == 0x82)
            {
                var highbyte = binr.ReadByte();
                var 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 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;
        }
 
        #endregion
 
    }
 
    /// <summary>
    /// RSA算法类型
    /// </summary>
    public enum RSAType
    {
        /// <summary>
        /// SHA1
        /// </summary>
        RSA = 0,
        /// <summary>
        /// RSA2 密钥长度至少为2048
        /// SHA256
        /// </summary>
        RSA2
    }
}

以上就是基于C#实现的RSA加密算法，我这边直接封装了个加密辅助类，这样在项目需要的地方可以直接实现复用。如果你们在用C#开发系统时也会用到使用RSA加密的功能，可以参考一下这篇文章的实现方式。