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前言：

书承上文，上回说到如何做加密，那我们在讲讲如何解密如何？

         /// <summary>
        /// DES解密
        /// </summary>
        /// <param name="value">需要解密的字符串（密文）</param>
        /// <returns>解密之后的字符串（明文）</returns>
        public static string DesDecrypt(string value)
        {
            DESCryptoServiceProvider des = new DESCryptoServiceProvider();

            byte[] inputByteArray = new byte[value.Length / 2];
            for (int x = 0; x < value.Length / 2; x++)
            {
                int i = (Convert.ToInt32(value.Substring(x * 2, 2), 16));
                inputByteArray[x] = (byte)i;
            }

            string key = "s1u&n*dy";

            des.Key = ASCIIEncoding.ASCII.GetBytes(key);
            des.IV = ASCIIEncoding.ASCII.GetBytes(key);
            MemoryStream ms = new MemoryStream();
            CryptoStream cs = new CryptoStream(ms, des.CreateDecryptor(), CryptoStreamMode.Write);
            cs.Write(inputByteArray, 0, inputByteArray.Length);
            cs.FlushFinalBlock();

            return Encoding.UTF8.GetString(ms.ToArray());
        }

        /// <summary>
        ///  MD5解密
        /// </summary>
        /// <param name="pToDecrypt"></param>
        /// <param name="sKey"></param>
        /// <returns></returns>
        public static string MD5Decrypt(string pToDecrypt, string sKey)
        {
            DESCryptoServiceProvider des = new DESCryptoServiceProvider();

            byte[] inputByteArray = new byte[pToDecrypt.Length / 2];
            for (int x = 0; x < pToDecrypt.Length / 2; x++)
            {
                int i = (Convert.ToInt32(pToDecrypt.Substring(x * 2, 2), 16));
                inputByteArray[x] = (byte)i;
            }

            des.Key = ASCIIEncoding.ASCII.GetBytes(sKey);
            des.IV = ASCIIEncoding.ASCII.GetBytes(sKey);
            MemoryStream ms = new MemoryStream();
            CryptoStream cs = new CryptoStream(ms, des.CreateDecryptor(), CryptoStreamMode.Write);
            cs.Write(inputByteArray, 0, inputByteArray.Length);
            cs.FlushFinalBlock();

            StringBuilder ret = new StringBuilder();

            return System.Text.Encoding.Default.GetString(ms.ToArray());
        }

        /// <summary>
        /// Base64解密
        /// </summary>
        /// <param name="codeName">解密采用的编码方式，注意和加密时采用的方式一致</param>
        /// <param name="result">待解密的密文</param>
        /// <returns>解密后的字符串</returns>
        public static string DecodeBase64(Encoding encode, string result)
        {
            string decode = "";
            byte[] bytes = Convert.FromBase64String(result);
            try
            {
                decode = encode.GetString(bytes);
            }
            catch
            {
                decode = result;
            }
            return decode;
        }
        /// <summary>
        /// AES解密(无向量)
        /// </summary>
        /// <param name="encryptedBytes">被加密的明文</param>
        /// <param name="key">密钥</param>
        /// <returns>明文</returns>
        public static string AESDecrypt(String Data, String Key)
        {
            Byte[] encryptedBytes = Convert.FromBase64String(Data);
            Byte[] bKey = new Byte[32];
            Array.Copy(Encoding.UTF8.GetBytes(Key.PadRight(bKey.Length)), bKey, bKey.Length);

            MemoryStream mStream = new MemoryStream(encryptedBytes);
            //mStream.Write( encryptedBytes, 0, encryptedBytes.Length );
            //mStream.Seek( 0, SeekOrigin.Begin );
            RijndaelManaged aes = new RijndaelManaged();
            aes.Mode = CipherMode.ECB;
            aes.Padding = PaddingMode.PKCS7;
            aes.KeySize = 128;
            aes.Key = bKey;
            //aes.IV = _iV;
            CryptoStream cryptoStream = new CryptoStream(mStream, aes.CreateDecryptor(), CryptoStreamMode.Read);
            try
            {
                byte[] tmp = new byte[encryptedBytes.Length + 32];
                int len = cryptoStream.Read(tmp, 0, encryptedBytes.Length + 32);
                byte[] ret = new byte[len];
                Array.Copy(tmp, 0, ret, 0, len);
                return Encoding.UTF8.GetString(ret);
            }
            finally
            {
                cryptoStream.Close();
                mStream.Close();
                aes.Clear();
            }
        }

        /// <summary>
        /// RSA解密
        /// </summary>
        /// <param name="privatekey"></param>
        /// <param name="content"></param>
        /// <returns></returns>
        public static string RSADecrypt(string privatekey, string content)
        {
            RSACryptoServiceProvider rsa = new RSACryptoServiceProvider();
            byte[] cipherbytes;
            rsa.FromXmlString(privatekey);
            cipherbytes = rsa.Decrypt(Convert.FromBase64String(content), false);

            return Encoding.UTF8.GetString(cipherbytes);
        }

简介：

• 可能你回有疑问了，为啥没有SHA128，SHA256，SHA384，SHA512的解密，他们都是一种加密（单向）哈希函数，因此没有直接的解码方法。加密哈希函数的全部目的是您无法撤消它。

总结：

有时间就积累一点知识点，也许都用不到，多积累，多学习，没什么坏处。
原文地址：https://www.cnblogs.com/2828sea/p/13491192.html