C# 各种加密

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Security.Cryptography;
using System.Text;
using System.Web;

namespace WebDemo.Until
{

    public class EncryptHelper
    {
        #region DES对称加密解密

        /// <summary> 加密字符串
        /// </summary>
        /// <param name="strText">需被加密的字符串</param>
        /// <param name="strEncrKey">密钥</param>
        /// <returns></returns>
        public static string DesEncrypt(string strText, string strEncrKey)
        {
            try
            {
                byte[] byKey = null;
                byte[] IV = { 0x12, 0x34, 0x56, 0x78, 0x90, 0xAB, 0xCD, 0xEF };

                byKey = Encoding.UTF8.GetBytes(strEncrKey.Substring(, ));
                DESCryptoServiceProvider des = new DESCryptoServiceProvider();
                byte[] inputByteArray = Encoding.UTF8.GetBytes(strText);
                MemoryStream ms = new MemoryStream();
                CryptoStream cs = new CryptoStream(ms, des.CreateEncryptor(byKey, IV), CryptoStreamMode.Write);
                cs.Write(inputByteArray, , inputByteArray.Length);
                cs.FlushFinalBlock();
                return Convert.ToBase64String(ms.ToArray());
            }
            catch
            {
                return "";
            }
        }

        /// <summary> 解密字符串
        /// </summary>
        /// <param name="strText">需被解密的字符串</param>
        /// <param name="sDecrKey">密钥</param>
        /// <returns></returns>
        public static string DesDecrypt(string strText, string sDecrKey)
        {
            try
            {
                byte[] byKey = null;
                byte[] IV = { 0x12, 0x34, 0x56, 0x78, 0x90, 0xAB, 0xCD, 0xEF };
                byte[] inputByteArray = new Byte[strText.Length];

                byKey = Encoding.UTF8.GetBytes(sDecrKey.Substring(, ));
                DESCryptoServiceProvider des = new DESCryptoServiceProvider();
                inputByteArray = Convert.FromBase64String(strText);
                MemoryStream ms = new MemoryStream();
                CryptoStream cs = new CryptoStream(ms, des.CreateDecryptor(byKey, IV), CryptoStreamMode.Write);
                cs.Write(inputByteArray, , inputByteArray.Length);
                cs.FlushFinalBlock();
                Encoding encoding = new UTF8Encoding();
                return encoding.GetString(ms.ToArray());
            }
            catch
            {
                return null;
            }
        }

        /// <summary> 加密文件
        ///
        /// </summary>
        /// <param name="m_InFilePath">原路径</param>
        /// <param name="m_OutFilePath">加密后的文件路径</param>
        /// <param name="strEncrKey">密钥</param>
        public static void DesEncryptFile(string m_InFilePath, string m_OutFilePath, string strEncrKey)
        {
            try
            {
                byte[] byKey = null;
                byte[] IV = { 0x12, 0x34, 0x56, 0x78, 0x90, 0xAB, 0xCD, 0xEF };

                byKey = Encoding.UTF8.GetBytes(strEncrKey.Substring(, ));
                FileStream fin = new FileStream(m_InFilePath, FileMode.Open, FileAccess.Read);
                FileStream fout = new FileStream(m_OutFilePath, FileMode.OpenOrCreate, FileAccess.Write);
                fout.SetLength();
                //Create variables to help with read and write.
                byte[] bin = new byte[]; //This is intermediate storage for the encryption.
                long rdlen = ; //This is the total number of bytes written.
                long totlen = fin.Length; //This is the total length of the input file.
                int len; //This is the number of bytes to be written at a time.

                DES des = new DESCryptoServiceProvider();
                CryptoStream encStream = new CryptoStream(fout, des.CreateEncryptor(byKey, IV), CryptoStreamMode.Write);

                //Read from the input file, then encrypt and write to the output file.
                while (rdlen < totlen)
                {
                    len = fin.Read(bin, , );
                    encStream.Write(bin, , len);
                    rdlen = rdlen + len;
                }
                encStream.Close();
                fout.Close();
                fin.Close();
            }
            catch
            {
            }

        }

        /// <summary> 解密文件
        ///
        /// </summary>
        /// <param name="m_InFilePath">被解密路径</param>
        /// <param name="m_OutFilePath">解密后的路径</param>
        /// <param name="sDecrKey">密钥</param>
        public static void DesDecryptFile(string m_InFilePath, string m_OutFilePath, string sDecrKey)
        {
            try
            {
                byte[] byKey = null;
                byte[] IV = { 0x12, 0x34, 0x56, 0x78, 0x90, 0xAB, 0xCD, 0xEF };

                byKey = Encoding.UTF8.GetBytes(sDecrKey.Substring(, ));
                FileStream fin = new FileStream(m_InFilePath, FileMode.Open, FileAccess.Read);
                FileStream fout = new FileStream(m_OutFilePath, FileMode.OpenOrCreate, FileAccess.Write);
                fout.SetLength();
                //Create variables to help with read and write.
                byte[] bin = new byte[]; //This is intermediate storage for the encryption.
                long rdlen = ; //This is the total number of bytes written.
                long totlen = fin.Length; //This is the total length of the input file.
                int len; //This is the number of bytes to be written at a time.

                DES des = new DESCryptoServiceProvider();
                CryptoStream encStream = new CryptoStream(fout, des.CreateDecryptor(byKey, IV), CryptoStreamMode.Write);

                //Read from the input file, then encrypt and write to the output file.
                while (rdlen < totlen)
                {
                    len = fin.Read(bin, , );
                    encStream.Write(bin, , len);
                    rdlen = rdlen + len;
                }
                encStream.Close();
                fout.Close();
                fin.Close();
            }
            catch
            {
            }
        }
        #endregion

        #region 3DES对称加密解密
        /// <summary>
        ///3DES加密
        /// </summary>
        /// <param name="originalValue">加密数据</param>
        /// <param name="key">24位字符的密钥字符串</param>
        /// <param name="IV">8位字符的初始化向量字符串</param>
        /// <returns></returns>
        public static string DESEncrypt(string originalValue, string key, string IV)
        {
            SymmetricAlgorithm sa = new TripleDESCryptoServiceProvider();
            sa.Mode = CipherMode.CBC;
            sa.Padding = PaddingMode.PKCS7;
            sa.Key = Encoding.UTF8.GetBytes(key);
            sa.IV = Encoding.UTF8.GetBytes(IV);
            ICryptoTransform ct = sa.CreateEncryptor();
            byte[] byt = Encoding.UTF8.GetBytes(originalValue);
            MemoryStream ms = new MemoryStream();
            CryptoStream cs = new CryptoStream(ms, ct, CryptoStreamMode.Write);
            cs.Write(byt, , byt.Length);
            cs.FlushFinalBlock();
            cs.Close();
            return Convert.ToBase64String(ms.ToArray());
        }
        /// <summary>
        /// 3DES解密
        /// </summary>
        /// <param name="data">解密数据</param>
        /// <param name="key">24位字符的密钥字符串(需要和加密时相同)</param>
        /// <param name="iv">8位字符的初始化向量字符串(需要和加密时相同)</param>
        /// <returns></returns>
        public static string DESDecrypst(string data, string key, string IV)
        {
            SymmetricAlgorithm mCSP = new TripleDESCryptoServiceProvider();
            mCSP.Mode = CipherMode.CBC;
            mCSP.Padding = PaddingMode.PKCS7;
            mCSP.Key = Encoding.UTF8.GetBytes(key);
            mCSP.IV = Encoding.UTF8.GetBytes(IV);
            ICryptoTransform ct = mCSP.CreateDecryptor(mCSP.Key, mCSP.IV);
            byte[] byt = Convert.FromBase64String(data);
            MemoryStream ms = new MemoryStream();
            CryptoStream cs = new CryptoStream(ms, ct, CryptoStreamMode.Write);
            cs.Write(byt, , byt.Length);
            cs.FlushFinalBlock();
            cs.Close();
            return Encoding.UTF8.GetString(ms.ToArray());
        }
        #endregion

        #region AES RijndaelManaged加密解密

        private static readonly string Default_AES_Key = "@#kim123";
        private static byte[] Keys = { 0x41, 0x72, 0x65, 0x79, 0x6F, 0x75, 0x6D, 0x79,
                                             0x53,0x6E, 0x6F, 0x77, 0x6D, 0x61, 0x6E, 0x3F };
        public static string AES_Encrypt(string encryptString)
        {
            return AES_Encrypt(encryptString, Default_AES_Key);
        }

        public static string AES_Decrypt(string decryptString)
        {
            return AES_Decrypt(decryptString, Default_AES_Key);
        }

        #region AES(CBC)有向量（IV）
        /// <summary>对称加密算法AES RijndaelManaged加密(RijndaelManaged（AES）算法是块式加密算法)
        ///
        /// </summary>
        /// <param name="encryptString">待加密字符串</param>
        /// <param name="encryptKey">加密密钥，须半角字符</param>
        /// <returns>加密结果字符串</returns>
        public static string AES_Encrypt(string encryptString, string encryptKey)
        {
            encryptKey = GetSubString(encryptKey, , "");
            encryptKey = encryptKey.PadRight(, ' ');

            RijndaelManaged rijndaelProvider = new RijndaelManaged();
            rijndaelProvider.Key = Encoding.UTF8.GetBytes(encryptKey.Substring(, ));
            rijndaelProvider.IV = Keys;
            ICryptoTransform rijndaelEncrypt = rijndaelProvider.CreateEncryptor();

            byte[] inputData = Encoding.UTF8.GetBytes(encryptString);
            byte[] encryptedData = rijndaelEncrypt.TransformFinalBlock(inputData, , inputData.Length);

            return Convert.ToBase64String(encryptedData);
        }

        /// <summary> 对称加密算法AES RijndaelManaged解密字符串
        ///
        /// </summary>
        /// <param name="decryptString">待解密的字符串</param>
        /// <param name="decryptKey">解密密钥,和加密密钥相同</param>
        /// <returns>解密成功返回解密后的字符串,失败返回空</returns>
        public static string AES_Decrypt(string decryptString, string decryptKey)
        {
            try
            {
                decryptKey = GetSubString(decryptKey, , "");
                decryptKey = decryptKey.PadRight(, ' ');

                RijndaelManaged rijndaelProvider = new RijndaelManaged();
                rijndaelProvider.Key = Encoding.UTF8.GetBytes(decryptKey);
                rijndaelProvider.IV = Keys;
                ICryptoTransform rijndaelDecrypt = rijndaelProvider.CreateDecryptor();

                byte[] inputData = Convert.FromBase64String(decryptString);
                byte[] decryptedData = rijndaelDecrypt.TransformFinalBlock(inputData, , inputData.Length);

                return Encoding.UTF8.GetString(decryptedData);
            }
            catch
            {
                return string.Empty;
            }
        }
        #endregion

        #region AES(ECB)无向量（IV）
        /// <summary>
        /// AES加密(无向量)
        /// </summary>
        /// <param name="plainBytes">被加密的明文</param>
        /// <param name="key">密钥 32 </param>
        /// <returns>密文</returns>
        public static string AESEncryptECB(string encryptString, string encryptKey)
        {
            try
            {
                encryptKey = GetSubString(encryptKey, , "");
                encryptKey = encryptKey.PadRight(, ' ');

                RijndaelManaged rijndaelProvider = new RijndaelManaged();
                rijndaelProvider.Key = Encoding.UTF8.GetBytes(encryptKey.Substring(, ));
                rijndaelProvider.Mode = CipherMode.ECB;
                rijndaelProvider.Padding = PaddingMode.PKCS7;
                ICryptoTransform rijndaelEncrypt = rijndaelProvider.CreateEncryptor();
                byte[] inputData = Encoding.UTF8.GetBytes(encryptString);
                byte[] encryptedData = rijndaelEncrypt.TransformFinalBlock(inputData, , inputData.Length);
                return Convert.ToBase64String(encryptedData);
            }
            catch (Exception ex)
            {
                return ex.Message;
            }
        }

        /// <summary>
        /// AES解密(无向量)
        /// </summary>
        /// <param name="decryptString">被加密的明文</param>
        /// <param name="decryptKey">密钥</param>
        /// <returns>明文</returns>
        public static string AESDecryptECB(string decryptString, string decryptKey)
        {
            try
            {
                decryptKey = GetSubString(decryptKey, , "");
                decryptKey = decryptKey.PadRight(, ' ');

                RijndaelManaged rijndaelProvider = new RijndaelManaged();
                rijndaelProvider.Key = Encoding.UTF8.GetBytes(decryptKey.Substring(, ));
                rijndaelProvider.Mode = CipherMode.ECB;
                rijndaelProvider.Padding = PaddingMode.PKCS7;
                ICryptoTransform rijndaelDecrypt = rijndaelProvider.CreateDecryptor();
                byte[] inputData = Convert.FromBase64String(decryptString);
                byte[] decryptedData = rijndaelDecrypt.TransformFinalBlock(inputData, , inputData.Length);
                return Encoding.UTF8.GetString(decryptedData);
            }
            catch (Exception ex)
            {
                return ex.Message;
            }
        }
        #endregion

        /// <summary>
        /// 按字节长度(按字节,一个汉字为2个字节)取得某字符串的一部分
        /// </summary>
        /// <param name="sourceString">源字符串</param>
        /// <param name="length">所取字符串字节长度</param>
        /// <param name="tailString">附加字符串(当字符串不够长时，尾部所添加的字符串，一般为"...")</param>
        /// <returns>某字符串的一部分</returns>
        private static string GetSubString(string sourceString, int length, string tailString)
        {
            return GetSubString(sourceString, , length, tailString);
        }

        /// <summary>
        /// 按字节长度(按字节,一个汉字为2个字节)取得某字符串的一部分
        /// </summary>
        /// <param name="sourceString">源字符串</param>
        /// <param name="startIndex">索引位置，以0开始</param>
        /// <param name="length">所取字符串字节长度</param>
        /// <param name="tailString">附加字符串(当字符串不够长时，尾部所添加的字符串，一般为"...")</param>
        /// <returns>某字符串的一部分</returns>
        private static string GetSubString(string sourceString, int startIndex, int length, string tailString)
        {
            string myResult = sourceString;

            //当是日文或韩文时(注:中文的范围:\u4e00 - \u9fa5, 日文在\u0800 - \u4e00, 韩文为\xAC00-\xD7A3)
            if (System.Text.RegularExpressions.Regex.IsMatch(sourceString, "[\u0800-\u4e00]+") ||
                System.Text.RegularExpressions.Regex.IsMatch(sourceString, "[\xAC00-\xD7A3]+"))
            {
                //当截取的起始位置超出字段串长度时
                if (startIndex >= sourceString.Length)
                {
                    return string.Empty;
                }
                else
                {
                    return sourceString.Substring(startIndex,
                                                   ((length + startIndex) > sourceString.Length) ? (sourceString.Length - startIndex) : length);
                }
            }

            //中文字符，如"中国人民abcd123"
            if (length <= )
            {
                return string.Empty;
            }
            byte[] bytesSource = Encoding.Default.GetBytes(sourceString);

            //当字符串长度大于起始位置
            if (bytesSource.Length > startIndex)
            {
                int endIndex = bytesSource.Length;

                //当要截取的长度在字符串的有效长度范围内
                if (bytesSource.Length > (startIndex + length))
                {
                    endIndex = length + startIndex;
                }
                else
                {   //当不在有效范围内时,只取到字符串的结尾
                    length = bytesSource.Length - startIndex;
                    tailString = "";
                }

                int[] anResultFlag = new int[length];
                int nFlag = ;
                //字节大于127为双字节字符
                for (int i = startIndex; i < endIndex; i++)
                {
                    if (bytesSource[i] > )
                    {
                        nFlag++;
                        if (nFlag == )
                        {
                            nFlag = ;
                        }
                    }
                    else
                    {
                        nFlag = ;
                    }
                    anResultFlag[i] = nFlag;
                }
                //最后一个字节为双字节字符的一半
                if ((bytesSource[endIndex - ] > ) && (anResultFlag[length - ] == ))
                {
                    length = length + ;
                }

                byte[] bsResult = new byte[length];
                Array.Copy(bytesSource, startIndex, bsResult, , length);
                myResult = Encoding.Default.GetString(bsResult);
                myResult = myResult + tailString;

                return myResult;
            }

            return string.Empty;

        }

        /// <summary>
        /// 加密文件流
        /// </summary>
        /// <param name="fs"></param>
        /// <returns></returns>
        public static CryptoStream AES_EncryptStrream(FileStream fs, string decryptKey)
        {
            decryptKey = GetSubString(decryptKey, , "");
            decryptKey = decryptKey.PadRight(, ' ');

            RijndaelManaged rijndaelProvider = new RijndaelManaged();
            rijndaelProvider.Key = Encoding.UTF8.GetBytes(decryptKey);
            rijndaelProvider.IV = Keys;

            ICryptoTransform encrypto = rijndaelProvider.CreateEncryptor();
            CryptoStream cytptostreamEncr = new CryptoStream(fs, encrypto, CryptoStreamMode.Write);
            return cytptostreamEncr;
        }

        /// <summary>
        /// 解密文件流
        /// </summary>
        /// <param name="fs"></param>
        /// <returns></returns>
        public static CryptoStream AES_DecryptStream(FileStream fs, string decryptKey)
        {
            decryptKey = GetSubString(decryptKey, , "");
            decryptKey = decryptKey.PadRight(, ' ');

            RijndaelManaged rijndaelProvider = new RijndaelManaged();
            rijndaelProvider.Key = Encoding.UTF8.GetBytes(decryptKey);
            rijndaelProvider.IV = Keys;
            ICryptoTransform Decrypto = rijndaelProvider.CreateDecryptor();
            CryptoStream cytptostreamDecr = new CryptoStream(fs, Decrypto, CryptoStreamMode.Read);
            return cytptostreamDecr;
        }

        /// <summary>
        /// 对指定文件加密
        /// </summary>
        /// <param name="InputFile"></param>
        /// <param name="OutputFile"></param>
        /// <returns></returns>
        public static bool AES_EncryptFile(string InputFile, string OutputFile)
        {
            try
            {
                string decryptKey = "www.iqidi.com";

                FileStream fr = new FileStream(InputFile, FileMode.Open);
                FileStream fren = new FileStream(OutputFile, FileMode.Create);
                CryptoStream Enfr = AES_EncryptStrream(fren, decryptKey);
                byte[] bytearrayinput = new byte[fr.Length];
                fr.Read(bytearrayinput, , bytearrayinput.Length);
                Enfr.Write(bytearrayinput, , bytearrayinput.Length);
                Enfr.Close();
                fr.Close();
                fren.Close();
            }
            catch
            {
                //文件异常
                return false;
            }
            return true;
        }

        /// <summary>
        /// 对指定的文件解压缩
        /// </summary>
        /// <param name="InputFile"></param>
        /// <param name="OutputFile"></param>
        /// <returns></returns>
        public static bool AES_DecryptFile(string InputFile, string OutputFile)
        {
            try
            {
                string decryptKey = "www.iqidi.com";
                FileStream fr = new FileStream(InputFile, FileMode.Open);
                FileStream frde = new FileStream(OutputFile, FileMode.Create);
                CryptoStream Defr = AES_DecryptStream(fr, decryptKey);
                byte[] bytearrayoutput = new byte[];
                int m_count = ;

                do
                {
                    m_count = Defr.Read(bytearrayoutput, , bytearrayoutput.Length);
                    frde.Write(bytearrayoutput, , m_count);
                    if (m_count < bytearrayoutput.Length)
                        break;
                } while (true);

                Defr.Close();
                fr.Close();
                frde.Close();
            }
            catch
            {
                //文件异常
                return false;
            }
            return true;
        }

        #endregion

        #region RSA加密 解密

        /// <summary>RSA加密
        ///
        /// </summary>
        /// <param name="plaintext">明文</param>
        /// <param name="publicKey">公钥</param>
        /// <returns>密文字符串</returns>
        public static string EncryptByRSA(string plaintext, string publicKey)
        {
            try
            {
                UnicodeEncoding ByteConverter = new UnicodeEncoding();
                byte[] dataToEncrypt = ByteConverter.GetBytes(plaintext);
                using (RSACryptoServiceProvider RSA = new RSACryptoServiceProvider())
                {
                    RSA.FromXmlString(publicKey);
                    byte[] encryptedData = RSA.Encrypt(dataToEncrypt, false);
                    return Convert.ToBase64String(encryptedData);
                }
            }
            catch (Exception)
            {
                return null;
            }

        }

        /// <summary> RSA解密
        ///
        /// </summary>
        /// <param name="ciphertext">密文</param>
        /// <param name="privateKey">私钥</param>
        /// <returns>明文字符串</returns>
        public static string DecryptByRSA(string ciphertext, string privateKey)
        {
            try
            {
                UnicodeEncoding byteConverter = new UnicodeEncoding();
                using (RSACryptoServiceProvider RSA = new RSACryptoServiceProvider())
                {
                    RSA.FromXmlString(privateKey);
                    byte[] encryptedData = Convert.FromBase64String(ciphertext);
                    byte[] decryptedData = RSA.Decrypt(encryptedData, false);
                    return byteConverter.GetString(decryptedData);
                }
            }
            catch (Exception)
            {
                return null;
            }

        }

        /// <summary>生成RSA加密 解密的 密钥
        /// 生成的key就是 方法EncryptByRSA与DecryptByRSA用的key了
        /// </summary>
        /// <param name="path">要生成的密钥文件的路径(文件夹)</param>
        public static void getRSAKey(string path)
        {
            RSACryptoServiceProvider rsa = new RSACryptoServiceProvider();
            string datetimestr = System.DateTime.Now.ToString("yyyyMMddHHmmss");
            using (StreamWriter writer = new StreamWriter("RSA解密_PrivateKey_" + datetimestr + ".xml"))  //这个文件要保密...
            {
                writer.WriteLine(rsa.ToXmlString(true));
            }
            using (StreamWriter writer = new StreamWriter("RSA加密_PublicKey_" + datetimestr + ".xml"))
            {
                writer.WriteLine(rsa.ToXmlString(false));
            }
        }
        #endregion

        #region Base64加密解密

        /// <summary>
        /// Base64是一種使用64基的位置計數法。它使用2的最大次方來代表僅可列印的ASCII 字元。
        /// 這使它可用來作為電子郵件的傳輸編碼。在Base64中的變數使用字元A-Z、a-z和0-9 ，
        /// 這樣共有62個字元，用來作為開始的64個數字，最後兩個用來作為數字的符號在不同的
        /// 系統中而不同。
        /// Base64加密
        /// </summary>
        /// <param name="str"></param>
        /// <returns></returns>
        public static string Base64Encrypt(string str)
        {
            byte[] encbuff = System.Text.Encoding.UTF8.GetBytes(str);
            return Convert.ToBase64String(encbuff);
        }

        /// <summary>
        /// Base64解密
        /// </summary>
        /// <param name="str"></param>
        /// <returns></returns>
        public static string Base64Decrypt(string str)
        {
            byte[] decbuff = Convert.FromBase64String(str);
            return System.Text.Encoding.UTF8.GetString(decbuff);
        }
        #endregion

        #region MD5
        /// <summary>

        /// 获得32位的MD5加密
        /// </summary>
        /// <param name="input"></param>
        /// <returns></returns>
        public static string GetMD5_32(string input)
        {
            MD5 md5 = MD5.Create();
            byte[] data = md5.ComputeHash(Encoding.Default.GetBytes(input));
            StringBuilder sb = new StringBuilder();
            for (int i = ; i < data.Length; i++)
            {
                sb.AppendFormat("{0:X2}", data[i]);
            }
            return sb.ToString();
        }

        /// <summary>
        /// 获得16位的MD5加密
        /// </summary>
        /// <param name="input"></param>
        /// <returns></returns>
        public static string GetMD5_16(string input)
        {
            return GetMD5_32(input).Substring(, );
        }
        /// <summary>
        /// 获得8位的MD5加密
        /// </summary>
        /// <param name="input"></param>
        /// <returns></returns>
        public static string GetMD5_8(string input)
        {
            return GetMD5_32(input).Substring(, );
        }
        /// <summary>
        /// 获得4位的MD5加密
        /// </summary>
        /// <param name="input"></param>
        /// <returns></returns>
        public static string GetMD5_4(string input)
        {
            return GetMD5_32(input).Substring(, );
        }

        public static string MD5EncryptHash(String input)
        {
            MD5 md5 = new MD5CryptoServiceProvider();
            //the GetBytes method returns byte array equavalent of a string
            byte[] res = md5.ComputeHash(Encoding.Default.GetBytes(input), , input.Length);
            char[] temp = new char[res.Length];
            //copy to a char array which can be passed to a String constructor
            Array.Copy(res, temp, res.Length);
            //return the result as a string
            return new String(temp);
        }
        #endregion

        #region MD5签名验证

        /// <summary>
        /// 对给定文件路径的文件加上标签
        /// </summary>
        /// <param name="path">要加密的文件的路径</param>
        /// <returns>标签的值</returns>
        public static bool AddMD5(string path)
        {
            bool IsNeed = true;

            if (CheckMD5(path))                                  //已进行MD5处理
                IsNeed = false;

            try
            {
                FileStream fsread = new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read);
                byte[] md5File = new byte[fsread.Length];
                fsread.Read(md5File, , (int)fsread.Length);                               // 将文件流读取到Buffer中
                fsread.Close();

                if (IsNeed)
                {
                    string result = MD5Buffer(md5File, , md5File.Length);             // 对Buffer中的字节内容算MD5
                    byte[] md5 = System.Text.Encoding.ASCII.GetBytes(result);       // 将字符串转换成字节数组以便写人到文件中
                    FileStream fsWrite = new FileStream(path, FileMode.Open, FileAccess.ReadWrite);
                    fsWrite.Write(md5File, , md5File.Length);                               // 将文件，MD5值 重新写入到文件中。
                    fsWrite.Write(md5, , md5.Length);
                    fsWrite.Close();
                }
                else
                {
                    FileStream fsWrite = new FileStream(path, FileMode.Open, FileAccess.ReadWrite);
                    fsWrite.Write(md5File, , md5File.Length);
                    fsWrite.Close();
                }
            }
            catch
            {
                return false;
            }

            return true;
        }

        /// <summary>
        /// 对给定路径的文件进行验证
        /// </summary>
        /// <param name="path"></param>
        /// <returns>是否加了标签或是否标签值与内容值一致</returns>
        public static bool CheckMD5(string path)
        {
            try
            {
                FileStream get_file = new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read);
                byte[] md5File = new byte[get_file.Length];                                      // 读入文件
                get_file.Read(md5File, , (int)get_file.Length);
                get_file.Close();

                string result = MD5Buffer(md5File, , md5File.Length - );             // 对文件除最后32位以外的字节计算MD5，这个32是因为标签位为32位。
                string md5 = System.Text.Encoding.ASCII.GetString(md5File, md5File.Length - , );   //读取文件最后32位，其中保存的就是MD5值
                return result == md5;
            }
            catch
            {
                return false;
            }
        }

        /// <summary>
        /// 计算文件的MD5值
        /// </summary>
        /// <param name="MD5File">MD5签名文件字符数组</param>
        /// <param name="index">计算起始位置</param>
        /// <param name="count">计算终止位置</param>
        /// <returns>计算结果</returns>
        private static string MD5Buffer(byte[] MD5File, int index, int count)
        {
            System.Security.Cryptography.MD5CryptoServiceProvider get_md5 = new System.Security.Cryptography.MD5CryptoServiceProvider();
            byte[] hash_byte = get_md5.ComputeHash(MD5File, index, count);
            string result = System.BitConverter.ToString(hash_byte);

            result = result.Replace("-", "");
            return result;
        }
        #endregion

        #region  SHA256加密算法

        /// <summary>
        /// SHA256函数
        /// </summary>
        /// <param name="str">原始字符串</param>
        /// <returns>SHA256结果(返回长度为44字节的字符串)</returns>
        public static string SHA256(string str)
        {
            byte[] SHA256Data = Encoding.UTF8.GetBytes(str);
            SHA256Managed Sha256 = new SHA256Managed();
            byte[] Result = Sha256.ComputeHash(SHA256Data);
            return Convert.ToBase64String(Result);  //返回长度为44字节的字符串
        }
        #endregion

        #region RC4加密 解密

        /// <summary>RC4加密算法
        /// 返回进过rc4加密过的字符
        /// </summary>
        /// <param name="str">被加密的字符</param>
        /// <param name="ckey">密钥</param>
        public static string EncryptRC4wq(string str, string ckey)
        {
            int[] s = new int[];
            for (int i = ; i < ; i++)
            {
                s[i] = i;
            }
            //密钥转数组
            char[] keys = ckey.ToCharArray();//密钥转字符数组
            int[] key = new int[keys.Length];
            for (int i = ; i < keys.Length; i++)
            {
                key[i] = keys[i];
            }
            //明文转数组
            char[] datas = str.ToCharArray();
            int[] mingwen = new int[datas.Length];
            for (int i = ; i < datas.Length; i++)
            {
                mingwen[i] = datas[i];
            }

            //通过循环得到256位的数组(密钥)
            int j = ;
            int k = ;
            int length = key.Length;
            int a;
            for (int i = ; i < ; i++)
            {
                a = s[i];
                j = (j + a + key[k]);
                if (j >= )
                {
                    j = j % ;
                }
                s[i] = s[j];
                s[j] = a;
                if (++k >= length)
                {
                    k = ;
                }
            }
            //根据上面的256的密钥数组 和 明文得到密文数组
            int x = , y = , a2, b, c;
            int length2 = mingwen.Length;
            int[] miwen = new int[length2];
            for (int i = ; i < length2; i++)
            {
                x = x + ;
                x = x % ;
                a2 = s[x];
                y = y + a2;
                y = y % ;
                s[x] = b = s[y];
                s[y] = a2;
                c = a2 + b;
                c = c % ;
                miwen[i] = mingwen[i] ^ s[c];
            }
            //密文数组转密文字符
            char[] mi = new char[miwen.Length];
            for (int i = ; i < miwen.Length; i++)
            {
                mi[i] = (char)miwen[i];
            }
            string miwenstr = new string(mi);
            return miwenstr;
        }

        /// <summary>RC4解密算法
        /// 返回进过rc4解密过的字符
        /// </summary>
        /// <param name="str">被解密的字符</param>
        /// <param name="ckey">密钥</param>
        public static string DecryptRC4wq(string str, string ckey)
        {
            int[] s = new int[];
            for (int i = ; i < ; i++)
            {
                s[i] = i;
            }
            //密钥转数组
            char[] keys = ckey.ToCharArray();//密钥转字符数组
            int[] key = new int[keys.Length];
            for (int i = ; i < keys.Length; i++)
            {
                key[i] = keys[i];
            }
            //密文转数组
            char[] datas = str.ToCharArray();
            int[] miwen = new int[datas.Length];
            for (int i = ; i < datas.Length; i++)
            {
                miwen[i] = datas[i];
            }

            //通过循环得到256位的数组(密钥)
            int j = ;
            int k = ;
            int length = key.Length;
            int a;
            for (int i = ; i < ; i++)
            {
                a = s[i];
                j = (j + a + key[k]);
                if (j >= )
                {
                    j = j % ;
                }
                s[i] = s[j];
                s[j] = a;
                if (++k >= length)
                {
                    k = ;
                }
            }
            //根据上面的256的密钥数组 和 密文得到明文数组
            int x = , y = , a2, b, c;
            int length2 = miwen.Length;
            int[] mingwen = new int[length2];
            for (int i = ; i < length2; i++)
            {
                x = x + ;
                x = x % ;
                a2 = s[x];
                y = y + a2;
                y = y % ;
                s[x] = b = s[y];
                s[y] = a2;
                c = a2 + b;
                c = c % ;
                mingwen[i] = miwen[i] ^ s[c];
            }
            //明文数组转明文字符
            char[] ming = new char[mingwen.Length];
            for (int i = ; i < mingwen.Length; i++)
            {
                ming[i] = (char)mingwen[i];
            }
            string mingwenstr = new string(ming);
            return mingwenstr;
        }
        #endregion
    }
}

原文：https://www.cnblogs.com/gygang/p/8873702.html