【小超_加密解密】Base64、DES、MD5加密解密原理

一、编码规则
      Base64编码的思想是是采用64个基本的ASCII码字符对数据进行重新编码。它将需要编码的数据拆分成字节数组。以3个字节为一组。按顺序排列24 位数据，再把这24位数据分成4组，即每组6位。再在每组的的最高位前补两个0凑足一个字节。这样就把一个3字节为一组的数据重新编码成了4个字节。当所要编码的数据的字节数不是3的整倍数，也就是说在分组时最后一组不够3个字节。这时在最后一组填充1到2个0字节。并在最后编码完成后在结尾添加1到2个 “=”。

例：将对ABC进行BASE64编码：

1、首先取ABC对应的ASCII码值。A（65）B（66）C（67）；

2、再取二进制值A（01000001）B（01000010）C（01000011）；

 3、然后把这三个字节的二进制码接起来（010000010100001001000011）；

4、 再以6位为单位分成4个数据块,并在最高位填充两个0后形成4个字节的编码后的值，（00010000）（00010100）（00001001）（00000011），其中蓝色部分为真实数据；

 5、再把这四个字节数据转化成10进制数得（16）（20）（9）（3）；

 6、最后根据BASE64给出的64个基本字符表，查出对应的ASCII码字符（Q）（U）（J）（D），这里的值实际就是数据在字符表中的索引。

注：BASE64字符表：ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/

二、解码规则
      解码过程就是把4个字节再还原成3个字节再根据不同的数据形式把字节数组重新整理成数据。

三、C#中的实现

编码类：

/// <summary>

    /// Base64编码类。

    /// 将byte[]类型转换成Base64编码的string类型。

    /// </summary>
    public class Base64Encoder

    {

        byte[] source;

        int length, length2;

        int blockCount;

        int paddingCount;

        public static Base64Encoder Encoder = new Base64Encoder();

        public Base64Encoder()

        {

        }

        private void init(byte[] input)

        {

            source = input;

            length = input.Length;

            if ((length % 3) == 0)

            {

                paddingCount = 0;

                blockCount = length / 3;

            }

            else

            {

                paddingCount = 3 - (length % 3);

                blockCount = (length + paddingCount) / 3;

            }

            length2 = length + paddingCount;

        }

        public string GetEncoded(byte[] input)

        {

            //初始化
            init(input);

            byte[] source2;

            source2 = new byte[length2];

            for (int x = 0; x < length2; x++)

            {

                if (x < length)

                {

                    source2[x] = source[x];

                }

                else

                {

                    source2[x] = 0;

                }

            }

            byte b1, b2, b3;

            byte temp, temp1, temp2, temp3, temp4;

            byte[] buffer = new byte[blockCount * 4];

            char[] result = new char[blockCount * 4];

            for (int x = 0; x < blockCount; x++)

            {

                b1 = source2[x * 3];

                b2 = source2[x * 3 + 1];

                b3 = source2[x * 3 + 2];

                temp1 = (byte)((b1 & 252) >> 2);

                temp = (byte)((b1 & 3) << 4);

                temp2 = (byte)((b2 & 240) >> 4);

                temp2 += temp;

                temp = (byte)((b2 & 15) << 2);

                temp3 = (byte)((b3 & 192) >> 6);

                temp3 += temp;

                temp4 = (byte)(b3 & 63);

                buffer[x * 4] = temp1;

                buffer[x * 4 + 1] = temp2;

                buffer[x * 4 + 2] = temp3;

                buffer[x * 4 + 3] = temp4;

            }

            for (int x = 0; x < blockCount * 4; x++)

            {

                result[x] = sixbit2char(buffer[x]);

            }

            switch (paddingCount)

            {

                case 0: break;

                case 1: result[blockCount * 4 - 1] = '='; break;

                case 2: result[blockCount * 4 - 1] = '=';

                    result[blockCount * 4 - 2] = '=';

                    break;

                default: break;

            }

            return new string(result);

        }

        private char sixbit2char(byte b)

        {

            char[] lookupTable = new char[64]{

                  'A','B','C','D','E','F','G','H','I','J','K','L','M',

                 'N','O','P','Q','R','S','T','U','V','W','X','Y','Z',

                 'a','b','c','d','e','f','g','h','i','j','k','l','m',

                 'n','o','p','q','r','s','t','u','v','w','x','y','z',

                 '0','1','2','3','4','5','6','7','8','9','+','/'};

            if ((b >= 0) && (b <= 63))

            {

                return lookupTable[(int)b];

            }

            else

            {

                return ' ';

            }

        }

    }

解码类：

/// <summary>

    /// Base64解码类

    /// 将Base64编码的string类型转换成byte[]类型

    /// </summary>
    public class Base64Decoder

    {

        char[] source;

        int length, length2, length3;

        int blockCount;

        int paddingCount;

        public static Base64Decoder Decoder = new Base64Decoder();

        public Base64Decoder()

        {

        }

        private void init(char[] input)

        {

            int temp = 0;

            source = input;

            length = input.Length;

            for (int x = 0; x < 2; x++)

            {

                if (input[length - x - 1] == '=')

                    temp++;

            }

            paddingCount = temp;

            blockCount = length / 4;

            length2 = blockCount * 3;

        }

        public byte[] GetDecoded(string strInput)

        {

            //初始化
            init(strInput.ToCharArray());

            byte[] buffer = new byte[length];

            byte[] buffer2 = new byte[length2];

            for (int x = 0; x < length; x++)

            {

                buffer[x] = char2sixbit(source[x]);

            }

            byte b, b1, b2, b3;

            byte temp1, temp2, temp3, temp4;

            for (int x = 0; x < blockCount; x++)

            {

                temp1 = buffer[x * 4];

                temp2 = buffer[x * 4 + 1];

                temp3 = buffer[x * 4 + 2];

                temp4 = buffer[x * 4 + 3];

                b = (byte)(temp1 << 2);

                b1 = (byte)((temp2 & 48) >> 4);

                b1 += b;

                b = (byte)((temp2 & 15) << 4);

                b2 = (byte)((temp3 & 60) >> 2);

                b2 += b;

                b = (byte)((temp3 & 3) << 6);

                b3 = temp4;

                b3 += b;

                buffer2[x * 3] = b1;

                buffer2[x * 3 + 1] = b2;

                buffer2[x * 3 + 2] = b3;

            }

            length3 = length2 - paddingCount;

            byte[] result = new byte[length3];

            for (int x = 0; x < length3; x++)

            {

                result[x] = buffer2[x];

            }

            return result;

        }

        private byte char2sixbit(char c)

        {

            char[] lookupTable = new char[64]{  

                 'A','B','C','D','E','F','G','H','I','J','K','L','M','N',

                 'O','P','Q','R','S','T','U','V','W','X','Y', 'Z',

                 'a','b','c','d','e','f','g','h','i','j','k','l','m','n',

                 'o','p','q','r','s','t','u','v','w','x','y','z',

                 '0','1','2','3','4','5','6','7','8','9','+','/'};

            if (c == '=')

                return 0;

            else

            {

                for (int x = 0; x < 64; x++)

                {

                    if (lookupTable[x] == c)

                        return (byte)x;

                }

                return 0;

            }

        }

    }

    //解码类结束

提示：

上面的代码只是说明base64编码的原理，以便用更多语言重写。但.net里面可以使用更简单的方法：
编码：


byte[] bytes=Encoding.Default.GetBytes("要转换的字符串");


Convert.ToBase64String(bytes);
解码：


byte[] outputb = Convert.FromBase64String("ztKwrsTj");


string orgStr= Encoding.Default.GetString(outputb);

四.C#中DES和MD5的加密解密处理

using System;
using System.Text;
using System.Security.Cryptography;
using System.IO;

using UnityEngine;

public class StringEncryption
{

#region  方法一 C#中对字符串加密解密（对称算法）
private static byte[] Keys = {
0x12,
0x34,
0x56,
0x78,
0x90,
0xAB,
0xCD,
0xEF
};
/// <summary>
/// DES加密字符串
/// </summary>
/// <param name="encryptString">待加密的字符串</param>
/// <param name="encryptKey">加密密钥,要求为8位</param>
/// <returns>加密成功返回加密后的字符串，失败返回源串</returns>
public static string EncryptDES (string encryptString, string encryptKey)
{
try {
byte[] rgbKey = Encoding.UTF8.GetBytes (encryptKey.Substring (0, 8));
byte[] rgbIV = Keys;
byte[] inputByteArray = Encoding.UTF8.GetBytes (encryptString);
DESCryptoServiceProvider dCSP = new DESCryptoServiceProvider ();
MemoryStream mStream = new MemoryStream ();
CryptoStream cStream = new CryptoStream (mStream, dCSP.CreateEncryptor (rgbKey, rgbIV), CryptoStreamMode.Write);
cStream.Write (inputByteArray, 0, inputByteArray.Length);
cStream.FlushFinalBlock ();
cStream.Close ();
return Convert.ToBase64String (mStream.ToArray ());
} catch {
return encryptString;
}
}

/// <summary>
/// DES解密字符串
/// </summary>
/// <param name="decryptString">待解密的字符串</param>
/// <param name="decryptKey">解密密钥,要求为8位,和加密密钥相同</param>
/// <returns>解密成功返回解密后的字符串，失败返源串</returns>
public static string DecryptDES (string decryptString, string decryptKey)
{
try {
byte[] rgbKey = Encoding.UTF8.GetBytes (decryptKey);
byte[] rgbIV = Keys;
byte[] inputByteArray = Convert.FromBase64String (decryptString);
DESCryptoServiceProvider DCSP = new DESCryptoServiceProvider ();
MemoryStream mStream = new MemoryStream ();
CryptoStream cStream = new CryptoStream (mStream, DCSP.CreateDecryptor (rgbKey, rgbIV), CryptoStreamMode.Write);
cStream.Write (inputByteArray, 0, inputByteArray.Length);
cStream.FlushFinalBlock ();
cStream.Close ();
return Encoding.UTF8.GetString (mStream.ToArray ());
} catch {
Debug.Log ("catch");
return decryptString;
}
}
#endregion

#region MD5不可逆加密
//32位加密
public string GetMD5_32 (string s, string _input_charset)
{
MD5 md5 = new MD5CryptoServiceProvider ();
byte[] t = md5.ComputeHash (Encoding.GetEncoding (_input_charset).GetBytes (s));
StringBuilder sb = new StringBuilder (32);
for (int i = 0; i < t.Length; i++) {
sb.Append (t [i].ToString ("x").PadLeft (2, '0'));
}
return sb.ToString ();
}

//16位加密
public static string GetMd5_16 (string ConvertString)
{
MD5CryptoServiceProvider md5 = new MD5CryptoServiceProvider ();
string t2 = BitConverter.ToString (md5.ComputeHash (UTF8Encoding.Default.GetBytes (ConvertString)), 2, 4);
t2 = t2.Replace ("-", "");
//t2 = ConvertStringToNumbers (t2);
return t2;
}