C#实现Base64编码与解码

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 0break;
                
case 1: result[blockCount * 4 - 1= '='break;
                
case 2: result[blockCount * 4 - 1= '=';
                    result[blockCount 
* 4 - 2= '=';
                    
break;
                
defaultbreak;
            }
            
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:
//"ztKwrsTj"是“我爱你”的base64编码
byte[] outputb = Convert.FromBase64String("ztKwrsTj");
string orgStr= Encoding.Default.GetString(outputb);


完!
posted @ 2008-01-17 16:43  小y  阅读(47084)  评论(6编辑  收藏  举报