如何使用Base64进行加密和解密
2006-03-17 10:59
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其实Base64的加密和解密的算法不是很复杂，首先是定义自己64位的密钥，64个字符是固定，但是顺序是可以随自己的设计而变化。例如：
char[] BaseTable=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','+','/'};
接下来，在加密的时候就是对于需要加密的每个字符，通过一定的算法，转换成上面64字符的一种；而在解密的时候则是把64字符中任意一个字符反算出加密前的字符。对于每个字符的操作有很多方法，这里就不一一介绍了。需要注意的是“=”字符，在Base64加密算法中，是很重要的，它是起到补零作用。
以下是完整代码：
//----------------------------- Base64 class --------------------------------------
//---------------------------------------------------------------------------------
//---File:clsBase64
//---Description:The class file to encode string or decode string in base algorith
//---Author:Knight
//---Date:Oct.8, 2005
//---------------------------------------------------------------------------------
//----------------------------{ Base64 class }-------------------------------------
using System;
namespace Base64
{
/// <summary>
/// Summary description for clsBase64.
/// </summary>
public class clsBase64
{
private char[] source;
private char[] lookupTable;
private int length, length2, length3;
private int blockCount;
private int paddingCount;
public clsBase64()
{
//
// TODO: Add constructor logic here
//
source = null;
length = length2 = length3 =0;
blockCount = 0;
paddingCount = 0;
}
/// <summary>
/// Create base64 char array using default base64 char array
/// </summary>
/// <param name="CreatePara"></param>
/// <returns>return the new base64 char array</returns>
private char[] CreateBase64Char( ref char[] CreatePara )
{
char[] BaseTable=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','+','/'};
const int CREATE_TYPE = 8;
byte bParaValue = 0;
byte bTemp;
for( int i = 0; i < CreatePara.Length; i++ )
{
bTemp = ( byte )( CreatePara[i] );
switch( bTemp % CREATE_TYPE )
{
case 1:
// 00000001
bTemp =( byte )( bTemp ^ 0x01 );
break;
case 2:
// 00000010
bTemp =( byte )( bTemp ^ 0x02 );
break;
case 3:
// 00000100
bTemp =( byte )( bTemp ^ 0x04 );
break;
case 4:
// 00001000
bTemp =( byte )( bTemp ^ 0x08 );
break;
case 5:
// 00010000
bTemp =( byte )( bTemp ^ 0x10 );
break;
case 6:
// 00100000
bTemp =( byte )( bTemp ^ 0x20 );
break;
case 7:
// 01000000
bTemp =( byte )( bTemp ^ 0x40 );
break;
default:
// 10000000
bTemp =( byte )( bTemp ^ 0x80 );
break;
}
bParaValue =( byte )( bParaValue ^ bTemp );
}
char chrTemp;
int nIndex;
switch( bParaValue % CREATE_TYPE )
{
case 1:
// Exechange 0 <--> 1, 2 <--> 3, 4 <--> 5, 6 <--> 7
for( int i = 0; i < BaseTable.Length / CREATE_TYPE; i++ )
{
nIndex = i * CREATE_TYPE;
chrTemp = BaseTable[nIndex];
BaseTable[nIndex] = BaseTable[nIndex + 1];
BaseTable[nIndex + 1] = chrTemp;
chrTemp = BaseTable[nIndex + 2];
BaseTable[nIndex + 2] = BaseTable[nIndex + 3];
BaseTable[nIndex + 3] = chrTemp;
chrTemp = BaseTable[nIndex + 4];
BaseTable[nIndex + 4] = BaseTable[nIndex + 5];
BaseTable[nIndex + 5] = chrTemp;
chrTemp = BaseTable[nIndex + 6];
BaseTable[nIndex + 6] = BaseTable[nIndex + 7];
BaseTable[nIndex + 7] = chrTemp;
}
break;
case 2:
// Exechange 0 <--> 2, 1 <--> 3, 4 <--> 6, 5 <--> 7
for( int i = 0; i < BaseTable.Length / CREATE_TYPE; i++ )
{
nIndex = i * CREATE_TYPE;
chrTemp = BaseTable[nIndex];
BaseTable[nIndex] = BaseTable[nIndex + 2];
BaseTable[nIndex + 2] = chrTemp;
chrTemp = BaseTable[nIndex + 1];
BaseTable[nIndex + 1] = BaseTable[nIndex + 3];
BaseTable[nIndex + 3] = chrTemp;
chrTemp = BaseTable[nIndex + 4];
BaseTable[nIndex + 4] = BaseTable[nIndex + 6];
BaseTable[nIndex + 6] = chrTemp;
chrTemp = BaseTable[nIndex + 5];
BaseTable[nIndex + 5] = BaseTable[nIndex + 7];
BaseTable[nIndex + 7] = chrTemp;
}
break;
case 3:
// Exechange 0 <--> 3, 1 <--> 2, 4 <--> 7, 5 <--> 6
for( int i = 0; i < BaseTable.Length / CREATE_TYPE; i++ )
{
nIndex = i * CREATE_TYPE;
chrTemp = BaseTable[nIndex];
BaseTable[nIndex] = BaseTable[nIndex + 3];
BaseTable[nIndex + 3] = chrTemp;
chrTemp = BaseTable[nIndex + 1];
BaseTable[nIndex + 1] = BaseTable[nIndex + 2];
BaseTable[nIndex + 2] = chrTemp;
chrTemp = BaseTable[nIndex + 4];
BaseTable[nIndex + 4] = BaseTable[nIndex + 7];
BaseTable[nIndex + 7] = chrTemp;
chrTemp = BaseTable[nIndex + 5];
BaseTable[nIndex + 5] = BaseTable[nIndex + 6];
BaseTable[nIndex + 6] = chrTemp;
}
break;
case 4:
// Mirror exechange
for( int i = 0; i < BaseTable.Length / CREATE_TYPE; i++ )
{
nIndex = i * CREATE_TYPE;
chrTemp = BaseTable[nIndex];
BaseTable[nIndex] = BaseTable[nIndex + CREATE_TYPE - 1];
BaseTable[nIndex + CREATE_TYPE - 1] = chrTemp;
chrTemp = BaseTable[nIndex + 1];
BaseTable[nIndex + 1] = BaseTable[nIndex + CREATE_TYPE - 2];
BaseTable[nIndex + CREATE_TYPE - 2] = chrTemp;
chrTemp = BaseTable[nIndex + 2];
BaseTable[nIndex + 2] = BaseTable[nIndex + CREATE_TYPE - 3];
BaseTable[nIndex + CREATE_TYPE - 3] = chrTemp;
chrTemp = BaseTable[nIndex + 3];
BaseTable[nIndex + 3] = BaseTable[nIndex + CREATE_TYPE - 4];
BaseTable[nIndex + CREATE_TYPE - 4] = chrTemp;
}
break;
case 5:
// Exechange 0 <--> 4, 1 <--> 5, 2 <--> 6, 3 <--> 7
for( int i = 0; i < BaseTable.Length / CREATE_TYPE; i++ )
{
nIndex = i * CREATE_TYPE;
chrTemp = BaseTable[nIndex];
BaseTable[nIndex] = BaseTable[nIndex + 4];
BaseTable[nIndex + 4] = chrTemp;
chrTemp = BaseTable[nIndex + 1];
BaseTable[nIndex + 1] = BaseTable[nIndex + 5];
BaseTable[nIndex + 5] = chrTemp;
chrTemp = BaseTable[nIndex + 2];
BaseTable[nIndex + 2] = BaseTable[nIndex + 6];
BaseTable[nIndex + 6] = chrTemp;
chrTemp = BaseTable[nIndex + 3];
BaseTable[nIndex + 3] = BaseTable[nIndex + 7];
BaseTable[nIndex + 7] = chrTemp;
}
break;
case 6:
// Exechange 0 <--> 5, 1 <--> 6, 2 <--> 7, 3 <--> 4
for( int i = 0; i < BaseTable.Length / CREATE_TYPE; i++ )
{
nIndex = i * CREATE_TYPE;
chrTemp = BaseTable[nIndex];
BaseTable[nIndex] = BaseTable[nIndex + 5];
BaseTable[nIndex + 5] = chrTemp;
chrTemp = BaseTable[nIndex + 1];
BaseTable[nIndex + 1] = BaseTable[nIndex + 6];
BaseTable[nIndex + 6] = chrTemp;
chrTemp = BaseTable[nIndex + 2];
BaseTable[nIndex + 2] = BaseTable[nIndex + 7];
BaseTable[nIndex + 7] = chrTemp;
chrTemp = BaseTable[nIndex + 3];
BaseTable[nIndex + 3] = BaseTable[nIndex + 4];
BaseTable[nIndex + 4] = chrTemp;
}
break;
case 7:
// Exechange 0 <--> 6, 1 <--> 7, 2 <--> 4, 3 <--> 5
for( int i = 0; i < BaseTable.Length / CREATE_TYPE; i++ )
{
nIndex = i * CREATE_TYPE;
chrTemp = BaseTable[nIndex];
BaseTable[nIndex] = BaseTable[nIndex + 6];
BaseTable[nIndex + 6] = chrTemp;
chrTemp = BaseTable[nIndex + 1];
BaseTable[nIndex + 1] = BaseTable[nIndex + 7];
BaseTable[nIndex + 7] = chrTemp;
chrTemp = BaseTable[nIndex + 2];
BaseTable[nIndex + 2] = BaseTable[nIndex + 4];
BaseTable[nIndex + 4] = chrTemp;
chrTemp = BaseTable[nIndex + 3];
BaseTable[nIndex + 3] = BaseTable[nIndex + 5];
BaseTable[nIndex + 5] = chrTemp;
}
break;
default:
break;
}
return BaseTable;
}
/// <summary>
/// Encode string at specific parameter
/// </summary>
/// <param name="Para"></param>
/// <param name="input"></param>
/// <returns>return encoded string</returns>
public char[] GetEncoded( char[] Para, byte[] input )
{
length=input.Length;
if((length % 3)==0)
{
paddingCount=0;
blockCount=length/3;
}
else
{
paddingCount=3-(length % 3);//need to add padding
blockCount=(length+paddingCount) / 3;
}
length2=length+paddingCount;//or blockCount *3
byte[] source2;
source2=new byte[length2];
//copy data over insert padding
for (int x=0; x<length2;x++)
{
if (x<length)
{
source2[x]=input[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);//first
temp=(byte)((b1 & 3)<<4);
temp2=(byte)((b2 & 240)>>4);
temp2+=temp; //second
temp=(byte)((b2 & 15)<<2);
temp3=(byte)((b3 & 192)>>6);
temp3+=temp; //third
temp4=(byte)(b3 & 63); //fourth
buffer[x*4]=temp1;
buffer[x*4+1]=temp2;
buffer[x*4+2]=temp3;
buffer[x*4+3]=temp4;
}
lookupTable = CreateBase64Char( ref Para );
for (int x=0; x<blockCount*4;x++)
{
result[x]=sixbit2char(buffer[x]);
}
//covert last "A"s to "=", based on paddingCount
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 result;
}
private char sixbit2char(byte b)
{
if((b>=0) &&(b<=63))
{
return lookupTable[(int)b];
}
else
{
//should not happen;
return ' ';
}
}
/// <summary>
/// Decode string using specific parameter
/// </summary>
/// <param name="Para"></param>
/// <param name="input"></param>
/// <returns>If decoded successfully, return the decoded string; else return NULL</returns>
public byte[] GetDecoded( char[] Para, char[] input )
{
int temp=0;
source=input;
length=input.Length;
if( ( length % 4 ) != 0 ) return null; // The string is not encoded with my base64;
//find how many padding there are
while( input[length - temp - 1] == '=' && temp < 3 )
{
temp++;
}
if( temp == 3 ) return null; // The string is not encoded with my base64;
paddingCount=temp;
//calculate the blockCount;
//assuming all whitespace and carriage returns/newline were removed.
blockCount=length/4;
length2=blockCount*3;
byte[] buffer=new byte[length];//first conversion result
byte[] buffer2=new byte[length2];//decoded array with padding
lookupTable = CreateBase64Char( ref Para );
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;
}
//remove paddings
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)
{
if( c=='=' )
return 0;
else
{
for (int x=0;x<64;x++)
{
if (lookupTable[x]==c)
return (byte)x;
}
//should not reach here
return 0;
}
}
}
}
char[] BaseTable=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','+','/'};
接下来，在加密的时候就是对于需要加密的每个字符，通过一定的算法，转换成上面64字符的一种；而在解密的时候则是把64字符中任意一个字符反算出加密前的字符。对于每个字符的操作有很多方法，这里就不一一介绍了。需要注意的是“=”字符，在Base64加密算法中，是很重要的，它是起到补零作用。
以下是完整代码：
//----------------------------- Base64 class --------------------------------------
//---------------------------------------------------------------------------------
//---File:clsBase64
//---Description:The class file to encode string or decode string in base algorith
//---Author:Knight
//---Date:Oct.8, 2005
//---------------------------------------------------------------------------------
//----------------------------{ Base64 class }-------------------------------------
using System;
namespace Base64
{
/// <summary>
/// Summary description for clsBase64.
/// </summary>
public class clsBase64
{
private char[] source;
private char[] lookupTable;
private int length, length2, length3;
private int blockCount;
private int paddingCount;
public clsBase64()
{
//
// TODO: Add constructor logic here
//
source = null;
length = length2 = length3 =0;
blockCount = 0;
paddingCount = 0;
}
/// <summary>
/// Create base64 char array using default base64 char array
/// </summary>
/// <param name="CreatePara"></param>
/// <returns>return the new base64 char array</returns>
private char[] CreateBase64Char( ref char[] CreatePara )
{
char[] BaseTable=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','+','/'};
const int CREATE_TYPE = 8;
byte bParaValue = 0;
byte bTemp;
for( int i = 0; i < CreatePara.Length; i++ )
{
bTemp = ( byte )( CreatePara[i] );
switch( bTemp % CREATE_TYPE )
{
case 1:
// 00000001
bTemp =( byte )( bTemp ^ 0x01 );
break;
case 2:
// 00000010
bTemp =( byte )( bTemp ^ 0x02 );
break;
case 3:
// 00000100
bTemp =( byte )( bTemp ^ 0x04 );
break;
case 4:
// 00001000
bTemp =( byte )( bTemp ^ 0x08 );
break;
case 5:
// 00010000
bTemp =( byte )( bTemp ^ 0x10 );
break;
case 6:
// 00100000
bTemp =( byte )( bTemp ^ 0x20 );
break;
case 7:
// 01000000
bTemp =( byte )( bTemp ^ 0x40 );
break;
default:
// 10000000
bTemp =( byte )( bTemp ^ 0x80 );
break;
}
bParaValue =( byte )( bParaValue ^ bTemp );
}
char chrTemp;
int nIndex;
switch( bParaValue % CREATE_TYPE )
{
case 1:
// Exechange 0 <--> 1, 2 <--> 3, 4 <--> 5, 6 <--> 7
for( int i = 0; i < BaseTable.Length / CREATE_TYPE; i++ )
{
nIndex = i * CREATE_TYPE;
chrTemp = BaseTable[nIndex];
BaseTable[nIndex] = BaseTable[nIndex + 1];
BaseTable[nIndex + 1] = chrTemp;
chrTemp = BaseTable[nIndex + 2];
BaseTable[nIndex + 2] = BaseTable[nIndex + 3];
BaseTable[nIndex + 3] = chrTemp;
chrTemp = BaseTable[nIndex + 4];
BaseTable[nIndex + 4] = BaseTable[nIndex + 5];
BaseTable[nIndex + 5] = chrTemp;
chrTemp = BaseTable[nIndex + 6];
BaseTable[nIndex + 6] = BaseTable[nIndex + 7];
BaseTable[nIndex + 7] = chrTemp;
}
break;
case 2:
// Exechange 0 <--> 2, 1 <--> 3, 4 <--> 6, 5 <--> 7
for( int i = 0; i < BaseTable.Length / CREATE_TYPE; i++ )
{
nIndex = i * CREATE_TYPE;
chrTemp = BaseTable[nIndex];
BaseTable[nIndex] = BaseTable[nIndex + 2];
BaseTable[nIndex + 2] = chrTemp;
chrTemp = BaseTable[nIndex + 1];
BaseTable[nIndex + 1] = BaseTable[nIndex + 3];
BaseTable[nIndex + 3] = chrTemp;
chrTemp = BaseTable[nIndex + 4];
BaseTable[nIndex + 4] = BaseTable[nIndex + 6];
BaseTable[nIndex + 6] = chrTemp;
chrTemp = BaseTable[nIndex + 5];
BaseTable[nIndex + 5] = BaseTable[nIndex + 7];
BaseTable[nIndex + 7] = chrTemp;
}
break;
case 3:
// Exechange 0 <--> 3, 1 <--> 2, 4 <--> 7, 5 <--> 6
for( int i = 0; i < BaseTable.Length / CREATE_TYPE; i++ )
{
nIndex = i * CREATE_TYPE;
chrTemp = BaseTable[nIndex];
BaseTable[nIndex] = BaseTable[nIndex + 3];
BaseTable[nIndex + 3] = chrTemp;
chrTemp = BaseTable[nIndex + 1];
BaseTable[nIndex + 1] = BaseTable[nIndex + 2];
BaseTable[nIndex + 2] = chrTemp;
chrTemp = BaseTable[nIndex + 4];
BaseTable[nIndex + 4] = BaseTable[nIndex + 7];
BaseTable[nIndex + 7] = chrTemp;
chrTemp = BaseTable[nIndex + 5];
BaseTable[nIndex + 5] = BaseTable[nIndex + 6];
BaseTable[nIndex + 6] = chrTemp;
}
break;
case 4:
// Mirror exechange
for( int i = 0; i < BaseTable.Length / CREATE_TYPE; i++ )
{
nIndex = i * CREATE_TYPE;
chrTemp = BaseTable[nIndex];
BaseTable[nIndex] = BaseTable[nIndex + CREATE_TYPE - 1];
BaseTable[nIndex + CREATE_TYPE - 1] = chrTemp;
chrTemp = BaseTable[nIndex + 1];
BaseTable[nIndex + 1] = BaseTable[nIndex + CREATE_TYPE - 2];
BaseTable[nIndex + CREATE_TYPE - 2] = chrTemp;
chrTemp = BaseTable[nIndex + 2];
BaseTable[nIndex + 2] = BaseTable[nIndex + CREATE_TYPE - 3];
BaseTable[nIndex + CREATE_TYPE - 3] = chrTemp;
chrTemp = BaseTable[nIndex + 3];
BaseTable[nIndex + 3] = BaseTable[nIndex + CREATE_TYPE - 4];
BaseTable[nIndex + CREATE_TYPE - 4] = chrTemp;
}
break;
case 5:
// Exechange 0 <--> 4, 1 <--> 5, 2 <--> 6, 3 <--> 7
for( int i = 0; i < BaseTable.Length / CREATE_TYPE; i++ )
{
nIndex = i * CREATE_TYPE;
chrTemp = BaseTable[nIndex];
BaseTable[nIndex] = BaseTable[nIndex + 4];
BaseTable[nIndex + 4] = chrTemp;
chrTemp = BaseTable[nIndex + 1];
BaseTable[nIndex + 1] = BaseTable[nIndex + 5];
BaseTable[nIndex + 5] = chrTemp;
chrTemp = BaseTable[nIndex + 2];
BaseTable[nIndex + 2] = BaseTable[nIndex + 6];
BaseTable[nIndex + 6] = chrTemp;
chrTemp = BaseTable[nIndex + 3];
BaseTable[nIndex + 3] = BaseTable[nIndex + 7];
BaseTable[nIndex + 7] = chrTemp;
}
break;
case 6:
// Exechange 0 <--> 5, 1 <--> 6, 2 <--> 7, 3 <--> 4
for( int i = 0; i < BaseTable.Length / CREATE_TYPE; i++ )
{
nIndex = i * CREATE_TYPE;
chrTemp = BaseTable[nIndex];
BaseTable[nIndex] = BaseTable[nIndex + 5];
BaseTable[nIndex + 5] = chrTemp;
chrTemp = BaseTable[nIndex + 1];
BaseTable[nIndex + 1] = BaseTable[nIndex + 6];
BaseTable[nIndex + 6] = chrTemp;
chrTemp = BaseTable[nIndex + 2];
BaseTable[nIndex + 2] = BaseTable[nIndex + 7];
BaseTable[nIndex + 7] = chrTemp;
chrTemp = BaseTable[nIndex + 3];
BaseTable[nIndex + 3] = BaseTable[nIndex + 4];
BaseTable[nIndex + 4] = chrTemp;
}
break;
case 7:
// Exechange 0 <--> 6, 1 <--> 7, 2 <--> 4, 3 <--> 5
for( int i = 0; i < BaseTable.Length / CREATE_TYPE; i++ )
{
nIndex = i * CREATE_TYPE;
chrTemp = BaseTable[nIndex];
BaseTable[nIndex] = BaseTable[nIndex + 6];
BaseTable[nIndex + 6] = chrTemp;
chrTemp = BaseTable[nIndex + 1];
BaseTable[nIndex + 1] = BaseTable[nIndex + 7];
BaseTable[nIndex + 7] = chrTemp;
chrTemp = BaseTable[nIndex + 2];
BaseTable[nIndex + 2] = BaseTable[nIndex + 4];
BaseTable[nIndex + 4] = chrTemp;
chrTemp = BaseTable[nIndex + 3];
BaseTable[nIndex + 3] = BaseTable[nIndex + 5];
BaseTable[nIndex + 5] = chrTemp;
}
break;
default:
break;
}
return BaseTable;
}
/// <summary>
/// Encode string at specific parameter
/// </summary>
/// <param name="Para"></param>
/// <param name="input"></param>
/// <returns>return encoded string</returns>
public char[] GetEncoded( char[] Para, byte[] input )
{
length=input.Length;
if((length % 3)==0)
{
paddingCount=0;
blockCount=length/3;
}
else
{
paddingCount=3-(length % 3);//need to add padding
blockCount=(length+paddingCount) / 3;
}
length2=length+paddingCount;//or blockCount *3
byte[] source2;
source2=new byte[length2];
//copy data over insert padding
for (int x=0; x<length2;x++)
{
if (x<length)
{
source2[x]=input[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);//first
temp=(byte)((b1 & 3)<<4);
temp2=(byte)((b2 & 240)>>4);
temp2+=temp; //second
temp=(byte)((b2 & 15)<<2);
temp3=(byte)((b3 & 192)>>6);
temp3+=temp; //third
temp4=(byte)(b3 & 63); //fourth
buffer[x*4]=temp1;
buffer[x*4+1]=temp2;
buffer[x*4+2]=temp3;
buffer[x*4+3]=temp4;
}
lookupTable = CreateBase64Char( ref Para );
for (int x=0; x<blockCount*4;x++)
{
result[x]=sixbit2char(buffer[x]);
}
//covert last "A"s to "=", based on paddingCount
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 result;
}
private char sixbit2char(byte b)
{
if((b>=0) &&(b<=63))
{
return lookupTable[(int)b];
}
else
{
//should not happen;
return ' ';
}
}
/// <summary>
/// Decode string using specific parameter
/// </summary>
/// <param name="Para"></param>
/// <param name="input"></param>
/// <returns>If decoded successfully, return the decoded string; else return NULL</returns>
public byte[] GetDecoded( char[] Para, char[] input )
{
int temp=0;
source=input;
length=input.Length;
if( ( length % 4 ) != 0 ) return null; // The string is not encoded with my base64;
//find how many padding there are
while( input[length - temp - 1] == '=' && temp < 3 )
{
temp++;
}
if( temp == 3 ) return null; // The string is not encoded with my base64;
paddingCount=temp;
//calculate the blockCount;
//assuming all whitespace and carriage returns/newline were removed.
blockCount=length/4;
length2=blockCount*3;
byte[] buffer=new byte[length];//first conversion result
byte[] buffer2=new byte[length2];//decoded array with padding
lookupTable = CreateBase64Char( ref Para );
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;
}
//remove paddings
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)
{
if( c=='=' )
return 0;
else
{
for (int x=0;x<64;x++)
{
if (lookupTable[x]==c)
return (byte)x;
}
//should not reach here
return 0;
}
}
}
}
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