C# 下base64加密解密实现

using System;

using System.Collections.Generic;

using System.Text;

namespace MyLibs.encrypt

{

public class Base64

{

private static string base64EncodeChars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";//编码后的字符集

private static int[] base64DecodeChars = new int[] { -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 62, -1, -1, -1, 63, 52,
53, 54, 55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -1, -1, -1, -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, -1, -1, -1, -1, -1, -1, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44,
45, 46, 47, 48, 49, 50, 51, -1, -1, -1, -1, -1 };//对应ASICC字符的位置

public static string base64encode(string str)

{ //加密

string Out = "";

int i = 0, len = str.Length;

char c1, c2, c3;

while (i < len)

{

c1 = Convert.ToChar(str[i++] & 0xff);

if (i == len)

{

Out += base64EncodeChars[c1 >> 2];

Out += base64EncodeChars[(c1 & 0x3) << 4];

Out += "==";

break;

}

c2 = str[i++];

if (i == len)

{

Out += base64EncodeChars[c1 >> 2];

Out += base64EncodeChars[((c1 & 0x3) << 4) | ((c2 & 0xF0) >> 4)];

Out += base64EncodeChars[(c2 & 0xF) << 2];

Out += "=";

break;

}

c3 = str[i++];

Out += base64EncodeChars[c1 >> 2];

Out += base64EncodeChars[((c1 & 0x3) << 4) | ((c2 & 0xF0) >> 4)];

Out += base64EncodeChars[((c2 & 0xF) << 2) | ((c3 & 0xC0) >> 6)];

Out += base64EncodeChars[c3 & 0x3F];

}

return Out;

}

public string utf16to8(string str)

{

string Out = "";

int i, len;

char c;//char为16位Unicode字符,范围0~0xffff,感谢vczh提醒

len = str.Length;

for (i = 0; i < len; i++)

{//根据字符的不同范围分别转化

c = str[i];

if ((c >= 0x0001) && (c <= 0x007F))

{

Out += str[i];

}

else if (c > 0x07FF)

{

Out += (char)(0xE0 | ((c >> 12) & 0x0F));

Out += (char)(0x80 | ((c >> 6) & 0x3F));

Out += (char)(0x80 | ((c >> 0) & 0x3F));

}

else

{

Out += (char)(0xC0 | ((c >> 6) & 0x1F));

Out += (char)(0x80 | ((c >> 0) & 0x3F));

}

}

return Out;

}

public static string base64decode(string str)

{//解密

int c1, c2, c3, c4;

int i, len;

string Out;

len = str.Length;

i = 0; Out = "";

while (i < len)

{

do

{

c1 = base64DecodeChars[str[i++] & 0xff];

} while (i < len && c1 == -1);

if (c1 == -1) break;

do

{

c2 = base64DecodeChars[str[i++] & 0xff];

} while (i < len && c2 == -1);

if (c2 == -1) break;

Out += (char)((c1 << 2) | ((c2 & 0x30) >> 4));

do

{

c3 = str[i++] & 0xff;

if (c3 == 61) return Out;

c3 = base64DecodeChars[c3];

} while (i < len && c3 == -1);

if (c3 == -1) break;

Out += (char)(((c2 & 0XF) << 4) | ((c3 & 0x3C) >> 2));

do

{

c4 = str[i++] & 0xff;

if (c4 == 61) return Out;

c4 = base64DecodeChars[c4];

} while (i < len && c4 == -1);

if (c4 == -1) break;

Out += (char)(((c3 & 0x03) << 6) | c4);

}

return Out;

}

public string utf8to16(string str)

{

string Out = "";

int i, len;

char c, char2, char3;

len = str.Length;

i = 0; while (i < len)

{

c = str[i++];

switch (c >> 4)

{

case 0:

case 1:

case 2:

case 3:

case 4:

case 5:

case 6:

case 7: Out += str[i - 1]; break;

case 12:

case 13: char2 = str[i++];

Out += (char)(((c & 0x1F) << 6) | (char2 & 0x3F)); break;

case 14: char2 = str[i++];

char3 = str[i++];

Out += (char)(((c & 0x0F) << 12) | ((char2 & 0x3F) << 6) | ((char3 & 0x3F) << 0)); break;

}

}

return Out;

}

}

}

来自http://blog.csdn.net/vince6799/article/details/6760586