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;}}
}

原文链接： http://blog.csdn.net/vince6799/article/details/6760586