private static string base64EncodeChars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";        private static int[] base64DecodeChars ={            -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 };

/// 
        /// Base64加密        /// 
        ///         /// 
             public static string Base64Encode(string str)        {            string res = "";            int i = 0, len;            int c1, c2, c3;            len = str.Length;            i = 0;            res = "";            while (i < len)            {                c1 = Convert.ToByte(str[i++]) & 0xff;                if (i == len)                {                    res += base64EncodeChars.CharAt(c1 >> 2);                    res += base64EncodeChars.CharAt((c1 & 0x3) << 4);                    res += "==";                    break;                }                c2 = Convert.ToByte(str[i++]);                if (i == len)                {                    res += base64EncodeChars.CharAt(c1 >> 2);                    res += base64EncodeChars.CharAt(((c1 & 0x3) << 4) | ((c2 & 0xF0) >> 4));                    res += base64EncodeChars.CharAt((c2 & 0xF) << 2);                    res += "=";                    break;                }                c3 = Convert.ToByte(str[i++]);                res += base64EncodeChars.CharAt(c1 >> 2);                res += base64EncodeChars.CharAt(((c1 & 0x3) << 4) | ((c2 & 0xF0) >> 4));                res += base64EncodeChars.CharAt(((c2 & 0xF) << 2) | ((c3 & 0xC0) >> 6));                res += base64EncodeChars.CharAt(c3 & 0x3F);            }            return res;        }

/// 
        /// Base64加解密        /// 
        ///         /// 
             public static string Base64Decode(string str)        {            string res = "";            int i = 0, len;            int c1, c2, c3, c4;            len = str.Length;            len = str.Length;            i = 0;            res = "";            while (i < len)            {                /* c1 */                do                {                    c1 = base64DecodeChars[Convert.ToByte(str[i++]) & 0xff];                } while (i < len && c1 == -1);                if (c1 == -1)                    break;                /* c2 */                do                {                    c2 = base64DecodeChars[Convert.ToByte(str[i++]) & 0xff];                } while (i < len && c2 == -1);                if (c2 == -1)                    break;                res += Convert.ToChar((c1 << 2) | ((c2 & 0x30) >> 4));                /* c3 */                do                {                    c3 = Convert.ToByte(str[i++]) & 0xff;                    if (c3 == 61)                        return res;                    c3 = base64DecodeChars[c3];                } while (i < len && c3 == -1);                if (c3 == -1)                    break;                res += Convert.ToChar(((c2 & 0XF) << 4) | ((c3 & 0x3C) >> 2));                /* c4 */                do                {                    c4 = Convert.ToByte(str[i++]) & 0xff;                    if (c4 == 61)                        return res;                    c4 = base64DecodeChars[c4];                } while (i < len && c4 == -1);                if (c4 == -1)                    break;                res += Convert.ToChar(((c3 & 0x03) << 6) | c4);            }            return res;        }