js base64位和c# Base64位转换

<script>
            /*
            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 “=”。 

            */

            var Base64 = {

                //下面是64个基本的编码
                base64EncodeChars: "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/",
                base64DecodeChars: new Array(
-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),
                //编码的方法
                base64encode: function (str) {
                    var out, i, len;
                    var c1, c2, c3;
                    len = str.length;
                    i = 0;
                    out = "";
                    while (i < len) {
                        c1 = str.charCodeAt(i++) & 0xff;
                        if (i == len) {
                            out += Base64.base64EncodeChars.charAt(c1 >> 2);
                            out += Base64.base64EncodeChars.charAt((c1 & 0x3) << 4);
                            out += "==";
                            break;
                        }
                        c2 = str.charCodeAt(i++);
                        if (i == len) {
                            out += Base64.base64EncodeChars.charAt(c1 >> 2);
                            out += Base64.base64EncodeChars.charAt(((c1 & 0x3) << 4) | ((c2 & 0xF0) >> 4));
                            out += Base64.base64EncodeChars.charAt((c2 & 0xF) << 2);
                            out += "=";
                            break;
                        }
                        c3 = str.charCodeAt(i++);
                        out += Base64.base64EncodeChars.charAt(c1 >> 2);
                        out += Base64.base64EncodeChars.charAt(((c1 & 0x3) << 4) | ((c2 & 0xF0) >> 4));
                        out += Base64.base64EncodeChars.charAt(((c2 & 0xF) << 2) | ((c3 & 0xC0) >> 6));
                        out += Base64.base64EncodeChars.charAt(c3 & 0x3F);
                    }
                    return out;
                },

                //解码的方法
                base64decode: function (str) {
                    var c1, c2, c3, c4;
                    var i, len, out;
                    len = str.length;
                    i = 0;
                    out = "";
                    while (i < len) {
                        do {
                            c1 = Base64.base64DecodeChars[str.charCodeAt(i++) & 0xff];
                        } while (i < len && c1 == -1);
                        if (c1 == -1)
                            break;
                        do {
                            c2 = Base64.base64DecodeChars[str.charCodeAt(i++) & 0xff];
                        } while (i < len && c2 == -1);
                        if (c2 == -1)
                            break;
                        out += String.fromCharCode((c1 << 2) | ((c2 & 0x30) >> 4));
                        do {
                            c3 = str.charCodeAt(i++) & 0xff;
                            if (c3 == 61)
                                return out;
                            c3 = Base64.base64DecodeChars[c3];
                        } while (i < len && c3 == -1);
                        if (c3 == -1)
                            break;
                        out += String.fromCharCode(((c2 & 0XF) << 4) | ((c3 & 0x3C) >> 2));
                        do {
                            c4 = str.charCodeAt(i++) & 0xff;
                            if (c4 == 61)
                                return out;
                            c4 = Base64.base64DecodeChars[c4];
                        } while (i < len && c4 == -1);
                        if (c4 == -1)
                            break;
                        out += String.fromCharCode(((c3 & 0x03) << 6) | c4);
                    }
                    return out;
                },

                utf16to8: function (str) {
                    var out, i, len, c;
                    out = "";
                    len = str.length;
                    for (i = 0; i < len; i++) {
                        c = str.charCodeAt(i);
                        if ((c >= 0x0001) && (c <= 0x007F)) {
                            out += str.charAt(i);
                        } else if (c > 0x07FF) {
                            out += String.fromCharCode(0xE0 | ((c >> 12) & 0x0F));
                            out += String.fromCharCode(0x80 | ((c >> 6) & 0x3F));
                            out += String.fromCharCode(0x80 | ((c >> 0) & 0x3F));
                        } else {
                            out += String.fromCharCode(0xC0 | ((c >> 6) & 0x1F));
                            out += String.fromCharCode(0x80 | ((c >> 0) & 0x3F));
                        }
                    }
                    return out;
                },

                utf8to16: function (str) {
                    var out, i, len, c;
                    var char2, char3;
                    out = "";
                    len = str.length;
                    i = 0;
                    while (i < len) {
                        c = str.charCodeAt(i++);
                        switch (c >> 4) {
                            case 0: case 1: case 2: case 3: case 4: case 5: case 6: case 7:
                                // 0xxxxxxx
                                out += str.charAt(i - 1);
                                break;
                            case 12: case 13:
                                // 110x xxxx   10xx xxxx
                                char2 = str.charCodeAt(i++);
                                out += String.fromCharCode(((c & 0x1F) << 6) | (char2 & 0x3F));
                                break;
                            case 14:
                                // 1110 xxxx  10xx xxxx  10xx xxxx
                                char2 = str.charCodeAt(i++);
                                char3 = str.charCodeAt(i++);
                                out += String.fromCharCode(((c & 0x0F) << 12) |
                               ((char2 & 0x3F) << 6) |
                               ((char3 & 0x3F) << 0));
                                break;
                        }
                    }
                    return out;
                }, //end
                encode: function (input) {
                    return Base64.base64encode(Base64.utf16to8(input));
                },
                decode: function (str) {
                    return Base64.utf8to16(Base64.base64decode(input))
                }


            };
    </script>

/// <summary>
        /// 服务器端Base64编码
        /// </summary>
        /// <param name="data"></param>
        /// <returns></returns>
        public static  string base64Encode(string data)
        {
            try
            {
                byte[] encData_byte = new byte[data.Length];
                encData_byte = System.Text.Encoding.UTF8.GetBytes(data);
                string encodedData = Convert.ToBase64String(encData_byte);
                return encodedData;
            }
            catch (Exception e)
            {
                throw new Exception("Error in base64Encode" + e.Message);
            }
        }
        /// <summary>
        /// 服务器端Base64解码
        /// </summary>
        /// <param name="data"></param>
        /// <returns></returns>
        public static string base64Decode(string data)
        {
            try
            {
                System.Text.UTF8Encoding encoder = new System.Text.UTF8Encoding();
                System.Text.Decoder utf8Decode = encoder.GetDecoder();
                byte[] todecode_byte = Convert.FromBase64String(data);
                int charCount = utf8Decode.GetCharCount(todecode_byte, 0, todecode_byte.Length);
                char[] decoded_char = new char[charCount];
                utf8Decode.GetChars(todecode_byte, 0, todecode_byte.Length, decoded_char, 0);
                string result = new String(decoded_char);
                return result;
            }
            catch (Exception e)
            {
                throw new Exception("Error in base64Decode" + e.Message);
            }
        }