JS加解密（3des）亦可用于小程序

/**

3DES 加密算法
该函数接受一个 8 字节字符串作为普通 DES 算法的密钥（也就是 64 位，但是算法只使用 56 位），或者接受一个 24 字节字符串作为 3DES
算法的密钥；第二个参数是要加密或解密的信息字符串；第三个布尔值参数用来说明信息是加密还是解密；接下来的可选参数 mode 如果是 0 表示 ECB
模式，1 表示 CBC 模式，默认是 ECB 模式；最后一个可选项是一个 8 字节的输入向量字符串（在 ECB 模式下不使用）。返回的密文是字符串。
参数：
key: 8字节字符串作为普通 DES 算法的密钥,或 24 字节字符串作为 3DES
message：加密或解密的信息字符串
encrypt: 布尔值参数用来说明信息是加密还是解密
mode: 1:CBC模式，0:ECB模式(默认)
iv:
padding: 可选项, 8字节的输入向量字符串（在 ECB 模式下不使用）
/
//this takes the key, the message, and whether to encrypt or decrypt
function des(key, message, encrypt, mode, iv, padding) {
if (encrypt) //如果是加密的话，首先转换编码
message = unescape(encodeURIComponent(message));
//declaring this locally speeds things up a bit
var spfunction1 = new Array(0x1010400, 0, 0x10000, 0x1010404, 0x1010004, 0x10404, 0x4, 0x10000, 0x400, 0x1010400, 0x1010404, 0x400, 0x1000404, 0x1010004, 0x1000000, 0x4, 0x404, 0x1000400, 0x1000400, 0x10400, 0x10400, 0x1010000, 0x1010000, 0x1000404, 0x10004, 0x1000004, 0x1000004, 0x10004, 0, 0x404, 0x10404, 0x1000000, 0x10000, 0x1010404, 0x4, 0x1010000, 0x1010400, 0x1000000, 0x1000000, 0x400, 0x1010004, 0x10000, 0x10400, 0x1000004, 0x400, 0x4, 0x1000404, 0x10404, 0x1010404, 0x10004, 0x1010000, 0x1000404, 0x1000004, 0x404, 0x10404, 0x1010400, 0x404, 0x1000400, 0x1000400, 0, 0x10004, 0x10400, 0, 0x1010004);
var spfunction2 = new Array(-0x7fef7fe0, -0x7fff8000, 0x8000, 0x108020, 0x100000, 0x20, -0x7fefffe0, -0x7fff7fe0, -0x7fffffe0, -0x7fef7fe0, -0x7fef8000, -0x80000000, -0x7fff8000, 0x100000, 0x20, -0x7fefffe0, 0x108000, 0x100020, -0x7fff7fe0, 0, -0x80000000, 0x8000, 0x108020, -0x7ff00000, 0x100020, -0x7fffffe0, 0, 0x108000, 0x8020, -0x7fef8000, -0x7ff00000, 0x8020, 0, 0x108020, -0x7fefffe0, 0x100000, -0x7fff7fe0, -0x7ff00000, -0x7fef8000, 0x8000, -0x7ff00000, -0x7fff8000, 0x20, -0x7fef7fe0, 0x108020, 0x20, 0x8000, -0x80000000, 0x8020, -0x7fef8000, 0x100000, -0x7fffffe0, 0x100020, -0x7fff7fe0, -0x7fffffe0, 0x100020, 0x108000, 0, -0x7fff8000, 0x8020, -0x80000000, -0x7fefffe0, -0x7fef7fe0, 0x108000);
var spfunction3 = new Array(0x208, 0x8020200, 0, 0x8020008, 0x8000200, 0, 0x20208, 0x8000200, 0x20008, 0x8000008, 0x8000008, 0x20000, 0x8020208, 0x20008, 0x8020000, 0x208, 0x8000000, 0x8, 0x8020200, 0x200, 0x20200, 0x8020000, 0x8020008, 0x20208, 0x8000208, 0x20200, 0x20000, 0x8000208, 0x8, 0x8020208, 0x200, 0x8000000, 0x8020200, 0x8000000, 0x20008, 0x208, 0x20000, 0x8020200, 0x8000200, 0, 0x200, 0x20008, 0x8020208, 0x8000200, 0x8000008, 0x200, 0, 0x8020008, 0x8000208, 0x20000, 0x8000000, 0x8020208, 0x8, 0x20208, 0x20200, 0x8000008, 0x8020000, 0x8000208, 0x208, 0x8020000, 0x20208, 0x8, 0x8020008, 0x20200);
var spfunction4 = new Array(0x802001, 0x2081, 0x2081, 0x80, 0x802080, 0x800081, 0x800001, 0x2001, 0, 0x802000, 0x802000, 0x802081, 0x81, 0, 0x800080, 0x800001, 0x1, 0x2000, 0x800000, 0x802001, 0x80, 0x800000, 0x2001, 0x2080, 0x800081, 0x1, 0x2080, 0x800080, 0x2000, 0x802080, 0x802081, 0x81, 0x800080, 0x800001, 0x802000, 0x802081, 0x81, 0, 0, 0x802000, 0x2080, 0x800080, 0x800081, 0x1, 0x802001, 0x2081, 0x2081, 0x80, 0x802081, 0x81, 0x1, 0x2000, 0x800001, 0x2001, 0x802080, 0x800081, 0x2001, 0x2080, 0x800000, 0x802001, 0x80, 0x800000, 0x2000, 0x802080);
var spfunction5 = new Array(0x100, 0x2080100, 0x2080000, 0x42000100, 0x80000, 0x100, 0x40000000, 0x2080000, 0x40080100, 0x80000, 0x2000100, 0x40080100, 0x42000100, 0x42080000, 0x80100, 0x40000000, 0x2000000, 0x40080000, 0x40080000, 0, 0x40000100, 0x42080100, 0x42080100, 0x2000100, 0x42080000, 0x40000100, 0, 0x42000000, 0x2080100, 0x2000000, 0x42000000, 0x80100, 0x80000, 0x42000100, 0x100, 0x2000000, 0x40000000, 0x2080000, 0x42000100, 0x40080100, 0x2000100, 0x40000000, 0x42080000, 0x2080100, 0x40080100, 0x100, 0x2000000, 0x42080000, 0x42080100, 0x80100, 0x42000000, 0x42080100, 0x2080000, 0, 0x40080000, 0x42000000, 0x80100, 0x2000100, 0x40000100, 0x80000, 0, 0x40080000, 0x2080100, 0x40000100);
var spfunction6 = new Array(0x20000010, 0x20400000, 0x4000, 0x20404010, 0x20400000, 0x10, 0x20404010, 0x400000, 0x20004000, 0x404010, 0x400000, 0x20000010, 0x400010, 0x20004000, 0x20000000, 0x4010, 0, 0x400010, 0x20004010, 0x4000, 0x404000, 0x20004010, 0x10, 0x20400010, 0x20400010, 0, 0x404010, 0x20404000, 0x4010, 0x404000, 0x20404000, 0x20000000, 0x20004000, 0x10, 0x20400010, 0x404000, 0x20404010, 0x400000, 0x4010, 0x20000010, 0x400000, 0x20004000, 0x20000000, 0x4010, 0x20000010, 0x20404010, 0x404000, 0x20400000, 0x404010, 0x20404000, 0, 0x20400010, 0x10, 0x4000, 0x20400000, 0x404010, 0x4000, 0x400010, 0x20004010, 0, 0x20404000, 0x20000000, 0x400010, 0x20004010);
var spfunction7 = new Array(0x200000, 0x4200002, 0x4000802, 0, 0x800, 0x4000802, 0x200802, 0x4200800, 0x4200802, 0x200000, 0, 0x4000002, 0x2, 0x4000000, 0x4200002, 0x802, 0x4000800, 0x200802, 0x200002, 0x4000800, 0x4000002, 0x4200000, 0x4200800, 0x200002, 0x4200000, 0x800, 0x802, 0x4200802, 0x200800, 0x2, 0x4000000, 0x200800, 0x4000000, 0x200800, 0x200000, 0x4000802, 0x4000802, 0x4200002, 0x4200002, 0x2, 0x200002, 0x4000000, 0x4000800, 0x200000, 0x4200800, 0x802, 0x200802, 0x4200800, 0x802, 0x4000002, 0x4200802, 0x4200000, 0x200800, 0, 0x2, 0x4200802, 0, 0x200802, 0x4200000, 0x800, 0x4000002, 0x4000800, 0x800, 0x200002);
var spfunction8 = new Array(0x10001040, 0x1000, 0x40000, 0x10041040, 0x10000000, 0x10001040, 0x40, 0x10000000, 0x40040, 0x10040000, 0x10041040, 0x41000, 0x10041000, 0x41040, 0x1000, 0x40, 0x10040000, 0x10000040, 0x10001000, 0x1040, 0x41000, 0x40040, 0x10040040, 0x10041000, 0x1040, 0, 0, 0x10040040, 0x10000040, 0x10001000, 0x41040, 0x40000, 0x41040, 0x40000, 0x10041000, 0x1000, 0x40, 0x10040040, 0x1000, 0x41040, 0x10001000, 0x40, 0x10000040, 0x10040000, 0x10040040, 0x10000000, 0x40000, 0x10001040, 0, 0x10041040, 0x40040, 0x10000040, 0x10040000, 0x10001000, 0x10001040, 0, 0x10041040, 0x41000, 0x41000, 0x1040, 0x1040, 0x40040, 0x10000000, 0x10041000);
//create the 16 or 48 subkeys we will need
var keys = des_createKeys(key);
var m = 0,
i, j, temp, temp2, right1, right2, left, right, looping;
var cbcleft, cbcleft2, cbcright, cbcright2
var endloop, loopinc;
var len = message.length;
var chunk = 0;
//set up the loops for single and triple des
var iterations = keys.length == 32 ? 3 : 9; //single or triple des
if (iterations == 3) {
looping = encrypt ? new Array(0, 32, 2) : new Array(30, -2, -2);
} else {
looping = encrypt ? new Array(0, 32, 2, 62, 30, -2, 64, 96, 2) : new Array(94, 62, -2, 32, 64, 2, 30, -2, -2);
}
//pad the message depending on the padding parameter
if (padding == 2) message += " "; //pad the message with spaces
else if (padding == 1) {
if (encrypt) {
temp = 8 - (len % 8);
message += String.fromCharCode(temp, temp, temp, temp, temp, temp, temp, temp);
if (temp === 8) len += 8;
}
} //PKCS7 padding
else if (!padding) message += "\0\0\0\0\0\0\0\0"; //pad the message out with null bytes
//store the result here
var result = "";
var tempresult = "";
if (mode == 1) { //CBC mode
cbcleft = (iv.charCodeAt(m++) << 24) | (iv.charCodeAt(m++) << 16) | (iv.charCodeAt(m++) << 8) | iv.charCodeAt(m++);
cbcright = (iv.charCodeAt(m++) << 24) | (iv.charCodeAt(m++) << 16) | (iv.charCodeAt(m++) << 8) | iv.charCodeAt(m++);
m = 0;
}
//loop through each 64 bit chunk of the message
while (m < len) {
left = (message.charCodeAt(m++) << 24) | (message.charCodeAt(m++) << 16) | (message.charCodeAt(m++) << 8) | message.charCodeAt(m++);
right = (message.charCodeAt(m++) << 24) | (message.charCodeAt(m++) << 16) | (message.charCodeAt(m++) << 8) | message.charCodeAt(m++);
//for Cipher Block Chaining mode, xor the message with the previous result
if (mode == 1) {
if (encrypt) {
left ^= cbcleft;
right ^= cbcright;
} else {
cbcleft2 = cbcleft;
cbcright2 = cbcright;
cbcleft = left;
cbcright = right;
}
}
//first each 64 but chunk of the message must be permuted according to IP
temp = ((left >>> 4) ^ right) & 0x0f0f0f0f;
right ^= temp;
left ^= (temp << 4);
temp = ((left >>> 16) ^ right) & 0x0000ffff;
right ^= temp;
left ^= (temp << 16);
temp = ((right >>> 2) ^ left) & 0x33333333;
left ^= temp;
right ^= (temp << 2);
temp = ((right >>> 8) ^ left) & 0x00ff00ff;
left ^= temp;
right ^= (temp << 8);
temp = ((left >>> 1) ^ right) & 0x55555555;
right ^= temp;
left ^= (temp << 1);
left = ((left << 1) | (left >>> 31));
right = ((right << 1) | (right >>> 31));
//do this either 1 or 3 times for each chunk of the message
for (j = 0; j < iterations; j += 3) {
endloop = looping[j + 1];
loopinc = looping[j + 2];
//now go through and perform the encryption or decryption
for (i = looping[j]; i != endloop; i += loopinc) { //for efficiency
right1 = right ^ keys[i];
right2 = ((right >>> 4) | (right << 28)) ^ keys[i + 1];
//the result is attained by passing these bytes through the S selection functions
temp = left;
left = right;
right = temp ^ (spfunction2[(right1 >>> 24) & 0x3f] | spfunction4[(right1 >>> 16) & 0x3f] | spfunction6[(right1 >>> 8) & 0x3f] | spfunction8[right1 & 0x3f] | spfunction1[(right2 >>> 24) & 0x3f] | spfunction3[(right2 >>> 16) & 0x3f] | spfunction5[(right2 >>> 8) & 0x3f] | spfunction7[right2 & 0x3f]);
}
temp = left;
left = right;
right = temp; //unreverse left and right
} //for either 1 or 3 iterations
//move then each one bit to the right
left = ((left >>> 1) | (left << 31));
right = ((right >>> 1) | (right << 31));
//now perform IP-1, which is IP in the opposite direction
temp = ((left >>> 1) ^ right) & 0x55555555;
right ^= temp;
left ^= (temp << 1);
temp = ((right >>> 8) ^ left) & 0x00ff00ff;
left ^= temp;
right ^= (temp << 8);
temp = ((right >>> 2) ^ left) & 0x33333333;
left ^= temp;
right ^= (temp << 2);
temp = ((left >>> 16) ^ right) & 0x0000ffff;
right ^= temp;
left ^= (temp << 16);
temp = ((left >>> 4) ^ right) & 0x0f0f0f0f;
right ^= temp;
left ^= (temp << 4);
//for Cipher Block Chaining mode, xor the message with the previous result
if (mode == 1) {
if (encrypt) {
cbcleft = left;
cbcright = right;
} else {
left ^= cbcleft2;
right ^= cbcright2;
}
}
tempresult += String.fromCharCode((left >>> 24), ((left >>> 16) & 0xff), ((left >>> 8) & 0xff), (left & 0xff), (right >>> 24), ((right >>> 16) & 0xff), ((right >>> 8) & 0xff), (right & 0xff));
chunk += 8;
if (chunk == 512) {
result += tempresult;
tempresult = "";
chunk = 0;
}
} //for every 8 characters, or 64 bits in the message
//return the result as an array
result += tempresult;
result = result.replace(/\0$/g, "");
if (!encrypt) { //如果是解密的话，解密结束后对PKCS7 padding进行解码，并转换成utf-8编码
if (padding === 1) { //PKCS7 padding解码
var len = result.length,
paddingChars = 0;
len && (paddingChars = result.charCodeAt(len - 1));
(paddingChars <= 8) && (result = result.substring(0, len - paddingChars));
}
//转换成UTF-8编码
result = decodeURIComponent(escape(result));
}
return result;
} //end of des
//des_createKeys
//this takes as input a 64 bit key (even though only 56 bits are used)
//as an array of 2 integers, and returns 16 48 bit keys
function des_createKeys(key) {
//declaring this locally speeds things up a bit
var pc2bytes0 = new Array(0, 0x4, 0x20000000, 0x20000004, 0x10000, 0x10004, 0x20010000, 0x20010004, 0x200, 0x204, 0x20000200, 0x20000204, 0x10200, 0x10204, 0x20010200, 0x20010204);
var pc2bytes1 = new Array(0, 0x1, 0x100000, 0x100001, 0x4000000, 0x4000001, 0x4100000, 0x4100001, 0x100, 0x101, 0x100100, 0x100101, 0x4000100, 0x4000101, 0x4100100, 0x4100101);
var pc2bytes2 = new Array(0, 0x8, 0x800, 0x808, 0x1000000, 0x1000008, 0x1000800, 0x1000808, 0, 0x8, 0x800, 0x808, 0x1000000, 0x1000008, 0x1000800, 0x1000808);
var pc2bytes3 = new Array(0, 0x200000, 0x8000000, 0x8200000, 0x2000, 0x202000, 0x8002000, 0x8202000, 0x20000, 0x220000, 0x8020000, 0x8220000, 0x22000, 0x222000, 0x8022000, 0x8222000);
var pc2bytes4 = new Array(0, 0x40000, 0x10, 0x40010, 0, 0x40000, 0x10, 0x40010, 0x1000, 0x41000, 0x1010, 0x41010, 0x1000, 0x41000, 0x1010, 0x41010);
var pc2bytes5 = new Array(0, 0x400, 0x20, 0x420, 0, 0x400, 0x20, 0x420, 0x2000000, 0x2000400, 0x2000020, 0x2000420, 0x2000000, 0x2000400, 0x2000020, 0x2000420);
var pc2bytes6 = new Array(0, 0x10000000, 0x80000, 0x10080000, 0x2, 0x10000002, 0x80002, 0x10080002, 0, 0x10000000, 0x80000, 0x10080000, 0x2, 0x10000002, 0x80002, 0x10080002);
var pc2bytes7 = new Array(0, 0x10000, 0x800, 0x10800, 0x20000000, 0x20010000, 0x20000800, 0x20010800, 0x20000, 0x30000, 0x20800, 0x30800, 0x20020000, 0x20030000, 0x20020800, 0x20030800);
var pc2bytes8 = new Array(0, 0x40000, 0, 0x40000, 0x2, 0x40002, 0x2, 0x40002, 0x2000000, 0x2040000, 0x2000000, 0x2040000, 0x2000002, 0x2040002, 0x2000002, 0x2040002);
var pc2bytes9 = new Array(0, 0x10000000, 0x8, 0x10000008, 0, 0x10000000, 0x8, 0x10000008, 0x400, 0x10000400, 0x408, 0x10000408, 0x400, 0x10000400, 0x408, 0x10000408);
var pc2bytes10 = new Array(0, 0x20, 0, 0x20, 0x100000, 0x100020, 0x100000, 0x100020, 0x2000, 0x2020, 0x2000, 0x2020, 0x102000, 0x102020, 0x102000, 0x102020);
var pc2bytes11 = new Array(0, 0x1000000, 0x200, 0x1000200, 0x200000, 0x1200000, 0x200200, 0x1200200, 0x4000000, 0x5000000, 0x4000200, 0x5000200, 0x4200000, 0x5200000, 0x4200200, 0x5200200);
var pc2bytes12 = new Array(0, 0x1000, 0x8000000, 0x8001000, 0x80000, 0x81000, 0x8080000, 0x8081000, 0x10, 0x1010, 0x8000010, 0x8001010, 0x80010, 0x81010, 0x8080010, 0x8081010);
var pc2bytes13 = new Array(0, 0x4, 0x100, 0x104, 0, 0x4, 0x100, 0x104, 0x1, 0x5, 0x101, 0x105, 0x1, 0x5, 0x101, 0x105);
//how many iterations (1 for des, 3 for triple des)
var iterations = key.length > 8 ? 3 : 1; //changed by Paul 16/6/2007 to use Triple DES for 9+ byte keys
//stores the return keys
var keys = new Array(32 * iterations);
//now define the left shifts which need to be done
var shifts = new Array(0, 0, 1, 1, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1, 0);
//other variables
var lefttemp, righttemp, m = 0,
n = 0,
temp;
for (var j = 0; j < iterations; j++) { //either 1 or 3 iterations
var left = (key.charCodeAt(m++) << 24) | (key.charCodeAt(m++) << 16) | (key.charCodeAt(m++) << 8) | key.charCodeAt(m++);
var right = (key.charCodeAt(m++) << 24) | (key.charCodeAt(m++) << 16) | (key.charCodeAt(m++) << 8) | key.charCodeAt(m++);
temp = ((left >>> 4) ^ right) & 0x0f0f0f0f;
right ^= temp;
left ^= (temp << 4);
temp = ((right >>> -16) ^ left) & 0x0000ffff;
left ^= temp;
right ^= (temp << -16);
temp = ((left >>> 2) ^ right) & 0x33333333;
right ^= temp;
left ^= (temp << 2);
temp = ((right >>> -16) ^ left) & 0x0000ffff;
left ^= temp;
right ^= (temp << -16);
temp = ((left >>> 1) ^ right) & 0x55555555;
right ^= temp;
left ^= (temp << 1);
temp = ((right >>> 8) ^ left) & 0x00ff00ff;
left ^= temp;
right ^= (temp << 8);
temp = ((left >>> 1) ^ right) & 0x55555555;
right ^= temp;
left ^= (temp << 1);
//the right side needs to be shifted and to get the last four bits of the left side
temp = (left << 8) | ((right >>> 20) & 0x000000f0);
//left needs to be put upside down
left = (right << 24) | ((right << 8) & 0xff0000) | ((right >>> 8) & 0xff00) | ((right >>> 24) & 0xf0);
right = temp;
//now go through and perform these shifts on the left and right keys
for (var i = 0; i < shifts.length; i++) {
//shift the keys either one or two bits to the left
if (shifts[i]) {
left = (left << 2) | (left >>> 26);
right = (right << 2) | (right >>> 26);
} else {
left = (left << 1) | (left >>> 27);
right = (right << 1) | (right >>> 27);
}
left &= -0xf;
right &= -0xf;
//now apply PC-2, in such a way that E is easier when encrypting or decrypting
//this conversion will look like PC-2 except only the last 6 bits of each byte are used
//rather than 48 consecutive bits and the order of lines will be according to
//how the S selection functions will be applied: S2, S4, S6, S8, S1, S3, S5, S7
lefttemp = pc2bytes0[left >>> 28] | pc2bytes1[(left >>> 24) & 0xf] | pc2bytes2[(left >>> 20) & 0xf] | pc2bytes3[(left >>> 16) & 0xf] | pc2bytes4[(left >>> 12) & 0xf] | pc2bytes5[(left >>> 8) & 0xf] | pc2bytes6[(left >>> 4) & 0xf];
righttemp = pc2bytes7[right >>> 28] | pc2bytes8[(right >>> 24) & 0xf] | pc2bytes9[(right >>> 20) & 0xf] | pc2bytes10[(right >>> 16) & 0xf] | pc2bytes11[(right >>> 12) & 0xf] | pc2bytes12[(right >>> 8) & 0xf] | pc2bytes13[(right >>> 4) & 0xf];
temp = ((righttemp >>> 16) ^ lefttemp) & 0x0000ffff;
keys[n++] = lefttemp ^ temp;
keys[n++] = righttemp ^ (temp << 16);
}
} //for each iterations
//return the keys we've created
return keys;
} //end of des_createKeys
function genkey(key, start, end) {
//8 byte / 64 bit Key (DES) or 192 bit Key
return {
key: pad(key.slice(start, end)),
vector: 1
};
}

function pad(key) {
for (var i = key.length; i < 24; i++) {
key += "0";
}
return key;
}

var base64hash = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/';

// btoa method
//base64 编码
function _btoa(s) {
if (/([^\u0000-\u00ff])/.test(s)) {
throw new Error('INVALID_CHARACTER_ERR');
}
var i = 0,
prev,
ascii,
mod,
result = [];

while (i < s.length) {
    ascii = s.charCodeAt(i);
    mod = i % 3;

    switch (mod) {
        // 第一個6位只需要讓8位二進制右移兩位
        case 0:
            result.push(base64hash.charAt(ascii >> 2));
            break;
            //第二個6位 = 第一個8位的後兩位 + 第二個8位的前4位
        case 1:
            result.push(base64hash.charAt((prev & 3) << 4 | (ascii >> 4)));
            break;
            //第三個6位 = 第二個8位的後4位 + 第三個8位的前2位
            //第4個6位 = 第三個8位的後6位
        case 2:
            result.push(base64hash.charAt((prev & 0x0f) << 2 | (ascii >> 6)));
            result.push(base64hash.charAt(ascii & 0x3f));
            break;
    }

    prev = ascii;
    i++;
}

// 循環結束後看mod, 為0 證明需補3個6位，第一個為最後一個8位的最後兩位後面補4個0。另外兩個6位對應的是異常的“=”；
// mod為1，證明還需補兩個6位，一個是最後一個8位的後4位補兩個0，另一個對應異常的“=”
if (mod == 0) {
    result.push(base64hash.charAt((prev & 3) << 4));
    result.push('==');
} else if (mod == 1) {
    result.push(base64hash.charAt((prev & 0x0f) << 2));
    result.push('=');
}

return result.join('');

}
//解码成 ASCII
function _atob(s) {
s = s.replace(/\s|=/g, '');
var cur,
prev,
mod,
i = 0,
result = [];

while (i < s.length) {
    cur = base64hash.indexOf(s.charAt(i));
    mod = i % 4;

    switch (mod) {
        case 0:
            //TODO
            break;
        case 1:
            result.push(String.fromCharCode(prev << 2 | cur >> 4));
            break;
        case 2:
            result.push(String.fromCharCode((prev & 0x0f) << 4 | cur >> 2));
            break;
        case 3:
            result.push(String.fromCharCode((prev & 3) << 6 | cur));
            break;

    }

    prev = cur;
    i++;
}

return result.join('');

}
var base64hash = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/';

// btoa method
//base64 编码
function _btoa(s) {
if (/([^\u0000-\u00ff])/.test(s)) {
throw new Error('INVALID_CHARACTER_ERR');
}
var i = 0,
prev,
ascii,
mod,
result = [];

while (i < s.length) {
    ascii = s.charCodeAt(i);
    mod = i % 3;

    switch (mod) {
        // 第一個6位只需要讓8位二進制右移兩位
        case 0:
            result.push(base64hash.charAt(ascii >> 2));
            break;
            //第二個6位 = 第一個8位的後兩位 + 第二個8位的前4位
        case 1:
            result.push(base64hash.charAt((prev & 3) << 4 | (ascii >> 4)));
            break;
            //第三個6位 = 第二個8位的後4位 + 第三個8位的前2位
            //第4個6位 = 第三個8位的後6位
        case 2:
            result.push(base64hash.charAt((prev & 0x0f) << 2 | (ascii >> 6)));
            result.push(base64hash.charAt(ascii & 0x3f));
            break;
    }

    prev = ascii;
    i++;
}

// 循環結束後看mod, 為0 證明需補3個6位，第一個為最後一個8位的最後兩位後面補4個0。另外兩個6位對應的是異常的“=”；
// mod為1，證明還需補兩個6位，一個是最後一個8位的後4位補兩個0，另一個對應異常的“=”
if (mod == 0) {
    result.push(base64hash.charAt((prev & 3) << 4));
    result.push('==');
} else if (mod == 1) {
    result.push(base64hash.charAt((prev & 0x0f) << 2));
    result.push('=');
}

return result.join('');

}
//解码成 ASCII
function _atob(s) {
s = s.replace(/\s|=/g, '');
var cur,
prev,
mod,
i = 0,
result = [];

while (i < s.length) {
    cur = base64hash.indexOf(s.charAt(i));
    mod = i % 4;

    switch (mod) {
        case 0:
            //TODO
            break;
        case 1:
            result.push(String.fromCharCode(prev << 2 | cur >> 4));
            break;
        case 2:
            result.push(String.fromCharCode((prev & 0x0f) << 4 | cur >> 2));
            break;
        case 3:
            result.push(String.fromCharCode((prev & 3) << 6 | cur));
            break;

    }

    prev = cur;
    i++;
}

return result.join('');

}