思路：
加密时：先把用户的密钥A用md5加密为B,然后用B异或源文件S0得到目标文件S1,把S1存入js变量中
解密时：询问密钥，然后操作同加密
因为用了md5，个人认为没有密钥的时候是无法破解的（暴力除外）
请运行代码查看效果：
代码实例：
<html>
<head>
<title>
web Encoder</title>
<style>
body {
font-size:12px;
line-height:12px;
background-Color:buttonface;
border-width:0px;
overflow:auto;
margin:0px;
padding:4px;
}
#t1, #t2 {
width:100%;
height:40%;
border-width:1px;
overflow:auto;
height:expression((document.body.clientHeight-100)/2);
}
input {
border-width:1px;
padding-left:10px;
padding-right:10px;
margin:4px;
}
</style>
<script>
function webEncode(){
strSource=escape(XOR(t1.value,STR.md5(p1.value)));
//strSource=t1.value;
strOut="<script> strHTML=""; ";
for(var i=0;i+70<strSource.length;i+=70){
strOut+="strHTML+=""+addSlash(strSource.substring(i,i+70))+""; ";
}
strOut+="strHTML+=""+addSlash(strSource.substring(i,strSource.length))+""; ";
strOut+=XOR+" ";
//below code load the STR object
strOut+="var STR = { hexcase : 0, /* hex output format. 0 - lowercase; 1 - ";
strOut+="uppercase */ b64pad : "", /* base-64 pad character. "=" for ";
strOut+="strict RFC compliance */ chrsz : 8, /* bits per input character";
strOut+=". 8 - ASCII; 16 - Unicode */ b64_hmac_md5: function(key, ";
strOut+="data) { return binl2b64(core_hmac_md5(key, data)); }, b64_md5: ";
strOut+=" function(s){ return binl2b64(core_md5(str2binl(s), s.length * this.c";
strOut+="hrsz));}, binl2b64: function(binarray){ var tab = "ABCDE";
strOut+="FGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"; var";
strOut+=" str = ""; for(var i = 0; i < binarray.length * 4; i += 3) {";
strOut+=" var triplet = (((binarray[i >> 2] >> 8 * ( i %4)) ; 0xFF) ";
strOut+="<< 16) | (((binarray[i+1 >> 2] >> 8 * ((i+1)%4)) ; ";
strOut+="0xFF) << 8 ) | ((binarray[i+2 >> 2] >> 8 * ((i+2)%";
strOut+="4)) ; 0xFF); for(var j = 0; j < 4; j++) { if(i ";
strOut+="* 8 + j * 6 > binarray.length * 32) str += this.b64pad; else ";
strOut+="str += tab.charAt((triplet >> 6*(3-j)) ; 0x3F); } } r";
strOut+="eturn str; }, binl2hex: function(binarray){ var hex_t";
strOut+="ab = this.hexcase ? "0123456789ABCDEF" : "0123456789abcdef"; var ";
strOut+="str = ""; for(var i = 0; i < binarray.length * 4; i++) { ";
strOut+=" str += hex_tab.charAt((binarray[i>>2] >> ((i%4)*8+4)) ; 0xF) + ";
strOut+=" hex_tab.charAt((binarray[i>>2] >> ((i%4)*8 )) ; 0xF); ";
strOut+=" } return str; }, binl2str: function(bin){ var st";
strOut+="r = ""; var mask = (1 << this.chrsz) - 1; for(var i = 0; i <";
strOut+=" bin.length * 32; i += this.chrsz) str += String.fromCharCode((";
strOut+="bin[i>>5] >>> (i % 32)) ; mask); return str; }, bit_rol:";
strOut+=" function(num, cnt){return (num << cnt) | (num >>> (32 - cnt));}, ";
strOut+=" core_hmac_md5: function(key, data){ var bkey = str2binl(k";
strOut+="ey); if(bkey.length > 16) bkey = core_md5(bkey, key.length * this";
strOut+=".chrsz); var ipad = Array(16), opad = Array(16); for(var";
strOut+=" i = 0; i < 16; i++) { ipad = bkey ^ 0x36363636; ";
strOut+=" opad = bkey ^ 0x5C5C5C5C; } var hash = core_md";
strOut+="5(ipad.concat(str2binl(data)), 512 + data.length * this.chrsz); r";
strOut+="eturn core_md5(opad.concat(hash), 512 + 128); }, core_md5: ";
strOut+=" function(x, len){ /* append padding */ x[len >> 5] |= 0x80 ";
strOut+="<< ((len) % 32); x[(((len + 64) >>> 9) << 4) + 14] = len; ";
strOut+=" var a = 1732584193; var b = -271733879; var c = -17325841";
strOut+="94; var d = 271733878; for(var i = 0; i < x.length; i +";
strOut+="= 16) { var olda = a; var oldb = b; var oldc";
strOut+=" = c; var oldd = d; a = this.md5_ff(a, b, c, d, x[i+";
strOut+=" 0], 7 , -680876936); d = this.md5_ff(d, a, b, c, x[i+ 1], 12, ";
strOut+="-389564586); c = this.md5_ff(c, d, a, b, x[i+ 2], 17, 60610581";
strOut+="9); b = this.md5_ff(b, c, d, a, x[i+ 3], 22, -1044525330); ";
strOut+=" a = this.md5_ff(a, b, c, d, x[i+ 4], 7 , -176418897); d = th";
strOut+="is.md5_ff(d, a, b, c, x[i+ 5], 12, 1200080426); c = this.md5_f";
strOut+="f(c, d, a, b, x[i+ 6], 17, -1473231341); b = this.md5_ff(b, c, ";
strOut+="d, a, x[i+ 7], 22, -45705983); a = this.md5_ff(a, b, c, d, x[i+";
strOut+=" 8], 7 , 1770035416); d = this.md5_ff(d, a, b, c, x[i+ 9], 12,";
strOut+=" -1958414417); c = this.md5_ff(c, d, a, b, x[i+10], 17, -42063)";
strOut+="; b = this.md5_ff(b, c, d, a, x[i+11], 22, -1990404162); ";
strOut+=" a = this.md5_ff(a, b, c, d, x[i+12], 7 , 1804603682); d = thi";
strOut+="s.md5_ff(d, a, b, c, x[i+13], 12, -40341101); c = this.md5_ff(c";
strOut+=", d, a, b, x[i+14], 17, -1502002290); b = this.md5_ff(b, c, d, ";
strOut+="a, x[i+15], 22, 1236535329); a = this.md5_gg(a, b, c, d, x";
strOut+="[i+ 1], 5 , -165796510); d = this.md5_gg(d, a, b, c, x[i+ 6], 9";
strOut+=" , -1069501632); c = this.md5_gg(c, d, a, b, x[i+11], 14, 6437";
strOut+="17713); b = this.md5_gg(b, c, d, a, x[i+ 0], 20, -373897302); ";
strOut+=" a = this.md5_gg(a, b, c, d, x[i+ 5], 5 , -701558691); d =";
strOut+=" this.md5_gg(d, a, b, c, x[i+10], 9 , 38016083); c = this.md5_";
strOut+="gg(c, d, a, b, x[i+15], 14, -660478335); b = this.md5_gg(b, c, ";
strOut+="d, a, x[i+ 4], 20, -405537848); a = this.md5_g
