下載下來查看html源碼和js源碼：
<html>
<head>
<title>Flag in your Hand</title>
<style type="text/css">
body {
padding-left: 30%;
}
#flag {
font-family: Garamond, serif;
font-size: 36px;
}
#flagtitle {
font-family: Garamond, serif;
font-size: 24px;
}
.rightflag {
color: green;
}
.wrongflag {
color: red;
}
</style>
<script src="script-min.js"></script>
<script type="text/javascript">
var ic = false;
var fg = "";
function getFlag() {
var token = document.getElementById("secToken").value;
ic = checkToken(token);
fg = bm(token);
showFlag()
}
function showFlag() {
var t = document.getElementById("flagTitle");
var f = document.getElementById("flag");
t.innerText = !!ic ? "You got the flag below!!" : "Wrong!";
t.className = !!ic ? "rightflag" : "wrongflag";
f.innerText = fg;
}
</script>
</head>
<body>
<h1>Flag in your Hand</h1>
<p>Type in some token to get the flag.</p>
<p>Tips: Flag is in your hand.</p>
<div>
<p>
<span>Token:</span>
<span><input type="text" id="secToken"/></span>
</p>
<p>
<input type="button" value="Get flag!" onclick="getFlag()" />
</p>
</div>
<div>
<p id="flagTitle"></p>
<p id="flag"></p>
</div>
</body>
</html>
function hm(s) {
return rh(rstr(str2rstr_utf8(s)));
}
function bm(s) {
return rb(rstr(str2rstr_utf8(s)));
}
function rstr(s) {
return binl2rstr(binl(rstr2binl(s), s.length * 8));
}
function checkToken(s) {
return s === "FAKE-TOKEN";
}
function rh(ip) {
try {
hc
} catch (e) {
hc = 0;
}
var ht = hc ? "0123456789ABCDEF" : "0123456789abcdef";
var op = "";
var x;
for (var i = 0; i < ip.length; i++) {
x = ip.charCodeAt(i);
op += ht.charAt((x >>> 4) & 0x0F) + ht.charAt(x & 0x0F);
}
return op;
}
function rb(ip) {
try {
bp
} catch (e) {
bp = '';
}
var b = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
var op = "";
var len = ip.length;
for (var i = 0; i < len; i += 3) {
var t = (ip.charCodeAt(i) << 16) | (i + 1 < len ? ip.charCodeAt(i + 1) << 8 : 0) | (i + 2 < len ? ip.charCodeAt(i + 2) : 0);
for (var j = 0; j < 4; j++) {
if (i * 8 + j * 6 > ip.length * 8)
op += bp;
else
op += b.charAt((t >>> 6 * (3 - j)) & 0x3F);
}
}
return op;
}
function ck(s) {
try {
ic
} catch (e) {
return;
}
var a = [118, 104, 102, 120, 117, 108, 119, 124, 48,123,101,120];
if (s.length == a.length) {
for (i = 0; i < s.length; i++) {
if (a[i] - s.charCodeAt(i) != 3)
return ic = false;
}
return ic = true;
}
return ic = false;
}
function str2rstr_utf8(input) {
var output = "";
var i = -1;
var x, y;
while (++i < input.length) {
x = input.charCodeAt(i);
y = i + 1 < input.length ? input.charCodeAt(i + 1) : 0;
if (0xD800 <= x && x <= 0xDBFF && 0xDC00 <= y && y <= 0xDFFF) {
x = 0x10000 + ((x & 0x03FF) << 10) + (y & 0x03FF);
i++;
}
if (x <= 0x7F)
output += String.fromCharCode(x);
else if (x <= 0x7FF)
output += String.fromCharCode(0xC0 | ((x >>> 6) & 0x1F), 0x80 | (x & 0x3F));
else if (x <= 0xFFFF)
output += String.fromCharCode(0xE0 | ((x >>> 12) & 0x0F), 0x80 | ((x >>> 6) & 0x3F), 0x80 | (x & 0x3F));
else if (x <= 0x1FFFFF)
output += String.fromCharCode(0xF0 | ((x >>> 18) & 0x07), 0x80 | ((x >>> 12) & 0x3F), 0x80 | ((x >>> 6) & 0x3F), 0x80 | (x & 0x3F));
}
return output;
}
function rstr2binl(input) {
console.log(20>>2)
var output = Array(input.length >> 2);
for (var i = 0; i < output.length; i++)
output[i] = 0;
for (var i = 0; i < input.length * 8; i += 8)
output[i >> 5] |= (input.charCodeAt(i / 8) & 0xFF) << (i % 32);
return output;
}
function binl2rstr(i) {
var o = "";
for (var j = 0; j < i.length * 32; j += 8)
o += String.fromCharCode((i[j >> 5] >>> (j % 32)) & 0xFF);
return o;
}
function binl(x, len) {
s = binl2rstr(x);
x[len >> 5] |= 0x80 << ((len) % 32);
x[(((len + 64) >>> 9) << 4) + 14] = len;
var a = 1732584193;
var b = -271733879;
var c = -1732584194;
var d = 271733878;
for (var i = 0; i < x.length; i += 16) {
var olda = a;
var oldb = b;
var oldc = c;
var oldd = d;
a = ff(a, b, c, d, x[i + 0], 7, -680876936);
d = ff(d, a, b, c, x[i + 1], 12, -389564586);
c = ff(c, d, a, b, x[i + 2], 17, 606105819);
b = ff(b, c, d, a, x[i + 3], 22, -1044525330);
a = ff(a, b, c, d, x[i + 4], 7, -176418897);
d = ff(d, a, b, c, x[i + 5], 12, 1200080426);
c = ff(c, d, a, b, x[i + 6], 17, -1473231341);
b = ff(b, c, d, a, x[i + 7], 22, -45705983);
a = ff(a, b, c, d, x[i + 8], 7, 1770035416);
d = ff(d, a, b, c, x[i + 9], 12, -1958414417);
c = ff(c, d, a, b, x[i + 10], 17, -42063);
b = ff(b, c, d, a, x[i + 11], 22, -1990404162);
a = ff(a, b, c, d, x[i + 12], 7, 1804603682);
d = ff(d, a, b, c, x[i + 13], 12, -40341101);
c = ff(c, d, a, b, x[i + 14], 17, -1502002290);
b = ff(b, c, d, a, x[i + 15], 22, 1236535329);
ck(s);
a = gg(a, b, c, d, x[i + 1], 5, -165796510);
d = gg(d, a, b, c, x[i + 6], 9, -1069501632);
c = gg(c, d, a, b, x[i + 11], 14, 643717713);
b = gg(b, c, d, a, x[i + 0], 20, -373897302);
a = gg(a, b, c, d, x[i + 5], 5, -701558691);
d = gg(d, a, b, c, x[i + 10], 9, 38016083);
c = gg(c, d, a, b, x[i + 15], 14, -660478335);
b = gg(b, c, d, a, x[i + 4], 20, -405537848);
a = gg(a, b, c, d, x[i + 9], 5, 568446438);
d = gg(d, a, b, c, x[i + 14], 9, -1019803690);
c = gg(c, d, a, b, x[i + 3], 14, -187363961);
b = gg(b, c, d, a, x[i + 8], 20, 1163531501);
a = gg(a, b, c, d, x[i + 13], 5, -1444681467);
d = gg(d, a, b, c, x[i + 2], 9, -51403784);
c = gg(c, d, a, b, x[i + 7], 14, 1735328473);
b = gg(b, c, d, a, x[i + 12], 20, -1926607734);
a = hh(a, b, c, d, x[i + 5], 4, -378558);
d = hh(d, a, b, c, x[i + 8], 11, -2022574463);
c = hh(c, d, a, b, x[i + 11], 16, 1839030562);
b = hh(b, c, d, a, x[i + 14], 23, -35309556);
a = hh(a, b, c, d, x[i + 1], 4, -1530992060);
d = hh(d, a, b, c, x[i + 4], 11, 1272893353);
c = hh(c, d, a, b, x[i + 7], 16, -155497632);
b = hh(b, c, d, a, x[i + 10], 23, -1094730640);
a = hh(a, b, c, d, x[i + 13], 4, 681279174);
d = hh(d, a, b, c, x[i + 0], 11, -358537222);
c = hh(c, d, a, b, x[i + 3], 16, -722521979);
b = hh(b, c, d, a, x[i + 6], 23, 76029189);
a = hh(a, b, c, d, x[i + 9], 4, -640364487);
d = hh(d, a, b, c, x[i + 12], 11, -421815835);
c = hh(c, d, a, b, x[i + 15], 16, 530742520);
b = hh(b, c, d, a, x[i + 2], 23, -995338651);
a = ii(a, b, c, d, x[i + 0], 6, -198630844);
d = ii(d, a, b, c, x[i + 7], 10, 1126891415);
c = ii(c, d, a, b, x[i + 14], 15, -1416354905);
b = ii(b, c, d, a, x[i + 5], 21, -57434055);
a = ii(a, b, c, d, x[i + 12], 6, 1700485571);
d = ii(d, a, b, c, x[i + 3], 10, -1894986606);
c = ii(c, d, a, b, x[i + 10], 15, -1051523);
b = ii(b, c, d, a, x[i + 1], 21, -2054922799);
a = ii(a, b, c, d, x[i + 8], 6, 1873313359);
d = ii(d, a, b, c, x[i + 15], 10, -30611744);
c = ii(c, d, a, b, x[i + 6], 15, -1560198380);
b = ii(b, c, d, a, x[i + 13], 21, 1309151649);
a = ii(a, b, c, d, x[i + 4], 6, -145523070);
d = ii(d, a, b, c, x[i + 11], 10, -1120210379);
c = ii(c, d, a, b, x[i + 2], 15, 718787259);
b = ii(b, c, d, a, x[i + 9], 21, -343485551);
a = sa(a, olda);
b = sa(b, oldb);
c = sa(c, oldc);
d = sa(d, oldd);
}
return Array(a, b, c, d);
}
function cmn(q, a, b, x, s, t) {
return sa(br(sa(sa(a, q), sa(x, t)), s), b);
}
function ff(a, b, c, d, x, s, t) {
return cmn((b & c) | ((~b) & d), a, b, x, s, t);
}
function gg(a, b, c, d, x, s, t) {
return cmn((b & d) | (c & (~d)), a, b, x, s, t);
}
function hh(a, b, c, d, x, s, t) {
return cmn(b ^ c ^ d, a, b, x, s, t);
}
function ii(a, b, c, d, x, s, t) {
return cmn(c ^ (b | (~d)), a, b, x, s, t);
}
function sa(x, y) {
var lsw = (x & 0xFFFF) + (y & 0xFFFF);
var msw = (x >> 16) + (y >> 16) + (lsw >> 16);
return (msw << 16) | (lsw & 0xFFFF);
}
function br(n, c) {
return (n << c) | (n >>> (32 - c));
}
明面上的
function checkToken(s) {
return s === "FAKE-TOKEN";
}
就是個障眼法。
接着看bm(s)這個方法：
str2rstr_utf8是一個將字符串轉爲utf8格式的字符串，不影響。繼續往下看這個函數：
function binl(x, len) {
s = binl2rstr(x);
x[len >> 5] |= 0x80 << ((len) % 32);
x[(((len + 64) >>> 9) << 4) + 14] = len;
var a = 1732584193;
var b = -271733879;
var c = -1732584194;
var d = 271733878;
for (var i = 0; i < x.length; i += 16) {
var olda = a;
var oldb = b;
var oldc = c;
var oldd = d;
a = ff(a, b, c, d, x[i + 0], 7, -680876936);
d = ff(d, a, b, c, x[i + 1], 12, -389564586);
c = ff(c, d, a, b, x[i + 2], 17, 606105819);
b = ff(b, c, d, a, x[i + 3], 22, -1044525330);
a = ff(a, b, c, d, x[i + 4], 7, -176418897);
d = ff(d, a, b, c, x[i + 5], 12, 1200080426);
c = ff(c, d, a, b, x[i + 6], 17, -1473231341);
b = ff(b, c, d, a, x[i + 7], 22, -45705983);
a = ff(a, b, c, d, x[i + 8], 7, 1770035416);
d = ff(d, a, b, c, x[i + 9], 12, -1958414417);
c = ff(c, d, a, b, x[i + 10], 17, -42063);
b = ff(b, c, d, a, x[i + 11], 22, -1990404162);
a = ff(a, b, c, d, x[i + 12], 7, 1804603682);
d = ff(d, a, b, c, x[i + 13], 12, -40341101);
c = ff(c, d, a, b, x[i + 14], 17, -1502002290);
b = ff(b, c, d, a, x[i + 15], 22, 1236535329);
ck(s);
a = gg(a, b, c, d, x[i + 1], 5, -165796510);
d = gg(d, a, b, c, x[i + 6], 9, -1069501632);
c = gg(c, d, a, b, x[i + 11], 14, 643717713);
b = gg(b, c, d, a, x[i + 0], 20, -373897302);
a = gg(a, b, c, d, x[i + 5], 5, -701558691);
d = gg(d, a, b, c, x[i + 10], 9, 38016083);
c = gg(c, d, a, b, x[i + 15], 14, -660478335);
b = gg(b, c, d, a, x[i + 4], 20, -405537848);
a = gg(a, b, c, d, x[i + 9], 5, 568446438);
d = gg(d, a, b, c, x[i + 14], 9, -1019803690);
c = gg(c, d, a, b, x[i + 3], 14, -187363961);
b = gg(b, c, d, a, x[i + 8], 20, 1163531501);
a = gg(a, b, c, d, x[i + 13], 5, -1444681467);
d = gg(d, a, b, c, x[i + 2], 9, -51403784);
c = gg(c, d, a, b, x[i + 7], 14, 1735328473);
b = gg(b, c, d, a, x[i + 12], 20, -1926607734);
a = hh(a, b, c, d, x[i + 5], 4, -378558);
d = hh(d, a, b, c, x[i + 8], 11, -2022574463);
c = hh(c, d, a, b, x[i + 11], 16, 1839030562);
b = hh(b, c, d, a, x[i + 14], 23, -35309556);
a = hh(a, b, c, d, x[i + 1], 4, -1530992060);
d = hh(d, a, b, c, x[i + 4], 11, 1272893353);
c = hh(c, d, a, b, x[i + 7], 16, -155497632);
b = hh(b, c, d, a, x[i + 10], 23, -1094730640);
a = hh(a, b, c, d, x[i + 13], 4, 681279174);
d = hh(d, a, b, c, x[i + 0], 11, -358537222);
c = hh(c, d, a, b, x[i + 3], 16, -722521979);
b = hh(b, c, d, a, x[i + 6], 23, 76029189);
a = hh(a, b, c, d, x[i + 9], 4, -640364487);
d = hh(d, a, b, c, x[i + 12], 11, -421815835);
c = hh(c, d, a, b, x[i + 15], 16, 530742520);
b = hh(b, c, d, a, x[i + 2], 23, -995338651);
a = ii(a, b, c, d, x[i + 0], 6, -198630844);
d = ii(d, a, b, c, x[i + 7], 10, 1126891415);
c = ii(c, d, a, b, x[i + 14], 15, -1416354905);
b = ii(b, c, d, a, x[i + 5], 21, -57434055);
a = ii(a, b, c, d, x[i + 12], 6, 1700485571);
d = ii(d, a, b, c, x[i + 3], 10, -1894986606);
c = ii(c, d, a, b, x[i + 10], 15, -1051523);
b = ii(b, c, d, a, x[i + 1], 21, -2054922799);
a = ii(a, b, c, d, x[i + 8], 6, 1873313359);
d = ii(d, a, b, c, x[i + 15], 10, -30611744);
c = ii(c, d, a, b, x[i + 6], 15, -1560198380);
b = ii(b, c, d, a, x[i + 13], 21, 1309151649);
a = ii(a, b, c, d, x[i + 4], 6, -145523070);
d = ii(d, a, b, c, x[i + 11], 10, -1120210379);
c = ii(c, d, a, b, x[i + 2], 15, 718787259);
b = ii(b, c, d, a, x[i + 9], 21, -343485551);
a = sa(a, olda);
b = sa(b, oldb);
c = sa(c, oldc);
d = sa(d, oldd);
}
return Array(a, b, c, d);
}
這道題的坑點就在這裏了，裏面有個ck()函數，偷偷更改了ic的布爾值。
根據這個ck()函數就能還原出正確的token。
來看這個ck()函數：
function ck(s) {
try {
ic
} catch (e) {
return;
}
var a = [118, 104, 102, 120, 117, 108, 119, 124, 48,123,101,120];
if (s.length == a.length) {
for (i = 0; i < s.length; i++) {
if (a[i] - s.charCodeAt(i) != 3)
return ic = false;
}
return ic = true;
}
return ic = false;
}
爲了判斷這個函數的輸入是什麼，我們在binl()函數裏的ck(s)前加一行console.log(s)，看看輸出，發現是輸入的token。
確定輸入之後開始分析ck(s):
這個函數很簡單，讀取s的每個字符，假如a[i]-s[i]!=3則返回false
因此，數組a代表的ascii碼-3就是s的值。
寫一個python3腳本輸出正確的token:
def main():
a = [118, 104, 102, 120, 117, 108, 119, 124, 48,123,101,120];
s = ""
for i in range(0,len(a)):
s+=chr(a[i]-3)
print(s)
if __name__ == '__main__':
main()
成功拿到結果：
