下载下来查看html源码和js源码：
<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";
}
就是个障眼法。
接着看bm(s)这个方法：
str2rstr_utf8是一个将字符串转为utf8格式的字符串，不影响。继续往下看这个函数：
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); }这道题的坑点就在这里了，里面有个ck()函数，偷偷更改了ic的布尔值。
根据这个ck()函数就能还原出正确的token。
来看这个ck()函数：
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; }为了判断这个函数的输入是什么，我们在binl()函数里的ck(s)前加一行console.log(s)，看看输出，发现是输入的token。
确定输入之后开始分析ck(s):
这个函数很简单，读取s的每个字符，假如a[i]-s[i]!=3则返回false
因此，数组a代表的ascii码-3就是s的值。
写一个python3脚本输出正确的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()成功拿到结果：
