国外的题果然考的与众不同

[secrypt_cen.html]

这次是HTML网页，然后JS加密判断

翻看JS代码

很显然，关键的代码在checkPassword

JS混淆是必备的

去混淆一条龙走起

先将关键代码提取出来

  JavaScript
  function _0x4857(_0x398c7a, _0x2b4590) { const _0x104914 =
  _0x25ec(); _0x4857 = function (_0x22f014, _0x212d58) { _0x22f014 =
  _0x22f014 - (0x347 + 0x46a * -0x7 + 0x1cc6); let _0x321373 =
  _0x104914[_0x22f014]; return _0x321373; }; return
  _0x4857(_0x398c7a, _0x2b4590); } (function (_0x414f9c, _0x3d4799)
  {
  //...................省略大量代码
  } function safe_add(a, b) { var c = (65535 & a) + (65535 & b); return
  (a >> 16) + (b >> 16) + (c >> 16) << 16 | 65535 & c } function
​
  bit_rol(a, b) { return a << b | a >>> 32 - b }

使用在线的javascript去混淆即可

deobfuscate.relative.im

得到去混淆后的结果

  function checkPassword(_0x38d32a) {
  try {
  if (_0x38d32a.length !== 21) {
  return false
  }
  if (
  //......省略大量代码
  return [c, d, j, k]
  }
  function md5_cmn(a, b, c, d, e, f) {
  return safe_add(bit_rol(safe_add(safe_add(b, a), safe_add(d, f)), e),
  c)
  }
  function md5_ff(a, b, c, d, e, f, g) {
  return md5_cmn((b & c) | (~b & d), a, b, e, f, g)
  }
  function md5_gg(a, b, c, d, e, f, g) {
  return md5_cmn((b & d) | (c & ~d), a, b, e, f, g)
  }
  function md5_hh(a, b, c, d, e, f, g) {
  return md5_cmn(b ^ c ^ d, a, b, e, f, g)
  }
  function md5_ii(a, b, c, d, e, f, g) {
  return md5_cmn(c ^ (b | ~d), a, b, e, f, g)
  }
  function safe_add(a, b) {
  var c = (65535 & a) + (65535 & b)
  return (((a >> 16) + (b >> 16) + (c >> 16)) << 16) | (65535 &
  c)
  }
  function bit_rol(a, b) {
  return (a << b) | (a >>> (32 - b))
​
  }

flag长度21

发现了MD5加密，和两个MD5字符串

看起来无关联？

后来审计整个代码发现，对输入的flag分部分进行判断比较

写出对应的部分，在控制台console输出相关信息是一个不错的选择

  function checkPassword(_0x38d32a) {
  try {
  // Password length is 21.
  if (_0x38d32a.length !== 21) {
  return false;
  }
  if (
  _0x38d32a.slice(1, 2) !==
  (String.fromCodePoint + "")[
  parseInt((parseInt + "").charCodeAt(3), 16) - 147
  ] /* password[1] = 'o' */ ||
  _0x38d32a[(parseInt(41, 6) >> 2) - 2] !==
  String.fromCodePoint(123) /* password[4] = '{' */ ||
  _0x38d32a[4].charCodeAt(0) !==
  _0x38d32a[7].charCodeAt(0) + 72 /* password[7] = '3'. */ ||
  JSON.stringify(
  Array.from(
  _0x38d32a.slice(5, 7).split("").reverse().join(),
  (_0x2d4d73) => _0x2d4d73.codePointAt(0)
  ).map((_0x5b85c5) => _0x5b85c5 + 213)
  ) !==
  JSON.stringify([
  285, 257, 297,
  ]) /* password[5] = 'T', password[6] = 'H' password[7] =
  '3'*/
  ) {
  return false;
  }
  /* For password[8], password[9], password[10], password[11]
  */
  let _0x3c7a5c = _0x38d32a.slice(8, 12).split("").reverse();
  
  try {
  for (let _0x396662 = 0; _0x396662 < 5; _0x396662++) {
  _0x3c7a5c[_0x396662] =
  _0x3c7a5c[_0x396662].charCodeAt(0) + _0x396662 +
  getAdder(_0x396662);
  }
  } catch (_0x1fbd51) {
  _0x3c7a5c = _0x3c7a5c.map(
  (_0x24cda7) => (_0x24cda7 += _0x1fbd51.constructor.name.length -
  4)
  );
  }
  
  if (
  MD5(String.fromCodePoint(..._0x3c7a5c)) !==
  "098f6bcd4621d373cade4e832627b4f6" /* password[8] = '0',
  password[9] = 'R', password[10] = '3', password[11] = 'M'
  */
  ) {
  return false;
  }
  
  if (
  MD5(_0x38d32a.charCodeAt(12) + "") !==
  "812b4ba287f5ee0bc9d43bbf5bbe87fb" /* password[12] = '_' */
  ) {
  return false;
  }
  _0x3c7a5c = (_0x38d32a[8] + _0x38d32a[11]).split("");
  _0x3c7a5c.push(_0x3c7a5c.shift());
  if (
  _0x38d32a.substring(14, 16) !==
  String.fromCodePoint(
  ..._0x3c7a5c.map((_0x5b5ec8) =>
  Number.isNaN(+_0x5b5ec8) ? _0x5b5ec8.charCodeAt(0) + 5 : 48
  )
  ) /* password[14] = 'R' password[15] = '0' */ ||
  _0x38d32a[_0x38d32a[7] - _0x38d32a[10]] !==
  atob("dQ==") /* password[0] = 'u' */ ||
  _0x38d32a.indexOf(String.fromCharCode(117)) !==
  _0x38d32a[7] - _0x38d32a[17] /* password[17] = '3' */ ||
  JSON.stringify(
  _0x38d32a
  .slice(2, 4)
  .split("")
  .map(
  (_0x7bf0a6) =>
  _0x7bf0a6.charCodeAt(0) ^
  getAdder.name[_0x38d32a[7]].charCodeAt(0)
  )
  ) !==
  JSON.stringify(
  [72, 90].map(
  (_0x40ab0d) =>
  _0x40ab0d ^
  String.fromCodePoint.name[_0x38d32a[17] - 1].charCodeAt(0)
  )
  ) /* password[2] = 'f', password[3] = 't' */
  ) {
  return false;
  }
  if (
  String.fromCodePoint(
  ..._0x38d32a
  .split("")
  .filter(
  (_0x5edfac, _0x2965d2) => _0x2965d2 > 15 && _0x2965d2 % 2 == 0
  )
  .map(
  (_0x2ffa6d) =>
  _0x2ffa6d.charCodeAt(0) ^ (_0x38d32a.length + _0x38d32a[7])
  )
  ) !==
  atob(
  "g5Go"
  ) /* password[16] = 'V', password[18] = 'D', password[20] =
  '}' */
  ) {
  return false;
  }
  if (
  _0x38d32a[_0x38d32a.length - 2] !==
  String.fromCharCode(Math.floor((({} + "").charCodeAt(0) + 9) / 3))
  ||
  _0x38d32a[1 + _0x38d32a[7]] !== giggity()[5] /* password[19]
  = ! */
  ) {
  return false;
  }
  return true;
  } catch (_0x4d4983) {
  return false;
  }
  }
  function getAdder(_0x430c9d) {
  switch (_0x430c9d) {
  case 0:
  return 34;
  case 1:
  return 44;
  case 2:
  return 26;
  case 3:
  return 60;
  }
  return 101;
  }
  function giggity() {
  return giggity.caller.name;
​
  }

得到flag

uoft{TH30R3M_PR0V3D!}