一、前言
本文是一次破解某网站 JS 加密数据的记录，网址为：
要获取的是本页面上的投资事件信息，首先可以确定的是数据是通过 AJax 来传输的，并非直接写在网页源码中的。
二、步骤
1.抓包
打开开发者工具，刷新页面，选择 XHR 选项，可以找到如下请求信息：
可以看到返回结果中包含有状态码“status”、返回信息“message”和加密数据“encrypt_data”，这个 encrypt_data 是一个加密了的字符串，那要怎么解密呢？往下看。
2.分析
这里猜测解密的方法包含在某个 JS 文件里了，但又不可能打开每个文件去找。所以偷个懒，按 Ctrl + F 全局搜索“encrypt_data”，得到如下结果：
搜索的结果中只有一个 JS 文件，打开它并格式化，然后在这个文件中搜索“encrypt_data”，虽然有六处匹配，但还是基本可以通过上下文定位到这一处：
这里 e.encrypt_data 就是返回的加密数据了，因而猜测上面代码中的 Object(u.a) 就是解密函数！
3.调试
, 在 Source 中打开上述 JS 文件，在10644行打上断点，刷新网页，可以看到变量 i 就是我们前面找到的接口“investEventVip”：
然后要做的是就是定位到 Object(u.a) 对应的函数，如下图：
可以发现 s 函数的六个参数中有五个是有默认值的，而我们只需要得到 a.a.decode(t) 的结果，然后传入 s 函数中就行了。
继续调试，在10940行打上断点，按 F8 继续运行，然后定位到 s 对应的函数，如下图：
这里也不用管 s 函数具体是怎么运行的，先去找 a.a.decode() 对应的函数，如下图：
三、解密
通过前面的抓包、分析和调试，我们已经知道了解密的方法是什么了，但这么多的 JavaScript 代码，如果要全部理解并且用 Python 来实现的话，会耗费掉不少的时间，这里可以选择用一种比较偷懒的方法--使用第三方库 PyExecJS 直接运行 JS 代码。
1.PyExecJS 简介
PyExecJS 是来自 Ruby 的 ExecJS 的移植。PyExecJS 自动选择最佳的运行时来评估 JavaScript 程序，然后将结果作为 Python 对象返回。如果还没有安装这个库，可以使用 pip 命令进行安装：
pip install PyExecJS
PyExecJS 库三个常用的方法，如下：
- eval() 用来执行一个字符串表达式，并返回表达式的结果。
- compile() 用来编译 JavaScript 代码，例如定义函数和方法。
- call() 用来调用通过 compile() 定义的函数和方法，可以传参。
下面是使用该库的示例，可作了解：
1 import execjs 2 3 4 n1 = execjs.eval("1 + 2") 5 print(n1) # 3 6 7 ctx = execjs.compile( 8 """ 9 function add(x, y) { 10 return x + y; 11 } 12 """ 13 ) 14 n2 = ctx.call("add", 3, 4) 15 print(n2) # 7
2.使用 Python 解密
要用 PyExecJS 来进行解密，需要把前面找到的 s 函数和 decode 函数复制过来，使用 compile 进行编译，如下：
js = execjs.compile(r""" //解密函数 function my_decrypt(t) { return new Buffer(s("5e5062e82f15fe4ca9d24bc5", my_decode(t), 0, 0, "012345677890123", 1)).toString("base64") } //解密函数依赖项 function my_decode(t) { c = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/" f = /[ f ]/g var e = (t = String(t).replace(f, "")).length; e % 4 == 0 && (e = (t = t.replace(/==?$/, "")).length), (e % 4 == 1 || /[^+a-zA-Z0-9/]/.test(t)) && l("Invalid character: the string to be decoded is not correctly encoded."); for (var n, r, i = 0, o = "", a = -1; ++a < e; ) r = c.indexOf(t.charAt(a)), n = i % 4 ? 64 * n + r : r, i++ % 4 && (o += String.fromCharCode(255 & n >> (-2 * i & 6))); return o } function s(t, e, i, n, a, s) { var o, r, c, l, u, d, h, p, f, v, m, g, b, y, C = new Array(16843776,0,65536,16843780,16842756,66564,4,65536,1024,16843776,16843780,1024,16778244,16842756,16777216,4,1028,16778240,16778240,66560,66560,16842752,16842752,16778244,65540,16777220,16777220,65540,0,1028,66564,16777216,65536,16843780,4,16842752,16843776,16777216,16777216,1024,16842756,65536,66560,16777220,1024,4,16778244,66564,16843780,65540,16842752,16778244,16777220,1028,66564,16843776,1028,16778240,16778240,0,65540,66560,0,16842756), _ = new Array(-2146402272,-2147450880,32768,1081376,1048576,32,-2146435040,-2147450848,-2147483616,-2146402272,-2146402304,-2147483648,-2147450880,1048576,32,-2146435040,1081344,1048608,-2147450848,0,-2147483648,32768,1081376,-2146435072,1048608,-2147483616,0,1081344,32800,-2146402304,-2146435072,32800,0,1081376,-2146435040,1048576,-2147450848,-2146435072,-2146402304,32768,-2146435072,-2147450880,32,-2146402272,1081376,32,32768,-2147483648,32800,-2146402304,1048576,-2147483616,1048608,-2147450848,-2147483616,1048608,1081344,0,-2147450880,32800,-2147483648,-2146435040,-2146402272,1081344), w = new Array(520,134349312,0,134348808,134218240,0,131592,134218240,131080,134217736,134217736,131072,134349320,131080,134348800,520,134217728,8,134349312,512,131584,134348800,134348808,131592,134218248,131584,131072,134218248,8,134349320,512,134217728,134349312,134217728,131080,520,131072,134349312,134218240,0,512,131080,134349320,134218240,134217736,512,0,134348808,134218248,131072,134217728,134349320,8,131592,131584,134217736,134348800,134218248,520,134348800,131592,8,134348808,131584), x = new Array(8396801,8321,8321,128,8396928,8388737,8388609,8193,0,8396800,8396800,8396929,129,0,8388736,8388609,1,8192,8388608,8396801,128,8388608,8193,8320,8388737,1,8320,8388736,8192,8396928,8396929,129,8388736,8388609,8396800,8396929,129,0,0,8396800,8320,8388736,8388737,1,8396801,8321,8321,128,8396929,129,1,8192,8388609,8193,8396928,8388737,8193,8320,8388608,8396801,128,8388608,8192,8396928), k = new Array(256,34078976,34078720,1107296512,524288,256,1073741824,34078720,1074266368,524288,33554688,1074266368,1107296512,1107820544,524544,1073741824,33554432,1074266112,1074266112,0,1073742080,1107820800,1107820800,33554688,1107820544,1073742080,0,1107296256,34078976,33554432,1107296256,524544,524288,1107296512,256,33554432,1073741824,34078720,1107296512,1074266368,33554688,1073741824,1107820544,34078976,1074266368,256,33554432,1107820544,1107820800,524544,1107296256,1107820800,34078720,0,1074266112,1107296256,524544,33554688,1073742080,524288,0,1074266112,34078976,1073742080), T = new Array(536870928,541065216,16384,541081616,541065216,16,541081616,4194304,536887296,4210704,4194304,536870928,4194320,536887296,536870912,16400,0,4194320,536887312,16384,4210688,536887312,16,541065232,541065232,0,4210704,541081600,16400,4210688,541081600,536870912,536887296,16,541065232,4210688,541081616,4194304,16400,536870928,4194304,536887296,536870912,16400,536870928,541081616,4210688,541065216,4210704,541081600,0,541065232,16,16384,541065216,4210704,16384,4194320,536887312,0,541081600,536870912,4194320,536887312), A = new Array(2097152,69206018,67110914,0,2048,67110914,2099202,69208064,69208066,2097152,0,67108866,2,67108864,69206018,2050,67110912,2099202,2097154,67110912,67108866,69206016,69208064,2097154,69206016,2048,2050,69208066,2099200,2,67108864,2099200,67108864,2099200,2097152,67110914,67110914,69206018,69206018,2,2097154,67108864,67110912,2097152,69208064,2050,2099202,69208064,2050,67108866,69208066,69206016,2099200,0,2,69208066,0,2099202,69206016,2048,67108866,67110912,2048,2097154), L = new Array(268439616,4096,262144,268701760,268435456,268439616,64,268435456,262208,268697600,268701760,266240,268701696,266304,4096,64,268697600,268435520,268439552,4160,266240,262208,268697664,268701696,4160,0,0,268697664,268435520,268439552,266304,262144,266304,262144,268701696,4096,64,268697664,4096,266304,268439552,64,268435520,268697600,268697664,268435456,262144,268439616,0,268701760,262208,268435520,268697600,268439552,268439616,0,268701760,266240,266240,4160,4160,262208,268435456,268701696), S = function(t) { for (var e, i, n, a = new Array(0,4,536870912,536870916,65536,65540,536936448,536936452,512,516,536871424,536871428,66048,66052,536936960,536936964), s = new Array(0,1,1048576,1048577,67108864,67108865,68157440,68157441,256,257,1048832,1048833,67109120,67109121,68157696,68157697), o = new Array(0,8,2048,2056,16777216,16777224,16779264,16779272,0,8,2048,2056,16777216,16777224,16779264,16779272), r = new Array(0,2097152,134217728,136314880,8192,2105344,134225920,136323072,131072,2228224,134348800,136445952,139264,2236416,134356992,136454144), c = new Array(0,262144,16,262160,0,262144,16,262160,4096,266240,4112,266256,4096,266240,4112,266256), l = new Array(0,1024,32,1056,0,1024,32,1056,33554432,33555456,33554464,33555488,33554432,33555456,33554464,33555488), u = new Array(0,268435456,524288,268959744,2,268435458,524290,268959746,0,268435456,524288,268959744,2,268435458,524290,268959746), d = new Array(0,65536,2048,67584,536870912,536936448,536872960,536938496,131072,196608,133120,198656,537001984,537067520,537004032,537069568), h = new Array(0,262144,0,262144,2,262146,2,262146,33554432,33816576,33554432,33816576,33554434,33816578,33554434,33816578), p = new Array(0,268435456,8,268435464,0,268435456,8,268435464,1024,268436480,1032,268436488,1024,268436480,1032,268436488), f = new Array(0,32,0,32,1048576,1048608,1048576,1048608,8192,8224,8192,8224,1056768,1056800,1056768,1056800), v = new Array(0,16777216,512,16777728,2097152,18874368,2097664,18874880,67108864,83886080,67109376,83886592,69206016,85983232,69206528,85983744), m = new Array(0,4096,134217728,134221824,524288,528384,134742016,134746112,16,4112,134217744,134221840,524304,528400,134742032,134746128), g = new Array(0,4,256,260,0,4,256,260,1,5,257,261,1,5,257,261), b = t.length > 8 ? 3 : 1, y = new Array(32 * b), C = new Array(0,0,1,1,1,1,1,1,0,1,1,1,1,1,1,0), _ = 0, w = 0, x = 0; x < b; x++) { var k = t.charCodeAt(_++) << 24 | t.charCodeAt(_++) << 16 | t.charCodeAt(_++) << 8 | t.charCodeAt(_++) , T = t.charCodeAt(_++) << 24 | t.charCodeAt(_++) << 16 | t.charCodeAt(_++) << 8 | t.charCodeAt(_++); k ^= (n = 252645135 & (k >>> 4 ^ T)) << 4, k ^= n = 65535 & ((T ^= n) >>> -16 ^ k), k ^= (n = 858993459 & (k >>> 2 ^ (T ^= n << -16))) << 2, k ^= n = 65535 & ((T ^= n) >>> -16 ^ k), k ^= (n = 1431655765 & (k >>> 1 ^ (T ^= n << -16))) << 1, k ^= n = 16711935 & ((T ^= n) >>> 8 ^ k), n = (k ^= (n = 1431655765 & (k >>> 1 ^ (T ^= n << 8))) << 1) << 8 | (T ^= n) >>> 20 & 240, k = T << 24 | T << 8 & 16711680 | T >>> 8 & 65280 | T >>> 24 & 240, T = n; for (var A = 0; A < C.length; A++) C[A] ? (k = k << 2 | k >>> 26, T = T << 2 | T >>> 26) : (k = k << 1 | k >>> 27, T = T << 1 | T >>> 27), T &= -15, e = a[(k &= -15) >>> 28] | s[k >>> 24 & 15] | o[k >>> 20 & 15] | r[k >>> 16 & 15] | c[k >>> 12 & 15] | l[k >>> 8 & 15] | u[k >>> 4 & 15], i = d[T >>> 28] | h[T >>> 24 & 15] | p[T >>> 20 & 15] | f[T >>> 16 & 15] | v[T >>> 12 & 15] | m[T >>> 8 & 15] | g[T >>> 4 & 15], n = 65535 & (i >>> 16 ^ e), y[w++] = e ^ n, y[w++] = i ^ n << 16 } return y }(t), z = 0, B = e.length, j = 0, I = 32 == S.length ? 3 : 9; p = 3 == I ? i ? new Array(0,32,2) : new Array(30,-2,-2) : i ? new Array(0,32,2,62,30,-2,64,96,2) : new Array(94,62,-2,32,64,2,30,-2,-2), 2 == s ? e += " " : 1 == s ? i && (c = 8 - B % 8, e += String.fromCharCode(c, c, c, c, c, c, c, c), 8 === c && (B += 8)) : s || (e += " "); var F = "" , O = ""; for (1 == n && (f = a.charCodeAt(z++) << 24 | a.charCodeAt(z++) << 16 | a.charCodeAt(z++) << 8 | a.charCodeAt(z++), m = a.charCodeAt(z++) << 24 | a.charCodeAt(z++) << 16 | a.charCodeAt(z++) << 8 | a.charCodeAt(z++), z = 0); z < B; ) { for (d = e.charCodeAt(z++) << 24 | e.charCodeAt(z++) << 16 | e.charCodeAt(z++) << 8 | e.charCodeAt(z++), h = e.charCodeAt(z++) << 24 | e.charCodeAt(z++) << 16 | e.charCodeAt(z++) << 8 | e.charCodeAt(z++), 1 == n && (i ? (d ^= f, h ^= m) : (v = f, g = m, f = d, m = h)), d ^= (c = 252645135 & (d >>> 4 ^ h)) << 4, d ^= (c = 65535 & (d >>> 16 ^ (h ^= c))) << 16, d ^= c = 858993459 & ((h ^= c) >>> 2 ^ d), d ^= c = 16711935 & ((h ^= c << 2) >>> 8 ^ d), d = (d ^= (c = 1431655765 & (d >>> 1 ^ (h ^= c << 8))) << 1) << 1 | d >>> 31, h = (h ^= c) << 1 | h >>> 31, r = 0; r < I; r += 3) { for (b = p[r + 1], y = p[r + 2], o = p[r]; o != b; o += y) l = h ^ S[o], u = (h >>> 4 | h << 28) ^ S[o + 1], c = d, d = h, h = c ^ (_[l >>> 24 & 63] | x[l >>> 16 & 63] | T[l >>> 8 & 63] | L[63 & l] | C[u >>> 24 & 63] | w[u >>> 16 & 63] | k[u >>> 8 & 63] | A[63 & u]); c = d, d = h, h = c } h = h >>> 1 | h << 31, h ^= c = 1431655765 & ((d = d >>> 1 | d << 31) >>> 1 ^ h), h ^= (c = 16711935 & (h >>> 8 ^ (d ^= c << 1))) << 8, h ^= (c = 858993459 & (h >>> 2 ^ (d ^= c))) << 2, h ^= c = 65535 & ((d ^= c) >>> 16 ^ h), h ^= c = 252645135 & ((d ^= c << 16) >>> 4 ^ h), d ^= c << 4, 1 == n && (i ? (f = d, m = h) : (d ^= v, h ^= g)), O += String.fromCharCode(d >>> 24, d >>> 16 & 255, d >>> 8 & 255, 255 & d, h >>> 24, h >>> 16 & 255, h >>> 8 & 255, 255 & h), 512 == (j += 8) && (F += O, O = "", j = 0) } if (F = (F += O).replace(/ *$/g, ""), !i) { if (1 === s) { var $ = 0; (B = F.length) && ($ = F.charCodeAt(B - 1)), $ <= 8 && (F = F.substring(0, B - $)) } F = decodeURIComponent(escape(F)) } return F } """)
然后使用 call() 方法进行调用解密，使用方法为：
js.call('my_decrypt', encrypt_data)
不过这一步得到的结果还是使用 base64 加密后的，所以还得用 base64.b64decode() 进行解密，就能得到最终的结果了。
完整代码已上传到 GitHub！