攻防世界 reverse secret-string-400
secret-string-400 school-ctf-winter-2015
解压文件得到html和js文件
Task.html
<html> <head> <title>JSMachine</title> <meta charset="UTF-8"> <script type='text/javascript' src='Machine.js'></script> </head> <body> <h1>Secret key</h1><br/> <h2>Test your luck! Enter valid string and you will know flag!</h2><br/> <input type='text'></input><br/> <br/> <input type='button' onclick="check()" value='Проверить'></button> </body> </html>
Machine.js
function createRegisters(obj){ obj.registers = []; for(i=0; i < 256; ++i){ obj.registers.push(0); } }; function Machine() { createRegisters(this); this.code = [0] this.PC = 0; this.callstack = []; this.pow = Math.pow(2,32) }; Machine.prototype = { opcodesCount: 16, run: run, loadcode: function(code){this.code = code}, end: function(){this.code=[]} }; function run(){ while(this.PC < this.code.length){ var command = parseCommand.call(this); command.execute(this); } //this.end() } function getOpcodeObject(){ var opNum = (this.code[this.PC] % this.opcodesCount); this.PC += 1; return eval('new Opcode'+opNum); } function parseCommand(){ var opcode = getOpcodeObject.call(this); opcode.consumeArgs(this); return opcode; } var opcCreate = ""; for(i=0;i<16;++i){ opcCreate += "function Opcode"+i+"(){this.args=[]}\n"; } eval(opcCreate); function makeFromImm(obj) { var res = obj.code[obj.PC + 2]; res <<=8; res += obj.code[obj.PC + 1]; res <<=8; res += obj.code[obj.PC]; res <<=8; res += obj.code[obj.PC+3]; res = res >>> 0; return res; } function getRegImm(obj){ this.args[0] = obj.code[obj.PC]; obj.PC += 1; this.args[1] = makeFromImm(obj); obj.PC += 4; } function getImm(obj){ this.args[0] = makeFromImm(obj); obj.PC += 4; } function getTwoRegs(obj){ this.args[0] = obj.code[obj.PC]; obj.PC += 1; this.args[1] = obj.code[obj.PC]; obj.PC += 1; } function getThreeRegs(obj){ this.args[0] = obj.code[obj.PC]; obj.PC += 1; this.args[1] = obj.code[obj.PC]; obj.PC += 1; this.args[2] = obj.code[obj.PC]; obj.PC += 1; } function getRegString(obj){ this.args[0] = obj.code[obj.PC]; obj.PC += 1; this.args[1] = getString(obj); } function getRegRegString(obj){ this.args[0] = obj.code[obj.PC]; obj.PC += 1; this.args[1] = obj.code[obj.PC]; obj.PC += 1; this.args[2] = getString(obj); } function getRegTwoString(obj){ this.args[0] = obj.code[obj.PC]; obj.PC += 1; this.args[1] = getString(obj); this.args[2] = getString(obj); } function getString(obj){ var res = ""; while(obj.code[obj.PC] != 0) { res += String.fromCharCode(obj.code[obj.PC]); obj.PC += 1; } obj.PC += 1; return res; } Opcode0.prototype = { consumeArgs : function(obj){}, execute: function(){} }; Opcode1.prototype = { consumeArgs: getRegImm, execute: function(obj){ obj.registers[this.args[0]] = (obj.registers[this.args[0]] + this.args[1]) % 0x100000000; } } Opcode2.prototype = { consumeArgs: getTwoRegs, execute: function(obj){ obj.registers[this.args[0]] = (obj.registers[this.args[0]] + obj.registers[this.args[1]]) % 0x100000000; } } Opcode3.prototype = { consumeArgs: getRegImm, execute: function(obj){ obj.registers[this.args[0]] = ((obj.registers[this.args[0]] - this.args[1]) % 0x100000000) >>> 0; } } Opcode4.prototype = { consumeArgs: getTwoRegs, execute: function(obj){ obj.regsiters[this.args[0]] = ((obj.registers[this.args[0]] - this.registers[this.args[1]])%100000000) >>> 0 } } Opcode5.prototype = { consumeArgs: getThreeRegs, execute: function(obj){ var mult = obj.registers[this.args[0]] * obj.registers[this.args[1]]; console.log(mult.toString(16)); obj.registers[this.args[2]] = (mult / obj.pow) >>> 0; obj.registers[this.args[2]+1] = (mult & 0xffffffff) >>> 0; } } Opcode6.prototype = { consumeArgs: getThreeRegs, execute: function(obj){ var divs = obj.registers[this.args[0]] * obj.pow + obj.registers[this.args[0]+1]; obj.registers[this.args[2]] = (divs / obj.registers[this.args[1]]) >>> 0; obj.registers[this.args[2]+1]= (divs % obj.registers[this.args[1]]) >>> 0; } } Opcode7.prototype = { consumeArgs: getRegImm, execute: function(obj) { obj.registers[this.args[0]] = this.args[1]; } } Opcode8.prototype = { consumeArgs: getImm, execute: function(obj){ obj.callstack.push(obj.PC); obj.PC = this.args[0]; } } Opcode9.prototype = { consumeArgs: getImm, execute: function(obj){ obj.PC = (obj.PC + this.args[0]) % obj.code.length; } } Opcode10.prototype = { consumeArgs: function(){}, execute: function(obj){ obj.PC = obj.callstack.pop(); } } Opcode11.prototype = { consumeArgs: getRegString, execute: function(obj){ obj.registers[this.args[0]] = eval('new '+this.args[1]); } } Opcode12.prototype = { consumeArgs: getRegTwoString, execute: function(obj){ obj.registers[this.args[0]][this.args[1]] = Function(this.args[2]); } } Opcode13.prototype = { consumeArgs: getRegRegString, execute: function(obj){ obj.registers[this.args[0]] = obj.registers[this.args[1]][this.args[2]]; } } Opcode14.prototype = { consumeArgs: getRegRegString, execute: function(obj){ obj.registers[this.args[1]][this.args[2]] = obj.registers[this.args[0]]; } } Opcode15.prototype = { consumeArgs: getRegRegString, execute: function(obj){ obj.registers[this.args[0]] = obj.registers[this.args[1]][this.args[2]](); } } function check(){ machine = new Machine; machine.loadcode([11, 1, 79, 98, 106, 101, 99, 116, 0, 12, 1, 120, 0, 114, 101, 116, 117, 114, 110, 32, 100, 111, 99, 117, 109, 101, 110, 116, 46, 103, 101, 116, 69, 108, 101, 109, 101, 110, 116, 115, 66, 121, 84, 97, 103, 78, 97, 109, 101, 40, 39, 105, 110, 112, 117, 116, 39, 41, 91, 48, 93, 46, 118, 97, 108, 117, 101, 47, 47, 0, 15, 3, 1, 120, 0, 14, 3, 1, 117, 115, 101, 114, 105, 110, 112, 117, 116, 0, 12, 1, 121, 0, 119, 105, 110, 100, 111, 119, 46, 109, 97, 99, 104, 105, 110, 101, 46, 101, 110, 100, 32, 61, 32, 102, 117, 110, 99, 116, 105, 111, 110, 40, 41, 123, 116, 104, 105, 115, 46, 99, 111, 100, 101, 61, 91, 93, 59, 116, 104, 105, 115, 46, 80, 67, 61, 49, 55, 51, 125, 47, 47, 0, 15, 3, 1, 121, 0, 12, 1, 122, 0, 97, 108, 101, 114, 116, 40, 49, 41, 59, 47, 47, 11, 234, 79, 98, 106, 101, 99, 116, 255, 9, 255, 255, 255, 12, 10, 97, 108, 101, 114, 116, 40, 50, 41, 59, 47, 47, 12, 234, 120, 255, 118, 97, 114, 32, 102, 61, 119, 105, 110, 100, 111, 119, 46, 109, 97, 99, 104, 105, 110, 101, 46, 114, 101, 103, 105, 115, 116, 101, 114, 115, 91, 49, 93, 46, 117, 115, 101, 114, 105, 110, 112, 117, 116, 47, 47, 10, 118, 97, 114, 32, 105, 32, 61, 32, 102, 46, 108, 101, 110, 103, 116, 104, 47, 47, 10, 118, 97, 114, 32, 110, 111, 110, 99, 101, 32, 61, 32, 39, 103, 114, 111, 107, 101, 39, 59, 47, 47, 10, 118, 97, 114, 32, 106, 32, 61, 32, 48, 59, 47, 47, 10, 118, 97, 114, 32, 111, 117, 116, 32, 61, 32, 91, 93, 59, 47, 47, 10, 118, 97, 114, 32, 101, 113, 32, 61, 32, 116, 114, 117, 101, 59, 47, 47, 10, 119, 104, 105, 108, 101, 40, 106, 32, 60, 32, 105, 41, 123, 47, 47, 10, 111, 117, 116, 46, 112, 117, 115, 104, 40, 102, 46, 99, 104, 97, 114, 67, 111, 100, 101, 65, 116, 40, 106, 41, 32, 94, 32, 110, 111, 110, 99, 101, 46, 99, 104, 97, 114, 67, 111, 100, 101, 65, 116, 40, 106, 37, 53, 41, 41, 47, 47, 10, 106, 43, 43, 59, 47, 47, 10, 125, 47, 47, 10, 118, 97, 114, 32, 101, 120, 32, 61, 32, 32, 91, 49, 44, 32, 51, 48, 44, 32, 49, 52, 44, 32, 49, 50, 44, 32, 54, 57, 44, 32, 49, 52, 44, 32, 49, 44, 32, 56, 53, 44, 32, 55, 53, 44, 32, 53, 48, 44, 32, 52, 48, 44, 32, 51, 55, 44, 32, 52, 56, 44, 32, 50, 52, 44, 32, 49, 48, 44, 32, 53, 54, 44, 32, 53, 53, 44, 32, 52, 54, 44, 32, 53, 54, 44, 32, 54, 48, 93, 59, 47, 47, 10, 105, 102, 32, 40, 101, 120, 46, 108, 101, 110, 103, 116, 104, 32, 61, 61, 32, 111, 117, 116, 46, 108, 101, 110, 103, 116, 104, 41, 32, 123, 47, 47, 10, 106, 32, 61, 32, 48, 59, 47, 47, 10, 119, 104, 105, 108, 101, 40, 106, 32, 60, 32, 101, 120, 46, 108, 101, 110, 103, 116, 104, 41, 123, 47, 47, 10, 105, 102, 40, 101, 120, 91, 106, 93, 32, 33, 61, 32, 111, 117, 116, 91, 106, 93, 41, 47, 47, 10, 101, 113, 32, 61, 32, 102, 97, 108, 115, 101, 59, 47, 47, 10, 106, 32, 43, 61, 32, 49, 59, 47, 47, 10, 125, 47, 47, 10, 105, 102, 40, 101, 113, 41, 123, 47, 47, 10, 97, 108, 101, 114, 116, 40, 39, 89, 79, 85, 32, 87, 73, 78, 33, 39, 41, 59, 47, 47, 10, 125, 101, 108, 115, 101, 123, 10, 97, 108, 101, 114, 116, 40, 39, 78, 79, 80, 69, 33, 39, 41, 59, 10, 125, 125, 101, 108, 115, 101, 123, 97, 108, 101, 114, 116, 40, 39, 78, 79, 80, 69, 33, 39, 41, 59, 125, 47, 47, 255, 9, 255, 255, 255, 12, 10, 97, 108, 101, 114, 116, 40, 51, 41, 59, 47, 47, 15, 1, 234, 120, 255, 9, 255, 255, 255, 12, 10, 97, 108, 101, 114, 116, 40, 52, 41, 59, 47, 47, 10, 97, 108, 101, 114, 116, 40, 53, 41, 59, 47, 47, 10, 97, 108, 101, 114, 116, 40, 54, 41, 59, 47, 47, 10, 97, 108, 101, 114, 116, 40, 55, 41, 59, 47, 47, 0, 12, 1, 103, 0, 118, 97, 114, 32, 105, 32, 61, 48, 59, 119, 104, 105, 108, 101, 40, 105, 60, 119, 105, 110, 100, 111, 119, 46, 109, 97, 99, 104, 105, 110, 101, 46, 99, 111, 100, 101, 46, 108, 101, 110, 103, 116, 104, 41, 123, 105, 102, 40, 119, 105, 110, 100, 111, 119, 46, 109, 97, 99, 104, 105, 110, 101, 46, 99, 111, 100, 101, 91, 105, 93, 32, 61, 61, 32, 50, 53, 53, 32, 41, 32, 119, 105, 110, 100, 111, 119, 46, 109, 97, 99, 104, 105, 110, 101, 46, 99, 111, 100, 101, 91, 105, 93, 32, 61, 32, 48, 59, 105, 43, 43, 125, 47, 47, 0, 12, 1, 104, 0, 119, 105, 110, 100, 111, 119, 46, 109, 97, 99, 104, 105, 110, 101, 46, 80, 67, 61, 49, 55, 50, 47, 47, 0, 15, 0, 1, 103, 0, 15, 0, 1, 104, 0]) machine.run(); }
修改js文件，添加打印输出
运行html
找到关键代码
1 var f=window.machine.registers[1].userinput// 2 var i = f.length// 3 var nonce = 'groke';// 4 var j = 0;// 5 var out = [];// 6 var eq = true;// 7 while(j < i){// 8 out.push(f.charCodeAt(j) ^ nonce.charCodeAt(j%5))// 9 j++;// 10 }// 11 var ex = [1, 30, 14, 12, 69, 14, 1, 85, 75, 50, 40, 37, 48, 24, 10, 56, 55, 46, 56, 60];// 12 if (ex.length == out.length) {// 13 j = 0;// 14 while(j < ex.length){// 15 if(ex[j] != out[j])// 16 eq = false;// 17 j += 1;// 18 }// 19 if(eq){// 20 alert('YOU WIN!');// 21 }else{ 22 alert('NOPE!'); 23 }}else{alert('NOPE!');}//
wp
ex = [1, 30, 14, 12, 69, 14, 1, 85, 75, 50, 40, 37, 48, 24, 10, 56, 55, 46, 56, 60]; nonce = 'groke'; flag='' for i in range(len(ex)): flag+=chr(ex[i]^ord(nonce[i%5])) print(flag)
flag is: WOW_so_EASY
