P.W.N. University - CTF 2018 - 130n@calvinlai.com

 Thinking out of the box
No advanced programming technique is required to solve the following CTF problem
JavaScript
var http = require('http');
const crypto = require('crypto');
var url = require('url');
var fs = require('fs');
​
var _0x86d1=["\x68\x65\x78","\x72\x61\x6E\x64\x6F\x6D\x42\x79\x74\x65\x73"];
​
function generatePart1() {
    return
         {
             x: crypto[_0x86d1[1]](8)
​
         }[x].toString(_0x86d1[0]);
}
function generatePart2() {
    return [+!+[]]+[!+[]+!+[]+!+[]]+[!+[]+!+[]+!+[]]+[!+[]+!+[]+!+[]+!+[]+!+[]+!+[]+!+[]];
}
​
http.createServer(function (req, res) {
    res.writeHead(200, {'Content-Type': 'text/html'});
    passwd = generatePart1() + generatePart2();
    var url_content = url.parse(req.url, true);
​
    if (passwd == url_content.query.passwd) {
       res.write(fs.readFileSync('flag.txt', 'utf8'));
    } else {
        res.write('<html><body><form method="get"><input type="text" name="passwd" value="password"><input type="submit" value="login" /></form></body></html>');
    }
    res.end();
}).listen(8888);
 Python
from flask import Flask, request, send_from_directory
​
app = Flask(__name__)
​
passwd = open("/opt/passwd.txt").read()
flag = open("/opt/flag.txt").read()
​
​
@app.route('/')
def index():
    userpw = request.args.get("passwd", "")
    if userpw == passwd:
        return flag, 200, {"Content-Type": "text/plain"}
    else:
        return '<html><body><form method="get"><input type="text" name="passwd" value="password"><input type="submit" value="login" /></form></body></html>'
​
​
if __name__ == '__main__':
    assert(len(passwd) == 3)
    assert(passwd.isdigit())
    app.run()
​
​

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