P.W.N. University - CTF 2018

https://uni.hctf.fun/

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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