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
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var http = require('http');
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const crypto = require('crypto');
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var url = require('url');
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var fs = require('fs');
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​
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var _0x86d1=["\x68\x65\x78","\x72\x61\x6E\x64\x6F\x6D\x42\x79\x74\x65\x73"];
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​
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function generatePart1() {
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    return
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         {
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             x: crypto[_0x86d1[1]](8)
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​
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         }[x].toString(_0x86d1[0]);
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}
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function generatePart2() {
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    return [+!+[]]+[!+[]+!+[]+!+[]]+[!+[]+!+[]+!+[]]+[!+[]+!+[]+!+[]+!+[]+!+[]+!+[]+!+[]];
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}
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​
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http.createServer(function (req, res) {
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    res.writeHead(200, {'Content-Type': 'text/html'});
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    passwd = generatePart1() + generatePart2();
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    var url_content = url.parse(req.url, true);
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​
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    if (passwd == url_content.query.passwd) {
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       res.write(fs.readFileSync('flag.txt', 'utf8'));
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    } else {
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        res.write('<html><body><form method="get"><input type="text" name="passwd" value="password"><input type="submit" value="login" /></form></body></html>');
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    }
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    res.end();
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}).listen(8888);
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 Python
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from flask import Flask, request, send_from_directory
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​
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app = Flask(__name__)
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​
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passwd = open("/opt/passwd.txt").read()
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flag = open("/opt/flag.txt").read()
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​
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​
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@app.route('/')
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def index():
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    userpw = request.args.get("passwd", "")
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    if userpw == passwd:
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        return flag, 200, {"Content-Type": "text/plain"}
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    else:
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        return '<html><body><form method="get"><input type="text" name="passwd" value="password"><input type="submit" value="login" /></form></body></html>'
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​
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​
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if __name__ == '__main__':
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    assert(len(passwd) == 3)
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    assert(passwd.isdigit())
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    app.run()
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​
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​

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