sequencehunt_server.js

#!/usr/bin/env node
// run with: node sequencehunt_server.js
// info page: http://localhost:8080/info
// correct values: http://localhost:8080/check?val0=4&val1=12&val2=77&val3=98&val4=35

var http = require('http');
var url = require('url');

var TimingAttackProtectionSeconds = 3;

var IOLoopCounter = 0;

// even loop blocking sleep
function sleep(s) {
  var e = new Date().getTime() + s;
  while (new Date().getTime() <= e) {;}
}

// check input, simulates algorithm vulnerable to timing attack
// for each correct value, additional delay of 0.45s is added.
function checkInput(params) {
  var correct = [4, 12, 77, 98, 35];

  // params into array
  var p = Object.keys(params).map(function(v) { return parseInt(params[v]); });

  console.log('working hard on our input ' + JSON.stringify(params));
  var sleepTime = 0.45;
  var result = true;

  if (p.length != correct.length) {
    result = false;
  }

  for (i = 0; i < p.length; i++) {
    if (p[i] == correct[i]) {
      sleepTime += 0.45;
    } else {
      result = false;
    }
  }
  sleep(sleepTime * 1000);
  return result;
}

http.createServer(function(request, response) {
  var u = url.parse(request.url, true);

  if (u.path.indexOf('/info') == 0) {
    IOLoopCounter++;
    response.writeHeader(200, {'Content-Type': 'text/html'});
    response.write('IOLoop: ' + IOLoopCounter);
    response.end();

  } else if (u.path.indexOf('/check') == 0) {
    IOLoopCounter++;
    var start = new Date().getTime();
    // check if the input valus are correct (algorithm is time sensitive to the input)
    var result = checkInput(u.query);
    var secondsSpent = ((new Date().getTime()) - start) / 1000.0;

    // "prevent" the timing attack. wait until 3 seconds pass
    var timeLeftToWait = TimingAttackProtectionSeconds - secondsSpent;

    setTimeout(function() {
      response.writeHeader(200, {'Content-Type': 'text/html'});
      if (result) {
        response.write('Congratulations, here is your price:</br>32C3_round_and_round_and_round_IT_goes</br>');
      } else {
        response.write('At least one value is wrong!</br>');
      }
      response.end();
      console.log('DEBUG: Blocked IO loop for: ' + secondsSpent.toFixed(2) + 's');
      console.log('DEBUG: Total request time: ' + TimingAttackProtectionSeconds + 's');
    }, timeLeftToWait * 1000);

  }
}).listen(8080);

console.log('Server running at http://localhost:8080/');