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exercise_two.html
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<!DOCTYPE html>
<html>
<head>
<title>Crypto Exercises</title>
<link rel="stylesheet" href="./cryptoexercises-stylesheet.css" />
<script src="./sjcl/sjcl.js"></script>
<script src="./functions.js"></script>
</head>
<body onload="loadProblem()">
<!----------------------------------------------------------------------------->
<header>
<table class="headerTable" cellspacing="0">
<tr>
<td class="left">
<img class="bannerImage" src="./LLCipher_logo.png" alt="Llcipher logo" />
</td>
<td class="middle">
<p>Cryptography Challenges</p>
</td>
<td class="right">
<img class="lincolnLogo" src="./lincoln_logo.png" alt="Lincoln logo" />
</td>
</tr>
</table>
</header>
<!----------------------------------------------------------------------------->
<nav>
<ul>
<li><a href="./index.html">Home</a></li>
</ul>
<br />
<ul>
<li class="title">Background</li>
<li><a href="./el_gamal_encryption.html">El Gamal Encryption</a>
<li><a href="./rsa_encryption.html">RSA Encryption</a>
</ul>
<br />
<ul>
<li class="title">Challenges</li>
<li><a href="./classical_crypto.html">Classical Crypto</a></li>
<li><a href="./exercise_one.html">RSA Challenge One</a></li>
<li><a href="./exercise_two.html">RSA Challenge Two</a></li>
<li><a href="./exercise_three.html">RSA Challenge Three</a></li>
<li><a href="./exercise_three_a.html">RSA Challenge Three (a)</a></li>
<li><a href="./exercise_four.html">RSA Challenge Four</a></li>
<li><a href="./exercise_five.html">El Gamal Challenge</a></li>
</ul>
<br />
<ul>
<li class="title">Other Stuff</li>
<li><a href="./references.html">References</a></li>
<li><a href="./credits.html">Credits</a></li>
</ul>
</nav>
<!----------------------------------------------------------------------------->
<article>
<table class="exerciseLayoutTable" cellspacing="0">
<tr>
<td class="exerciseDetails">
<h1>RSA Challenge Two: RSA Small Plaintext and Encryption Exponent Attack</h1>
<div class="exerciseDescription">
<p><b>The Problem:</b> Given an RSA ciphertext encrypting a small message with a small public key (e.g. e = 3), recover the message.</p>
</div>
<div class="problemStatement">
<p>Malland sent another message to Horridland; however, this time, you don't really know what they might be saying.
You do, however, know that the encryption exponent is e = 3, and that Mallanders tend to be very brief and to the point, so you think the message in question is probably very short.
Use this knowledge to figure out what the message is.
</p>
<p>For this exercise, use the following values:</p>
<table class="exerciseValuesTable" cellspacing="0">
<tr class="headerRow">
<td class="name">Name</td>
<td class="value">Value</td>
</tr>
<tr class="oddRow">
<td class="name">Modulus: </td>
<td class="value"><div id="modulus"></div></td>
</tr>
<tr class="evenRow">
<td class="name">Public exponent: </td>
<td class="value"><div id="exponent"></div></td>
</tr>
<tr class="oddRow">
<td class="name">Ciphertext: </td>
<td class="value"><div id="ciphertext"></div></td>
</tr>
</table>
<form class="new_exercise">
<table class="answerFormTable" cellspacing="0">
<tr>
<td>
<!--
# The size of this text area is probably much smaller, but may
# also vary from exercise to exercise. The right answer is
# probably to see if this value can be moved into CSS, and
# then change the class name based on the exercise.
-->
<label class="answer" for="exercise_answer">Your Answer:</label>
<textarea class="answer" name="exercise[answer]" id="exercise_answer" cols="100" rows="20">
</textarea>
</td>
</tr>
<tr>
<td>
<!--
# Save the answer hash
-->
<input value="" type="hidden" id="ans_hash" />
<input type="submit" name="commit" value="Check Your Answer" onclick="checkAnswer(); return false;" />
<div id="anscheck_result"></div>
</td>
</tr>
</table>
</form>
</div>
<!-- Create and check problems -->
<script>
function loadProblem() {
let msg = getVeryShortMessage();
let msgval = textToNumber(msg);
let rsa = genRSAWithPubExp(rsa_bits, 3);
let modulus = rsa[0];
let exponent = rsa[1];
let ctext = modExp(msgval, exponent, modulus);
document.getElementById('modulus').innerHTML = modulus;
document.getElementById('exponent').innerHTML = exponent;
document.getElementById('ciphertext').innerHTML = ctext;
let answerhash = sjcl.hash.sha256.hash(msg);
document.getElementById('ans_hash').value = answerhash;
return false;
}
function checkAnswer() {
let ans = document.getElementById('exercise_answer').value;
let anshash = sjcl.hash.sha256.hash(ans);
let realanshash = document.getElementById('ans_hash').value;
if (anshash == realanshash) {
document.getElementById('anscheck_result').innerHTML = "Correct!";
}
else {
document.getElementById('anscheck_result').innerHTML = "Incorrect";
}
return false;
}
</script>
</td>
<!-- start tool panel -->
<td class="cryptoToolkit">
<iframe
src="./toolpanel.html"
frameborder="0"
scrolling="yes"
seamless="seamless"
style="display:block;
width:100%;
height:85vh;"
>
</iframe>
</td>
<!-- end tool panel -->
</tr>
</table>
</article>
<!----------------------------------------------------------------------------->
<footer>
<small>
© 2016, by Uri Blumenthal, Jeff Diewald, and Sophia Yakoubov, and 2024, by David Wilson and Nick Cunningham.
</small>
</footer>
</body>
</html>