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<?xml version="1.0" encoding="ascii"?>
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<title>Crypto.Cipher.PKCS1_v1_5</title>
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<a href="Crypto-module.html">Package Crypto</a> ::
<a href="Crypto.Cipher-module.html">Package Cipher</a> ::
Module PKCS1_v1_5
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<!-- ==================== MODULE DESCRIPTION ==================== -->
<h1 class="epydoc">Module PKCS1_v1_5</h1><p class="nomargin-top"></p>
<p>RSA encryption protocol according to PKCS#1 v1.5</p>
<p>See <a class="rst-reference external" href="http://www.ietf.org/rfc/rfc3447.txt" target="_top">RFC3447</a> or the <a class="rst-reference external" href="http://www.rsa.com/rsalabs/node.asp?id=2125." target="_top">original RSA Labs specification</a> .</p>
<p>This scheme is more properly called <tt class="rst-docutils literal"><span class="pre">RSAES-PKCS1-v1_5</span></tt>.</p>
<p><strong>If you are designing a new protocol, consider using the more robust PKCS#1 OAEP.</strong></p>
<p>As an example, a sender may encrypt a message in this way:</p>
<blockquote>
<pre class="py-doctest">
<span class="py-prompt">>>> </span><span class="py-keyword">from</span> Crypto.Cipher <span class="py-keyword">import</span> PKCS1_v1_5
<span class="py-prompt">>>> </span><span class="py-keyword">from</span> Crypto.PublicKey <span class="py-keyword">import</span> RSA
<span class="py-prompt">>>> </span><span class="py-keyword">from</span> Crypto.Hash <span class="py-keyword">import</span> SHA
<span class="py-prompt">>>></span>
<span class="py-prompt">>>> </span>message = <span class="py-string">'To be encrypted'</span>
<span class="py-prompt">>>> </span>h = SHA.new(message)
<span class="py-prompt">>>></span>
<span class="py-prompt">>>> </span>key = RSA.importKey(open(<span class="py-string">'pubkey.der'</span>).read())
<span class="py-prompt">>>> </span>cipher = PKCS1_v1_5.new(key)
<span class="py-prompt">>>> </span>ciphertext = cipher.encrypt(message+h.digest())</pre>
</blockquote>
<p>At the receiver side, decryption can be done using the private part of
the RSA key:</p>
<blockquote>
<pre class="py-doctest">
<span class="py-prompt">>>> </span>From Crypto.Hash <span class="py-keyword">import</span> SHA
<span class="py-prompt">>>> </span><span class="py-keyword">from</span> Crypto <span class="py-keyword">import</span> Random
<span class="py-prompt">>>></span>
<span class="py-prompt">>>> </span>key = RSA.importKey(open(<span class="py-string">'privkey.der'</span>).read())
<span class="py-prompt">>>></span>
<span class="py-prompt">>>> </span>dsize = SHA.digest_size
<span class="py-prompt">>>> </span>sentinel = Random.new().read(15+dsize) <span class="py-comment"># Let's assume that average data length is 15</span>
<span class="py-prompt">>>></span>
<span class="py-prompt">>>> </span>cipher = PKCS1_v1_5.new(key)
<span class="py-prompt">>>> </span>message = cipher.decrypt(ciphertext, sentinel)
<span class="py-prompt">>>></span>
<span class="py-prompt">>>> </span>digest = SHA.new(message[:-dsize]).digest()
<span class="py-prompt">>>> </span><span class="py-keyword">if</span> digest==message[-dsize:]: <span class="py-comment"># Note how we DO NOT look for the sentinel</span>
<span class="py-prompt">>>> </span> <span class="py-keyword">print</span> <span class="py-string">"Encryption was correct."</span>
<span class="py-prompt">>>> </span><span class="py-keyword">else</span>:
<span class="py-prompt">>>> </span> <span class="py-keyword">print</span> <span class="py-string">"Encryption was not correct."</span></pre>
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<a href="Crypto.Cipher.PKCS1_v1_5.PKCS115_Cipher-class.html" class="summary-name">PKCS115_Cipher</a><br />
This cipher can perform PKCS#1 v1.5 RSA encryption or decryption.
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<!-- ==================== FUNCTIONS ==================== -->
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<span class="summary-type"> </span>
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<td><span class="summary-sig"><a href="Crypto.Cipher.PKCS1_v1_5-module.html#new" class="summary-sig-name">new</a>(<span class="summary-sig-arg">key</span>)</span><br />
Return a cipher object <a href="Crypto.Cipher.PKCS1_v1_5.PKCS115_Cipher-class.html" class="link">PKCS115_Cipher</a> that can be used to perform PKCS#1 v1.5 encryption or decryption.</td>
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<!-- ==================== FUNCTION DETAILS ==================== -->
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<h3 class="epydoc"><span class="sig"><span class="sig-name">new</span>(<span class="sig-arg">key</span>)</span>
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Return a cipher object <a href="Crypto.Cipher.PKCS1_v1_5.PKCS115_Cipher-class.html" class="link">PKCS115_Cipher</a> that can be used to perform PKCS#1 v1.5 encryption or decryption.
<dl class="fields">
<dt>Parameters:</dt>
<dd><ul class="nomargin-top">
<li><strong class="pname"><code>key</code></strong> (RSA key object) - The key to use to encrypt or decrypt the message. This is a <a href="Crypto.PublicKey.RSA-module.html" class="link">Crypto.PublicKey.RSA</a> object.
Decryption is only possible if <em>key</em> is a private RSA key.</li>
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