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<a href="Crypto-module.html">Package Crypto</a> ::
<a href="Crypto.Cipher-module.html">Package Cipher</a> ::
Module DES
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<!-- ==================== MODULE DESCRIPTION ==================== -->
<h1 class="epydoc">Module DES</h1><p class="nomargin-top"></p>
<p>DES symmetric cipher</p>
<p>DES <a class="rst-reference external" href="http://en.wikipedia.org/wiki/Data_Encryption_Standard" target="_top">(Data Encryption Standard)</a> is a symmetric block cipher standardized
by <a class="rst-reference external" href="http://csrc.nist.gov/publications/fips/fips46-3/fips46-3.pdf" target="_top">NIST</a> . It has a fixed data block size of 8 bytes.
Its keys are 64 bits long, even though 8 bits were used for integrity (now they
are ignored) and do not contribute to securty.</p>
<p>DES is cryptographically secure, but its key length is too short by nowadays
standards and it could be brute forced with some effort.</p>
<p>DES should not be used for new designs. Use <a href="Crypto.Cipher.AES-module.html" class="link">AES</a>.</p>
<p>As an example, encryption can be done as follows:</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> DES3
<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 = b<span class="py-string">'Sixteen byte key'</span>
<span class="py-prompt">>>> </span>iv = Random.new().read(DES3.block_size)
<span class="py-prompt">>>> </span>cipher = DES3.new(key, DES3.MODE_OFB, iv)
<span class="py-prompt">>>> </span>plaintext = b<span class="py-string">'sona si latine loqueris '</span>
<span class="py-prompt">>>> </span>msg = iv + cipher.encrypt(plaintext)</pre>
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<span class="summary-type"> </span>
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<a href="Crypto.Cipher.DES.DESCipher-class.html" class="summary-name">DESCipher</a><br />
DES cipher object
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<span class="table-header">Functions</span></td>
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<span class="summary-type"> </span>
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<td><span class="summary-sig"><a href="Crypto.Cipher.DES-module.html#new" class="summary-sig-name">new</a>(<span class="summary-sig-arg">key</span>,
<span class="summary-sig-arg">*args</span>,
<span class="summary-sig-arg">**kwargs</span>)</span><br />
Create a new DES cipher</td>
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<span class="summary-type"> </span>
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<a name="MODE_ECB"></a><span class="summary-name">MODE_ECB</span> = <code title="1">1</code><br />
Electronic Code Book (ECB). See <a href="Crypto.Cipher.blockalgo-module.html#MODE_ECB" class="link">blockalgo.MODE_ECB</a>.
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<span class="summary-type"> </span>
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<a name="MODE_CBC"></a><span class="summary-name">MODE_CBC</span> = <code title="2">2</code><br />
Cipher-Block Chaining (CBC). See <a href="Crypto.Cipher.blockalgo-module.html#MODE_CBC" class="link">blockalgo.MODE_CBC</a>.
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<span class="summary-type"> </span>
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<a name="MODE_CFB"></a><span class="summary-name">MODE_CFB</span> = <code title="3">3</code><br />
Cipher FeedBack (CFB). See <a href="Crypto.Cipher.blockalgo-module.html#MODE_CFB" class="link">blockalgo.MODE_CFB</a>.
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<span class="summary-type"> </span>
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<a name="MODE_PGP"></a><span class="summary-name">MODE_PGP</span> = <code title="4">4</code><br />
This mode should not be used.
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<span class="summary-type"> </span>
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<a name="MODE_OFB"></a><span class="summary-name">MODE_OFB</span> = <code title="5">5</code><br />
Output FeedBack (OFB). See <a href="Crypto.Cipher.blockalgo-module.html#MODE_OFB" class="link">blockalgo.MODE_OFB</a>.
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<span class="summary-type"> </span>
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<a name="MODE_CTR"></a><span class="summary-name">MODE_CTR</span> = <code title="6">6</code><br />
CounTer Mode (CTR). See <a href="Crypto.Cipher.blockalgo-module.html#MODE_CTR" class="link">blockalgo.MODE_CTR</a>.
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<span class="summary-type"> </span>
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<a name="MODE_OPENPGP"></a><span class="summary-name">MODE_OPENPGP</span> = <code title="7">7</code><br />
OpenPGP Mode. See <a href="Crypto.Cipher.blockalgo-module.html#MODE_OPENPGP" class="link">blockalgo.MODE_OPENPGP</a>.
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<span class="summary-type"> </span>
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<a name="block_size"></a><span class="summary-name">block_size</span> = <code title="8">8</code><br />
Size of a data block (in bytes)
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<a name="key_size"></a><span class="summary-name">key_size</span> = <code title="8">8</code><br />
Size of a key (in bytes)
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<h3 class="epydoc"><span class="sig"><span class="sig-name">new</span>(<span class="sig-arg">key</span>,
<span class="sig-arg">*args</span>,
<span class="sig-arg">**kwargs</span>)</span>
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Create a new DES cipher
<dl class="fields">
<dt>Parameters:</dt>
<dd><ul class="nomargin-top">
<li><strong class="pname"><code>key</code></strong> (byte string) - The secret key to use in the symmetric cipher.
It must be 8 byte long. The parity bits will be ignored.</li>
<li><strong class="pname"><code>mode</code></strong> (a <em>MODE_*</em> constant) - The chaining mode to use for encryption or decryption.
Default is <a href="Crypto.Cipher.DES-module.html#MODE_ECB" class="link">MODE_ECB</a>.</li>
<li><p><strong class="pname"><code>IV</code></strong> (byte string) - The initialization vector to use for encryption or decryption.</p>
<p>It is ignored for <a href="Crypto.Cipher.DES-module.html#MODE_ECB" class="link">MODE_ECB</a> and <a href="Crypto.Cipher.DES-module.html#MODE_CTR" class="link">MODE_CTR</a>.</p>
<p>For <a href="Crypto.Cipher.DES-module.html#MODE_OPENPGP" class="link">MODE_OPENPGP</a>, IV must be <a href="Crypto.Cipher.DES-module.html#block_size" class="link">block_size</a> bytes long for encryption
and <a href="Crypto.Cipher.DES-module.html#block_size" class="link">block_size</a> +2 bytes for decryption (in the latter case, it is
actually the <em>encrypted</em> IV which was prefixed to the ciphertext).
It is mandatory.</p>
<p>For all other modes, it must be <a href="Crypto.Cipher.DES-module.html#block_size" class="link">block_size</a> bytes longs.</p></li>
<li><strong class="pname"><code>counter</code></strong> (callable) - (<em>Only</em> <a href="Crypto.Cipher.DES-module.html#MODE_CTR" class="link">MODE_CTR</a>). A stateful function that returns the next
<em>counter block</em>, which is a byte string of <a href="Crypto.Cipher.DES-module.html#block_size" class="link">block_size</a> bytes.
For better performance, use <a href="Crypto.Util.Counter-module.html" class="link">Crypto.Util.Counter</a>.</li>
<li><strong class="pname"><code>segment_size</code></strong> (integer) - (<em>Only</em> <a href="Crypto.Cipher.DES-module.html#MODE_CFB" class="link">MODE_CFB</a>).The number of bits the plaintext and ciphertext
are segmented in.
It must be a multiple of 8. If 0 or not specified, it will be assumed to be 8.</li>
</ul></dd>
<dt>Returns:</dt>
<dd>an <a href="Crypto.Cipher.DES.DESCipher-class.html" class="link">DESCipher</a> object</dd>
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