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<?xml version="1.0" encoding="ascii"?>
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  <title>Crypto.Cipher.ARC2</title>
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        <a href="Crypto-module.html">Package&nbsp;Crypto</a> ::
        <a href="Crypto.Cipher-module.html">Package&nbsp;Cipher</a> ::
        Module&nbsp;ARC2
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<!-- ==================== MODULE DESCRIPTION ==================== -->
<h1 class="epydoc">Module ARC2</h1><p class="nomargin-top"></p>
<p>RC2 symmetric cipher</p>
<p><a class="rst-reference external" href="http://en.wikipedia.org/wiki/RC2" target="_top">RC2</a> (Rivest's Cipher version 2)  is a symmetric block cipher designed
by Ron Rivest in 1987. The cipher started as a proprietary design,
that was reverse engineered and anonymously posted on Usenet in 1996.
For this reason, the algorithm was first called <em>Alleged</em> RC2 (ARC2),
since the company that owned RC2 (RSA Data Inc.) did not confirm whether
the details leaked into public domain were really correct.</p>
<p>The company eventually published its full specification in <a class="rst-reference external" href="http://tools.ietf.org/html/rfc2268" target="_top">RFC2268</a>.</p>
<p>RC2 has a fixed data block size of 8 bytes. Length of its keys can vary from
8 to 128 bits. One particular property of RC2 is that the actual
cryptographic strength of the key (<em>effective key length</em>) can be reduced
via a parameter.</p>
<p>Even though RC2 is not cryptographically broken, it has not been analyzed as
thoroughly as AES, which is also faster than RC2.</p>
<p>New designs should not use RC2.</p>
<p>As an example, encryption can be done as follows:</p>
<blockquote>
<pre class="py-doctest">
<span class="py-prompt">&gt;&gt;&gt; </span><span class="py-keyword">from</span> Crypto.Cipher <span class="py-keyword">import</span> ARC2
<span class="py-prompt">&gt;&gt;&gt; </span><span class="py-keyword">from</span> Crypto <span class="py-keyword">import</span> Random
<span class="py-prompt">&gt;&gt;&gt;</span>
<span class="py-prompt">&gt;&gt;&gt; </span>key = b<span class="py-string">'Sixteen byte key'</span>
<span class="py-prompt">&gt;&gt;&gt; </span>iv = Random.new().read(ARC2.block_size)
<span class="py-prompt">&gt;&gt;&gt; </span>cipher = ARC2.new(key, ARC2.MODE_CFB, iv)
<span class="py-prompt">&gt;&gt;&gt; </span>msg = iv + cipher.encrypt(b<span class="py-string">'Attack at dawn'</span>)</pre>
</blockquote>

<!-- ==================== CLASSES ==================== -->
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      <span class="summary-type">&nbsp;</span>
    </td><td class="summary">
        <a href="Crypto.Cipher.ARC2.RC2Cipher-class.html" class="summary-name">RC2Cipher</a><br />
      RC2 cipher object
    </td>
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<!-- ==================== FUNCTIONS ==================== -->
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    <span class="table-header">Functions</span></td>
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      <span class="summary-type">&nbsp;</span>
    </td><td class="summary">
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          <td><span class="summary-sig"><a href="Crypto.Cipher.ARC2-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 RC2 cipher</td>
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          </td>
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    </td>
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<!-- ==================== VARIABLES ==================== -->
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    <span class="table-header">Variables</span></td>
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      <span class="summary-type">&nbsp;</span>
    </td><td class="summary">
        <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>.
    </td>
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      <span class="summary-type">&nbsp;</span>
    </td><td class="summary">
        <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>.
    </td>
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      <span class="summary-type">&nbsp;</span>
    </td><td class="summary">
        <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>.
    </td>
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      <span class="summary-type">&nbsp;</span>
    </td><td class="summary">
        <a name="MODE_PGP"></a><span class="summary-name">MODE_PGP</span> = <code title="4">4</code><br />
      This mode should not be used.
    </td>
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    <td width="15%" align="right" valign="top" class="summary">
      <span class="summary-type">&nbsp;</span>
    </td><td class="summary">
        <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>.
    </td>
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      <span class="summary-type">&nbsp;</span>
    </td><td class="summary">
        <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>.
    </td>
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      <span class="summary-type">&nbsp;</span>
    </td><td class="summary">
        <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>.
    </td>
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      <span class="summary-type">&nbsp;</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)
    </td>
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      <span class="summary-type">&nbsp;</span>
    </td><td class="summary">
        <a name="key_size"></a><span class="summary-name">key_size</span> = <code title="xrange(1, 17)">xrange(1, 17)</code><br />
      Size of a key (in bytes)
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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 class="sig-arg">*args</span>,
        <span class="sig-arg">**kwargs</span>)</span>
  </h3>
  </td><td align="right" valign="top"
    >&nbsp;
    </td>
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  Create a new RC2 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.
Its length can vary from 1 to 128 bytes.</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.ARC2-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.ARC2-module.html#MODE_ECB" class="link">MODE_ECB</a> and <a href="Crypto.Cipher.ARC2-module.html#MODE_CTR" class="link">MODE_CTR</a>.</p>
<p>For <a href="Crypto.Cipher.ARC2-module.html#MODE_OPENPGP" class="link">MODE_OPENPGP</a>, IV must be <a href="Crypto.Cipher.ARC2-module.html#block_size" class="link">block_size</a> bytes long for encryption
and <a href="Crypto.Cipher.ARC2-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.ARC2-module.html#block_size" class="link">block_size</a> bytes longs. It is optional and
when not present it will be given a default value of all zeroes.</p></li>
        <li><strong class="pname"><code>counter</code></strong> (callable) - (<em>Only</em> <a href="Crypto.Cipher.ARC2-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.ARC2-module.html#block_size" class="link">block_size</a> bytes.
For better performance, use <a href="Crypto.Util.Counter-module.html" class="link" onclick="show_private();">Crypto.Util.Counter</a>.</li>
        <li><strong class="pname"><code>segment_size</code></strong> (integer) - (<em>Only</em> <a href="Crypto.Cipher.ARC2-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>
        <li><strong class="pname"><code>effective_keylen</code></strong> (integer) - Maximum cryptographic strength of the key, in bits.
It can vary from 0 to 1024. The default value is 1024.</li>
    </ul></dd>
    <dt>Returns:</dt>
        <dd>an <a href="Crypto.Cipher.ARC2.RC2Cipher-class.html" class="link">RC2Cipher</a> object</dd>
  </dl>
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