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<a href="Crypto-module.html">Package Crypto</a> ::
<a href="Crypto.PublicKey-module.html">Package PublicKey</a> ::
<a href="Crypto.PublicKey.ElGamal-module.html">Module ElGamal</a> ::
Class ElGamalobj
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<!-- ==================== CLASS DESCRIPTION ==================== -->
<h1 class="epydoc">Class ElGamalobj</h1><p class="nomargin-top"></p>
<pre class="base-tree">
pubkey.pubkey --+
|
<strong class="uidshort">ElGamalobj</strong>
</pre>
<hr />
Class defining an ElGamal key.
<!-- ==================== INSTANCE METHODS ==================== -->
<a name="section-InstanceMethods"></a>
<table class="summary" border="1" cellpadding="3"
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<span class="table-header">Instance Methods</span></td>
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<span class="summary-type"> </span>
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<td><span class="summary-sig"><a href="Crypto.PublicKey.ElGamal.ElGamalobj-class.html#encrypt" class="summary-sig-name">encrypt</a>(<span class="summary-sig-arg">self</span>,
<span class="summary-sig-arg">plaintext</span>,
<span class="summary-sig-arg">K</span>)</span><br />
Encrypt a piece of data with ElGamal.</td>
<td align="right" valign="top">
</td>
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</td>
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<tr>
<td width="15%" align="right" valign="top" class="summary">
<span class="summary-type"> </span>
</td><td class="summary">
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<td><span class="summary-sig"><a href="Crypto.PublicKey.ElGamal.ElGamalobj-class.html#decrypt" class="summary-sig-name">decrypt</a>(<span class="summary-sig-arg">self</span>,
<span class="summary-sig-arg">ciphertext</span>)</span><br />
Decrypt a piece of data with ElGamal.</td>
<td align="right" valign="top">
</td>
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<span class="summary-type"> </span>
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<td><span class="summary-sig"><a href="Crypto.PublicKey.ElGamal.ElGamalobj-class.html#sign" class="summary-sig-name">sign</a>(<span class="summary-sig-arg">self</span>,
<span class="summary-sig-arg">M</span>,
<span class="summary-sig-arg">K</span>)</span><br />
Sign a piece of data with ElGamal.</td>
<td align="right" valign="top">
</td>
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</td>
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<td width="15%" align="right" valign="top" class="summary">
<span class="summary-type"> </span>
</td><td class="summary">
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<tr>
<td><span class="summary-sig"><a href="Crypto.PublicKey.ElGamal.ElGamalobj-class.html#verify" class="summary-sig-name">verify</a>(<span class="summary-sig-arg">self</span>,
<span class="summary-sig-arg">M</span>,
<span class="summary-sig-arg">signature</span>)</span><br />
Verify the validity of an ElGamal signature.</td>
<td align="right" valign="top">
</td>
</tr>
</table>
</td>
</tr>
<tr>
<td width="15%" align="right" valign="top" class="summary">
<span class="summary-type"> </span>
</td><td class="summary">
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<td><span class="summary-sig"><a href="Crypto.PublicKey.ElGamal.ElGamalobj-class.html#size" class="summary-sig-name">size</a>(<span class="summary-sig-arg">self</span>)</span><br />
Tell the maximum number of bits that can be handled by this key.</td>
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</td>
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</td>
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<span class="summary-type"> </span>
</td><td class="summary">
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<td><span class="summary-sig"><a href="Crypto.PublicKey.ElGamal.ElGamalobj-class.html#has_private" class="summary-sig-name">has_private</a>(<span class="summary-sig-arg">self</span>)</span><br />
Tell if the key object contains private components.</td>
<td align="right" valign="top">
</td>
</tr>
</table>
</td>
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<tr>
<td width="15%" align="right" valign="top" class="summary">
<span class="summary-type"> </span>
</td><td class="summary">
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<tr>
<td><span class="summary-sig"><a href="Crypto.PublicKey.ElGamal.ElGamalobj-class.html#publickey" class="summary-sig-name">publickey</a>(<span class="summary-sig-arg">self</span>)</span><br />
Construct a new key carrying only the public information.</td>
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</td>
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</table>
</td>
</tr>
<tr>
<td colspan="2" class="summary">
<p class="indent-wrapped-lines"><b>Inherited from <code>pubkey.pubkey</code></b>:
<code>__init__</code>,
<code>blind</code>,
<code>can_blind</code>,
<code>can_encrypt</code>,
<code>can_sign</code>,
<code>unblind</code>
</p>
</td>
</tr>
</table>
<!-- ==================== CLASS VARIABLES ==================== -->
<a name="section-ClassVariables"></a>
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cellspacing="0" width="100%" bgcolor="white">
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<td align="left" colspan="2" class="table-header">
<span class="table-header">Class Variables</span></td>
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<span class="summary-type"> </span>
</td><td class="summary">
<a href="Crypto.PublicKey.ElGamal.ElGamalobj-class.html#keydata" class="summary-name">keydata</a> = <code title="['p', 'g', 'y', 'x']"><code class="variable-group">[</code><code class="variable-quote">'</code><code class="variable-string">p</code><code class="variable-quote">'</code><code class="variable-op">, </code><code class="variable-quote">'</code><code class="variable-string">g</code><code class="variable-quote">'</code><code class="variable-op">, </code><code class="variable-quote">'</code><code class="variable-string">y</code><code class="variable-quote">'</code><code class="variable-op">, </code><code class="variable-quote">'</code><code class="variable-string">x</code><code class="variable-quote">'</code><code class="variable-group">]</code></code><br />
Dictionary of ElGamal parameters.
</td>
</tr>
</table>
<!-- ==================== METHOD DETAILS ==================== -->
<a name="section-MethodDetails"></a>
<table class="details" border="1" cellpadding="3"
cellspacing="0" width="100%" bgcolor="white">
<tr bgcolor="#70b0f0" class="table-header">
<td align="left" colspan="2" class="table-header">
<span class="table-header">Method Details</span></td>
</tr>
</table>
<a name="encrypt"></a>
<div>
<table class="details" border="1" cellpadding="3"
cellspacing="0" width="100%" bgcolor="white">
<tr><td>
<table width="100%" cellpadding="0" cellspacing="0" border="0">
<tr valign="top"><td>
<h3 class="epydoc"><span class="sig"><span class="sig-name">encrypt</span>(<span class="sig-arg">self</span>,
<span class="sig-arg">plaintext</span>,
<span class="sig-arg">K</span>)</span>
</h3>
</td><td align="right" valign="top"
>
</td>
</tr></table>
Encrypt a piece of data with ElGamal.
<dl class="fields">
<dt>Parameters:</dt>
<dd><ul class="nomargin-top">
<li><strong class="pname"><code>plaintext</code></strong> (byte string or long) - The piece of data to encrypt with ElGamal.
It must be numerically smaller than the module (<em>p</em>).</li>
<li><strong class="pname"><code>K</code></strong> (long (recommended) or byte string (not recommended)) - A secret number, chosen randomly in the closed
range <em>[1,p-2]</em>.</li>
</ul></dd>
<dt>Returns:</dt>
<dd>A tuple with two items. Each item is of the same type as the
plaintext (string or long).</dd>
<dt>Overrides:
pubkey.pubkey.encrypt
</dt>
</dl>
<div class="fields"> <strong>Attention:</strong>
<ul class="nomargin-top">
<li>
selection of <em>K</em> is crucial for security. Generating a
random number larger than <em>p-1</em> and taking the modulus by <em>p-1</em> is
<strong>not</strong> secure, since smaller values will occur more frequently.
Generating a random number systematically smaller than <em>p-1</em>
(e.g. <em>floor((p-1)/8)</em> random bytes) is also <strong>not</strong> secure.
In general, it shall not be possible for an attacker to know
the value of any bit of K.
</li>
<li>
The number <em>K</em> shall not be reused for any other
operation and shall be discarded immediately.
</li>
</ul>
</div></td></tr></table>
</div>
<a name="decrypt"></a>
<div>
<table class="details" border="1" cellpadding="3"
cellspacing="0" width="100%" bgcolor="white">
<tr><td>
<table width="100%" cellpadding="0" cellspacing="0" border="0">
<tr valign="top"><td>
<h3 class="epydoc"><span class="sig"><span class="sig-name">decrypt</span>(<span class="sig-arg">self</span>,
<span class="sig-arg">ciphertext</span>)</span>
</h3>
</td><td align="right" valign="top"
>
</td>
</tr></table>
Decrypt a piece of data with ElGamal.
<dl class="fields">
<dt>Parameters:</dt>
<dd><ul class="nomargin-top">
<li><strong class="pname"><code>ciphertext</code></strong> (byte string, long or a 2-item tuple as returned
by <a href="Crypto.PublicKey.ElGamal.ElGamalobj-class.html#encrypt" class="link">encrypt</a>) - The piece of data to decrypt with ElGamal.</li>
</ul></dd>
<dt>Returns:</dt>
<dd>A byte string if ciphertext was a byte string or a tuple
of byte strings. A long otherwise.</dd>
<dt>Overrides:
pubkey.pubkey.decrypt
</dt>
</dl>
</td></tr></table>
</div>
<a name="sign"></a>
<div>
<table class="details" border="1" cellpadding="3"
cellspacing="0" width="100%" bgcolor="white">
<tr><td>
<table width="100%" cellpadding="0" cellspacing="0" border="0">
<tr valign="top"><td>
<h3 class="epydoc"><span class="sig"><span class="sig-name">sign</span>(<span class="sig-arg">self</span>,
<span class="sig-arg">M</span>,
<span class="sig-arg">K</span>)</span>
</h3>
</td><td align="right" valign="top"
>
</td>
</tr></table>
Sign a piece of data with ElGamal.
<dl class="fields">
<dt>Parameters:</dt>
<dd><ul class="nomargin-top">
<li><strong class="pname"><code>M</code></strong> (byte string or long) - The piece of data to sign with ElGamal. It may
not be longer in bit size than <em>p-1</em>.</li>
<li><strong class="pname"><code>K</code></strong> (long (recommended) or byte string (not recommended)) - A secret number, chosen randomly in the closed
range <em>[1,p-2]</em> and such that <em>gcd(k,p-1)=1</em>.</li>
</ul></dd>
<dt>Returns:</dt>
<dd>A tuple with 2 longs.</dd>
<dt>Overrides:
pubkey.pubkey.sign
</dt>
</dl>
<div class="fields"> <strong>Attention:</strong>
<ul class="nomargin-top">
<li>
selection of <em>K</em> is crucial for security. Generating a
random number larger than <em>p-1</em> and taking the modulus by <em>p-1</em> is
<strong>not</strong> secure, since smaller values will occur more frequently.
Generating a random number systematically smaller than <em>p-1</em>
(e.g. <em>floor((p-1)/8)</em> random bytes) is also <strong>not</strong> secure.
In general, it shall not be possible for an attacker to know
the value of any bit of K.
</li>
<li>
The number <em>K</em> shall not be reused for any other
operation and shall be discarded immediately.
</li>
<li>
M must be be a cryptographic hash, otherwise an
attacker may mount an existential forgery attack.
</li>
</ul>
</div></td></tr></table>
</div>
<a name="verify"></a>
<div>
<table class="details" border="1" cellpadding="3"
cellspacing="0" width="100%" bgcolor="white">
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<table width="100%" cellpadding="0" cellspacing="0" border="0">
<tr valign="top"><td>
<h3 class="epydoc"><span class="sig"><span class="sig-name">verify</span>(<span class="sig-arg">self</span>,
<span class="sig-arg">M</span>,
<span class="sig-arg">signature</span>)</span>
</h3>
</td><td align="right" valign="top"
>
</td>
</tr></table>
Verify the validity of an ElGamal signature.
<dl class="fields">
<dt>Parameters:</dt>
<dd><ul class="nomargin-top">
<li><strong class="pname"><code>M</code></strong> (byte string or long) - The expected message.</li>
<li><strong class="pname"><code>signature</code></strong> (A tuple with 2 longs as return by <a href="Crypto.PublicKey.ElGamal.ElGamalobj-class.html#sign" class="link">sign</a>) - The ElGamal signature to verify.</li>
</ul></dd>
<dt>Returns:</dt>
<dd>True if the signature is correct, False otherwise.</dd>
<dt>Overrides:
pubkey.pubkey.verify
</dt>
</dl>
</td></tr></table>
</div>
<a name="size"></a>
<div>
<table class="details" border="1" cellpadding="3"
cellspacing="0" width="100%" bgcolor="white">
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<table width="100%" cellpadding="0" cellspacing="0" border="0">
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<h3 class="epydoc"><span class="sig"><span class="sig-name">size</span>(<span class="sig-arg">self</span>)</span>
</h3>
</td><td align="right" valign="top"
>
</td>
</tr></table>
Tell the maximum number of bits that can be handled by this key.
<dl class="fields">
<dt>Returns:</dt>
<dd>int</dd>
<dt>Overrides:
pubkey.pubkey.size
<dd><em class="note">(inherited documentation)</em></dd>
</dt>
</dl>
</td></tr></table>
</div>
<a name="has_private"></a>
<div>
<table class="details" border="1" cellpadding="3"
cellspacing="0" width="100%" bgcolor="white">
<tr><td>
<table width="100%" cellpadding="0" cellspacing="0" border="0">
<tr valign="top"><td>
<h3 class="epydoc"><span class="sig"><span class="sig-name">has_private</span>(<span class="sig-arg">self</span>)</span>
</h3>
</td><td align="right" valign="top"
>
</td>
</tr></table>
Tell if the key object contains private components.
<dl class="fields">
<dt>Returns:</dt>
<dd>bool</dd>
<dt>Overrides:
pubkey.pubkey.has_private
<dd><em class="note">(inherited documentation)</em></dd>
</dt>
</dl>
</td></tr></table>
</div>
<a name="publickey"></a>
<div>
<table class="details" border="1" cellpadding="3"
cellspacing="0" width="100%" bgcolor="white">
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<table width="100%" cellpadding="0" cellspacing="0" border="0">
<tr valign="top"><td>
<h3 class="epydoc"><span class="sig"><span class="sig-name">publickey</span>(<span class="sig-arg">self</span>)</span>
</h3>
</td><td align="right" valign="top"
>
</td>
</tr></table>
Construct a new key carrying only the public information.
<dl class="fields">
<dt>Returns:</dt>
<dd>A new pubkey object.</dd>
<dt>Overrides:
pubkey.pubkey.publickey
<dd><em class="note">(inherited documentation)</em></dd>
</dt>
</dl>
</td></tr></table>
</div>
<br />
<!-- ==================== CLASS VARIABLE DETAILS ==================== -->
<a name="section-ClassVariableDetails"></a>
<table class="details" border="1" cellpadding="3"
cellspacing="0" width="100%" bgcolor="white">
<tr bgcolor="#70b0f0" class="table-header">
<td align="left" colspan="2" class="table-header">
<span class="table-header">Class Variable Details</span></td>
</tr>
</table>
<a name="keydata"></a>
<div>
<table class="details" border="1" cellpadding="3"
cellspacing="0" width="100%" bgcolor="white">
<tr><td>
<h3 class="epydoc">keydata</h3>
<p>Dictionary of ElGamal parameters.</p>
<p>A public key will only have the following entries:</p>
<blockquote>
<ul class="rst-simple">
<li><strong>y</strong>, the public key.</li>
<li><strong>g</strong>, the generator.</li>
<li><strong>p</strong>, the modulus.</li>
</ul>
</blockquote>
<p>A private key will also have:</p>
<blockquote>
<ul class="rst-simple">
<li><strong>x</strong>, the private key.</li>
</ul>
</blockquote>
<dl class="fields">
</dl>
<dl class="fields">
<dt>Value:</dt>
<dd><table><tr><td><pre class="variable">
<code class="variable-group">[</code><code class="variable-quote">'</code><code class="variable-string">p</code><code class="variable-quote">'</code><code class="variable-op">, </code><code class="variable-quote">'</code><code class="variable-string">g</code><code class="variable-quote">'</code><code class="variable-op">, </code><code class="variable-quote">'</code><code class="variable-string">y</code><code class="variable-quote">'</code><code class="variable-op">, </code><code class="variable-quote">'</code><code class="variable-string">x</code><code class="variable-quote">'</code><code class="variable-group">]</code>
</pre></td></tr></table>
</dd>
</dl>
</td></tr></table>
</div>
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