1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
|
<?xml version="1.0" encoding="ascii"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
<head>
<title>Crypto.PublicKey.DSA</title>
<link rel="stylesheet" href="epydoc.css" type="text/css" />
<script type="text/javascript" src="epydoc.js"></script>
</head>
<body bgcolor="white" text="black" link="blue" vlink="#204080"
alink="#204080">
<!-- ==================== NAVIGATION BAR ==================== -->
<table class="navbar" border="0" width="100%" cellpadding="0"
bgcolor="#a0c0ff" cellspacing="0">
<tr valign="middle">
<!-- Home link -->
<th> <a
href="Crypto-module.html">Home</a> </th>
<!-- Tree link -->
<th> <a
href="module-tree.html">Trees</a> </th>
<!-- Index link -->
<th> <a
href="identifier-index.html">Indices</a> </th>
<!-- Help link -->
<th> <a
href="help.html">Help</a> </th>
<!-- Project homepage -->
<th class="navbar" align="right" width="100%">
<table border="0" cellpadding="0" cellspacing="0">
<tr><th class="navbar" align="center"
><a href="http://www.pycrypto.org/">PyCrypto.org</a></th>
</tr></table></th>
</tr>
</table>
<table width="100%" cellpadding="0" cellspacing="0">
<tr valign="top">
<td width="100%">
<span class="breadcrumbs">
<a href="Crypto-module.html">Package Crypto</a> ::
<a href="Crypto.PublicKey-module.html">Package PublicKey</a> ::
Module DSA
</span>
</td>
<td>
<table cellpadding="0" cellspacing="0">
<!-- hide/show private -->
<tr><td align="right"><span class="options"
>[<a href="frames.html" target="_top">frames</a
>] | <a href="Crypto.PublicKey.DSA-module.html"
target="_top">no frames</a>]</span></td></tr>
</table>
</td>
</tr>
</table>
<!-- ==================== MODULE DESCRIPTION ==================== -->
<h1 class="epydoc">Module DSA</h1><p class="nomargin-top"></p>
<p>DSA public-key signature algorithm.</p>
<p><a class="rst-reference external" href="http://en.wikipedia.org/wiki/Digital_Signature_Algorithm" target="_top">DSA</a> is a widespread public-key signature algorithm. Its security is
based on the discrete logarithm problem (<a class="rst-reference external" href="http://www.cosic.esat.kuleuven.be/publications/talk-78.pdf" target="_top">DLP</a>). Given a cyclic
group, a generator <em>g</em>, and an element <em>h</em>, it is hard
to find an integer <em>x</em> such that <em>g^x = h</em>. The problem is believed
to be difficult, and it has been proved such (and therefore secure) for
more than 30 years.</p>
<p>The group is actually a sub-group over the integers modulo <em>p</em>, with <em>p</em> prime.
The sub-group order is <em>q</em>, which is prime too; it always holds that <em>(p-1)</em> is a multiple of <em>q</em>.
The cryptographic strength is linked to the magnitude of <em>p</em> and <em>q</em>.
The signer holds a value <em>x</em> (<em>0<x<q-1</em>) as private key, and its public
key (<em>y</em> where <em>y=g^x mod p</em>) is distributed.</p>
<p>In 2012, a sufficient size is deemed to be 2048 bits for <em>p</em> and 256 bits for <em>q</em>.
For more information, see the most recent <a class="rst-reference external" href="http://www.ecrypt.eu.org/documents/D.SPA.17.pdf" target="_top">ECRYPT</a> report.</p>
<p>DSA is reasonably secure for new designs.</p>
<p>The algorithm can only be used for authentication (digital signature).
DSA cannot be used for confidentiality (encryption).</p>
<p>The values <em>(p,q,g)</em> are called <em>domain parameters</em>;
they are not sensitive but must be shared by both parties (the signer and the verifier).
Different signers can share the same domain parameters with no security
concerns.</p>
<p>The DSA signature is twice as big as the size of <em>q</em> (64 bytes if <em>q</em> is 256 bit
long).</p>
<p>This module provides facilities for generating new DSA keys and for constructing
them from known components. DSA keys allows you to perform basic signing and
verification.</p>
<blockquote>
<pre class="py-doctest">
<span class="py-prompt">>>> </span><span class="py-keyword">from</span> Crypto.Random <span class="py-keyword">import</span> random
<span class="py-prompt">>>> </span><span class="py-keyword">from</span> Crypto.PublicKey <span class="py-keyword">import</span> DSA
<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">"Hello"</span>
<span class="py-prompt">>>> </span>key = DSA.generate(1024)
<span class="py-prompt">>>> </span>h = SHA.new(message).digest()
<span class="py-prompt">>>> </span>k = random.StrongRandom().randint(1,key.q-1)
<span class="py-prompt">>>> </span>sig = key.sign(h,k)
<span class="py-prompt">>>> </span>...
<span class="py-prompt">>>> </span><span class="py-keyword">if</span> key.verify(h,sig):
<span class="py-prompt">>>> </span> <span class="py-keyword">print</span> <span class="py-string">"OK"</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">"Incorrect signature"</span></pre>
</blockquote>
<!-- ==================== CLASSES ==================== -->
<a name="section-Classes"></a>
<table class="summary" 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">Classes</span></td>
</tr>
<tr>
<td width="15%" align="right" valign="top" class="summary">
<span class="summary-type"> </span>
</td><td class="summary">
<a href="Crypto.PublicKey.DSA._DSAobj-class.html" class="summary-name">_DSAobj</a><br />
Class defining an actual DSA key.
</td>
</tr>
<tr>
<td width="15%" align="right" valign="top" class="summary">
<span class="summary-type"> </span>
</td><td class="summary">
<a href="Crypto.PublicKey.DSA.DSAImplementation-class.html" class="summary-name">DSAImplementation</a><br />
A DSA key factory.
</td>
</tr>
<tr>
<td width="15%" align="right" valign="top" class="summary">
<span class="summary-type"> </span>
</td><td class="summary">
<a href="Crypto.PublicKey.RSA.error-class.html" class="summary-name">error</a>
</td>
</tr>
</table>
<!-- ==================== FUNCTIONS ==================== -->
<a name="section-Functions"></a>
<table class="summary" 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">Functions</span></td>
</tr>
<tr>
<td width="15%" align="right" valign="top" class="summary">
<span class="summary-type"> </span>
</td><td class="summary">
<table width="100%" cellpadding="0" cellspacing="0" border="0">
<tr>
<td><span class="summary-sig"><a href="Crypto.PublicKey.DSA-module.html#generate" class="summary-sig-name">generate</a>(<span class="summary-sig-arg">bits</span>,
<span class="summary-sig-arg">randfunc</span>=<span class="summary-sig-default">None</span>,
<span class="summary-sig-arg">progress_func</span>=<span class="summary-sig-default">None</span>)</span><br />
Randomly generate a fresh, new DSA key.</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">
<table width="100%" cellpadding="0" cellspacing="0" border="0">
<tr>
<td><span class="summary-sig"><a href="Crypto.PublicKey.DSA-module.html#construct" class="summary-sig-name">construct</a>(<span class="summary-sig-arg">tup</span>)</span><br />
Construct a DSA key from a tuple of valid DSA components.</td>
<td align="right" valign="top">
</td>
</tr>
</table>
</td>
</tr>
</table>
<!-- ==================== FUNCTION DETAILS ==================== -->
<a name="section-FunctionDetails"></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">Function Details</span></td>
</tr>
</table>
<a name="generate"></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">generate</span>(<span class="sig-arg">bits</span>,
<span class="sig-arg">randfunc</span>=<span class="sig-default">None</span>,
<span class="sig-arg">progress_func</span>=<span class="sig-default">None</span>)</span>
</h3>
</td><td align="right" valign="top"
>
</td>
</tr></table>
Randomly generate a fresh, new DSA key.
<dl class="fields">
<dt>Parameters:</dt>
<dd><ul class="nomargin-top">
<li><strong class="pname"><code>bits</code></strong> (int) - Key length, or size (in bits) of the DSA modulus
<em>p</em>.
It must be a multiple of 64, in the closed
interval [512,1024].</li>
<li><strong class="pname"><code>randfunc</code></strong> (callable) - Random number generation function; it should accept
a single integer N and return a string of random data
N bytes long.
If not specified, a new one will be instantiated
from <tt class="rst-docutils literal">Crypto.Random</tt>.</li>
<li><strong class="pname"><code>progress_func</code></strong> (callable) - Optional function that will be called with a short string
containing the key parameter currently being generated;
it's useful for interactive applications where a user is
waiting for a key to be generated.</li>
</ul></dd>
<dt>Returns:</dt>
<dd>A DSA key object (<a href="Crypto.PublicKey.DSA._DSAobj-class.html" class="link">_DSAobj</a>).</dd>
<dt>Raises:</dt>
<dd><ul class="nomargin-top">
<li><code><strong class='fraise'>ValueError</strong></code> - When <strong>bits</strong> is too little, too big, or not a multiple of 64.</li>
</ul></dd>
</dl>
<div class="fields"> <p><strong>Attention:</strong>
You should always use a cryptographically secure random number generator,
such as the one defined in the <tt class="rst-docutils literal">Crypto.Random</tt> module; <strong>don't</strong> just use the
current time and the <tt class="rst-docutils literal">random</tt> module.
</p>
</div></td></tr></table>
</div>
<a name="construct"></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">construct</span>(<span class="sig-arg">tup</span>)</span>
</h3>
</td><td align="right" valign="top"
>
</td>
</tr></table>
<p>Construct a DSA key from a tuple of valid DSA components.</p>
<p>The modulus <em>p</em> must be a prime.</p>
<p>The following equations must apply:</p>
<ul class="rst-simple">
<li>p-1 = 0 mod q</li>
<li>g^x = y mod p</li>
<li>0 < x < q</li>
<li>1 < g < p</li>
</ul>
<dl class="fields">
<dt>Parameters:</dt>
<dd><ul class="nomargin-top">
<li><p><strong class="pname"><code>tup</code></strong> (tuple) - A tuple of long integers, with 4 or 5 items
in the following order:</p>
<ol class="rst-arabic simple">
<li>Public key (<em>y</em>).</li>
<li>Sub-group generator (<em>g</em>).</li>
<li>Modulus, finite field order (<em>p</em>).</li>
<li>Sub-group order (<em>q</em>).</li>
<li>Private key (<em>x</em>). Optional.</li>
</ol></li>
</ul></dd>
<dt>Returns:</dt>
<dd>A DSA key object (<a href="Crypto.PublicKey.DSA._DSAobj-class.html" class="link">_DSAobj</a>).</dd>
</dl>
</td></tr></table>
</div>
<br />
<!-- ==================== NAVIGATION BAR ==================== -->
<table class="navbar" border="0" width="100%" cellpadding="0"
bgcolor="#a0c0ff" cellspacing="0">
<tr valign="middle">
<!-- Home link -->
<th> <a
href="Crypto-module.html">Home</a> </th>
<!-- Tree link -->
<th> <a
href="module-tree.html">Trees</a> </th>
<!-- Index link -->
<th> <a
href="identifier-index.html">Indices</a> </th>
<!-- Help link -->
<th> <a
href="help.html">Help</a> </th>
<!-- Project homepage -->
<th class="navbar" align="right" width="100%">
<table border="0" cellpadding="0" cellspacing="0">
<tr><th class="navbar" align="center"
><a href="http://www.pycrypto.org/">PyCrypto.org</a></th>
</tr></table></th>
</tr>
</table>
<table border="0" cellpadding="0" cellspacing="0" width="100%%">
<tr>
<td align="left" class="footer">
Generated by Epydoc 3.0.1 on Thu May 24 09:02:36 2012
</td>
<td align="right" class="footer">
<a target="mainFrame" href="http://epydoc.sourceforge.net"
>http://epydoc.sourceforge.net</a>
</td>
</tr>
</table>
<script type="text/javascript">
<!--
// Private objects are initially displayed (because if
// javascript is turned off then we want them to be
// visible); but by default, we want to hide them. So hide
// them unless we have a cookie that says to show them.
checkCookie();
// -->
</script>
</body>
</html>
|
