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
|
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<!-- This manual is last updated 3 June 2013 for version
3.2.1 of GnuTLS.
Copyright (C) 2001-2013 Free Software Foundation, Inc.\\
Copyright (C) 2001-2013 Nikos Mavrogiannopoulos
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3 or
any later version published by the Free Software Foundation; with no
Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A
copy of the license is included in the section entitled "GNU Free
Documentation License". -->
<!-- Created by GNU Texinfo 5.1, http://www.gnu.org/software/texinfo/ -->
<head>
<title>GnuTLS 3.2.1: X.509 certificate structure</title>
<meta name="description" content="GnuTLS 3.2.1: X.509 certificate structure">
<meta name="keywords" content="GnuTLS 3.2.1: X.509 certificate structure">
<meta name="resource-type" content="document">
<meta name="distribution" content="global">
<meta name="Generator" content="makeinfo">
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<link href="index.html#Top" rel="start" title="Top">
<link href="Function-and-Data-Index.html#Function-and-Data-Index" rel="index" title="Function and Data Index">
<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
<link href="X_002e509-certificates.html#X_002e509-certificates" rel="up" title="X.509 certificates">
<link href="Importing-an-X_002e509-certificate.html#Importing-an-X_002e509-certificate" rel="next" title="Importing an X.509 certificate">
<link href="X_002e509-certificates.html#X_002e509-certificates" rel="previous" title="X.509 certificates">
<style type="text/css">
<!--
a.summary-letter {text-decoration: none}
blockquote.smallquotation {font-size: smaller}
div.display {margin-left: 3.2em}
div.example {margin-left: 3.2em}
div.indentedblock {margin-left: 3.2em}
div.lisp {margin-left: 3.2em}
div.smalldisplay {margin-left: 3.2em}
div.smallexample {margin-left: 3.2em}
div.smallindentedblock {margin-left: 3.2em; font-size: smaller}
div.smalllisp {margin-left: 3.2em}
kbd {font-style:oblique}
pre.display {font-family: inherit}
pre.format {font-family: inherit}
pre.menu-comment {font-family: serif}
pre.menu-preformatted {font-family: serif}
pre.smalldisplay {font-family: inherit; font-size: smaller}
pre.smallexample {font-size: smaller}
pre.smallformat {font-family: inherit; font-size: smaller}
pre.smalllisp {font-size: smaller}
span.nocodebreak {white-space:nowrap}
span.nolinebreak {white-space:nowrap}
span.roman {font-family:serif; font-weight:normal}
span.sansserif {font-family:sans-serif; font-weight:normal}
ul.no-bullet {list-style: none}
body {
margin: 2%;
padding: 0 5%;
background: #ffffff;
}
h1,h2,h3,h4,h5 {
font-weight: bold;
padding: 5px 5px 5px 5px;
background-color: #c2e0ff;
color: #336699;
}
h1 {
padding: 2em 2em 2em 5%;
color: white;
background: #336699;
text-align: center;
letter-spacing: 3px;
}
h2 { text-decoration: underline; }
pre {
margin: 0 5%;
padding: 0.5em;
}
pre.example,pre.verbatim {
padding-bottom: 1em;
border: solid #c2e0ff;
background: #f0faff;
border-width: 1px 1px 1px 5px;
margin: 1em auto;
width: 90%;
}
div.node {
margin: 0 -5% 0 -2%;
padding: 0.5em 0.5em;
margin-top: 0.5em;
margin-bottom: 0.5em;
font-weight: bold;
}
dd, li {
padding-top: 0.1em;
padding-bottom: 0.1em;
}
div.float {
margin-bottom: 0.5em;
text-align: center;
}
table {
text-align: left;
margin-left:auto;
margin-right:auto;
width: 50%;
}
th {
padding: 0;
color: #336699;
background-color: #c2e0ff;
border: solid #000000;
border-width: 0px;
margin: 1em auto;
text-align: center;
margin-left:auto;
margin-right:auto;
}
td {
padding: 0;
border: solid #000000;
background-color: #f0faff;
border-width: 0px;
margin: 1em auto;
text-align: left;
margin-left:auto;
margin-right:auto;
padding-left: 1em;
}
dl {
text-align: left;
margin-left:auto;
margin-right:auto;
width: 50%;
padding-left: 1em;
border: solid #c2e0ff;
background: #f0faff;
border-width: 5px 1px 1px 1px;
margin: 1em auto;
}
-->
</style>
</head>
<body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000">
<a name="X_002e509-certificate-structure"></a>
<div class="header">
<p>
Next: <a href="Importing-an-X_002e509-certificate.html#Importing-an-X_002e509-certificate" accesskey="n" rel="next">Importing an X.509 certificate</a>, Up: <a href="X_002e509-certificates.html#X_002e509-certificates" accesskey="u" rel="up">X.509 certificates</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Function-and-Data-Index.html#Function-and-Data-Index" title="Index" rel="index">Index</a>]</p>
</div>
<hr>
<a name="X_002e509-certificate-structure-1"></a>
<h4 class="subsubsection">4.1.1.1 <acronym>X.509</acronym> certificate structure</h4>
<p>An <acronym>X.509</acronym> certificate usually contains information about the
certificate holder, the signer, a unique serial number, expiration
dates and some other fields [<em>PKIX</em>] as shown in <a href="#tab_003ax509">Table 4.2</a>.
</p>
<div class="float"><a name="tab_003ax509"></a>
<table>
<thead><tr><th width="20%">Field</th><th width="70%">Description</th></tr></thead>
<tr><td width="20%">version</td><td width="70%">The field that indicates the version of the certificate.</td></tr>
<tr><td width="20%">serialNumber</td><td width="70%">This field holds a unique serial number per certificate.</td></tr>
<tr><td width="20%">signature</td><td width="70%">The issuing authority’s signature.</td></tr>
<tr><td width="20%">issuer</td><td width="70%">Holds the issuer’s distinguished name.</td></tr>
<tr><td width="20%">validity</td><td width="70%">The activation and expiration dates.</td></tr>
<tr><td width="20%">subject</td><td width="70%">The subject’s distinguished name of the certificate.</td></tr>
<tr><td width="20%">extensions</td><td width="70%">The extensions are fields only present in version 3 certificates.</td></tr>
</table>
<div class="float-caption"><p><strong>Table 4.2: </strong>X.509 certificate fields.</p></div></div>
<p>The certificate’s <em>subject or issuer name</em> is not just a single
string. It is a Distinguished name and in the <acronym>ASN.1</acronym>
notation is a sequence of several object identifiers with their corresponding
values. Some of available OIDs to be used in an <acronym>X.509</acronym>
distinguished name are defined in <samp>gnutls/x509.h</samp>.
</p>
<p>The <em>Version</em> field in a certificate has values either 1 or 3 for
version 3 certificates. Version 1 certificates do not support the
extensions field so it is not possible to distinguish a CA from a
person, thus their usage should be avoided.
</p>
<p>The <em>validity</em> dates are there to indicate the date that the
specific certificate was activated and the date the certificate’s key
would be considered invalid.
</p>
<p>Certificate <em>extensions</em> are there to include information about
the certificate’s subject that did not fit in the typical certificate
fields. Those may be e-mail addresses, flags that indicate whether the
belongs to a CA etc. All the supported <acronym>X.509</acronym> version 3
extensions are shown in <a href="#tab_003ax509_002dext">Table 4.3</a>.
</p>
<div class="float"><a name="tab_003ax509_002dext"></a>
<table>
<thead><tr><th width="30%">Extension</th><th width="20%">OID</th><th width="40%">Description</th></tr></thead>
<tr><td width="30%">Subject key id</td><td width="20%">2.5.29.14</td><td width="40%">An identifier of the key of the subject.</td></tr>
<tr><td width="30%">Authority key id</td><td width="20%">2.5.29.35</td><td width="40%">An identifier of the authority’s key used to sign the certificate.</td></tr>
<tr><td width="30%">Subject alternative name</td><td width="20%">2.5.29.17</td><td width="40%">Alternative names to subject’s distinguished name.</td></tr>
<tr><td width="30%">Key usage</td><td width="20%">2.5.29.15</td><td width="40%">Constraints the key’s usage of the certificate.</td></tr>
<tr><td width="30%">Extended key usage</td><td width="20%">2.5.29.37</td><td width="40%">Constraints the purpose of the certificate.</td></tr>
<tr><td width="30%">Basic constraints</td><td width="20%">2.5.29.19</td><td width="40%">Indicates whether this is a CA certificate or not, and specify the
maximum path lengths of certificate chains.</td></tr>
<tr><td width="30%">CRL distribution points</td><td width="20%">2.5.29.31</td><td width="40%">This extension is set by the CA, in order to inform about the issued
CRLs.</td></tr>
<tr><td width="30%">Certificate policy</td><td width="20%">2.5.29.32</td><td width="40%">This extension is set to indicate the certificate policy as object
identifier and may contain a descriptive string or URL.</td></tr>
<tr><td width="30%">Proxy Certification Information</td><td width="20%">1.3.6.1.5.5.7.1.14</td><td width="40%">Proxy Certificates includes this extension that contains the OID of
the proxy policy language used, and can specify limits on the maximum
lengths of proxy chains. Proxy Certificates are specified in
[<em>RFC3820</em>].</td></tr>
</table>
<div class="float-caption"><p><strong>Table 4.3: </strong>X.509 certificate extensions.</p></div></div>
<p>In <acronym>GnuTLS</acronym> the <acronym>X.509</acronym> certificate structures are
handled using the <code>gnutls_x509_crt_t</code> type and the corresponding
private keys with the <code>gnutls_x509_privkey_t</code> type. All the
available functions for <acronym>X.509</acronym> certificate handling have
their prototypes in <samp>gnutls/x509.h</samp>. An example program to
demonstrate the <acronym>X.509</acronym> parsing capabilities can be found in
<a href="X_002e509-certificate-parsing-example.html#ex_003ax509_002dinfo">ex:x509-info</a>.
</p>
<hr>
<div class="header">
<p>
Next: <a href="Importing-an-X_002e509-certificate.html#Importing-an-X_002e509-certificate" accesskey="n" rel="next">Importing an X.509 certificate</a>, Up: <a href="X_002e509-certificates.html#X_002e509-certificates" accesskey="u" rel="up">X.509 certificates</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Function-and-Data-Index.html#Function-and-Data-Index" title="Index" rel="index">Index</a>]</p>
</div>
</body>
</html>
|
