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
|
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<!-- This manual is last updated 4 March 2015 for version
3.5.3 of GnuTLS.
Copyright (C) 2001-2015 Free Software Foundation, Inc.\\
Copyright (C) 2001-2015 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 6.1, http://www.gnu.org/software/texinfo/ -->
<head>
<title>GnuTLS 3.5.3: Re-authentication</title>
<meta name="description" content="GnuTLS 3.5.3: Re-authentication">
<meta name="keywords" content="GnuTLS 3.5.3: Re-authentication">
<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="Advanced-topics.html#Advanced-topics" rel="up" title="Advanced topics">
<link href="Parameter-generation.html#Parameter-generation" rel="next" title="Parameter generation">
<link href="Certificate-verification.html#Certificate-verification" rel="prev" title="Certificate verification">
<style type="text/css">
<!--
a.summary-letter {text-decoration: none}
blockquote.indentedblock {margin-right: 0em}
blockquote.smallindentedblock {margin-right: 0em; font-size: smaller}
blockquote.smallquotation {font-size: smaller}
div.display {margin-left: 3.2em}
div.example {margin-left: 3.2em}
div.lisp {margin-left: 3.2em}
div.smalldisplay {margin-left: 3.2em}
div.smallexample {margin-left: 3.2em}
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.nolinebreak {white-space: nowrap}
span.roman {font-family: initial; 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;
border-spacing: 7px;
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">
<a name="Re_002dauthentication"></a>
<div class="header">
<p>
Next: <a href="Parameter-generation.html#Parameter-generation" accesskey="n" rel="next">Parameter generation</a>, Previous: <a href="Certificate-verification.html#Certificate-verification" accesskey="p" rel="prev">Certificate verification</a>, Up: <a href="Advanced-topics.html#Advanced-topics" accesskey="u" rel="up">Advanced topics</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="Re_002dauthentication-1"></a>
<h4 class="subsection">6.12.3 Re-authentication</h4>
<a name="index-renegotiation-1"></a>
<a name="index-reauthentication"></a>
<p>In TLS there is no distinction between rekey, re-authentication, and re-negotiation.
All of these use cases are handled by the TLS’ rehandshake process. For that reason
in GnuTLS rehandshake is not transparent to the application, and the application
must explicitly take control of that process. In addition GnuTLS since version 3.5.0 will not
allow the peer to switch identities during a rehandshake.
The threat addressed by that behavior depends on the application protocol,
but primarily it protects applications from being misled
by a rehandshake which switches the peer’s identity. Applications can
disable this protection by using the <code>GNUTLS_ALLOW_ID_CHANGE</code> flag in
<a href="Core-TLS-API.html#gnutls_005finit">gnutls_init</a>.
</p>
<p>The following paragraphs explain how to safely use the rehandshake process.
</p>
<a name="Client-side"></a>
<h4 class="subsubsection">6.12.3.1 Client side</h4>
<p>According to the TLS specification a client may initiate a rehandshake at any
time. That can be achieved by calling <a href="Core-TLS-API.html#gnutls_005fhandshake">gnutls_handshake</a> and rely on its
return value for the outcome of the handshake (the server may deny a rehandshake).
If a server requests a re-handshake, then a call to <a href="Core-TLS-API.html#gnutls_005frecord_005frecv">gnutls_record_recv</a> will
return GNUTLS_E_REHANDSHAKE in the client, instructing it to call <a href="Core-TLS-API.html#gnutls_005fhandshake">gnutls_handshake</a>.
To deny a rehandshake request by the server it is recommended to send a warning alert
of type GNUTLS_A_NO_RENEGOTIATION.
</p>
<p>Due to limitations of early protocol versions, it is required to check whether
safe renegotiation is in place, i.e., using <a href="Core-TLS-API.html#gnutls_005fsafe_005frenegotiation_005fstatus">gnutls_safe_renegotiation_status</a>,
which ensures that the server remains the same as the initial.
</p>
<dl>
<dt><a name="index-gnutls_005fsafe_005frenegotiation_005fstatus"></a>Function: <em>int</em> <strong>gnutls_safe_renegotiation_status</strong> <em>(gnutls_session_t <var>session</var>)</em></dt>
<dd><p><var>session</var>: is a <code>gnutls_session_t</code> type.
</p>
<p>Can be used to check whether safe renegotiation is being used
in the current session.
</p>
<p><strong>Returns:</strong> 0 when safe renegotiation is not used and non (0) when
safe renegotiation is used.
</p>
<p><strong>Since:</strong> 2.10.0
</p></dd></dl>
<a name="Server-side"></a>
<h4 class="subsubsection">6.12.3.2 Server side</h4>
<p>A server which wants to instruct the client to re-authenticate, should call
<a href="Core-TLS-API.html#gnutls_005frehandshake">gnutls_rehandshake</a> and wait for the client to re-authenticate.
It is recommended to only request re-handshake when safe renegotiation is
enabled for that session (see <a href="Core-TLS-API.html#gnutls_005fsafe_005frenegotiation_005fstatus">gnutls_safe_renegotiation_status</a> and
the discussion in <a href="Safe-renegotiation.html#Safe-renegotiation">Safe renegotiation</a>).
</p>
<dl>
<dt><a name="index-gnutls_005frehandshake"></a>Function: <em>int</em> <strong>gnutls_rehandshake</strong> <em>(gnutls_session_t <var>session</var>)</em></dt>
<dd><p><var>session</var>: is a <code>gnutls_session_t</code> type.
</p>
<p>This function will renegotiate security parameters with the
client. This should only be called in case of a server.
</p>
<p>This message informs the peer that we want to renegotiate
parameters (perform a handshake).
</p>
<p>If this function succeeds (returns 0), you must call the
<code>gnutls_handshake()</code> function in order to negotiate the new
parameters.
</p>
<p>Since TLS is full duplex some application data might have been
sent during peer’s processing of this message. In that case
one should call <code>gnutls_record_recv()</code> until GNUTLS_E_REHANDSHAKE
is returned to clear any pending data. Care must be taken, if
rehandshake is mandatory, to terminate if it does not start after
some threshold.
</p>
<p>If the client does not wish to renegotiate parameters he
should reply with an alert message, thus the return code will be
<code>GNUTLS_E_WARNING_ALERT_RECEIVED</code> and the alert will be
<code>GNUTLS_A_NO_RENEGOTIATION</code> . A client may also choose to ignore
this message.
</p>
<p><strong>Returns:</strong> <code>GNUTLS_E_SUCCESS</code> on success, otherwise a negative error code.
</p></dd></dl>
<hr>
<div class="header">
<p>
Next: <a href="Parameter-generation.html#Parameter-generation" accesskey="n" rel="next">Parameter generation</a>, Previous: <a href="Certificate-verification.html#Certificate-verification" accesskey="p" rel="prev">Certificate verification</a>, Up: <a href="Advanced-topics.html#Advanced-topics" accesskey="u" rel="up">Advanced topics</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>
|
