1SSL_EXTENSION_SUPPORTED(3ossl) OpenSSL SSL_EXTENSION_SUPPORTED(3ossl)
2
6 SSL_extension_supported, SSL_custom_ext_add_cb_ex,
7 SSL_custom_ext_free_cb_ex, SSL_custom_ext_parse_cb_ex,
8 SSL_CTX_add_custom_ext, SSL_CTX_add_client_custom_ext,
9 SSL_CTX_add_server_custom_ext, custom_ext_add_cb, custom_ext_free_cb,
10 custom_ext_parse_cb - custom TLS extension handling
11
13 #include <openssl/ssl.h>
14 typedef int (*SSL_custom_ext_add_cb_ex)(SSL *s, unsigned int ext_type,
16 unsigned int context,
17 const unsigned char **out,
18 size_t *outlen, X509 *x,
19 size_t chainidx, int *al,
20 void *add_arg);
21 typedef void (*SSL_custom_ext_free_cb_ex)(SSL *s, unsigned int ext_type,
23 unsigned int context,
24 const unsigned char *out,
25 void *add_arg);
26 typedef int (*SSL_custom_ext_parse_cb_ex)(SSL *s, unsigned int ext_type,
28 unsigned int context,
29 const unsigned char *in,
30 size_t inlen, X509 *x,
31 size_t chainidx, int *al,
32 void *parse_arg);
33 int SSL_CTX_add_custom_ext(SSL_CTX *ctx, unsigned int ext_type,
35 unsigned int context,
36 SSL_custom_ext_add_cb_ex add_cb,
37 SSL_custom_ext_free_cb_ex free_cb,
38 void *add_arg,
39 SSL_custom_ext_parse_cb_ex parse_cb,
40 void *parse_arg);
41 typedef int (*custom_ext_add_cb)(SSL *s, unsigned int ext_type,
43 const unsigned char **out,
44 size_t *outlen, int *al,
45 void *add_arg);
46 typedef void (*custom_ext_free_cb)(SSL *s, unsigned int ext_type,
48 const unsigned char *out,
49 void *add_arg);
50 typedef int (*custom_ext_parse_cb)(SSL *s, unsigned int ext_type,
52 const unsigned char *in,
53 size_t inlen, int *al,
54 void *parse_arg);
55 int SSL_CTX_add_client_custom_ext(SSL_CTX *ctx, unsigned int ext_type,
57 custom_ext_add_cb add_cb,
58 custom_ext_free_cb free_cb, void *add_arg,
59 custom_ext_parse_cb parse_cb,
60 void *parse_arg);
61 int SSL_CTX_add_server_custom_ext(SSL_CTX *ctx, unsigned int ext_type,
63 custom_ext_add_cb add_cb,
64 custom_ext_free_cb free_cb, void *add_arg,
65 custom_ext_parse_cb parse_cb,
66 void *parse_arg);
67 int SSL_extension_supported(unsigned int ext_type);
69
71 SSL_CTX_add_custom_ext() adds a custom extension for a TLS/DTLS client
72 or server for all supported protocol versions with extension type
73 ext_type and callbacks add_cb, free_cb and parse_cb (see the "EXTENSION
74 CALLBACKS" section below). The context value determines which messages
75 and under what conditions the extension will be added/parsed (see the
76 "EXTENSION CONTEXTS" section below).
77 SSL_CTX_add_client_custom_ext() adds a custom extension for a TLS/DTLS
79 client with extension type ext_type and callbacks add_cb, free_cb and
80 parse_cb. This function is similar to SSL_CTX_add_custom_ext() except
81 it only applies to clients, uses the older style of callbacks, and
82 implicitly sets the context value to:
83 SSL_EXT_TLS1_2_AND_BELOW_ONLY | SSL_EXT_CLIENT_HELLO
85 | SSL_EXT_TLS1_2_SERVER_HELLO | SSL_EXT_IGNORE_ON_RESUMPTION
86 SSL_CTX_add_server_custom_ext() adds a custom extension for a TLS/DTLS
88 server with extension type ext_type and callbacks add_cb, free_cb and
89 parse_cb. This function is similar to SSL_CTX_add_custom_ext() except
90 it only applies to servers, uses the older style of callbacks, and
91 implicitly sets the context value to the same as for
92 SSL_CTX_add_client_custom_ext() above.
93 The ext_type parameter corresponds to the extension_type field of
95 RFC5246 et al. It is not a NID. In all cases the extension type must
96 not be handled by OpenSSL internally or an error occurs.
97 SSL_extension_supported() returns 1 if the extension ext_type is
99 handled internally by OpenSSL and 0 otherwise.
100
102 The callback add_cb is called to send custom extension data to be
103 included in various TLS messages. The ext_type parameter is set to the
104 extension type which will be added and add_arg to the value set when
105 the extension handler was added. When using the new style callbacks the
106 context parameter will indicate which message is currently being
107 constructed e.g. for the ClientHello it will be set to
108 SSL_EXT_CLIENT_HELLO.
109 If the application wishes to include the extension ext_type it should
111 set *out to the extension data, set *outlen to the length of the
112 extension data and return 1.
113 If the add_cb does not wish to include the extension it must return 0.
115 If add_cb returns -1 a fatal handshake error occurs using the TLS alert
117 value specified in *al.
118 When constructing the ClientHello, if add_cb is set to NULL a zero
120 length extension is added for ext_type. For all other messages if
121 add_cb is set to NULL then no extension is added.
122 When constructing a Certificate message the callback will be called for
124 each certificate in the message. The x parameter will indicate the
125 current certificate and the chainidx parameter will indicate the
126 position of the certificate in the message. The first certificate is
127 always the end entity certificate and has a chainidx value of 0. The
128 certificates are in the order that they were received in the
129 Certificate message.
130 For all messages except the ServerHello and EncryptedExtensions every
132 registered add_cb is always called to see if the application wishes to
133 add an extension (as long as all requirements of the specified context
134 are met).
135 For the ServerHello and EncryptedExtension messages every registered
137 add_cb is called once if and only if the requirements of the specified
138 context are met and the corresponding extension was received in the
139 ClientHello. That is, if no corresponding extension was received in the
140 ClientHello then add_cb will not be called.
141 If an extension is added (that is add_cb returns 1) free_cb is called
143 (if it is set) with the value of out set by the add callback. It can be
144 used to free up any dynamic extension data set by add_cb. Since out is
145 constant (to permit use of constant data in add_cb) applications may
146 need to cast away const to free the data.
147 The callback parse_cb receives data for TLS extensions. The callback is
149 only called if the extension is present and relevant for the context
150 (see "EXTENSION CONTEXTS" below).
151 The extension data consists of inlen bytes in the buffer in for the
153 extension ext_type.
154 If the message being parsed is a TLSv1.3 compatible Certificate message
156 then parse_cb will be called for each certificate contained within the
157 message. The x parameter will indicate the current certificate and the
158 chainidx parameter will indicate the position of the certificate in the
159 message. The first certificate is always the end entity certificate and
160 has a chainidx value of 0.
161 If the parse_cb considers the extension data acceptable it must return
163 1. If it returns 0 or a negative value a fatal handshake error occurs
164 using the TLS alert value specified in *al.
165 The buffer in is a temporary internal buffer which will not be valid
167 after the callback returns.
168
170 An extension context defines which messages and under which conditions
171 an extension should be added or expected. The context is built up by
172 performing a bitwise OR of multiple pre-defined values together. The
173 valid context values are:
174 SSL_EXT_TLS_ONLY
176 The extension is only allowed in TLS
177 SSL_EXT_DTLS_ONLY
179 The extension is only allowed in DTLS
180 SSL_EXT_TLS_IMPLEMENTATION_ONLY
182 The extension is allowed in DTLS, but there is only a TLS
183 implementation available (so it is ignored in DTLS).
184 SSL_EXT_SSL3_ALLOWED
186 Extensions are not typically defined for SSLv3. Setting this value
187 will allow the extension in SSLv3. Applications will not typically
188 need to use this.
189 SSL_EXT_TLS1_2_AND_BELOW_ONLY
191 The extension is only defined for TLSv1.2/DTLSv1.2 and below.
192 Servers will ignore this extension if it is present in the
193 ClientHello and TLSv1.3 is negotiated.
194 SSL_EXT_TLS1_3_ONLY
196 The extension is only defined for TLS1.3 and above. Servers will
197 ignore this extension if it is present in the ClientHello and
198 TLSv1.2 or below is negotiated.
199 SSL_EXT_IGNORE_ON_RESUMPTION
201 The extension will be ignored during parsing if a previous session
202 is being successfully resumed.
203 SSL_EXT_CLIENT_HELLO
205 The extension may be present in the ClientHello message.
206 SSL_EXT_TLS1_2_SERVER_HELLO
208 The extension may be present in a TLSv1.2 or below compatible
209 ServerHello message.
210 SSL_EXT_TLS1_3_SERVER_HELLO
212 The extension may be present in a TLSv1.3 compatible ServerHello
213 message.
214 SSL_EXT_TLS1_3_ENCRYPTED_EXTENSIONS
216 The extension may be present in an EncryptedExtensions message.
217 SSL_EXT_TLS1_3_HELLO_RETRY_REQUEST
219 The extension may be present in a HelloRetryRequest message.
220 SSL_EXT_TLS1_3_CERTIFICATE
222 The extension may be present in a TLSv1.3 compatible Certificate
223 message.
224 SSL_EXT_TLS1_3_NEW_SESSION_TICKET
226 The extension may be present in a TLSv1.3 compatible
227 NewSessionTicket message.
228 SSL_EXT_TLS1_3_CERTIFICATE_REQUEST
230 The extension may be present in a TLSv1.3 compatible
231 CertificateRequest message.
232 The context must include at least one message value (otherwise the
234 extension will never be used).
235
237 The add_arg and parse_arg parameters can be set to arbitrary values
238 which will be passed to the corresponding callbacks. They can, for
239 example, be used to store the extension data received in a convenient
240 structure or pass the extension data to be added or freed when adding
241 extensions.
242 If the same custom extension type is received multiple times a fatal
244 decode_error alert is sent and the handshake aborts. If a custom
245 extension is received in a ServerHello/EncryptedExtensions message
246 which was not sent in the ClientHello a fatal unsupported_extension
247 alert is sent and the handshake is aborted. The
248 ServerHello/EncryptedExtensions add_cb callback is only called if the
249 corresponding extension was received in the ClientHello. This is
250 compliant with the TLS specifications. This behaviour ensures that each
251 callback is called at most once and that an application can never send
252 unsolicited extensions.
253
255 SSL_CTX_add_custom_ext(), SSL_CTX_add_client_custom_ext() and
256 SSL_CTX_add_server_custom_ext() return 1 for success and 0 for failure.
257 A failure can occur if an attempt is made to add the same ext_type more
258 than once, if an attempt is made to use an extension type handled
259 internally by OpenSSL or if an internal error occurs (for example a
260 memory allocation failure).
261 SSL_extension_supported() returns 1 if the extension ext_type is
263 handled internally by OpenSSL and 0 otherwise.
264
266 ssl(7)
267
269 The SSL_CTX_add_custom_ext() function was added in OpenSSL 1.1.1.
270
272 Copyright 2014-2020 The OpenSSL Project Authors. All Rights Reserved.
273 Licensed under the Apache License 2.0 (the "License"). You may not use
275 this file except in compliance with the License. You can obtain a copy
276 in the file LICENSE in the source distribution or at
277 <https://www.openssl.org/source/license.html>.
2783.1.1 2023-08-31 SSL_EXTENSION_SUPPORTED(3ossl)