int SSL_CTX_set_generate_session_id(SSL_CTX *ctx, GEN_SESSION_CB cb);
int SSL_set_generate_session_id(SSL *ssl, GEN_SESSION_CB, cb);
int SSL_has_matching_session_id(const SSL *ssl, const unsigned char *id,
- unsigned int id_len);
+ unsigned int id_len);
=head1 DESCRIPTION
When a new session is established between client and server, the server
generates a session id. The session id is an arbitrary sequence of bytes.
-The length of the session id is 16 bytes for SSLv2 sessions and between
-1 and 32 bytes for SSLv3/TLSv1. The session id is not security critical
-but must be unique for the server. Additionally, the session id is
+The length of the session id is between 1 and 32 bytes. The session id is not
+security critical but must be unique for the server. Additionally, the session id is
transmitted in the clear when reusing the session so it must not contain
sensitive information.
the callback B<must never> increase B<id_len> or write to the location
B<id> exceeding the given limit.
-If a SSLv2 session id is generated and B<id_len> is reduced, it will be
-restored after the callback has finished and the session id will be padded
-with 0x00. It is not recommended to change the B<id_len> for SSLv2 sessions.
-The callback can use the L<SSL_get_version(3)|SSL_get_version(3)> function
-to check, whether the session is of type SSLv2.
-
The location B<id> is filled with 0x00 before the callback is called, so the
callback may only fill part of the possible length and leave B<id_len>
untouched while maintaining reproducibility.
Since the sessions must be distinguished, session ids must be unique.
Without the callback a random number is used, so that the probability
-of generating the same session id is extremely small (2^128 possible ids
-for an SSLv2 session, 2^256 for SSLv3/TLSv1). In order to assure the
-uniqueness of the generated session id, the callback must call
+of generating the same session id is extremely small (2^256 for SSLv3/TLSv1).
+In order to assure the uniqueness of the generated session id, the callback must call
SSL_has_matching_session_id() and generate another id if a conflict occurs.
If an id conflict is not resolved, the handshake will fail.
If the application codes e.g. a unique host id, a unique process number, and
the external cache is not tested with SSL_has_matching_session_id()
and the same race condition applies.
-When calling SSL_has_matching_session_id() for an SSLv2 session with
-reduced B<id_len>, the match operation will be performed using the
-fixed length required and with a 0x00 padded id.
-
The callback must return 0 if it cannot generate a session id for whatever
reason and return 1 on success.
#define MAX_SESSION_ID_ATTEMPTS 10
static int generate_session_id(const SSL *ssl, unsigned char *id,
unsigned int *id_len)
- {
+ {
unsigned int count = 0;
- const char *version;
-
- version = SSL_get_version(ssl);
- if (!strcmp(version, "SSLv2"))
- /* we must not change id_len */;
-
- do {
- RAND_pseudo_bytes(id, *id_len);
- /* Prefix the session_id with the required prefix. NB: If our
- * prefix is too long, clip it - but there will be worse effects
- * anyway, eg. the server could only possibly create 1 session
- * ID (ie. the prefix!) so all future session negotiations will
- * fail due to conflicts. */
- memcpy(id, session_id_prefix,
- (strlen(session_id_prefix) < *id_len) ?
- strlen(session_id_prefix) : *id_len);
- }
- while(SSL_has_matching_session_id(ssl, id, *id_len) &&
+ do {
+ RAND_pseudo_bytes(id, *id_len);
+ /*
+ * Prefix the session_id with the required prefix. NB: If our
+ * prefix is too long, clip it - but there will be worse effects
+ * anyway, eg. the server could only possibly create 1 session
+ * ID (ie. the prefix!) so all future session negotiations will
+ * fail due to conflicts.
+ */
+ memcpy(id, session_id_prefix,
+ (strlen(session_id_prefix) < *id_len) ?
+ strlen(session_id_prefix) : *id_len);
+ }
+ while (SSL_has_matching_session_id(ssl, id, *id_len) &&
(++count < MAX_SESSION_ID_ATTEMPTS));
- if(count >= MAX_SESSION_ID_ATTEMPTS)
+ if (count >= MAX_SESSION_ID_ATTEMPTS)
return 0;
return 1;
- }
+ }
=head1 RETURN VALUES
=head1 SEE ALSO
-L<ssl(3)|ssl(3)>, L<SSL_get_version(3)|SSL_get_version(3)>
+L<ssl(3)>, L<SSL_get_version(3)>
+
+=head1 COPYRIGHT
-=head1 HISTORY
+Copyright 2001-2016 The OpenSSL Project Authors. All Rights Reserved.
-SSL_CTX_set_generate_session_id(), SSL_set_generate_session_id()
-and SSL_has_matching_session_id() have been introduced in
-OpenSSL 0.9.7.
+Licensed under the OpenSSL license (the "License"). You may not use
+this file except in compliance with the License. You can obtain a copy
+in the file LICENSE in the source distribution or at
+L<https://www.openssl.org/source/license.html>.
=cut
projects / cassiopeia.git / blobdiff