1.\" $OpenBSD: SSL_CTX_set_session_id_context.3,v 1.6 2019/06/08 15:25:43 schwarze Exp $ 2.\" OpenSSL b97fdb57 Nov 11 09:33:09 2016 +0100 3.\" 4.\" This file was written by Lutz Jaenicke <jaenicke@openssl.org>. 5.\" Copyright (c) 2001, 2004 The OpenSSL Project. All rights reserved. 6.\" 7.\" Redistribution and use in source and binary forms, with or without 8.\" modification, are permitted provided that the following conditions 9.\" are met: 10.\" 11.\" 1. Redistributions of source code must retain the above copyright 12.\" notice, this list of conditions and the following disclaimer. 13.\" 14.\" 2. Redistributions in binary form must reproduce the above copyright 15.\" notice, this list of conditions and the following disclaimer in 16.\" the documentation and/or other materials provided with the 17.\" distribution. 18.\" 19.\" 3. All advertising materials mentioning features or use of this 20.\" software must display the following acknowledgment: 21.\" "This product includes software developed by the OpenSSL Project 22.\" for use in the OpenSSL Toolkit. (http://www.openssl.org/)" 23.\" 24.\" 4. The names "OpenSSL Toolkit" and "OpenSSL Project" must not be used to 25.\" endorse or promote products derived from this software without 26.\" prior written permission. For written permission, please contact 27.\" openssl-core@openssl.org. 28.\" 29.\" 5. Products derived from this software may not be called "OpenSSL" 30.\" nor may "OpenSSL" appear in their names without prior written 31.\" permission of the OpenSSL Project. 32.\" 33.\" 6. Redistributions of any form whatsoever must retain the following 34.\" acknowledgment: 35.\" "This product includes software developed by the OpenSSL Project 36.\" for use in the OpenSSL Toolkit (http://www.openssl.org/)" 37.\" 38.\" THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY 39.\" EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 40.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 41.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE OpenSSL PROJECT OR 42.\" ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 43.\" SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 44.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; 45.\" LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 46.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, 47.\" STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 48.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED 49.\" OF THE POSSIBILITY OF SUCH DAMAGE. 50.\" 51.Dd $Mdocdate: June 8 2019 $ 52.Dt SSL_CTX_SET_SESSION_ID_CONTEXT 3 53.Os 54.Sh NAME 55.Nm SSL_CTX_set_session_id_context , 56.Nm SSL_set_session_id_context 57.Nd set context within which session can be reused (server side only) 58.Sh SYNOPSIS 59.In openssl/ssl.h 60.Ft int 61.Fo SSL_CTX_set_session_id_context 62.Fa "SSL_CTX *ctx" 63.Fa "const unsigned char *sid_ctx" 64.Fa "unsigned int sid_ctx_len" 65.Fc 66.Ft int 67.Fo SSL_set_session_id_context 68.Fa "SSL *ssl" 69.Fa "const unsigned char *sid_ctx" 70.Fa "unsigned int sid_ctx_len" 71.Fc 72.Sh DESCRIPTION 73.Fn SSL_CTX_set_session_id_context 74sets the context 75.Fa sid_ctx 76of length 77.Fa sid_ctx_len 78within which a session can be reused for the 79.Fa ctx 80object. 81.Pp 82.Fn SSL_set_session_id_context 83sets the context 84.Fa sid_ctx 85of length 86.Fa sid_ctx_len 87within which a session can be reused for the 88.Fa ssl 89object. 90.Pp 91Sessions are generated within a certain context. 92When exporting/importing sessions with 93.Xr i2d_SSL_SESSION 3 94and 95.Xr d2i_SSL_SESSION 3 , 96it would be possible to re-import a session generated from another context 97(e.g., another application), which might lead to malfunctions. 98Therefore each application must set its own session id context 99.Fa sid_ctx 100which is used to distinguish the contexts and is stored in exported sessions. 101The 102.Fa sid_ctx 103can be any kind of binary data with a given length; it is therefore possible 104to use, for instance, the name of the application, the hostname, the service 105name... 106.Pp 107The session id context becomes part of the session. 108The session id context is set by the SSL/TLS server. 109The 110.Fn SSL_CTX_set_session_id_context 111and 112.Fn SSL_set_session_id_context 113functions are therefore only useful on the server side. 114.Pp 115OpenSSL clients will check the session id context returned by the server when 116reusing a session. 117.Pp 118The maximum length of the 119.Fa sid_ctx 120is limited to 121.Dv SSL_MAX_SSL_SESSION_ID_LENGTH . 122.Sh WARNINGS 123If the session id context is not set on an SSL/TLS server and client 124certificates are used, stored sessions will not be reused but a fatal error 125will be flagged and the handshake will fail. 126.Pp 127If a server returns a different session id context to an OpenSSL client 128when reusing a session, an error will be flagged and the handshake will 129fail. 130OpenSSL servers will always return the correct session id context, 131as an OpenSSL server checks the session id context itself before reusing 132a session as described above. 133.Sh RETURN VALUES 134.Fn SSL_CTX_set_session_id_context 135and 136.Fn SSL_set_session_id_context 137return the following values: 138.Bl -tag -width Ds 139.It 0 140The length 141.Fa sid_ctx_len 142of the session id context 143.Fa sid_ctx 144exceeded 145the maximum allowed length of 146.Dv SSL_MAX_SSL_SESSION_ID_LENGTH . 147The error is logged to the error stack. 148.It 1 149The operation succeeded. 150.El 151.Sh SEE ALSO 152.Xr ssl 3 , 153.Xr SSL_SESSION_set1_id_context 3 154.Sh HISTORY 155.Fn SSL_set_session_id_context 156first appeared in OpenSSL 0.9.2b. 157.Fn SSL_CTX_set_session_id_context 158first appeared in OpenSSL 0.9.3. 159Both functions have been available since 160.Ox 2.6 . 161