.\" $OpenBSD: SSL_CTX_set_session_id_context.3,v 1.6 2019/06/08 15:25:43 schwarze Exp $ .\" OpenSSL b97fdb57 Nov 11 09:33:09 2016 +0100 .\" .\" This file was written by Lutz Jaenicke . .\" Copyright (c) 2001, 2004 The OpenSSL Project. All rights reserved. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in .\" the documentation and/or other materials provided with the .\" distribution. .\" .\" 3. 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IN NO EVENT SHALL THE OpenSSL PROJECT OR .\" ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, .\" SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT .\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; .\" LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, .\" STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) .\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED .\" OF THE POSSIBILITY OF SUCH DAMAGE. .\" .Dd $Mdocdate: June 8 2019 $ .Dt SSL_CTX_SET_SESSION_ID_CONTEXT 3 .Os .Sh NAME .Nm SSL_CTX_set_session_id_context , .Nm SSL_set_session_id_context .Nd set context within which session can be reused (server side only) .Sh SYNOPSIS .In openssl/ssl.h .Ft int .Fo SSL_CTX_set_session_id_context .Fa "SSL_CTX *ctx" .Fa "const unsigned char *sid_ctx" .Fa "unsigned int sid_ctx_len" .Fc .Ft int .Fo SSL_set_session_id_context .Fa "SSL *ssl" .Fa "const unsigned char *sid_ctx" .Fa "unsigned int sid_ctx_len" .Fc .Sh DESCRIPTION .Fn SSL_CTX_set_session_id_context sets the context .Fa sid_ctx of length .Fa sid_ctx_len within which a session can be reused for the .Fa ctx object. .Pp .Fn SSL_set_session_id_context sets the context .Fa sid_ctx of length .Fa sid_ctx_len within which a session can be reused for the .Fa ssl object. .Pp Sessions are generated within a certain context. When exporting/importing sessions with .Xr i2d_SSL_SESSION 3 and .Xr d2i_SSL_SESSION 3 , it would be possible to re-import a session generated from another context (e.g., another application), which might lead to malfunctions. Therefore each application must set its own session id context .Fa sid_ctx which is used to distinguish the contexts and is stored in exported sessions. The .Fa sid_ctx can be any kind of binary data with a given length; it is therefore possible to use, for instance, the name of the application, the hostname, the service name... .Pp The session id context becomes part of the session. The session id context is set by the SSL/TLS server. The .Fn SSL_CTX_set_session_id_context and .Fn SSL_set_session_id_context functions are therefore only useful on the server side. .Pp OpenSSL clients will check the session id context returned by the server when reusing a session. .Pp The maximum length of the .Fa sid_ctx is limited to .Dv SSL_MAX_SSL_SESSION_ID_LENGTH . .Sh WARNINGS If the session id context is not set on an SSL/TLS server and client certificates are used, stored sessions will not be reused but a fatal error will be flagged and the handshake will fail. .Pp If a server returns a different session id context to an OpenSSL client when reusing a session, an error will be flagged and the handshake will fail. OpenSSL servers will always return the correct session id context, as an OpenSSL server checks the session id context itself before reusing a session as described above. .Sh RETURN VALUES .Fn SSL_CTX_set_session_id_context and .Fn SSL_set_session_id_context return the following values: .Bl -tag -width Ds .It 0 The length .Fa sid_ctx_len of the session id context .Fa sid_ctx exceeded the maximum allowed length of .Dv SSL_MAX_SSL_SESSION_ID_LENGTH . The error is logged to the error stack. .It 1 The operation succeeded. .El .Sh SEE ALSO .Xr ssl 3 , .Xr SSL_SESSION_set1_id_context 3 .Sh HISTORY .Fn SSL_set_session_id_context first appeared in OpenSSL 0.9.2b. .Fn SSL_CTX_set_session_id_context first appeared in OpenSSL 0.9.3. Both functions have been available since .Ox 2.6 .