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Diffstat (limited to 'static/freebsd/man3/SSL_CTX_set_generate_session_id.3')
| -rw-r--r-- | static/freebsd/man3/SSL_CTX_set_generate_session_id.3 | 194 |
1 files changed, 194 insertions, 0 deletions
diff --git a/static/freebsd/man3/SSL_CTX_set_generate_session_id.3 b/static/freebsd/man3/SSL_CTX_set_generate_session_id.3 new file mode 100644 index 00000000..e2613215 --- /dev/null +++ b/static/freebsd/man3/SSL_CTX_set_generate_session_id.3 @@ -0,0 +1,194 @@ +.\" -*- mode: troff; coding: utf-8 -*- +.\" Automatically generated by Pod::Man v6.0.2 (Pod::Simple 3.45) +.\" +.\" Standard preamble: +.\" ======================================================================== +.de Sp \" Vertical space (when we can't use .PP) +.if t .sp .5v +.if n .sp +.. +.de Vb \" Begin verbatim text +.ft CW +.nf +.ne \\$1 +.. +.de Ve \" End verbatim text +.ft R +.fi +.. +.\" \*(C` and \*(C' are quotes in nroff, nothing in troff, for use with C<>. +.ie n \{\ +. ds C` "" +. ds C' "" +'br\} +.el\{\ +. ds C` +. ds C' +'br\} +.\" +.\" Escape single quotes in literal strings from groff's Unicode transform. +.ie \n(.g .ds Aq \(aq +.el .ds Aq ' +.\" +.\" If the F register is >0, we'll generate index entries on stderr for +.\" titles (.TH), headers (.SH), subsections (.SS), items (.Ip), and index +.\" entries marked with X<> in POD. Of course, you'll have to process the +.\" output yourself in some meaningful fashion. +.\" +.\" Avoid warning from groff about undefined register 'F'. +.de IX +.. +.nr rF 0 +.if \n(.g .if rF .nr rF 1 +.if (\n(rF:(\n(.g==0)) \{\ +. if \nF \{\ +. de IX +. tm Index:\\$1\t\\n%\t"\\$2" +.. +. if !\nF==2 \{\ +. nr % 0 +. nr F 2 +. \} +. \} +.\} +.rr rF +.\" +.\" Required to disable full justification in groff 1.23.0. +.if n .ds AD l +.\" ======================================================================== +.\" +.IX Title "SSL_CTX_SET_GENERATE_SESSION_ID 3ossl" +.TH SSL_CTX_SET_GENERATE_SESSION_ID 3ossl 2026-04-07 3.5.6 OpenSSL +.\" For nroff, turn off justification. Always turn off hyphenation; it makes +.\" way too many mistakes in technical documents. +.if n .ad l +.nh +.SH NAME +SSL_CTX_set_generate_session_id, SSL_set_generate_session_id, +SSL_has_matching_session_id, GEN_SESSION_CB +\&\- manipulate generation of SSL session IDs (server only) +.SH SYNOPSIS +.IX Header "SYNOPSIS" +.Vb 1 +\& #include <openssl/ssl.h> +\& +\& typedef int (*GEN_SESSION_CB)(SSL *ssl, unsigned char *id, +\& unsigned int *id_len); +\& +\& 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); +.Ve +.SH DESCRIPTION +.IX Header "DESCRIPTION" +\&\fBSSL_CTX_set_generate_session_id()\fR sets the callback function for generating +new session ids for SSL/TLS sessions for \fBctx\fR to be \fBcb\fR. +.PP +\&\fBSSL_set_generate_session_id()\fR sets the callback function for generating +new session ids for SSL/TLS sessions for \fBssl\fR to be \fBcb\fR. +.PP +\&\fBSSL_has_matching_session_id()\fR checks, whether a session with id \fBid\fR +(of length \fBid_len\fR) is already contained in the internal session cache +of the parent context of \fBssl\fR. +.SH NOTES +.IX Header "NOTES" +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 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. +.PP +Without a callback being set, an OpenSSL server will generate a unique +session id from pseudo random numbers of the maximum possible length. +Using the callback function, the session id can be changed to contain +additional information like e.g. a host id in order to improve load balancing +or external caching techniques. +.PP +The callback function receives a pointer to the memory location to put +\&\fBid\fR into and a pointer to the maximum allowed length \fBid_len\fR. The +buffer at location \fBid\fR is only guaranteed to have the size \fBid_len\fR. +The callback is only allowed to generate a shorter id and reduce \fBid_len\fR; +the callback \fBmust never\fR increase \fBid_len\fR or write to the location +\&\fBid\fR exceeding the given limit. +.PP +The location \fBid\fR is filled with 0x00 before the callback is called, so the +callback may only fill part of the possible length and leave \fBid_len\fR +untouched while maintaining reproducibility. +.PP +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 (2^256 for SSLv3/TLSv1). +In order to assure the uniqueness of the generated session id, the callback must call +\&\fBSSL_has_matching_session_id()\fR 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 +a unique sequence number into the session id, uniqueness could easily be +achieved without randomness added (it should however be taken care that +no confidential information is leaked this way). If the application can not +guarantee uniqueness, it is recommended to use the maximum \fBid_len\fR and +fill in the bytes not used to code special information with random data +to avoid collisions. +.PP +\&\fBSSL_has_matching_session_id()\fR will only query the internal session cache, +not the external one. Since the session id is generated before the +handshake is completed, it is not immediately added to the cache. If +another thread is using the same internal session cache, a race condition +can occur in that another thread generates the same session id. +Collisions can also occur when using an external session cache, since +the external cache is not tested with \fBSSL_has_matching_session_id()\fR +and the same race condition applies. +.PP +The callback must return 0 if it cannot generate a session id for whatever +reason and return 1 on success. +.SH "RETURN VALUES" +.IX Header "RETURN VALUES" +\&\fBSSL_CTX_set_generate_session_id()\fR and \fBSSL_set_generate_session_id()\fR +return 1 on success and 0 for failure. +.PP +\&\fBSSL_has_matching_session_id()\fR returns 1 if another session with the +same id is already in the cache, or 0 otherwise. +.SH EXAMPLES +.IX Header "EXAMPLES" +The callback function listed will generate a session id with the +server id given, and will fill the rest with pseudo random bytes: +.PP +.Vb 1 +\& const char session_id_prefix = "www\-18"; +\& +\& #define MAX_SESSION_ID_ATTEMPTS 10 +\& static int generate_session_id(SSL *ssl, unsigned char *id, +\& unsigned int *id_len) +\& { +\& unsigned int count = 0; +\& +\& 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, e.g. the server could only possibly create 1 session +\& * ID (i.e. 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) +\& return 0; +\& return 1; +\& } +.Ve +.SH "SEE ALSO" +.IX Header "SEE ALSO" +\&\fBssl\fR\|(7), \fBSSL_get_version\fR\|(3) +.SH COPYRIGHT +.IX Header "COPYRIGHT" +Copyright 2001\-2020 The OpenSSL Project Authors. All Rights Reserved. +.PP +Licensed under the Apache License 2.0 (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 +<https://www.openssl.org/source/license.html>. |