diff options
Diffstat (limited to 'secure/lib/libssl/man/SSL_CTX_set_generate_session_id.3')
| -rw-r--r-- | secure/lib/libssl/man/SSL_CTX_set_generate_session_id.3 | 272 |
1 files changed, 272 insertions, 0 deletions
diff --git a/secure/lib/libssl/man/SSL_CTX_set_generate_session_id.3 b/secure/lib/libssl/man/SSL_CTX_set_generate_session_id.3 new file mode 100644 index 0000000..c8f02d0 --- /dev/null +++ b/secure/lib/libssl/man/SSL_CTX_set_generate_session_id.3 @@ -0,0 +1,272 @@ +.\" Automatically generated by Pod::Man 2.25 (Pod::Simple 3.23) +.\" +.\" 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 +.. +.\" Set up some character translations and predefined strings. \*(-- will +.\" give an unbreakable dash, \*(PI will give pi, \*(L" will give a left +.\" double quote, and \*(R" will give a right double quote. \*(C+ will +.\" give a nicer C++. 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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 \- manipulate generation of SSL session IDs (server only) +.SH "SYNOPSIS" +.IX Header "SYNOPSIS" +.Vb 1 +\& #include <openssl/ssl.h> +\& +\& typedef int (*GEN_SESSION_CB)(const 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" +\&\fISSL_CTX_set_generate_session_id()\fR sets the callback function for generating +new session ids for \s-1SSL/TLS\s0 sessions for \fBctx\fR to be \fBcb\fR. +.PP +\&\fISSL_set_generate_session_id()\fR sets the callback function for generating +new session ids for \s-1SSL/TLS\s0 sessions for \fBssl\fR to be \fBcb\fR. +.PP +\&\fISSL_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 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 +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 +If a SSLv2 session id is generated and \fBid_len\fR 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 \fBid_len\fR for SSLv2 sessions. +The callback can use the \fISSL_get_version\fR\|(3) function +to check, whether the session is of type SSLv2. +.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 (2^128 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 +\&\fISSL_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 +\&\fISSL_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 \fISSL_has_matching_session_id()\fR +and the same race condition applies. +.PP +When calling \fISSL_has_matching_session_id()\fR for an SSLv2 session with +reduced \fBid_len\fR, the match operation will be performed using the +fixed length required and with a 0x00 padded id. +.PP +The callback must return 0 if it cannot generate a session id for whatever +reason and return 1 on success. +.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(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) && +\& (++count < MAX_SESSION_ID_ATTEMPTS)); +\& if(count >= MAX_SESSION_ID_ATTEMPTS) +\& return 0; +\& return 1; +\& } +.Ve +.SH "RETURN VALUES" +.IX Header "RETURN VALUES" +\&\fISSL_CTX_set_generate_session_id()\fR and \fISSL_set_generate_session_id()\fR +always return 1. +.PP +\&\fISSL_has_matching_session_id()\fR returns 1 if another session with the +same id is already in the cache. +.SH "SEE ALSO" +.IX Header "SEE ALSO" +\&\fIssl\fR\|(3), \fISSL_get_version\fR\|(3) +.SH "HISTORY" +.IX Header "HISTORY" +\&\fISSL_CTX_set_generate_session_id()\fR, \fISSL_set_generate_session_id()\fR +and \fISSL_has_matching_session_id()\fR have been introduced in +OpenSSL 0.9.7. |
