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Diffstat (limited to 'secure/lib/libssl/man/SSL_CTX_set_tlsext_ticket_key_cb.3')
| -rw-r--r-- | secure/lib/libssl/man/SSL_CTX_set_tlsext_ticket_key_cb.3 | 316 |
1 files changed, 316 insertions, 0 deletions
diff --git a/secure/lib/libssl/man/SSL_CTX_set_tlsext_ticket_key_cb.3 b/secure/lib/libssl/man/SSL_CTX_set_tlsext_ticket_key_cb.3 new file mode 100644 index 0000000000000..e1078f06df38e --- /dev/null +++ b/secure/lib/libssl/man/SSL_CTX_set_tlsext_ticket_key_cb.3 @@ -0,0 +1,316 @@ +.\" Automatically generated by Pod::Man 2.27 (Pod::Simple 3.28) +.\" +.\" 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_tlsext_ticket_key_cb \- set a callback for session ticket processing +.SH "SYNOPSIS" +.IX Header "SYNOPSIS" +.Vb 1 +\& #include <openssl/tls1.h> +\& +\& long SSL_CTX_set_tlsext_ticket_key_cb(SSL_CTX sslctx, +\& int (*cb)(SSL *s, unsigned char key_name[16], +\& unsigned char iv[EVP_MAX_IV_LENGTH], +\& EVP_CIPHER_CTX *ctx, HMAC_CTX *hctx, int enc)); +.Ve +.SH "DESCRIPTION" +.IX Header "DESCRIPTION" +\&\fISSL_CTX_set_tlsext_ticket_key_cb()\fR sets a callback fuction \fIcb\fR for handling +session tickets for the ssl context \fIsslctx\fR. Session tickets, defined in +\&\s-1RFC5077\s0 provide an enhanced session resumption capability where the server +implementation is not required to maintain per session state. It only applies +to \s-1TLS\s0 and there is no SSLv3 implementation. +.PP +The callback is available when the OpenSSL library was built without +\&\fI\s-1OPENSSL_NO_TLSEXT\s0\fR being defined. +.PP +The callback function \fIcb\fR will be called for every client instigated \s-1TLS\s0 +session when session ticket extension is presented in the \s-1TLS\s0 hello +message. It is the responsibility of this function to create or retrieve the +cryptographic parameters and to maintain their state. +.PP +The OpenSSL library uses your callback function to help implement a common \s-1TLS \s0 +ticket construction state according to \s-1RFC5077\s0 Section 4 such that per session +state is unnecessary and a small set of cryptographic variables needs to be +maintained by the callback function implementation. +.PP +In order to reuse a session, a \s-1TLS\s0 client must send the a session ticket +extension to the server. The client can only send exactly one session ticket. +The server, through the callback function, either agrees to reuse the session +ticket information or it starts a full \s-1TLS\s0 handshake to create a new session +ticket. +.PP +Before the callback function is started \fIctx\fR and \fIhctx\fR have been +initialised with EVP_CIPHER_CTX_init and HMAC_CTX_init respectively. +.PP +For new sessions tickets, when the client doesn't present a session ticket, or +an attempted retreival of the ticket failed, or a renew option was indicated, +the callback function will be called with \fIenc\fR equal to 1. The OpenSSL +library expects that the function will set an arbitary \fIname\fR, initialize +\&\fIiv\fR, and set the cipher context \fIctx\fR and the hash context \fIhctx\fR. +.PP +The \fIname\fR is 16 characters long and is used as a key identifier. +.PP +The \fIiv\fR length is the length of the \s-1IV\s0 of the corresponding cipher. The +maximum \s-1IV\s0 length is \s-1EVP_MAX_IV_LENGTH\s0 bytes defined in \fBevp.h\fR. +.PP +The initialization vector \fIiv\fR should be a random value. The cipher context +\&\fIctx\fR should use the initialisation vector \fIiv\fR. The cipher context can be +set using EVP_EncryptInit_ex. The hmac context can be set using HMAC_Init_ex. +.PP +When the client presents a session ticket, the callback function with be called +with \fIenc\fR set to 0 indicating that the \fIcb\fR function should retreive a set +of parameters. In this case \fIname\fR and \fIiv\fR have already been parsed out of +the session ticket. The OpenSSL library expects that the \fIname\fR will be used +to retrieve a cryptographic parameters and that the cryptographic context +\&\fIctx\fR will be set with the retreived parameters and the initialization vector +\&\fIiv\fR. using a function like EVP_DecryptInit_ex. The \fIhctx\fR needs to be set +using HMAC_Init_ex. +.PP +If the \fIname\fR is still valid but a renewal of the ticket is required the +callback function should return 2. The library will call the callback again +with an arguement of enc equal to 1 to set the new ticket. +.PP +The return value of the \fIcb\fR function is used by OpenSSL to determine what +further processing will occur. The following return values have meaning: +.IP "2" 4 +.IX Item "2" +This indicates that the \fIctx\fR and \fIhctx\fR have been set and the session can +continue on those parameters. Additionally it indicates that the session +ticket is in a renewal period and should be replaced. The OpenSSL library will +call \fIcb\fR again with an enc argument of 1 to set the new ticket (see \s-1RFC5077 +3.3\s0 paragraph 2). +.IP "1" 4 +.IX Item "1" +This indicates that the \fIctx\fR and \fIhctx\fR have been set and the session can +continue on those parameters. +.IP "0" 4 +This indicates that it was not possible to set/retrieve a session ticket and +the \s-1SSL/TLS\s0 session will continue by by negiotationing a set of cryptographic +parameters or using the alternate \s-1SSL/TLS\s0 resumption mechanism, session ids. +.Sp +If called with enc equal to 0 the library will call the \fIcb\fR again to get +a new set of parameters. +.IP "less than 0" 4 +.IX Item "less than 0" +This indicates an error. +.SH "NOTES" +.IX Header "NOTES" +Session resumption shortcuts the \s-1TLS\s0 so that the client certificate +negiotation don't occur. It makes up for this by storing client certificate +an all other negotiated state information encrypted within the ticket. In a +resumed session the applications will have all this state information available +exactly as if a full negiotation had occured. +.PP +If an attacker can obtain the key used to encrypt a session ticket, they can +obtain the master secret for any ticket using that key and decrypt any traffic +using that session: even if the ciphersuite supports forward secrecy. As +a result applications may wish to use multiple keys and avoid using long term +keys stored in files. +.PP +Applications can use longer keys to maintain a consistent level of security. +For example if a ciphersuite uses 256 bit ciphers but only a 128 bit ticket key +the overall security is only 128 bits because breaking the ticket key will +enable an attacker to obtain the session keys. +.SH "EXAMPLES" +.IX Header "EXAMPLES" +Reference Implemention: + SSL_CTX_set_tlsext_ticket_key_cb(\s-1SSL\s0,ssl_tlsext_ticket_key_cb); + .... +.PP +.Vb 6 +\& static int ssl_tlsext_ticket_key_cb(SSL *s, unsigned char key_name[16], unsigned char *iv, EVP_CIPHER_CTX *ctx, HMAC_CTX *hctx, int enc) +\& { +\& if (enc) { /* create new session */ +\& if (RAND_bytes(iv, EVP_MAX_IV_LENGTH) ) { +\& return \-1; /* insufficient random */ +\& } +\& +\& key = currentkey(); /* something that you need to implement */ +\& if ( !key ) { +\& /* current key doesn\*(Aqt exist or isn\*(Aqt valid */ +\& key = createkey(); /* something that you need to implement. +\& * createkey needs to initialise, a name, +\& * an aes_key, a hmac_key and optionally +\& * an expire time. */ +\& if ( !key ) { /* key couldn\*(Aqt be created */ +\& return 0; +\& } +\& } +\& memcpy(key_name, key\->name, 16); +\& +\& EVP_EncryptInit_ex(&ctx, EVP_aes_128_cbc(), NULL, key\->aes_key, iv); +\& HMAC_Init_ex(&hctx, key\->hmac_key, 16, EVP_sha256(), NULL); +\& +\& return 1; +\& +\& } else { /* retrieve session */ +\& key = findkey(name); +\& +\& if (!key || key\->expire < now() ) { +\& return 0; +\& } +\& +\& HMAC_Init_ex(&hctx, key\->hmac_key, 16, EVP_sha256(), NULL); +\& EVP_DecryptInit_ex(&ctx, EVP_aes_128_cbc(), NULL, key\->aes_key, iv ); +\& +\& if (key\->expire < ( now() \- RENEW_TIME ) ) { +\& /* return 2 \- this session will get a new ticket even though the current is still valid */ +\& return 2; +\& } +\& return 1; +\& +\& } +\& } +.Ve +.SH "RETURN VALUES" +.IX Header "RETURN VALUES" +returns 0 to indicate the callback function was set. +.SH "SEE ALSO" +.IX Header "SEE ALSO" +\&\fIssl\fR\|(3), \fISSL_set_session\fR\|(3), +\&\fISSL_session_reused\fR\|(3), +\&\fISSL_CTX_add_session\fR\|(3), +\&\fISSL_CTX_sess_number\fR\|(3), +\&\fISSL_CTX_sess_set_get_cb\fR\|(3), +\&\fISSL_CTX_set_session_id_context\fR\|(3), +.SH "HISTORY" +.IX Header "HISTORY" +This function was introduced in OpenSSL 0.9.8h |