=head1 NAME
-SSL_CTX_set_tlsext_ticket_key_cb - set a callback for session ticket processing
+SSL_CTX_set_tlsext_ticket_key_evp_cb,
+SSL_CTX_set_tlsext_ticket_key_cb
+- set a callback for session ticket processing
=head1 SYNOPSIS
#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));
+ int SSL_CTX_set_tlsext_ticket_key_evp_cb(SSL_CTX sslctx,
+ int (*cb)(SSL *s, unsigned char key_name[16],
+ unsigned char iv[EVP_MAX_IV_LENGTH],
+ EVP_CIPHER_CTX *ctx, EVP_MAC_CTX *hctx, int enc));
+
+Deprecated since OpenSSL 3.0, can be hidden entirely by defining
+B<OPENSSL_API_COMPAT> with a suitable version value, see
+L<openssl_user_macros(7)>:
+
+ int 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));
=head1 DESCRIPTION
-SSL_CTX_set_tlsext_ticket_key_cb() sets a callback function I<cb> for handling
+SSL_CTX_set_tlsext_ticket_key_evp_cb() sets a callback function I<cb> for handling
session tickets for the ssl context I<sslctx>. Session tickets, defined in
RFC5077 provide an enhanced session resumption capability where the server
implementation is not required to maintain per session state. It only applies
ticket.
Before the callback function is started I<ctx> and I<hctx> have been
-initialised with EVP_CIPHER_CTX_init and HMAC_CTX_init respectively.
+initialised with L<EVP_CIPHER_CTX_reset(3)> and L<EVP_MAC_CTX_new(3)>
+respectively.
For new sessions tickets, when the client doesn't present a session ticket, or
an attempted retrieval of the ticket failed, or a renew option was indicated,
The I<name> is 16 characters long and is used as a key identifier.
The I<iv> length is the length of the IV of the corresponding cipher. The
-maximum IV length is B<EVP_MAX_IV_LENGTH> bytes defined in B<evp.h>.
+maximum IV length is B<EVP_MAX_IV_LENGTH> bytes defined in F<< <openssl/evp.h> >>.
The initialization vector I<iv> should be a random value. The cipher context
I<ctx> should use the initialisation vector I<iv>. The cipher context can be
-set using L<EVP_EncryptInit_ex(3)>. The hmac context can be set using
-L<HMAC_Init_ex(3)>.
+set using L<EVP_EncryptInit_ex(3)>. The hmac context and digest can be set using
+L<EVP_MAC_CTX_set_params(3)> with the B<OSSL_MAC_PARAM_KEY> and
+B<OSSL_MAC_PARAM_DIGEST> parameters respectively.
When the client presents a session ticket, the callback function with be called
with I<enc> set to 0 indicating that the I<cb> function should retrieve a set
the session ticket. The OpenSSL library expects that the I<name> will be used
to retrieve a cryptographic parameters and that the cryptographic context
I<ctx> will be set with the retrieved parameters and the initialization vector
-I<iv>. using a function like L<EVP_DecryptInit_ex(3)>. The I<hctx> needs to be
-set using L<HMAC_Init_ex(3)>.
+I<iv>. using a function like L<EVP_DecryptInit_ex(3)>. The key material and
+digest for I<hctx> need to be set using L<EVP_MAC_CTX_set_params(3)> with the
+B<OSSL_MAC_PARAM_KEY> and B<OSSL_MAC_PARAM_DIGEST> parameters respectively.
If the I<name> is still valid but a renewal of the ticket is required the
callback function should return 2. The library will call the callback again
=back
+The SSL_CTX_set_tlsext_ticket_key_cb() function is identical to
+SSL_CTX_set_tlsext_ticket_key_evp_cb() except that it takes a deprecated
+HMAC_CTX pointer instead of an EVP_MAC_CTX one.
+Before this callback function is started I<hctx> will have been
+initialised with L<EVP_MAC_CTX_new(3)> and the digest set with
+L<EVP_MAC_CTX_set_params(3)>.
+The I<hctx> key material can be set using L<HMAC_Init_ex(3)>.
+
=head1 NOTES
Session resumption shortcuts the TLS so that the client certificate
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
+using that session: even if the cipher suite supports forward secrecy. As
a result applications may wish to use multiple keys and avoid using long term
keys stored in files.
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
+For example if a cipher suite 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.
-=head1 EXAMPLES
-
-Reference Implementation:
- SSL_CTX_set_tlsext_ticket_key_cb(SSL, ssl_tlsext_ticket_key_cb);
- ....
-
- 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't exist or isn't 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't 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;
-
- }
- }
+=head1 RETURN VALUES
+returns 0 to indicate the callback function was set.
+=head1 EXAMPLES
-=head1 RETURN VALUES
+Reference Implementation:
-returns 0 to indicate the callback function was set.
+ SSL_CTX_set_tlsext_ticket_key_evp_cb(SSL, ssl_tlsext_ticket_key_cb);
+ ...
+
+ static int ssl_tlsext_ticket_key_cb(SSL *s, unsigned char key_name[16],
+ unsigned char *iv, EVP_CIPHER_CTX *ctx,
+ EVP_MAC_CTX *hctx, int enc)
+ {
+ OSSL_PARAM params[3];
+ your_type_t *key; /* something that you need to implement */
+
+ if (enc) { /* create new session */
+ if (RAND_bytes(iv, EVP_MAX_IV_LENGTH) <= 0)
+ return -1; /* insufficient random */
+
+ key = currentkey(); /* something that you need to implement */
+ if (key == NULL) {
+ /* current key doesn't exist or isn't 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 == NULL) /* key couldn't be created */
+ return 0;
+ }
+ memcpy(key_name, key->name, 16);
+
+ EVP_EncryptInit_ex(&ctx, EVP_aes_256_cbc(), NULL, key->aes_key, iv);
+
+ params[0] = OSSL_PARAM_construct_octet_string(OSSL_MAC_PARAM_KEY,
+ key->hmac_key, 32);
+ params[1] = OSSL_PARAM_construct_utf8_string(OSSL_MAC_PARAM_DIGEST,
+ "sha256", 0);
+ params[2] = OSSL_PARAM_construct_end();
+ EVP_MAC_CTX_set_params(hctx, params);
+
+ return 1;
+
+ } else { /* retrieve session */
+ time_t t = time(NULL);
+ key = findkey(key_name); /* something that you need to implement */
+
+ if (key == NULL || key->expire < t)
+ return 0;
+
+ params[0] = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_KEY,
+ key->hmac_key, 32);
+ params[1] = OSSL_PARAM_construct_utf8_string(OSSL_MAC_PARAM_DIGEST,
+ "sha256", 0);
+ params[2] = OSSL_PARAM_construct_end();
+ EVP_MAC_CTX_set_params(hctx, params);
+
+ EVP_DecryptInit_ex(&ctx, EVP_aes_256_cbc(), NULL, key->aes_key, iv);
+
+ if (key->expire < t - RENEW_TIME) { /* RENEW_TIME: implement */
+ /*
+ * return 2 - This session will get a new ticket even though the
+ * current one is still valid.
+ */
+ return 2;
+ }
+ return 1;
+ }
+ }
=head1 SEE ALSO
L<SSL_CTX_sess_set_get_cb(3)>,
L<SSL_CTX_set_session_id_context(3)>,
+=head1 HISTORY
+
+The SSL_CTX_set_tlsext_ticket_key_cb() function was deprecated in OpenSSL 3.0.
+
+The SSL_CTX_set_tlsext_ticket_key_evp_cb() function was introduced in
+OpenSSL 3.0.
+
=head1 COPYRIGHT
-Copyright 2014-2016 The OpenSSL Project Authors. All Rights Reserved.
+Copyright 2014-2021 The OpenSSL Project Authors. All Rights Reserved.
-Licensed under the OpenSSL license (the "License"). You may not use
+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
L<https://www.openssl.org/source/license.html>.
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