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tls13: srv: Add/Improve comments

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Signed-off-by: Ronald Cron <ronald.cron@arm.com>
This commit is contained in:
Ronald Cron 2024-03-05 09:05:46 +01:00
parent 74a1629231
commit 3811765c0c
1 changed files with 37 additions and 3 deletions
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40
library/ssl_tls13_server.c
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@ -50,9 +50,9 @@ static void ssl_tls13_select_ciphersuite(
*selected_ciphersuite_info = NULL;
/*
* This function assumes that the length of the list of ciphersuites is
* even and it should have been checked it is so in the main ClientHello
* parsing function. Double check here.
* In a compliant ClientHello the byte-length of the list of ciphersuites
* is even and this function relies on this fact. This should have been
* checked in the main ClientHello parsing function. Double check here.
*/
if ((cipher_suites_end - cipher_suites) & 1) {
return;
@ -146,6 +146,27 @@ static int ssl_tls13_parse_key_exchange_modes_ext(mbedtls_ssl_context *ssl,
return 0;
}
/*
* Non-error return values of
* ssl_tls13_offered_psks_check_identity_match_ticket() and
* ssl_tls13_offered_psks_check_identity_match(). They are positive to
* not collide with error codes that are negative. Zero
* (SSL_TLS1_3_PSK_IDENTITY_MATCH) in case of success as it may be propagated
* up by the callers of this function as a generic success condition.
*
* The return value SSL_TLS1_3_PSK_IDENTITY_MATCH_BUT_PSK_NOT_USABLE means
* that the pre-shared-key identity matches that of a ticket or an external
* provisioned pre-shared-key. We have thus been able to retrieve the
* attributes of the pre-shared-key but at least one of them does not meet
* some criteria and the pre-shared-key cannot be used. For example, a ticket
* is expired or its version is not TLS 1.3. Note eventually that the return
* value SSL_TLS1_3_PSK_IDENTITY_MATCH_BUT_PSK_NOT_USABLE does not have
* anything to do with binder check. A binder check is done only when a
* suitable pre-shared-key has been selected and only for that selected
* pre-shared-key: if the binder check fails, we fail the handshake and we do
* not try to find another pre-shared-key for which the binder check would
* succeed as recommended by the specification.
*/
#define SSL_TLS1_3_PSK_IDENTITY_DOES_NOT_MATCH 2
#define SSL_TLS1_3_PSK_IDENTITY_MATCH_BUT_PSK_NOT_USABLE 1
#define SSL_TLS1_3_PSK_IDENTITY_MATCH 0
@ -220,6 +241,10 @@ static int ssl_tls13_offered_psks_check_identity_match_ticket(
goto exit;
}
/*
* The identity matches that of a ticket. Now check that it has suitable
* attributes and bet it will not be the case.
*/
ret = SSL_TLS1_3_PSK_IDENTITY_MATCH_BUT_PSK_NOT_USABLE;
if (session->tls_version != MBEDTLS_SSL_VERSION_TLS1_3) {
@ -281,6 +306,9 @@ static int ssl_tls13_offered_psks_check_identity_match_ticket(
}
#endif /* MBEDTLS_HAVE_TIME */
/*
* All good, we have found a suitable ticket.
*/
ret = SSL_TLS1_3_PSK_IDENTITY_MATCH;
exit:
@ -360,6 +388,12 @@ static int ssl_tls13_offered_psks_check_identity_match(
return SSL_TLS1_3_PSK_IDENTITY_DOES_NOT_MATCH;
}
/*
* Non-error return values of ssl_tls13_offered_psks_check_binder_match().
* They are positive to not collide with error codes that are negative. Zero
* (SSL_TLS1_3_BINDER_MATCH) in case of success as it may be propagated up
* by the callers of this function as a generic success condition.
*/
#define SSL_TLS1_3_BINDER_DOES_NOT_MATCH 1
#define SSL_TLS1_3_BINDER_MATCH 0
MBEDTLS_CHECK_RETURN_CRITICAL