One test for running with MBEDTLS_ECDH_C on and one
for running MBEDTLS_ECDH_C off. Run ssl-opt.sh with Default, DTLS
and compatibility tests with TLS-ECDHE-ECDSA-WITH-AES-256-CBC-SHA.
tinyCrypt is still tested in the baremetal tests since it
is enabled in baremetal.h. Tests for minimal modifictions
of the default / full config enabling tinyCrypt will be
added elsewhere.
The use of tinyCrypt is restricted Secp256r1-only, and a check in
ssl_ciphersuite_is_match() ensures that an EC ciphersuite is chosen
only if the client advertised support for Secp256r1, too.
In a way inconsistent with the rest of the library restricting the
use of tinyCrypt to pure-ECDHE, the previous ServerKeyExchange writing
routine would use tinyCrypt also for ECDHE-PSK-based ciphersuites.
This commit fixes this.
Previously, MBEDTLS_KEY_EXCHANGE_ECDH[E]_XXX_ENABLED would imply
that MBEDTLS_ECDH_C is set, but with the introduction of tinyCrypt
as an alternative ECDH implementation, this is no longer the case.
tinyCrypt uses a global RNG without context parameter while Mbed TLS in its
default configuration uses RNG+CTX bound to the SSL configuration.
This commit restricts the use of tinyCrypt to configurations that use a
global RNG function with NULL context by setting MBEDTLS_SSL_CONF_RNG in
the configuration. This allows to define a wrapper RNG to be used by
tinyCrypt which maps to this global hardcoded RNG.
Eventually, all HS parsing/writing functions should take an arbitrary buffer +
length pair as their argument, and return MBEDTLS_ERR_SSL_BUFFER_TOO_SMALL if
the provided buffer is too short. So far, we've only made a first step by
allowing to pass an arbitrary buffer, but don't yet add bounds checks
throughout. While deliberate for now, this must be clearly documented.
This makes grepping the functions more difficult, and also leads to compilation failures
when trying to build the library from a single source file (which might be useful for
code-size reasons).
Previously, ssl_ecrs_ske_start_processing was used to indicate that
the ServerKeyExchange has been fetched from the record layer, but
that parsing its ECDHE parameter component has been preempted by the
restartable ECP feature. On re-entry of ssl_parse_server_key_exchange()
in this state, the code would directly jump into the parsing routine.
However, the only non-reentrant code that's jumped over this way is
the record fetching routine mbedtls_ssl_parse_record(), which is now
made re-entrant by setting `ssl->keep_current_message = 1` in case of
pre-emption due to restartable ECC.
The ssl_ecrs_ske_start_processing state is therefore redundant and
can be removed, which is what this commit does.
IAR doesn't like `((void) var);` as a means to indicate an unused
variable if that variable hasn't been initialized before. Make it
happy by initializing the variable before.
ssl_server_key_exchange_parse() is compiled even if there's no ciphersuite
enabled which uses it (for example, that's the case in RSA-only builds).
The rationale for that is to avoid cluttering the code with numerous
compile-time guards. A consequence, however, is the top of
ssl_server_key_exchange_parse() contains declarations for variables
which are never put to use, and rightfully leading to compiler warnings.
This commit silences these warnings by putting `((void) VAR);` statements
in the branch which detects if we ever happen to call the function in an
unexpected ciphersuite.
