The NO_INLINE annotation of tls_prf_sha256() and tls_prf_sha384() from
the last commit surprisingly had an influence on ARMC5 compilation in
that tls_prf_generic() was no longer automatically inlined into
tls_prf_sha256() if only the latter was enabled (and is the point
where tls_prf_generic() is called). This commit forces inlining
of tls_prf_generic() in this case.
Usually, compilers are clever enough to pick the best inlining
strategy, but in this instance, it appears that compiling on ARMC6,
the compilers inlines xxx_prf_yyy() and xxx_calc_finished_yyy()
even though it really shouldn't. Forbid inlining through the use
of __attribute__((noinline)).
Somehow, at least ARMC5 isn't able to recognize this automatically.
Since some of the arguments to ssl_populate_transform() are compile-
time constants in reduced configurations, inlining leads to slightly
shorter code.
This saves a few bytes in configurations where only one hash
is enabled, and configurations allowing multiple hashes probably
don't care about code-size anyway.
This function is called on client-only once the ciphersuite has
been chosen and it it is known which digest the client will need
for the handshake transcript throughout the handshake, and causes
all other unneeded handshake transcripts to be discontinued.
(On the server, we cannot call this function because we don't know
which hash the client will those in its CertificateVerify message).
However, the benefit of this call is marginal, since transcript hash
computation is negligible compared to asymmetric crypto, and moreover
the handshake transcript contexts for the unused digests are still
stored in the SSL handshake parameter structure and not freed until
the end of the handshake.
Finally, if we're running on a _really_ constrained client, there
will be only one hash function enabled anyway, and in this case
the checksum optimization has no effect.
This commit therefore removes checksum optimization altogether,
saving some code on constrained systems.
- a comment regarding the implementation of hmac_drbg_reseed_core()
was misplaced.
- add more references to the standard, and add details on how the
comments in the code refer to various parts of the standard.
Now function mbedtls_ssl_set_hostname is compile-time configurable
in config.h with define MBEDTLS_X509_REMOVE_HOSTNAME_VERIFICATION.
This affects to many x509 API's. See config.h for details.
According to SP800-90A, the DRBG seeding process should use a nonce
of length `security_strength / 2` bits as part of the DRBG seed. It
further notes that this nonce may be drawn from the same source of
entropy that is used for the first `security_strength` bits of the
DRBG seed. The present HMAC DRBG implementation does that, requesting
`security_strength * 3 / 2` bits of entropy from the configured entropy
source in total to form the initial part of the DRBG seed.
However, some entropy sources may have thresholds in terms of how much
entropy they can provide in a single call to their entropy gathering
function which may be exceeded by the present HMAC DRBG implementation
even if the threshold is not smaller than `security_strength` bits.
Specifically, this is the case for our own entropy module implementation
which only allows requesting at most 32 Bytes of entropy at a time
in configurations disabling SHA-512, and this leads to runtime failure
of HMAC DRBG when used with Mbed TLS' own entropy callbacks in such
configurations.
This commit fixes this by splitting the seed entropy acquisition into
two calls, one requesting `security_strength` bits first, and another
one requesting `security_strength / 2` bits for the nonce.
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.
