According to https://www.bearssl.org/ctmul.html even single-precision
multiplication is not constant-time on some older platforms.
An added benefit of the new code is that it removes the somewhat mysterious
constant 0x1ff - which was selected because at that point the maximum value of
padlen was 256. The new code is perhaps a bit more readable for that reason.
Signed-off-by: Manuel Pégourié-Gonnard <manuel.pegourie-gonnard@arm.com>
The previous code used comparison operators >= and == that are quite likely to
be compiled to branches by some compilers on some architectures (with some
optimisation levels).
For example, take the following function:
void old_update( size_t data_len, size_t *padlen )
{
*padlen *= ( data_len >= *padlen + 1 );
}
With Clang 3.8, let's compile it for the Arm v6-M architecture:
% clang --target=arm-none-eabi -march=armv6-m -Os foo.c -S -o - |
sed -n '/^old_update:$/,/\.size/p'
old_update:
.fnstart
@ BB#0:
.save {r4, lr}
push {r4, lr}
ldr r2, [r1]
adds r4, r2, #1
movs r3, #0
cmp r4, r0
bls .LBB0_2
@ BB#1:
mov r2, r3
.LBB0_2:
str r2, [r1]
pop {r4, pc}
.Lfunc_end0:
.size old_update, .Lfunc_end0-old_update
We can see an unbalanced secret-dependant branch, resulting in a total
execution time depends on the value of the secret (here padlen) in a
straightforward way.
The new version, based on bit operations, doesn't have this issue:
new_update:
.fnstart
@ BB#0:
ldr r2, [r1]
subs r0, r0, #1
subs r0, r0, r2
asrs r0, r0, #31
bics r2, r0
str r2, [r1]
bx lr
.Lfunc_end1:
.size new_update, .Lfunc_end1-new_update
(As a bonus, it's smaller and uses less stack.)
While there's no formal guarantee that the version based on bit operations in
C won't be translated using branches by the compiler, experiments tend to show
that's the case [1], and it is commonly accepted knowledge in the practical
crypto community that if we want to sick to C, bit operations are the safest
bet [2].
[1] https://github.com/mpg/ct/blob/master/results
[2] https://github.com/veorq/cryptocoding
Signed-off-by: Manuel Pégourié-Gonnard <manuel.pegourie-gonnard@arm.com>
* Reworked the cipher context once again to be more robustly defined
* Removed redundant memset
* Unified behaviour on failure between driver and software in cipher_finish
* Cipher test driver setup function now also returns early when its status
is overridden, like the other test driver functions
* Removed redundant test cases
* Added bad-order checking to verify the driver doesn't get called where
the spec says it won't.
Signed-off-by: Steven Cooreman <steven.cooreman@silabs.com>
As pointed out by Ronald. The key slot is populated using
get_key_from_slot, and after calling the driver the slot is
validated to not contain an external key, so calling
get_transparent_key is superfluous.
Signed-off-by: Steven Cooreman <steven.cooreman@silabs.com>
Added zeroization of the wrapper context on failure/abort, and reliance on
the crypto core to not call an uninitialised wrapper.
Signed-off-by: Steven Cooreman <steven.cooreman@silabs.com>
Once an operation has been 'accepted' by a driver, the remainder is bound
to the same driver, since driver-specific context structs cannot be shared.
This provides a pretty good gate mechanism for the fallback logic, too.
Signed-off-by: Steven Cooreman <steven.cooreman@silabs.com>
ssl_tls1_3_keys.c exports a structure containing all labels used
in the TLS 1.3 key schedule, but the TLS 1.3 key scheduling unit
tests so far replicated those labels in the test file. In particular,
wrong label values in ssl_tls1_3_keys.c wouldn't have been caught
by the unit tests.
This commit modifies the TLS 1.3 key schedule unit tests to use
the TLS 1.3 labels as exported by ssl_tls1_3_keys.c. This not only
makes sure that those labels are correct, but also avoids hardcoding
their hex-encoding in the test file.
Signed-off-by: Hanno Becker <hanno.becker@arm.com>
Needed to make additional fixes so that when MBEDTLS_USE_PSA_CRYPTO
is defined, the depends-hashes test will succeed. There are two
versions of the ecdsa_verify_wrap() function, one with
MBEDTLS_USE_PSA_CRYPTO and when when it is not enabled. The non PSA
version is not using the md_alg parameter since it is not required.
The PSA version was using that parameter to derive a different value
it needed for PSA_ALG_ECDSA. The arguement of PSA_ALG_ECDSA is
ignored for psa_sign_hash and psa_verify_hash. It is present because
it is used and must be a valid hash, not zero, for psa_sign_hash
(but not psa_verify_hash) with PSA_ALG_DETERMINISTIC_ECDSA, and it is
needed for psa_sign_message and psa_verify_message which are not
implemented yet. The local parameter now uses PSA_ALG_ECDSA_ANY for
the verify function to avoid using the md_alg parameter and avoids
returning incorrect error codes.
Fixes#3587
Signed-off-by: John Durkop <john.durkop@fermatsoftware.com>
This is in line with how the entries of the TLS 1.3 label
structure `mbedtls_ssl_tls1_3_labels` are initialized.
Signed-off-by: Hanno Becker <hanno.becker@arm.com>
