Previously, ecp_add_mixed(), commputing say P+Q, would allow for the
Q parameter to have an unset Z coordinate as a shortcut for Z == 1.
This was leveraged during computation and usage of the T-table
(storing low multiples of the to-be-multiplied point on the curve).
It is a potentially error-prone corner case, though, since an MPIs
with unset data pointer coordinate and limb size 0 is also a valid
representation of the number 0.
As a first step towards removing ECP points with unset Z coordinate,
the constant time T-array getter ecp_select_comb() has previously
been modified to return 'full' mbedtls_ecp_point structures,
including a 1-initialized Z-coordinate.
Similarly, this commit ...
- Modifies ecp_normalize_jac_many() to set the Z coordinates
of the points it operates on to 1 instead of freeing them.
- Frees the Z-coordinates of the T[]-array explicitly
once the computation and normalization of the T-table has finished.
As a minimal functional difference between old and new code,
the new code also frees the Z-coordinate of T[0]=P, which the
old code did not.
- Modifies ecp_add_mixed() to no longer allow unset Z coordinates.
Except for the post-precomputation storage form of the T[] array,
the code does therefore no longer use EC points with unset Z coordinate.
Signed-off-by: Hanno Becker <hanno.becker@arm.com>
ecp_select_comb() did previously not set the Z coordinate of the target point.
Instead, callers would either set it explicitly or leave it uninitialized,
relying on the (only partly upheld) convention that sometimes an uninitialized
Z value represents 1.
This commit modifies ecp_select_comb() to always set the Z coordinate to 1.
This comes at the cost of memory for a single coordinate, which seems worth
it for the increased robustness.
Signed-off-by: Hanno Becker <hanno.becker@arm.com>
This improves readibility and prepares for further changes
like the introduction of a single double-width temporary for
ECP arithmetic.
Signed-off-by: Hanno Becker <hanno.becker@arm.com>
`ecp_add_mixed()` and `ecp_double_jac()` are the core subroutines
for elliptic curve arithmetic, and as such crucial for the performance
of ECP primitives like ECDHE and ECDSA.
This commit provides a very slight simplification and performance and
memory usage improvement to `ecp_add_mixed()` by removing the use of
three temporary MPIs used for coordinate calculations.
Where those variables were used, the code now writes directly to the
coordinate MPIs of the target elliptic curve point.
This is a valid change even if there is aliasing between input and
output, since at the time any of the coordinate MPIs in question is
written, the corresponding coordinates of both inputs are no longer
read.
(The analogous change in `ecp_double_jac()` can not be made since
this property does not hold for `ecp_double_jac()`.)
Signed-off-by: Hanno Becker <hanno.becker@arm.com>
Having an automatically generated header file makes it harder to have
working build scripts. The content of ssl_debug_helpers_generated.h isn't
likely to change often, so we can update it manually.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
Running `generate_ssl_debug_helpers.py` generates both
`ssl_debug_helpers_generated.c` and `ssl_debug_helpers_generated.h`.
List the `.h` file as well as the `.c` file in `check-generated-files.sh` so
that `check-generated-files.sh -u` will complain if it isn't up to date.
List it in `Makefile` and `CMakeLists.txt` so that parallel builds know when
to wait until the `.h` file is present. In `Makefile`, declare the `.c` file
as depending on the `.h` file for order. This way, a dependency for either
will wait until the `.h` file is present, and since the `.h` file is
generated after the `.c` file, this guarantees that the `.c` file is
present.
This fixes random failures of `make -j` from a fresh checkout.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
Zeroize temporary buffers used to sanity-check the signature.
If there is an error, overwrite the tentative signature in the output
buffer.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
Declare mbedtls_md functions as MBEDTLS_CHECK_RETURN_TYPICAL, meaning that
their return values should be checked.
Do check the return values in our code. We were already doing that
everywhere for hash calculations, but not for HMAC calculations.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
Zeroize local MAC variables used for CBC+HMAC cipher suites. In encryption,
this is just good hygiene but probably not needed for security since the
data protected by the MAC that could leak is about to be transmitted anyway.
In DTLS decryption, this could be a security issue since an adversary could
learn the MAC of data that they were trying to inject. At least with
encrypt-then-MAC, the adversary could then easily inject a datagram with
a corrected packet. TLS would still be safe since the receiver would close
the connection after the bad MAC.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
As we have now a minimal viable implementation of TLS 1.3,
let's remove EXPERIMENTAL from the config option enabling
it.
Signed-off-by: Ronald Cron <ronald.cron@arm.com>
