The loop ends when there are no more bits to process, with one twist: when
that happens, we need to clear the window one last time. Since the window
does not start empty (E_limbs==0 is not supported), the loop always starts
with a non-empty window and some bits to process. So it's correct to move
the window clearing logic to the end of the loop. This lets us exit the loop
when the end of the exponent is reached.
It would be clearer not to do the final window clearing inside the loop, so
we wouldn't need to repeat the loop termination condition (end of exponent
reached) inside the loop. However, this requires duplicating the code to
clear the window. Empirically, this causes a significant code size increase,
even if the window clearing code is placed into a function.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
We are looking at the exponent at limb granularity and therefore
exponent bits can't go below 32.
The `mpi_` prefix is also removed as it is better not to have prefix at
all than to have just a partial. (Full prefix would be overly long and
would hurt readability.)
Signed-off-by: Janos Follath <janos.follath@arm.com>
Now that we have a function that calls
mbedtls_mpi_core_ct_uint_table_lookup(), the compiler won't complain if
we make it static.
Signed-off-by: Janos Follath <janos.follath@arm.com>
On platforms with size_t different from int, mismatch between size_t and
mpi_uint can cause incorrect results or complaints from the compiler.
Signed-off-by: Janos Follath <janos.follath@arm.com>
mpi_core_exp_mod: Cast local variable explicitly
Signed-off-by: Janos Follath <janos.follath@arm.com>
This will be needed for extracting modular exponentiation from the
prototype. The function signature is kept aligned to the prototype, but
the implementation is new. (The implementation of this function in the
prototype has further optimisations which are out of scope for now.)
The function is not reused in the bignum counterpart as it will become
redundant soon.
This function is meant to be static, but doesn't have the qualifier as
it is not used yet and would cause compiler warnings. The
MBEDTLS_STATIC_TESTABLE macro will be added in a later commit.
Signed-off-by: Janos Follath <janos.follath@arm.com>
'mbedtls_mpi_core_get_mont_R2_unsafe' aligns const
keyword to match the style of the rest of the module.
Documentation is also updated to remove
`MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED`.
Signed-off-by: Minos Galanakis <minos.galanakis@arm.com>
We used to include platform.h only when MBEDTLS_PLATFORM_C was enabled, and
to define ad hoc replacements for mbedtls_xxx functions on a case-by-case
basis when MBEDTLS_PLATFORM_C was disabled. The only reason for this
complication was to allow building individual source modules without copying
platform.h. This is not something we support or recommend anymore, so get
rid of the complication: include platform.h unconditionally.
There should be no change in behavior since just including the header should
not change the behavior of a program.
This commit replaces most occurrences of conditional inclusion of
platform.h, using the following code:
```
perl -i -0777 -pe 's!#if.*\n#include "mbedtls/platform.h"\n(#else.*\n(#define (mbedtls|MBEDTLS)_.*\n|#include <(stdarg|stddef|stdio|stdlib|string|time)\.h>\n)*)?#endif.*!#include "mbedtls/platform.h"!mg' $(git grep -l '#include "mbedtls/platform.h"')
```
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
Since a is not a pointer, it is passed by value and declaring it const
doesn’t make any sense and on the first read can make me miss the fact
that a is not a pointer.
Signed-off-by: Janos Follath <janos.follath@arm.com>
Co-authored-by: Tom Cosgrove <81633263+tom-cosgrove-arm@users.noreply.github.com>
Co-authored-by: Werner Lewis <Werner.Lewis@arm.com>
Signed-off-by: Janos Follath <janos.follath@arm.com>
Co-authored-by: Tom Cosgrove <81633263+tom-cosgrove-arm@users.noreply.github.com>
Co-authored-by: Werner Lewis <werner.wmlewis@gmail.com>
Signed-off-by: Janos Follath <janos.follath@arm.com>
Numbers:
- A, B for mbedtls_mpi_uint* operands
- a, b for mbedtls_mpi_uint operands
- X or x for result
- HAC references where applicable
Lengths:
- Reserve size or length for length/size in bytes or byte buffers.
- For length of mbedtls_mpi_uint* buffers use limbs
- Length parameters are qualified if possible (eg. input_length or
a_limbs)
Setup functions:
- The parameters match the corresponding structure member's name
- The structure to set up is a standard lower case name even if in other
functions different naming conventions would apply
Scope of changes/conventions:
- bignum_core
- bignum_mod
- bignum_mod_raw
Signed-off-by: Janos Follath <janos.follath@arm.com>
In the new bignum files (bignum_core.c, bignum_mod_raw.c and
bignum_mod.c) the loop variables are declared in the loop head wherever
this change is beneficial.
There are loops where the loop variable is used after the end of the
loop (this might not be good practice, but that is out of scope for this
commit) and others where there are several loop variables and declaring
them there would hurt readability.
Signed-off-by: Janos Follath <janos.follath@arm.com>
Skip reading if output pointer is NULL even if the length of the input buffer is 0.
The memory sanitizer will mark this as an error.
Signed-off-by: Gabor Mezei <gabor.mezei@arm.com>
These functions have full documentation in the header. Maintaing two
copies does not worth the effort and having an out of sync reduced
duplicate is not helpful.
Signed-off-by: Janos Follath <janos.follath@arm.com>
This used to resize MPIs in the legacy interface, which is not
needed/possible as the new interface has fixed size MPIs.
Inlining this function makes the code easier to read and maintain, while
there is no obvious drawback to it.
Signed-off-by: Janos Follath <janos.follath@arm.com>
A null pointer dereference, or null pointer plus small offset, is a
clean runtime error in most environments. So it's not particularly
useful to protect against this.
While at it make a null pointer check that is actually necessary more
robust.
Signed-off-by: Janos Follath <janos.follath@arm.com>
Extract functions declared in bignum_core.h into a source file with a
matching name.
We are doing this because:
- This is a general best practice/convention
- We hope that this will make resolving merge conflicts in the future
easier
- Having them in a unified source file is a premature optimisation at
this point
Signed-off-by: Janos Follath <janos.follath@arm.com>
