This is to enable hardening the security when changing
states in state machine so that the state cannot be changed by bit flipping.
The later commit changes the enumerations so that the states have large
hamming distance in between them to prevent this kind of attack.
Duplicating the g_rng_function variable in ecc_dsa.c means it's not the same
as set in ecc.c, resulting if no randomisation here. The proper way to access
the RNG function from outside ecc.c is uECC_get_rng(), so use that.
This is a side-port of upstream commit
87d74dd8d64a99aaa188961fe763d0841c5abfef
I've verified that there are no other occurrences (the duplication of
g_rng_function in ecc_dh.c had already been removed earlier when centralising
projective coordinate randomisation to mult_safer()).
-Replace usage of rand() with mbedtls_platform_random_in_range()
-Prevent for-ever loop by hardcoding SCA countermeasure position in
case of used random function is always returning constant number.
-Use separate control bytes for start and final round to get them
randomized separately.
-Remove struct name.
-Fix comments and follow Mbed TLS coding style.
SCA CM implementation caused AES performance drop. For example
AES-CCM-128 calculation speed was dropped from 240 KB/s to 111 KB/s.
(-54%), Similarily AES-CBC-128 calculation speed was dropped from
536 KB/s to 237 KB/s (-56%).
Use functions instead of macros to reduce code indirections and
therefore increase performance. Now the performance is 163 KB/s for
AES-CCM-128 (-32%) and 348 KB/s for AES-CBC-128 (-35%).
When SCA countermeasures are activated the performance is as follows:
122 KB/s for AES-CCM-128 (-49%) and 258 KB/s for AES-CBC-128 (-52%)
compared to the original AES implementation.
Use control bytes to instruct AES calculation rounds. Each
calculation round has a control byte that indicates what data
(real/fake) is used and if any offset is required for AES data
positions.
First and last AES calculation round are calculated with SCA CM data
included. The calculation order is randomized by the control bytes.
Calculations between the first and last rounds contains 3 SCA CMs
in randomized positions.
- Add configuration for AES_SCA_COUNTERMEASURES to config.h. By
default the feature is disabled.
- Add AES_SCA_COUNTERMEASURES configuration check to check_config.h
- Add AES_SCA_COUNTERMEASURES test to all.sh
- 3 additional dummy AES rounds calculated with random data for each
AES encryption/decryption
- additional rounds can be occur in any point in sequence of rounds
Found by the IAR compiler.
While at it, make 'diff' non-volatile in uECC_check_curve_integrity(), as
there is no good reason to make it volatile, and making it volatile only
increases the code size and the burden of defining access ordering.
- MSVC doesn't like -1u
- We need to include platform.h for MBEDTLS_ERR_PLATFORM_FAULT_DETECTED - in
some configurations it was already included indirectly, but not in all
configurations, so better include it directly.
This commit first changes the return convention of EccPoint_mult_safer() so
that it properly reports when faults are detected. Then all functions that
call it need to be changed to (1) follow the same return convention and (2)
properly propagate UECC_FAULT_DETECTED when it occurs.
Here's the reverse call graph from EccPoint_mult_safer() to the rest of the
library (where return values are translated to the MBEDTLS_ERR_ space) and test
functions (where expected return values are asserted explicitly).
EccPoint_mult_safer()
EccPoint_compute_public_key()
uECC_compute_public_key()
pkparse.c
tests/suites/test_suite_pkparse.function
uECC_make_key_with_d()
uECC_make_key()
ssl_cli.c
ssl_srv.c
tests/suites/test_suite_pk.function
tests/suites/test_suite_tinycrypt.function
uECC_shared_secret()
ssl_tls.c
tests/suites/test_suite_tinycrypt.function
uECC_sign_with_k()
uECC_sign()
pk.c
tests/suites/test_suite_tinycrypt.function
Note: in uECC_sign_with_k() a test for uECC_vli_isZero(p) is suppressed
because it is redundant with a more thorough test (point validity) done at the
end of EccPoint_mult_safer(). This redundancy was introduced in a previous
commit but not noticed earlier.
We don't really need a secure hash for that, something like CRC32 would
probably be enough - but we have SHA-256 handy, not CRC32, so use that for the
sake of simplicity.
By semi-internal I mean functions that are only public because they're used in
more than once compilation unit in the library (for example in ecc.c and
ecc_dsa.c) but should not really be part of the public-facing API.
Same motivation as for the other parameters. This is the last one, making the
curve structure empty, so it's left with a dummy parameter for legal reasons.
