This issue has been reported by Tuba Yavuz, Farhaan Fowze, Ken (Yihang) Bai,
Grant Hernandez, and Kevin Butler (University of Florida) and
Dave Tian (Purdue University).
In AES encrypt and decrypt some variables were left on the stack. The value
of these variables can be used to recover the last round key. To follow best
practice and to limit the impact of buffer overread vulnerabilities (like
Heartbleed) we need to zeroize them before exiting the function.
There is a 50% performance drop in the SCA_CM enabled encrypt and
decrypt functions. Therefore use the older version of encrypt/decypt
functions when SCA_CM is disabled.
-Do not reuse any part of randomized number, use separate byte for
each purpose.
-Combine some separate loops together to get rid of gap between them
-Extend usage of flow_control
When reading the input, buffer will be initialised with random data
and the reading will start from a random offset. When writing the data,
the output will be initialised with random data and the writing will start
from a random offset.
-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
-Add config option for AES encyption only to config.h. Feature is
disabled by default.
-Enable AES encrypt only feature in baremetal.h configuration
-Remove AES encypt only feature from full config
We call xxx_init() on a structure when it has been freshly allocated (on the
stack or heap).
At this point it contains random-looking data none of which should be
sensitive, as all sensitive data is wiped using mbedtls_platform_zeroize()
when we're done using it and the memory area is going to be reclaimed (by
exiting the function or free()ing the buffer).
Steps:
1. sed -i 's/\bmemset(\([^)]\)/mbedtls_platform_memset(\1/g' library/*.c tinycrypt/*.c include/mbedtls/*.h scripts/data_files/*.fmt
2. Manually edit library/platform_util.c to revert to memset() in the
implementations of mbedtls_platform_memset() and mbedtls_platform_memcpy()
3. egrep -n '\<memset\>' library/*.c include/mbedtls/*.h tinycrypt/*.c
The remaining occurrences are in three categories:
a. From point 2 above.
b. In comments.
c. In the initialisation of memset_func, to be changed in a future commit.
This commit improves hygiene and formatting of macro definitions
throughout the library. Specifically:
- It adds brackets around parameters to avoid unintended
interpretation of arguments, e.g. due to operator precedence.
- It adds uses of the `do { ... } while( 0 )` idiom for macros that
can be used as commands.
The check was already done later when calling ECB, (as evidenced by the tests
passing, which have a call with data_unit set to NULL), but it's more readable
to have it here too, and more helpful when debugging.
Deprecate the module-specific XXX_HW_ACCEL_FAILED and
XXX_FEATURE_UNAVAILABLE errors, as alternative implementations should now
return `MBEDTLS_ERR_PLATFORM_HW_FAILED` and
`MBEDTLS_ERR_PLATFORM_FEATURE_UNSUPPORTED`.
Correct a typo in an AES XTS implementation comment where the relevant
NIST standard was incorrectly referred to as NIST 80-38E instead of NIST
800-38E.
