[base/hardened_memory] Add a hardened_add, hardened_sub, and hardened_range_check#29667
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nasahlpa merged 2 commits intolowRISC:earlgrey_1.0.0from Apr 9, 2026
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[base/hardened_memory] Add a hardened_add, hardened_sub, and hardened_range_check#29667nasahlpa merged 2 commits intolowRISC:earlgrey_1.0.0from
nasahlpa merged 2 commits intolowRISC:earlgrey_1.0.0from
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siemen11
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The OTBN calculates with shared keys using arithmetic masking. When we require the same operation on Ibex, we implement the hardened_add and the hardened_sub. Note that due to the addition/subtraction nature, this loop is not randomized against SCA. Implement a test that the hardened_sub of the hardened_add comes back to the same result. hardened_xor's test was missing, implement the same reversibility test for that as well. Signed-off-by: Siemen Dhooghe <sdhooghe@google.com>
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This is nice @siemen11. I will try to make use of these functions in the testcases for the ECC raw key import.
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Thanks @siemen11 this is helpful for some integrations.
Add a function that can check whether a value is between 0 and a given value N. The function works on word buffers and is protected against fault injections and is made to be constant time. However, the function is not protected against side-channel attacks as it operates on non-masked values. The function expects buffers in little-endian format. Signed-off-by: Siemen Dhooghe <sdhooghe@google.com>
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The OTBN calculates with shared keys using arithmetic masking. When we require the same operation on Ibex, we implement the hardened_add and the hardened_sub.
Note that due to the addition/subtraction nature, this loop is not randomized against SCA.
We also provide a range check function to check whether a buffer is between a value N and 0. Again, this is not hardened against SCA but it provides fault countermeasures.
Implement a test that the hardened_sub of the hardened_add comes back to the same result.
hardened_xor's test was missing, implement the same reversibility test for that as well.
Tests are also added for the range check.