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Fix leakage when the cacheline is 32-bytes in CBC_MAC_ROTATE_IN_PLACE #18050

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Fix leakage when the cacheline is 32-bytes in CBC_MAC_ROTATE_IN_PLACE #18050

wants to merge 1 commit into from

Commits on Apr 5, 2022

  1. Fix leakage when the cacheline is 32-bytes in CBC_MAC_ROTATE_IN_PLACE 

    rotated_mac is a 64-byte aligned buffer of size 64 and rotate_offset is secret.
Consider a weaker leakage model(CL) where only cacheline base address is leaked,
i.e address/32 for 32-byte cacheline(CL32).

Previous code used to perform two loads
    1. rotated_mac[rotate_offset ^ 32] and
    2. rotated_mac[rotate_offset++]
which would leak 2q + 1, 2q for 0 <= rotate_offset < 32
and 2q, 2q + 1 for 32 <= rotate_offset < 64

The proposed fix performs load operations which will always leak 2q, 2q + 1 and
selects the appropriate value in constant-time.
    @basavesh
    basavesh committed Apr 5, 2022
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