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| author | Jack Lloyd <[email protected]> | 2017-10-20 18:03:27 -0400 |
|---|---|---|
| committer | Jack Lloyd <[email protected]> | 2017-10-20 18:03:27 -0400 |
| commit | d34d1edc22e947b8b4a95ee86d268592d03675a8 (patch) | |
| tree | f1447db122eafeeecf216744019b6c4ea28ed4c4 /doc/manual/side_channels.rst | |
| parent | 0b246a836cc106695516d532412b79068a913bc2 (diff) | |
Update side channel notes
Diffstat (limited to 'doc/manual/side_channels.rst')
| -rw-r--r-- | doc/manual/side_channels.rst | 13 |
1 files changed, 5 insertions, 8 deletions
diff --git a/doc/manual/side_channels.rst b/doc/manual/side_channels.rst index f7b7cdd6d..5656001e4 100644 --- a/doc/manual/side_channels.rst +++ b/doc/manual/side_channels.rst @@ -104,12 +104,9 @@ See eme_oaep.cpp. Modular Exponentiation ------------------------ -Modular exponentiation uses a fixed window algorithm with Montgomery representation. -In the current code, information about the exponent is leaked through the -sequence of memory indexes; we currently rely on randomized blinding at higher -levels of the cryptographic stack to hide this. A future project would be to -change this to use either Montgomery ladder or use a side channel silent table -lookup. See powm_mnt.cpp. +Modular exponentiation uses a fixed window algorithm with Montgomery +representation. A side channel silent table lookup is used to access the +precomputed powers. See powm_mnt.cpp. The Karatsuba multiplication algorithm has some conditional branches that probably expose information through the branch predictor, but probably? does not @@ -239,8 +236,8 @@ const time 8x bitsliced AES could be integrated fairly easily. GCM --------------------- -On x86 platforms which support the clmul instruction, GCM support is fast and -constant time. +On platforms that support a carryless multiply instruction (recent x86 and ARM), +GCM is fast and constant time. On all other platforms, GCM is slow and constant time. It uses a simple bit at at time loop. It would be much faster using a table lookup, but we wish to avoid |