We currently require clmul instructions for constant-time GHASH
on x86_64. Otherwise, it falls back to a variable-time 4-bit table
implementation. However, a significant proportion of clients lack these
instructions.
Inspired by vpaes, we can use pshufb and a slightly different order of
incorporating the bits to make a constant-time GHASH. This requires
SSSE3, which is very common. Benchmarking old machines we had on hand,
it appears to be a no-op on Sandy Bridge and a small slowdown for
Penryn.
Sandy Bridge (Intel Pentium CPU 987 @ 1.50GHz):
(Note: these numbers are before 16-byte-aligning the table. That was an
improvement on Penryn, so it's possible Sandy Bridge is now better.)
Before:
Did 4244750 AES-128-GCM (16 bytes) seal operations in 4015000us (1057222.9 ops/sec): 16.9 MB/s
Did 442000 AES-128-GCM (1350 bytes) seal operations in 4016000us (110059.8 ops/sec): 148.6 MB/s
Did 84000 AES-128-GCM (8192 bytes) seal operations in 4015000us (20921.5 ops/sec): 171.4 MB/s
Did 3349250 AES-256-GCM (16 bytes) seal operations in 4016000us (833976.6 ops/sec): 13.3 MB/s
Did 343500 AES-256-GCM (1350 bytes) seal operations in 4016000us (85532.9 ops/sec): 115.5 MB/s
Did 65250 AES-256-GCM (8192 bytes) seal operations in 4015000us (16251.6 ops/sec): 133.1 MB/s
After:
Did 4229250 AES-128-GCM (16 bytes) seal operations in 4016000us (1053100.1 ops/sec): 16.8 MB/s [-0.4%]
Did 442250 AES-128-GCM (1350 bytes) seal operations in 4016000us (110122.0 ops/sec): 148.7 MB/s [+0.1%]
Did 83500 AES-128-GCM (8192 bytes) seal operations in 4015000us (20797.0 ops/sec): 170.4 MB/s [-0.6%]
Did 3286500 AES-256-GCM (16 bytes) seal operations in 4016000us (818351.6 ops/sec): 13.1 MB/s [-1.9%]
Did 342750 AES-256-GCM (1350 bytes) seal operations in 4015000us (85367.4 ops/sec): 115.2 MB/s [-0.2%]
Did 65250 AES-256-GCM (8192 bytes) seal operations in 4016000us (16247.5 ops/sec): 133.1 MB/s [-0.0%]
Penryn (Intel Core 2 Duo CPU P8600 @ 2.40GHz):
Before:
Did 1179000 AES-128-GCM (16 bytes) seal operations in 1000139us (1178836.1 ops/sec): 18.9 MB/s
Did 97000 AES-128-GCM (1350 bytes) seal operations in 1006347us (96388.2 ops/sec): 130.1 MB/s
Did 18000 AES-128-GCM (8192 bytes) seal operations in 1028943us (17493.7 ops/sec): 143.3 MB/s
Did 977000 AES-256-GCM (16 bytes) seal operations in 1000197us (976807.6 ops/sec): 15.6 MB/s
Did 82000 AES-256-GCM (1350 bytes) seal operations in 1012434us (80992.9 ops/sec): 109.3 MB/s
Did 15000 AES-256-GCM (8192 bytes) seal operations in 1006528us (14902.7 ops/sec): 122.1 MB/s
After:
Did 1306000 AES-128-GCM (16 bytes) seal operations in 1000153us (1305800.2 ops/sec): 20.9 MB/s [+10.8%]
Did 94000 AES-128-GCM (1350 bytes) seal operations in 1009852us (93082.9 ops/sec): 125.7 MB/s [-3.4%]
Did 17000 AES-128-GCM (8192 bytes) seal operations in 1012096us (16796.8 ops/sec): 137.6 MB/s [-4.0%]
Did 1070000 AES-256-GCM (16 bytes) seal operations in 1000929us (1069006.9 ops/sec): 17.1 MB/s [+9.4%]
Did 79000 AES-256-GCM (1350 bytes) seal operations in 1002209us (78825.9 ops/sec): 106.4 MB/s [-2.7%]
Did 15000 AES-256-GCM (8192 bytes) seal operations in 1061489us (14131.1 ops/sec): 115.8 MB/s [-5.2%]
Change-Id: I1c3760a77af7bee4aee3745d1c648d9e34594afb
Reviewed-on: https://boringssl-review.googlesource.com/c/34267
Commit-Queue: David Benjamin <davidben@google.com>
Reviewed-by: Adam Langley <agl@google.com>
