hash performance sha256 vs. sha512

[ThomasWaldmann]

I just learned that sha512 is faster than sha256 (on 64bit platforms, see benchmark below). attic uses sha256 at some places, could/should it be replaced by sha512?

Attic uses hmac-sha256. I did similar measurements for hmac-sha256 and -sha512 and the speed was as shown below.

$ python3.2 -m timeit -r 10 -s 'from hashlib import new; h = new("sha256"); x=b"foobar"*1000000' 'h.update(x)'
10 loops, best of 10: 29.2 msec per loop

$ python3.2 -m timeit -r 10 -s 'from hashlib import new; h = new("sha512"); x=b"foobar"*1000000' 'h.update(x)'
100 loops, best of 10: 18.6 msec per loop

[ThomasWaldmann]

Some 32bit linux, py 2.7.6 values from a helpful guy on IRC:

$ python -m timeit -r 10 -s 'from hashlib import new; h = new("sha256"); x=b"foobar"_1000000' 'h.update(x)'
10 loops, best of 10: 41.5 msec per loop
$ python -m timeit -r 10 -s 'from hashlib import new; h = new("sha512"); x=b"foobar"_1000000' 'h.update(x)'
10 loops, best of 10: 43.9 msec per loop

Vendor ID: GenuineIntel
CPU family: 6
Model: 23
Stepping: 6
CPU MHz: 800.000

sha512 is just a little slower than sha256 there.

[ThomasWaldmann]

Just for completeness: if anybody could post values from non-x86/amd64 platforms for 32 and/or 64bit, that would be helpful.

[ThomasWaldmann]

Note: attic could use hmac-sha512 or hmac-sha512-256 (truncated to 256bits).
Both would be incompatible to old repositories, but with the latter, record layout would stay the same.

[ThomasWaldmann]

https://eprint.iacr.org/2010/548.pdf

[ThomasWaldmann]

More data from helpful IRC guy:

Raspberry PI, Python 2.7.3, CPU: ARMv6-compatible processor rev 7 (v6l)

$ python -m timeit -r 10 -s 'from hashlib import new; h = new("sha256"); x=b"foobar"*1000000' 'h.update(x)'
10 loops, best of 10: 231 msec per loop

$ python -m timeit -r 10 -s 'from hashlib import new; h = new("sha512"); x=b"foobar"*1000000' 'h.update(x)'
10 loops, best of 10: 451 msec per loop

So, obviously we need BOTH sha256 and sha512, for best performance depending on the CPU architecture.

[ThomasWaldmann]

see measurements in PR #207. as there are a lot of factors contributing to backup speed, the faster hash improved speed about 2-3% for me.

[tgharold]

AMD Phenom(tm) II X4 810 Processor (64bit CentOS 6)

SHA256 - 10 loops, best of 10: 36.5 msec per loop
SHA512 - 10 loops, best of 10: 22.6 msec per loop

AMD Opteron(tm) Processor 4180 (64bit CentOS 6)

SHA256 - 10 loops, best of 10: 36 msec per loop
SHA512 - 10 loops, best of 10: 23.3 msec per loop