[openssl-dev] [openssl.org #3897] request: add BLAKE2 hash function (let's kill md5sum!)

[Bill Cox]

By the way, parallel hashing works much better than I thought it would.
For a memory-hard password hashing such as Scrypt, parallel threads need to
operate on very different areas of memory, or performance goes out the
window.  Apparently the overhead in cache coherency dominates if multiple
threads are writing to the same page.  Also, using OpenMP on memory-hard
hashing works poorly compared to manually managing pthreads, and I expected
to see that with parallel hashing, but didn't.  I think what happens is
that when one thread starts outpacing the others, it sees cache misses and
slows down.  A thread that falls behind never sees a cache miss, and
quickly catches up.  Interleaved multi-threaded hashing is a very cool
algorithm!  It looks simple to write for any of the OpenSSL hash functions.

Bill
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