SHA256 hash based on OpenSSL

[Anilm3]

This PR introduces a class to compute the sha256 digest, the code is based on the openssl implementation. At first, the objective is to use this hash for request fingerprinting purposes, however it could be used for other purposes:

• As a processor generator, in order to produce a hash of part of the request, in a similar fashion to a fingerprint although more targeted.
• As a transformer, to match obfuscated data.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 94.11765% with 9 lines in your changes missing coverage. Please review.

Project coverage is 83.66%. Comparing base (0bcb84c) to head (153eab1).

Files	Patch %	Lines
src/sha256.cpp	93.87%	5 Missing and 4 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #304      +/-   ##
==========================================
+ Coverage   83.39%   83.66%   +0.27%     
==========================================
  Files         135      137       +2     
  Lines        5854     6007     +153     
  Branches     2808     2829      +21     
==========================================
+ Hits         4882     5026     +144     
- Misses        361      366       +5     
- Partials      611      615       +4     

Flag	Coverage Δ
waf_test	83.66% <94.11%> (+0.27%)	⬆️

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[pr-commenter]

Benchmarks

Benchmark execution time: 2024-06-17 19:31:06

Comparing candidate commit fae4113 in PR branch anilm3/openssl-sha256 with baseline commit a425414 in branch master.

Found 2 performance improvements and 0 performance regressions! Performance is the same for 17 metrics, 0 unstable metrics.

scenario:signed_equals_matcher.random

• 🟩 execution_time [-38.937µs; -38.059µs] or [-3.206%; -3.133%]

scenario:unsigned_equals_matcher.random

• 🟩 execution_time [-41.321µs; -37.832µs] or [-3.399%; -3.112%]

[Anilm3]

Benchmarked three different variants:

• (V1) OpenSSL long version (the one used in this PR)
• (V2) OpenSSL short version
• (V3) https://github.com/Taiki-San/Rakshata/blob/master/C/Security/crypto/sha256.c based on LibreSSL (By far the most readable)

Benchmark                           Time             CPU   Iterations
---------------------------------------------------------------------
BM_SHA256V1HashDigest/64          362 ns          362 ns      1943479
BM_SHA256V1HashDigest/128         528 ns          528 ns      1323954
BM_SHA256V1HashDigest/256         839 ns          839 ns       817359
BM_SHA256V1HashDigest/512        1468 ns         1468 ns       475595
BM_SHA256V1HashDigest/1024       2763 ns         2762 ns       255095
BM_SHA256V2HashDigest/64          390 ns          390 ns      1785310
BM_SHA256V2HashDigest/128         560 ns          560 ns      1184360
BM_SHA256V2HashDigest/256         905 ns          905 ns       760367
BM_SHA256V2HashDigest/512        1588 ns         1588 ns       439426
BM_SHA256V2HashDigest/1024       2953 ns         2953 ns       233425
BM_SHA256V3HashDigest/64          590 ns          590 ns      1127086
BM_SHA256V3HashDigest/128         876 ns          876 ns       764616
BM_SHA256V3HashDigest/256        1468 ns         1468 ns       491038
BM_SHA256V3HashDigest/512        2508 ns         2508 ns       280887
BM_SHA256V3HashDigest/1024       4671 ns         4671 ns       150827

[cataphract]

Fine. As mentioned, it would interesting to see a version using instructions dedicated to it (SHA256H/SHA256H2/SHA256SU0/SHA256SU1 for aarch64) and SHA256MSG1/SHA256MSG2/SHA256RNDS2 for amd64.