Fuzzing PKCS7 encrypted inputs

[justsmth]

Issues:

Addresses: CryptoAlg-2786

Description of changes:

Add fuzz testing around processing of PKCS7 encrypted inputs.

Call-outs:

I created an initial fuzz corpus by serializing the test cases from PKCS7Test.TestEnvelope into files.

I completed a several iterations of: running the fuzz test for awhile, then minimizing the corpora, then repeat.

Build

CC=clang CXX=clang++ cmake -GNinja -DFUZZ=1 -B ./build
cmake --build ./build

Fuzzing:

cd fuzz
../build/fuzz/pkcs7_decrypt -max_len=4000 -jobs=8 -workers=8 ./pkcs7_decrypt_corpus

Minimize:

mv pkcs7_decrypt_corpus pkcs7_decrypt_corpus_old && mkdir pkcs7_decrypt_corpus  
../build/fuzz/pkcs7_decrypt -max_len=50000 -merge=1 pkcs7_decrypt_corpus pkcs7_decrypt_corpus_old
rm -Rf pkcs7_decrypt_corpus_old

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license and the ISC license.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.77%. Comparing base (637b5d2) to head (3ff5960).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2027      +/-   ##
==========================================
- Coverage   78.79%   78.77%   -0.03%     
==========================================
  Files         598      598              
  Lines      103722   103724       +2     
  Branches    14743    14742       -1     
==========================================
- Hits        81727    81705      -22     
- Misses      21342    21367      +25     
+ Partials      653      652       -1     

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[WillChilds-Klein]

note to other reviewers -- i had trouble with the "files changed" tab. i found it easier to review fuzz/pkcs7_decrypt.cc in the "commits" tab.