Replace openssl by crates num-bigint, sha2

[Patrik-Stas]

OpenSSL in libvcx is increasing build complexity and has occasionally produced build issues on some platforms.
However there's only 2 use cases for OpenSSL - big numbers and sha256. These problems has been implemented in pure Rust already.
Big numbers and sha hashing is used for encoding credential attributes and is being tested by following tests:

    aries::handlers::issuance::issuer::utils::tests::test_encode_empty_field
    aries::handlers::issuance::issuer::utils::tests::test_encode_with_aries_format_several_attributes_success
    aries::handlers::issuance::issuer::utils::tests::test_encode_with_mixed_format_several_attributes_success
    aries::handlers::issuance::issuer::utils::tests::test_encode_with_new_format_one_attribute_success
    aries::handlers::issuance::issuer::utils::tests::test_encode_with_new_format_several_attributes_success
    aries::handlers::issuance::issuer::utils::tests::test_encode_with_one_attribute_success
    aries::handlers::issuance::issuer::utils::tests::test_encode_with_several_attributes_success
    utils::openssl::test::test_encoding

Signed-off-by: Patrik Stas patrik.stas@absa.africa

[codecov-commenter]

Codecov Report

Merging #317 (1638231) into main (cfea9f7) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #317      +/-   ##
==========================================
+ Coverage   44.45%   44.46%   +0.01%     
==========================================
  Files         417      417              
  Lines       28975    28964      -11     
  Branches     6176     6178       +2     
==========================================
  Hits        12880    12880              
+ Misses      12296    12285      -11     
  Partials     3799     3799              

Flag	Coverage Δ
unittests-aries-vcx	44.46% <100.00%> (+0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files Changed	Coverage Δ
aries_vcx/src/utils/validation.rs	0.00% <ø> (ø)
aries_vcx/src/utils/openssl.rs	39.28% <100.00%> (+14.28%)	⬆️

... and 3 files with indirect coverage changes

[mirgee]

LGTM! 👍 However, there are many newly redundant references to openssl in Android and iOS build scripts, dockerfiles, build.rs, etc. now. I would prefer to remove these as part of this PR to avoid letting the dead code rot indefinitely.

[Patrik-Stas]

LGTM! 👍 However, there are many newly redundant references to openssl in Android and iOS build scripts, dockerfiles, build.rs, etc. now. I would prefer to remove these as part of this PR to avoid letting the dead code rot indefinitely.

agree, will do

[gmulhearn]

@Patrik-Stas just looking at old PRs. is this PR still relevant? libvcx doesn't depend on openssl anymore. but aries-vcx does, should it be migrated?

[bobozaur]

Reviving this. We should get back to it at some point in the near future, after the refactors are done.

[mirgee]

Can we use the latest releases?