Performance | Use lower-allocation AlwaysEncrypted primitives

[edwardneal]

Description

This builds on #3554, using the lower-allocation AE primitives in SqlColumnEncryptionCspProvider and SqlColumnEncryptionCngProvider. Benchmarks for this are located in the original PR.

I'm separating these two changes from SqlColumnEncryptionCertificateStoreProvider due to the latter's size, but it'll be fairly similar once the use of X509Certificate2 has been refactored into an RSA instance. I'll incorporate the feedback from this PR into the second one.

We make some minor code style changes, largely to remove a few Yoda conditions, replace == null with is null comparisons and clean up the comments. Besides this though, almost all of the DecryptColumnEncryptionKey and EncryptColumnEncryptionKey methods are replaced with references to the new AE primitives.

While not the main goal, I also noticed and fixed one case where we were opening a CngKey and never disposing it.

Issues

Builds on #3554.

Testing

Automated tests pass.

I also created an AE-enabled table in SSMS which used a CNG-based master key, and confirmed that I was able to query values from it. This should confirm that data created outside of SqlClient can now be read successfully.

Could someone run CI please?

[paulmedynski]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 2 pipeline(s).

[paulmedynski]

Overall looks great. Some comments about [NotNull] and usings.

[paulmedynski]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 2 pipeline(s).

[codecov]

Codecov Report

❌ Patch coverage is 96.77419% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 59.61%. Comparing base (cd3dbd1) to head (3152361).
⚠️ Report is 17 commits behind head on main.

Files with missing lines	Patch %	Lines
...qlClient/SqlColumnEncryptionCngProvider.Windows.cs	93.75%	2 Missing ⚠️

❗ There is a different number of reports uploaded between BASE (cd3dbd1) and HEAD (3152361). Click for more details.

HEAD has 1 upload less than BASE

Flag	BASE (cd3dbd1)	HEAD (3152361)
addons	1	0

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3612      +/-   ##
==========================================
- Coverage   65.48%   59.61%   -5.88%     
==========================================
  Files         275      271       -4     
  Lines       61518    61253     -265     
==========================================
- Hits        40288    36517    -3771     
- Misses      21230    24736    +3506     

Flag	Coverage Δ
addons	?
netcore	63.84% <96.77%> (-3.82%)	⬇️
netfx	60.81% <98.33%> (-8.40%)	⬇️

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