Correct Argon2 settings when creating new database

[droidmonkey]

• Argon2 default parallelism settings were set to the number of threads on the computer. That is excessive on high cpu count computers.

See #11852 (comment)

Testing strategy

Tested manually and unit tests

Type of change

• ✅ Bug fix (non-breaking change that fixes an issue)

[codecov]

Codecov Report

Attention: Patch coverage is 76.47059% with 4 lines in your changes missing coverage. Please review.

Project coverage is 63.89%. Comparing base (37ddbb3) to head (6b36b33).

Files with missing lines	Patch %	Lines
src/crypto/kdf/Argon2Kdf.cpp	57.14%	3 Missing ⚠️
...ui/dbsettings/DatabaseSettingsWidgetEncryption.cpp	83.33%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop   #11853      +/-   ##
===========================================
- Coverage    63.92%   63.89%   -0.03%     
===========================================
  Files          369      370       +1     
  Lines        38920    38921       +1     
===========================================
- Hits         24878    24868      -10     
- Misses       14042    14053      +11     

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[phoerious]

2 sounds a bit low to me. What about using idealThreadCount(), but cap it to, say, 8.

[droidmonkey]

The way parallelism works in argon2 is that it divides the total memory (e.g., 64 MiB) by the parallelism number (called a lane) and then performs the argon2 algorithm on each lane at the same time. So if you make parallelism 8 but keep memory at 64 MiB, you actually don't improve security at all. But if you want to set memory to 512 MiB, you can set parallelism to 8, and the total time will stay the same as 64 MiB and parallelism of 1. This ultimately reduces the capability of a GPU attack, but only if you also increase memory.

This is a good writeup: https://community.bitwarden.com/t/argon2id-parallelism-explanation/54189/6

At the end of the day, I think a max default of 4 is fine, but we should also be upping the default memory by the parallelism perhaps?

[phoerious]

Capping it a four is fine with me as well. Just up the memory cost accordingly as well.