protect wallet password and private key

[simlecode]

Motivation

Proposed changes

Closes #

[codecov-commenter]

Codecov Report

Merging #4427 (069f02f) into master (2447607) will increase coverage by 0%.
The diff coverage is 52%.

❗ Current head 069f02f differs from pull request most recent head b95ca71. Consider uploading reports for the commit b95ca71 to get more accurate results

@@          Coverage Diff           @@
##           master   #4427   +/-   ##
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  Coverage      30%     30%           
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  Files         249     248    -1     
  Lines       20240   20219   -21     
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+ Hits         6084    6134   +50     
+ Misses      12852   12790   -62     
+ Partials     1304    1295    -9     

[keks]

I think this looks pretty promising! There are still a few cases where the keys escape memguard's protection, and I flagged everything I could find throughout the call graph. I did not flag the same issues with the password enclaves, but ideally they also would not leave memguard protected memory. I am aware this is not always possible because you have to deal with external APIs such as scrypt.

I think this biggest step was taken, because the key are only in insecure memory for a very short time, i.e. during processing. The biggest danger came from the long-term storage of keys, which is not encrypted.