Passphrase setup for EKM keys

[ekievsky]

This PR adds passphrase setup with ekmkes

close #279

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Tests:

• Tests will be added later

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To be filled by reviewers

I have reviewed that this PR... (tick whichever items you personally focused on during this review):

• addresses the issue it closes (if any)
• code is readable and understandable
• is accompanied with tests, or tests are not needed
• is free of vulnerabilities
• is documented clearly and usefully, or doesn't need documentation

[tomholub]

It's progressing well. For comments that you have addressed, please click "Resolve conversation" after you have pushed the appropriate commit, to make it clear which ones were addressed and which not.

[tomholub]

All looks good. Code is clear and well structured. Functionality works now.

In the future, more careful studying of the issue definition and larger context will help you code with more confidence, and reduce my workload when reviewing.

Thank you.

[tomholub]

To clarify, it still holds that in cases when the issue is not well defined, asking questions is way better then guessing.