cleanup(cryptography): Remove unused shielded key and address code

[teor2345]

Motivation

We want to remove unused shielded key and address code before the audit, because it contains known bugs that break consensus rules.

We also want to remove all the code that is impacted by these known bugs:

• Stop assuming testnet when parsing keys and addresses #4691
• the key parsing panics we found in PR lint(clippy): add unwrap_used lint #4732
• Orchard: derive OutgoingCipherKey ( Sapling and Orchard) #2041
• Check address and key lengths when parsing strings #4692
• unimplemented cryptographic algorithms
• there might be 2-3 other bugs in our cryptographic parsing or conversion code. For example, panicking when point conversions fail, and panicking on malformed addresses.

Close #5446
Close #4691
Close #2496
Close #2041

Solution

This PR removes 3000 lines of unused cryptographic code:

• all unused shielded key code
• dependent unused shielded address, note, commitment, nullifier, and test code

As a consequence, it removes:

• unimplemented cryptographic algorithms and conversions
• buggy cryptographic algorithms and conversions
• known panics during conversions
• untested code

It also makes Zebra's code easier to review and audit, because some of the removed types had the same name as the types from the ECC crates.

Review

Anyone can review this PR, it's a high priority because it's needed for the audit.

Reviewer Checklist

• Will the PR name make sense to users?
  • Does it need extra CHANGELOG info? (new features, breaking changes, large changes)
• Are the PR labels correct?
• Does the code do what the ticket and PR says?
• How do you know it works? Does it have tests?

[codecov]

Codecov Report

Merging #5476 (d388faf) into main (7b47aac) will decrease coverage by 0.06%.
The diff coverage is 100.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5476      +/-   ##
==========================================
- Coverage   79.32%   79.25%   -0.07%     
==========================================
  Files         309      305       -4     
  Lines       39348    37873    -1475     
==========================================
- Hits        31211    30016    -1195     
+ Misses       8137     7857     -280     

[teor2345]

I found this extra bug:

• Orchard: derive OutgoingCipherKey ( Sapling and Orchard) #2041

[teor2345]

Actually, I think I might be able to remove some of the broken Orchard code here.

[teor2345]

Actually, I think I might be able to remove some of the broken Orchard code here.

I worked out why it's tricky with Orchard - we need most of the key types to generate valid random Orchard addresses for tests.

So I'm going to move the keys that aren't used in production into a test module, and add a note about what needs to be done to the code to make it production-quality. (We're not getting test code audited, so that achieves the goals of the ticket.)

I might not get to finish it all today.

[teor2345]

Ok, I think I'm done here.

See the PR description for a summary of these changes, it's almost all removed code.

[oxarbitrage]

This seems to be done. @conradoplg or @dconnolly , can you please approve if that is the case ? Thank you.

[dconnolly]

lgtm

If we do wallet work / scanning work in the future we can dig the sapling/orchard stuff out of the history and fix it up, if needed