## Issue Addressed
Closes#1889
## Proposed Changes
- Error when passwords which use invalid UTF-8 characters during encryption.
- Add some tests
## Additional Info
I've decided to error when bad characters are used to create/encrypt a keystore but think we should allow them during decryption since either the keystore was created
- with invalid UTF-8 characters (possibly by another client or someone whose password is random bytes) in which case we'd want them to be able to decrypt their keystore using the right key.
- without invalid characters then the password checksum would almost certainly fail.
Happy to add them to decryption if we want to make the decryption more trigger happy 😋 , it would only be a one line change and would tell the user which character index is causing the issue.
See https://eips.ethereum.org/EIPS/eip-2335#password-requirements
## Issue Addressed
- Resolves#1361
## Proposed Changes
Loosens the constraints imposed by EIP-2335 so we can import keys from Prysm.
## Additional Info
NA
## Issue Addressed
NA
## Proposed Changes
- Refactor the `bls` crate to support multiple BLS "backends" (e.g., milagro, blst, etc).
- Removes some duplicate, unused code in `common/rest_types/src/validator.rs`.
- Removes the old "upgrade legacy keypairs" functionality (these were unencrypted keys that haven't been supported for a few testnets, no one should be using them anymore).
## Additional Info
Most of the files changed are just inconsequential changes to function names.
## TODO
- [x] Optimization levels
- [x] Infinity point: https://github.com/supranational/blst/issues/11
- [x] Ensure milagro *and* blst are tested via CI
- [x] What to do with unsafe code?
- [x] Test infinity point in signature sets
