## Issue Addressed
Closes#1906Closes#1907
## Proposed Changes
- Emits warnings when the KDF parameters are two low.
- Returns errors when the KDF parameters are high enough to pose a potential DoS threat.
- Validates AES IV length is 128 bits, errors if empty, warnings otherwise.
## Additional Info
NIST advice used for PBKDF2 ranges https://nvlpubs.nist.gov/nistpubs/Legacy/SP/nistspecialpublication800-132.pdf.
Scrypt ranges are based on the maximum value of the `u32` (i.e 4GB of memory)
The minimum range has been set to anything below the default fields.
## 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
