Support for FIPS series

[aurabindo]

Both Yubico 4 and 5 series has separate FIPS version listed in the official website. Are the FIPS versions of v4 and v5 supported as well? It would be useful to clarify this in the readme.

[tony-iqlusion]

That's an interesting question. Unfortunately we don't have the FIPS devices to test against.

The ciphersuites supported by YubiKeys are all FIPS-approved algorithms. Hypothetically it could work, but we would really need someone to test against an actual hardware device to know for sure.

[joostd]

Running

cargo test -- --ignored --skip generate_self_signed_rsa_cert

on a YubiKey 4 FIPS (fw 4.4.5) passes. The reason generate_self_signed_rsa_cert fails is that RSA 1024 is not FIPS 140-2 approved (Changing to RSA2048 does pass).

Willing to test on a newer YubiKey 5 FIPS as soon as #589 is merged (TDES is not FIPS 104-3 approved).