As far as I&#x27;m aware, Yubikey 4 and Yubikey Nano 4 can do 4096; the older ones like the NEO can only do 2048.<p>Not that 2048 is flawed as such: it&#x27;s still north of 100 bits workfactor at the moment, as far as I gather. 3072 would be equivalent to about 128 (similar to the EC algorithms secp256r1 or Curve25519), and 4096 is some extra insurance on top. (As a benchmark: Snowden used 4096-bit RSA keys for GnuPG.) Anything bigger than that could introduce OpenPGP compatibility troubles.<p>All of these are secure when correctly implemented. (Yubikey use NXP chips. I don&#x27;t have much to say beyond that, I haven&#x27;t audited them.) All of them will fall to Shor&#x27;s algorithm on a quantum computer of sufficient size, but we&#x27;re not likely to have one of those for a good few years, if they&#x27;re possible.