Yubico Forum

If made random & secret the public id can be used to strengthen a user's existing password, and provide a kind of 2-factor authentication (obviously not as strong as with an online OTP). Applications would only have to strip off the encrypted one-time part (last 32 modhex characters). This can be a simple way to strengthen passwords where it's too hard/impossible to verify OTPs online, e.g. from the TrueCrypt bootloader. The advantage over static OTP mode is that people can use the same YubiKey for online OTP authentication.

Currently though, the YubiKey is limited to a 6-byte static id which only gives 48 bits of entropy.. while not too bad, is there any chance of letting this be longer? Also it’d be very useful to be able to change this static id at the client without changing the AES key (which would usually be stored centrally).