4 ms·

Why can't yubikey use a single root secret and derive all sub-secrets from that root secret?

by EthanHeilman 7y ago

nickez 7y ago
They should be doing that. Maybe the OP means the limitations on passwordless credentials and not u2f credentials.
- lars_francke 7y ago
  I might get the terminology wrong. What I meant are the HOTP and TOTP secrets. They can only store 32 of them.
  - lars_francke 7y ago
    This is what I'm referring to https://support.yubico.com/support/solutions/articles/15000014219-yubikey-5-series-technical-manual#OATHkht9hr https://support.yubico.com/support/solutions/articles/150000...
juriansluiman 7y ago
Because usually the server sends the shared secret and there are just 32 slots for shared secrets available.
- EthanHeilman 7y ago
  Yubikey and webauthn[0] supports public key authentication where the client chooses the secret. [0]: https://webauthn.io/ https://webauthn.io/
  - juriansluiman 7y ago
    Yes but that's a whole different 2FA implementation, where sites must support U2F (webauthn). Unfortunately, the implementation of TOTP is far more common than U2F. Ideally all sites will implement U2F as two factor authentication, but there aren't that many users who have a U2F compatible token. The reach of TOTP is far more beyond U2F, which is probably why sites use TOTP more than U2F. When sites offer both, choose U2F. When sites offer TOTP only, use it. It is better than nothing. When you have a yubikey already, use the Yubico authenticator app to store the TOTP secret to make your TOTP attack surface less and to have the availability to change your phone without losing TOTP secrets.
    - EthanHeilman 7y ago
      >When sites offer both, choose U2F. When sites offer TOTP only, use it. This, 100% In some sense TOTP, basically HMAC, seems like it would be harder to screw up than a public key system. RSA is amazingly hard to get right. I wonder if the order of preference should be: 1. U2F ECDSA/EdDSA 2. TOTP 3. U2F RSA ... Infinity. SMS 2FA No idea where ECDAA [0] fits. [0]: https://paragonie.com/blog/2018/08/security-concerns-surrounding-webauthn-don-t-implement-ecdaa-yet https://paragonie.com/blog/2018/08/security-concerns-surroun...

Why can't yubikey use a single root secret and derive all sub-secrets from that root secret?

nickez 7y ago

They should be doing that. Maybe the OP means the limitations on passwordless credentials and not u2f credentials.

lars_francke 7y ago
I might get the terminology wrong. What I meant are the HOTP and TOTP secrets. They can only store 32 of them.
- lars_francke 7y ago
  This is what I'm referring to https://support.yubico.com/support/solutions/articles/15000014219-yubikey-5-series-technical-manual#OATHkht9hr https://support.yubico.com/support/solutions/articles/150000...

juriansluiman 7y ago

Because usually the server sends the shared secret and there are just 32 slots for shared secrets available.

EthanHeilman 7y ago
Yubikey and webauthn[0] supports public key authentication where the client chooses the secret. [0]: https://webauthn.io/ https://webauthn.io/
- juriansluiman 7y ago
  Yes but that's a whole different 2FA implementation, where sites must support U2F (webauthn). Unfortunately, the implementation of TOTP is far more common than U2F. Ideally all sites will implement U2F as two factor authentication, but there aren't that many users who have a U2F compatible token. The reach of TOTP is far more beyond U2F, which is probably why sites use TOTP more than U2F. When sites offer both, choose U2F. When sites offer TOTP only, use it. It is better than nothing. When you have a yubikey already, use the Yubico authenticator app to store the TOTP secret to make your TOTP attack surface less and to have the availability to change your phone without losing TOTP secrets.
  - EthanHeilman 7y ago
    >When sites offer both, choose U2F. When sites offer TOTP only, use it. This, 100% In some sense TOTP, basically HMAC, seems like it would be harder to screw up than a public key system. RSA is amazingly hard to get right. I wonder if the order of preference should be: 1. U2F ECDSA/EdDSA 2. TOTP 3. U2F RSA ... Infinity. SMS 2FA No idea where ECDAA [0] fits. [0]: https://paragonie.com/blog/2018/08/security-concerns-surrounding-webauthn-don-t-implement-ecdaa-yet https://paragonie.com/blog/2018/08/security-concerns-surroun...