Which one among OATH HOTP, OATH TOTP on one side (say in the form of a credit card-sized token) and U2F (say in the form of a USB key) on the other side you think is more secure for purposes like online banking, email, and similar? What are the pros and cons of each, both at the technical crypto level and as usability?

A third option I can see, e.g. to use with a password manager like keepass or PGP key, is to store the key on USB stick: how does this compare in security to the above ones?

  • I don't know from a technical security point of view, but U2F is way nicer to deal with as a user (plug in key and tap button compared to grabbing a phone and opening the authenticator app and entering a series of digits). I really wish I could always use it as the preferred second factor. Jan 26, 2017 at 18:41
  • Although there's no way to use it on mobile (that I know of), which means falling back to HOTP/TOTP. Jan 26, 2017 at 18:41

1 Answer 1


Standard password (even locally encrypted), xOTP (OTP, HOTP, TOTP) [with or without SMS codes] have many vulnerabilities and the most important now is : NO REAL PROTECTION AGAINST PHISHING. A quick visual reminder about that : http://www.neowave.fr/pleaseno/SMS_OTP_TOTP_QRCODE_SSL_ARE_NOT_SOLUTIONS.pdf

FIDO U2F is a true but simple PKI based solution (Elliptic curve / assymmetric cryptography), even if not perfect, no easy relay / phishing attack will work on FIDO U2F.

Regarding Xiong Chiamiox comment : FIDO U2F already exists for desktop/laptop (Windows, Linux, OSX) as USB Security keys but there are FIDO U2F NFC Cards available too for Android smartphones and tablets. Later this year, there will even be Bluetooth Low Energy (BLE) device that will -at laaaast- bring FIDO U2F to iOS device.

  • Thanks for the nice reply. Why in your opinion banks are not adopting such simple solution to secure online banking?
    – jj_p
    Feb 24, 2017 at 9:15
  • 1
    oh, they will... FIDOD U2F is just a young solution/standard and banks are used to be slow adopters but many FIDO U2F manufacturers already have contacts with banks. The other explanation is that NFC and BLE parts of FIDO U2F specifications have just been finalized. Many web service providers are waiting for the first true multi-platform working prototypes compatible with smartphone and tablets. FIDO U2F (and derivated technologies) are here to stay ... Feb 24, 2017 at 10:57
  • OTP doesn't have protection against phishing, but depending on how it's used, they may not need to anyway. When OTP is used as a second factor, you usually still need to type in your password. If your password manager is configured so it will only autofill when the site is in the correct URL/domain, then you won't be vulnerable to said phishing.
    – Lie Ryan
    Jan 22, 2019 at 9:35
  • U2F isn't really PKI based. There's a PKI involved, but its only use is to exclude known bad devices, and even that functionality isn't utilized by most implementations. Jan 22, 2019 at 14:01

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