OTP may known as new generation of password security techniques, but I want to know does it still safe enough after several years of appearance or it will deprecate soon? & what would be the possible replacement for that?


3 Answers 3


One-Time Passwords (not to be confused with "One-Time Pad", a theoretically perfect but practically heavyweight technique for encryption) are a sound concept which cannot, as itself, deprecate. It just means: a given password (i.e. a secret value shared between prover and verifier, used for authentication) can be used just once with the verifier; in other words, if the verifier (e.g. a server you want to log on) accepts a password but will reject any further attempt with the same password, then it is a one-time password.

One-Time Password schemes are systems which use the One-Time Password concept and establish rules and mechanisms for the two parties (prover and verifier) to actually share one-time passwords. Any given scheme can be weak or strong, broken, deprecated... but the concept is unharmed.

RSA SecurID tokens can be viewed as an incarnation of the concept of one-time passwords -- a variant with a clock, actually -- and they are very much alive.

HOTP is a free and open standard for generation of one-time passwords (with an internal counter), which can be implemented by extremely cheap hardware tokens.

(Traditional one-time password authentication schemes for Unix servers use software generation of lists of passwords, which users are supposed to print and keep in their wallet, striking out used passwords. This never got popular -- I guess it is too low-tech; users are not amazed enough to forget the inconvenience of fiddling with a tangible object).


One time passwords (as implemented by RSA SecurID or other vendors) are theoretically safe but as with all security controls have limits that must be considered when designing your security system.

The OTP implementation may have implementation or design flaws that may permit to circumvent them.

OTP can be intercepted and used by attackers through the intermediary of trojans or XSS attacks for instance at the authentication stage (often with an apparent denial of service to you as a user since another party is using your freshly inputted OTP, thus invalidating it).

Most importantly, OTP systems often limits themselves to authenticate a user instead of authenticating a transaction. Once a user is authenticated, a trojan may re-use your authenticated web session with your bank for instance to perform transactions on your behalf in a sneaky manner.

Although I think OTPs still have a bright future ahead of them, they will be augmented with further security controls and will in particular increasingly try to address the problem of transaction authentication instead of limiting themselves to authenticating the user only.


One Time Passwords are one concept of doing two factor authentication. Something the user knows (password) and something the user has (OTP Generator).

The One Time Password being the proof of the possession. In this case the "possession proof" works like this:

The One Time Password is generated by an algorithm like HOTP (RFC4226) or TOTP (RFC6238) based on a secret kryptographic key and some moving factor. The user is only capable of presenting the correct one time password if he is in the possession of the secret key.

This is why you should take care of this secret key and be suspicious about smartphone applications for OTP like the Google Authenticator.

But the basic concept of OTP is the same like doing public key crypto with challenge response. The possession is the possession of a secret or private key.

OTP uses a secret key and not a private key, since the user should be capable of typing in the result (OTP value). Using a private key, this would not be possible, since the result of the private key operation is too long.

A private key scenario always needs the hardware to be connected to the machine (see smartcard login). ...and this requires drivers and connectors. (Try this with the iphone 11 ;-)

So yes, I think the basic concept of OTP - a.k.a. using a secret key - will still be around for a while.

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