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I understand that Lamport OTP uses hash chains to generate passwords. Is it practically feasible to use them? Where are Lamport OTP being currently being used?

I read some online papers that state that Lamport OTPs are computationally intensive and hence other schemes are preferred over them. Is there any known service that uses this?(like banks OTPs)

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  • I don't see a reason to ever use them over CTR mode based OTPs with when you want short OTPs. – CodesInChaos Dec 1 '16 at 9:36
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As Lampport OTP's doesn't require a shared secret, it is extremely feasible to use them, particularly where services which require successive authentication.

Assume the following

A = Hash(B)
B = Hash(C)
.
.
.
Y = Hash(Z)

The entire hash chain above will be generated at the client and will be stored. The exchanges between client and server will be as follows.

[Client] -----------A-----------> [Server] Stores A
[Client] -----------B-----------> [Server] Verifies if Hash(B) == A; If yes, authenticates and discard A and stores B. If No, authentication failure.
[Client] -----------C-----------> [Server] Verifies if Hash(C) == B; If yes, authenticates and discard B and stores C. If No, authentication failure.

And coming to your question, here is an example on how Lamport OTPs are used for securing client service interactions.

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  • What if an attacker intercepts the seed value, A? Or are we assuming the communication is over a secure channel? – Rads Oct 29 '16 at 2:28
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    @Rads A isn't the seed value. The seed here is Z. Attacker wouldn't be able to do anything even if he or she has A from the first transaction. Because for the attacker to successfully authenticate, he/she will have to get B from A. B = Hashinverse(A) . Since hash inverse is not mathematically feasible it is useless. Of course the protocol is still vulnerable to MITM kind of attacks but consider this strictly as an authenticationechanism – hax Oct 29 '16 at 3:21
  • I read some online papers that state that Lamport OTPs are computationally intensive and hence other schemes are preferred over these. Is there any known service that uses this?(eg. banks OTPs) – Rads Oct 30 '16 at 8:30

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