The Stanford license for SRP says:

Broader use of the SRP authentication technology, such as variants incorporating the use of an explicit server secret (SRP-Z), may require a license;

Yet I cannot find a succinct description of the SRP-Z protocol and why it might be useful. As a follow up question assuming it is useful and patented when does the patent expire?

  • $\begingroup$ From the terms I understand that this is mutual authentication while SRP itself is client only authentication. If you mix in a server secret in the session key derivation then the above description may make sense. Did you search the patent database for SRP? $\endgroup$
    – Maarten Bodewes
    Jul 1, 2015 at 11:14

1 Answer 1


This question both describes the SRP-Z variant and mentions that the patent should expire in three years.

I think the patent in question is this one, but I'm not sure: US 6539479. If it is, it seems to actually have expired earlier this year due to non-payment of fees. Looking it up on the USPTO PAIR says:

Status: Patent Expired Due to NonPayment of Maintenance Fees Under 37 CFR 1.362

Status Date: 04-20-2015

It is still possible it could be revived after such expiry, but IANAL, etc.


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