[strongSwan] Authenticated encryption algorithms syntax

Emeric POUPON emeric.poupon at stormshield.eu
Wed Nov 5 15:28:22 CET 2014

Thanks for your answer!

> For AEAD-only proposals, an integrity algorithm is not used. However,
> you may still specify one to at the same time implicitly define a PRF in
> an IKE proposal. The integrity algorithm is stripped implicitly from
> AEAD-only proposals.

Ok, that is what I wanted to know: the integrity algorithm is not used except for ike where it implicitly defines a PRF algorithm.

> Yes. With multiple algorithms, the peer may select any algorithm from
> each type and mix-and-match them as it likes. With multiple proposals,
> the peer has to select a single proposal, i.e. you can limit the
> combinations allowed.

The question was about the same algorithms and combinations, as in my example:
esp=enc1-auth1-modpX, enc1-auth2-modpX,enc2-auth1-modpX,enc2-auth2-modP

It may look like the same, but there seems to be a difference: in first case the first matching proposal has to be chosen, in the second case the remote peer may choose any algorithm in the multi algorithm list.
AFAIU, they are not strictly equivalent since they may lead to different proposal choices.

I was wondering if it may lead to unexpected issues?
What is the advantage of using multiple algorithms? Maybe reducing the produced packet size?



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