Re: [IPsec] Questions about RFC 5723

[Paul Wouters <[e-mail]>]

On Fri, 12 Jul 2019, Valery Smyslov wrote:

> A single (pair of ) IPsec SA is created as result of IKE_AUTH following
> IKE_SA_RESUME, as if it follows IKE_SA_INIT instead of IKE_SA_RESUME.
> If more IPsec SAs are needed they are created via CREATE_CHILD_SA,
> as usual.

Ahhhhh I totally missed this part when reading the document. Things make
a lot more sense now. Thanks!

>> Also, when using PFS, these CREATE_CHILD_SA's would do a DH again, at
>> which point one wonders why to do resumption at all if you have more
>> than one IPsec SA, as you would be doing DH's anyway for all children,
>> you might as well do one more for a regular IKE_SA_INIT ?
>
> In any case you save on authentication (this may involve signature
> computing/verification and probably human intervention in case of EAP).

Indeed. Thanks for the clarifications!

I guess formally, we would need to add the previous IKE traffic counters
to the current one, since these are all derived from the same DH.

(yes, for FIPS we need to ensure there is not more than 2^20 or so AES
packets of IKE traffic, even though reaching that would be quite the
accomplishment)

Paul