Re: [IPsec] Fw: Preshared key authentication in IKEv2

"Valery Smyslov" <svanru@gmail.com> Mon, 02 November 2009 14:40 UTC

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Message-ID: <1A567F18E9E144989D2F06830DB24CC6@trustworks.com>
From: "Valery Smyslov" <svanru@gmail.com>
To: "Tero Kivinen" <kivinen@iki.fi>, "Paul Hoffman" <paul.hoffman@vpnc.org>
References: <82DFB96E88E54DE98E9B6B5F766C3EB8@trustworks.com><p06240896c710cc6eae34@[10.20.30.158]> <19182.59664.628328.76563@fireball.kivinen.iki.fi>
Date: Mon, 2 Nov 2009 17:40:57 +0300
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Cc: ipsec@ietf.org
Subject: Re: [IPsec] Fw: Preshared key authentication in IKEv2
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Hi Paul and Tero,

thank you for your answers.

> > The PRF (or set of PRFs) is known by the receiving party. If the two
> > parties always only use one PRF, it is known. The padding is not a
> > universal solution for the reasons you give, but it works in the
> > common case of peers who know each other's crypto choices.
>
> As Paul said recipient knows which algorithms it support, and it can

Sometimes it doesn't. I refer to implementations with pluggable
crypto, when crypto providers are separated from IKE implementation
and can be added/removed later.

> store the pre-shared key using all of those algoritms to its database.
> I.e. if it supports PRF_HMAC_SHA1, and PRF_AES128_XCBC then it needs
> to calculate the PRF(Shared Secret, "Key Pad for IKEv2") using those
> two PRFs and store both of the results to its authentication database.

With this approach in case of pluggable crypto user must re-enter shared
secret
after any change in crypto configuration. It's not a big deal, just a bit
inconvinient...

Regards,
Smyslov Valery.