Sigh.  C'mon, folks, there is no problem.

View the algorithm as simply part of the shared secret.  All authentication is done between consenting adults and there has to be out-of-band and a priori agreement on the parameters or the authentication fails.  Nobody is going to be guessing the algorithm in use on a particular session any more than they would be guessing the secret.  And if you want to switch algorithms (which is essentially just switching secrets) the key ID mechanism is present.

At the end of the day it doesn't matter if the value of 2 or 3 or 42 is used;  if there's a mismatch on the the algorithm ID, the algorithm, or the key, the authentication will fail, and if it all matches, it will work.  For that matter, I don't think that even the existing algorithm ID is necessary, since the entire thing has to be agreed upon a priori anyhow.

For what it's worth, type 2 fits the bill just fine, defined the way that it is.  If one box does only MD5 and the other box only does SHA, they cannot talk.  If they share an algorithm, it is up to the user to configure the two boxes compatibly, like a thousand other parameters.  While having a separate code point for SHA would have marginal debugging utility ("wrong algorithm, dummy!") it's no harder to make sure that this matches on both sides than it is to make sure the shared secret matches.

--Dave


On Aug 23, 2006, at 3:06 AM, sujay wrote:

Yes,

If an authentication fails it could mean the algo's used are different.

And if one implementation supports MD5 alone( "which I believe is commonly used !" ), the others

support otherwise, It could be a problem, there is no explicit way we are converying which algo is being used.

The Au Type = 2 is overloaded.

Now a "MUST" clause is for the WG to decide.

Regds,
Sujay G
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From: Manav Bhatia [mailto:[EMAIL PROTECTED]]
Sent: 2006年8月23日 13:04
To: 'sujay'
Cc: 'Mailing List'
Subject: RE: [OSPF] Revised OSPF HMAC SHA Authentication Draft

Sujay,

>
>Can we have a default algo. concept??
>

What do you mean by the default algo? Is it one authentication algorithm that all implementations MUST support?

Manav

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