Subject: [MSEC] new TESLA draft

From: Ran Canetti <[email-masked]>
Date: Sat, 2 Mar 2002 10:08:29 -0500

[Co-chair hat off]

Folks,

Please take a look at the following new I-D:

http://search.ietf.org/internet-drafts/draft-perrig-msec-tesla-intro-00.txt

It provides a general algorithmic/informational presentation of the TESLA
source authentication mechanism. (This is an updated version of the
irtf-smug draft from a year ago.)

While you read, please keep in mind the following issue. Our planned next
step is to write a standards-track draft describing how to implement
TESLA in a specific scenario. The question is: how to go about it?
In particular, should we first implement TESLA in the application layer
or in the IP layer? There are advantages to each option (they are discussed
in the draft). We would like to get the WG feedback on the draft in general
and on this question in particular.

Thanks,

Ran

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From: [email-masked]
Date: Thu, 7 Mar 2002 11:41:56 +0100

Ran,

The option to use multiple sets of authentication keys corresponding to
different disclosure delays such that receivers with very different RTTs
can use different disclosure delays (which I saw in a previous version) is
not discussed anymore. Is there a reason to leave this out of the draft or
will it be in the technical draft?
Isn't there a DoS threat by buffer overflow at the receiver? In the
previous draft there was a solution proposed to cope with this which turned
the receiver buffering into sender buffereing, providing immediate
authentication for the receiver. Apparently this isn't anymore in the
latest version of your draft?

Do you mean by implementing TESLA in the IP layer, modifying IPsec to
support TESLA?

Kind regards,
 Annelies Van Moffaert.

Ran Canetti <[email-masked]> on 02/03/2002 16:08:29

 To:      [email-masked]                            
                                                              
 cc:      (bcc: Annelies VAN MOFFAERT/BE/ALCATEL)             

 Subject: [MSEC] new TESLA draft                              

[Co-chair hat off]

Folks,

Thanks,

Ran

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From: Ran Canetti <[email-masked]>
Date: Fri, 8 Mar 2002 15:47:22 -0500

Annelies,

Thanks for the comments!

> From [email-masked] Thu Mar  7 05:42:45 2002
> 
> Ran,
> 

Indeed, in a second thought the two features you mentioned (multiple 
keys for different RTTs, and buffering at the sender) should appear 
also in the general algorithmic document and not only in the implementation
draft(s). Will do.

> Do you mean by implementing TESLA in the IP layer, modifying IPsec to

Basically, yes. More specifically, modify ESP to support TESLA authentication 
(along the lines of MESP, if you're familiar with the SMUG draft.)

Ran

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From: LANIEPCE Sylvie FTRD/DMI/CAE <[email-masked]>
Date: Thu, 28 Mar 2002 10:27:01 +0100

Ran,

I would have some questions :

Paragraph 4.4 : P_j={M_j||MAC(K'_i,M_j||K_{i-d}}
Sorry, I do not understand why the interval i is not explicitely included in
P_j. To my understanding, the receiver NEED to know i to match P_j with a
given interval i (at least to check the security condition x<i-d), right ? 

I do not understand why there is no more need for the second security
condition defined in the TESLA SMUG draft (check that i is not an interval
in the future, i.e. i<floor((t_j-t_0)/T_int))

Could you please add some comments about F(k)=f_k (0), F'(k)=f'_k(1) : 0 ? 1
?

And also some minor comments :

"synchronisation" erroneously repeated 2 times in the second paragraph
section 4.3

Paragraph 4.5, does c stand for something in t_c ?

Section 4.5, I felt a bit confused with the sentence "when the receiver
receives packet P_j sent in interval i at local time t_c...". Could "when
the receiver receives at local time t_c packet P_j sent in interval i..."
avoid a possible confusion (at least, this was MY confusion...) : local time
t_c related to the receiving or to the sending ? 

Kind regards
Sylvie Laniepce

-----Message d'origine-----
De : Ran Canetti [mailto:[email-masked]]
Envoye : samedi 2 mars 2002 16:08
A : [email-masked]
Objet : [MSEC] new TESLA draft

[Co-chair hat off]

Folks,

Thanks,

Ran