Re: [AVT] SRTP question

["Steffen Fries" <steffen.fries at siemens.com>]

Hi,

ah, this would also explain, why in the sorceforge SRTP
implementation "TMMH" is provided as well.
Okay, this makes it even clearer.

Ciao
	Steffen

Date sent:      	Tue, 13 Jul 2004 09:37:39 +0200
From:           	Mats Näslund <mats.naslund at ericsson.com>
To:             	Mark Baugher <mbaugher at cisco.com>
Copies to:      	steffen.fries at siemens.com,
  	"Karl Norrman (KI/EAB)" <karl.norrman at ericsson.com>, avt at ietf.org
Subject:        	Re: [AVT] SRTP question

> Hi
>
> In fact, I think it was David who provided this test vector. As you
> say though, the sole purpose is to provide an example, and it is in no
> way connected to the use of HMAC.
>
> If you are interested, I think I can also explain why the (rather
> large) value of 94 octets is chosen. I believe it is a remainder from
> an earlier version of SRTP that had the "TMMH" function as default
> MAC, and this MAC required large keys.
>
> Cheers
>
> /Mats
>
> Mark Baugher wrote:
>
> > Steffen
> >    I think Karl wrote that section so I am copying him on my reply
> >    and he
> > can correct me if I'm wrong:  The key length is there for the sole
> > purpose of illustrating key derivation and doe not imply that  94
> > octet key is to be used for HMAC-SHA1.
> >
> > regards, Mark
> > At 08:28 AM 7/12/2004, Steffen Fries wrote:
> >  >Hi,
> >  >
> >  >I've got a question to the authentication key length in SRTP.
> >  >RFC3711 describes the authentication function and the
> >  >authentication key length within section 4.2 and the key
> >  >derivation within section 4.3. Within section 8.2 the values for a
> >  >SRTP policy are stated. For the session authentication key a
> >  >default length of 160 bits is pointed out. Later in the key
> >  >derivation test vector section B.3 the authentication key length
> >  >is mentioned with 94 octets.
> >  >
> >  >What is the reason for the length differences?
> >  >
> >  >Steffen
> >  >
>
>

-----------------------------------------------------------
    Steffen Fries,     Siemens AG, CT IC 3
    Otto-Hahn-Ring 6,  D-81730 Munich, Germany
    Phone:  (+49) 89 / 636-53403,
    Fax  :  (+49) 89 / 636-48000
    Email:  Steffen.Fries at siemens.com
-----------------------------------------------------------



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