Subject: [ietf-tls] Re: draft-ietf-tls-wireless-00.txt

From: "Simon Blake-Wilson" <[email-masked]>
Date: Tue, 5 Jun 2001 04:21:15 -0400

Hi Eric,

On the MAC truncation issue, I think the MAC.type field may well be useful going
forward. As a client, I might prefer not to knowingly weaken the MAC by
truncation, and thus be prepared to use 80 bit SHA1 but not 80 bit SHA2. Make
sense? The text in the draft was meant to clarify what clients and servers do if
something untoward happens ... here's the text:

Servers receiving MAC truncation negotiation requests requesting values
other than the allowed values, MUST abort the handshake. Similarly
clients receiving MAC truncation negotiation responses that differ from
the values they suggested, or that do not match the established cipher
suite, MUST abort the handshake.

Could we address this issue by clarifying this text, and if so, how?

Best regards. Simon

Eric Murray <[email-masked]> on 06/04/2001 03:31:45 PM

Please respond to "IETF Transport Layer Security WG"
      <[email-masked]>

To:   "IETF Transport Layer Security WG" <[email-masked]>
cc:    (bcc: Simon Blake-Wilson/Certicom)

Subject:  [ietf-tls] draft-ietf-tls-wireless-00.txt

What's the status of draft-ietf-tls-wireless-00.txt?  It's recently
expired, but various people here on the TLS list have implied that there
will be a revised version out soon.

I'm writing an I-D to propose using the generic extension mechanisim
from draft-ietf-tls-wireless-00.txt to allow negotiation of a simpler
PRF function, and I'd like to refer to draft-ietf-tls-wireless-00.txt
or its successor.

4

Also, I've found a small potential problem in draft-ietf-tls-wireless-00.txt.
Section 3.5 (truncated MACs) specifies the following in the "unknown_extensions"
field:

          MACTruncation MACTruncations<0..2^8-1>;

          struct {
              MACAlgorithm mac_type;
              uint16 trucation_size_in_bits
          } MACTruncation;

          enum { null(0), md5(1), sha1(2), (255) } MACAlgorithm;

What's potentially confusing is the MAC specification... what happens
if sha1 is specified in MACTruncation and the pending ciphersuite is
say TLS_RSA_EXPORT_WITH_RC2_CBC_40_MD5?  Would md5 or sha1 be used?
Or should MACTruncation.MAC_type always match the hash algorithim in
the pending ciphersuite?

Unless there's a reason why MACTruncation.MAC_type is there, I'd
suggest dropping it and always using the hash that's been negotiated
as part of the ciphersuite.

Eric

---
You are currently subscribed to ietf-tls as: [email-masked]
To unsubscribe send a blank email to [email-masked]

---
You are currently subscribed to ietf-tls as: [email-masked]
To unsubscribe send a blank email to [email-masked]