Re: [TLS] rfc4366-bis-03 Discuss #3: Applicability of MAC Truncation

[<Pasi.Eronen at nokia.com>]

Alfred HÎnes wrote:

> Thus, a couple of questions arises:
> 
> -  Do we need MAC truncation for the SHA-2 family based HMACs?
> 
> -  If yes, is truncation to 80 bits appropriate?
> 
> -  Or should the extension be expanded to allow specification of
>    the truncation lenght?
>    (Compatibility issues?)
> 
> -  Or do we need a complementary extension that allows the
>    explicit specification of the truncation lenght?

Given how much real-world use this extension has seen (as far as 
I know, none), I don't think adding functionality to it would be very 
useful.

> -  Should the applicability of the Truncated (H)MAC extension be
>    restricted to cipher suites using HMAC-MD5 od HMAC-SHA1 ?

Why?

> -  Should the applicability be clearly restricted to cipher
>    suites using HMAC, excluding all AEAD cipher suites and/or
>    future cipher suites using other MACs (e.g., SIV) ?

The applicability is already restricted to cipher suites using HMAC
("Note that if new cipher suites are added that do not use HMAC, and
the session negotiates one of these cipher suites, this extension will
have no effect.") -- what are you proposing to change?

Best regards,
Pasi
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