Re: [TLS] [Cfrg] 3DES diediedie

Watson Ladd <watsonbladd@gmail.com> Fri, 26 August 2016 17:59 UTC

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From: Watson Ladd <watsonbladd@gmail.com>
Date: Fri, 26 Aug 2016 10:59:44 -0700
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To: "David McGrew (mcgrew)" <mcgrew@cisco.com>
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Subject: Re: [TLS] [Cfrg] 3DES diediedie
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On Fri, Aug 26, 2016 at 10:55 AM, David McGrew (mcgrew)
<mcgrew@cisco.com> wrote:
> Hi Tony,
>
> Thanks for bringing this up; an RFC deprecating and/or discouraging 3DES
> would be a good thing.  The only good reason to use it is backwards
> compatibility, and too many applications don’t heed the birthday bound.
>
> There is another issue to be considered, though.   Most of the lightweight
> “designed for IoT” block ciphers have a 64 bit block size (and sometimes
> even smaller); see for instance Table 1.1 of
> https://eprint.iacr.org/2013/404.pdf     So perhaps what the Internet needs
> here is sound guidance on how to use 64-bit block ciphers.   Best practices
> here include both mandatory rekeying well below the birthday bound and/or
> the use of secure beyond the birthday bound modes of operation such as
> Iwata’s CENC.

Or use PRF instead of PRP for counter mode. I'm happy to check the
arithmetic if we want an RFC for this, but am very overcommitted on
editing right now.

>
> Best,
>
> David
>
> From: Cfrg <cfrg-bounces@irtf.org> on behalf of Tony Arcieri
> <bascule@gmail.com>
> Date: Wednesday, August 24, 2016 at 10:08 PM
> To: "tls@ietf.org" <tls@ietf.org>rg>, "cfrg@irtf.org" <cfrg@irtf.org>
> Subject: [Cfrg] 3DES diediedie
>
> This attack was published today[*]:
>
> https://sweet32.info/
>
> I bring it up because I think the threat model is similar to the threats
> that lead to RC4 "diediedie"
>
> https://www.rfc-editor.org/info/rfc7465
>
> Should there be a 3DES "diediedie"?
>
> I believe 3DES is MTI for TLS 1.0/1.1(?) but I think it would make sense for
> it to be banned from TLS 1.3.
>
> [*] Lest anyone claim the contrary, I am not surprised by this attack, and
> have pushed to have 3DES removed from TLS prior to the publication of this
> attack, and can probably find a TLS implementer who can back me up on that.
>
> --
> Tony Arcieri
>
>
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>



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