Re: [Cfrg] Encrypt in place guidance

Robert Moskowitz <rgm-sec@htt-consult.com> Wed, 01 April 2020 12:16 UTC

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To: Leo Perrin <leo.perrin@inria.fr>, Stephen Farrell <stephen.farrell@cs.tcd.ie>
Cc: cfrg@ietf.org
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From: Robert Moskowitz <rgm-sec@htt-consult.com>
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Date: Wed, 1 Apr 2020 08:15:56 -0400
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Subject: Re: [Cfrg] Encrypt in place guidance
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Leo,

Thank for this paper. I will investigate the various ciphers in it.

I suspect that after Apr 9 (next ASTM meeting), I will need to encrypt 
96 bits as they address the lack of Operator altitude in the message.  I 
cannot attend the meeting, as it schedule during Passover.  Oh well, my 
colleagues will be there to put forth my position.

So I am looking for both a 64 bit and 96 bit block cipher.  I figured 
out that if there is no 96 bit, I can do this by first encrypting the 
1st 64 bits and then the last 64 bits.  The middle 32bits are double 
encrypted, but I not seeing that as a problem. But then I am not a 
cryptographer, only a crypto-plumber.

Again thank you for your assistance.

Bob

On 4/1/20 4:07 AM, Leo Perrin wrote:
> Hi,
>
>>> Speck
>> Hmm. Were the design criteria for that algorithm
>> ever published in the end? (I've not followed it,
>> so they may have been.)
> The authors of SPECK put something on eprint [1] but it merely lists public results and claims they already knew about the corresponding attacks. I personally don't find this document convincing at all since it came *after* a public analysis. In my opinion (and it is not a controversial one in the academic symmetric crypto community), if the designers of a cipher did not publish their security analysis along with its specification then you should not even consider using the corresponding cipher. Of course, there is also the elephant in the room: SPECK was designed by the same entity as the backdoored DUAL_EC.
>
> By the way, there are many (many!) 64-bit block ciphers in the literature---see Table 6 of [2]. Full disclosure: I am a co-author of this survey. If you have questions about it, feel free to ask!
>
> [1] https://eprint.iacr.org/2017/560
> [2] https://eprint.iacr.org/2017/511
>
> Cheers,
>
> /Léo
>
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