Re: [Cfrg] Analysis of ipcrypt?

Greg Rose <ggr@seer-grog.net> Fri, 23 February 2018 00:14 UTC

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From: Greg Rose <ggr@seer-grog.net>
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Date: Thu, 22 Feb 2018 16:14:48 -0800
Cc: Greg Rose <ggr@seer-grog.net>, "Jason A. Donenfeld" <Jason@zx2c4.com>, Samuel Neves <sneves@dei.uc.pt>, Paul Hoffman <paul.hoffman@icann.org>, "cfrg@irtf.org" <cfrg@irtf.org>
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To: Daniel Kahn Gillmor <dkg@fifthhorseman.net>
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Subject: Re: [Cfrg] Analysis of ipcrypt?
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> On Feb 22, 2018, at 16:06 , Daniel Kahn Gillmor <dkg@fifthhorseman.net>; wrote:
> 
> On Thu 2018-02-22 06:11:38 -0800, Greg Rose wrote:
>> I cooked up "skip32" for a similar purpose a decade or two ago. It's
>> based on Skipjack. Googling for it just now, it appears to be the most
>> widely-deployed cipher I worked on... lots of implementations.
> 
> yeah, skip32 is available all over the place, but...
> 
>> void
>> skip32(BYTE key[10], BYTE buf[4], int encrypt)
> 
> 80-bit keys don't seem appropriate for modern use, even for a 32-bit
> format-preserving encryption (FPE) cipher.
> 
> NIST SP.800-38G identifies FF1 and FF3 as FPE options, both based on AES
> with 128-bit or larger keys.

Anyone who wants to do 32-bit encryption with a key longer than 80 bits already needs to have their threat model reviewed ;-).

Greg.