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Re: [saag] Perfect Forward Secrecy vs Forward Secrecy

"Hao, Feng" <Feng.Hao@warwick.ac.uk> Wed, 18 March 2020 17:16 UTC

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From: "Hao, Feng" <Feng.Hao@warwick.ac.uk>
To: Nico Williams <nico@cryptonector.com>, Robert Moskowitz <rgm-sec@htt-consult.com>
CC: "saag@ietf.org" <saag@ietf.org>
Thread-Topic: [saag] Perfect Forward Secrecy vs Forward Secrecy
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Subject: Re: [saag] Perfect Forward Secrecy vs Forward Secrecy
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The use of PFS is very prevalent in the past literature on key exchange. In 2010, when I was working on the YAK protocol [1], I did wonder why the term PFS was used everywhere despite that the word "perfect" obviously has no concreate meaning. At the time I found the very few papers that suggest the word "perfect" in PFS is redundant are MQV papers (1998, and the later 2003 journal version). In [1], I explicitly dropped the word "perfect" from PFS as it really has no concrete meaning. But within the context of the protocol that I was designing, I defined half/full forward secrecy to explicitly distinguish the two cases that when one or both parties' static keys are compromised. 

[1] https://eprint.iacr.org/2010/136.pdf

Cheers,
Feng

On 18/03/2020, 15:59, "saag on behalf of Nico Williams" <saag-bounces@ietf.org on behalf of nico@cryptonector.com> wrote:

    On Wed, Mar 18, 2020 at 10:53:32AM -0400, Robert Moskowitz wrote:
    > On 3/18/20 10:48 AM, Salz, Rich wrote:
    > > Was the person who asked you to make the change a security person?
    > 
    > A Sec AD.
    > 
    > > Can you ask them for a rationale?
    > 
    > His preference as, "perfection is hard to attain."
    
    The switch from calling it PFS to just FS came a long time ago -- I
    don't recall exactly, but it feels like roughly a decade ago.  I'm not
    sure why, and "perfection is hard to attain" does seem a bit silly
    considering PFS is a term of art, but then, our terms of art get used by
    snake oil salespeople.
    
    Not that making one term of art harder to repurpose for snake oil sales
    -if that was the intent- will make much of a dent.  But as you note,
    this ship has sailed.
    
    Nico
    -- 
    
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