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Re: [Cfrg] Summary of the poll: Elliptic Curves - signature scheme: friendliness to low memory implementations (ends on June 3rd)

Adam Langley <agl@imperialviolet.org> Fri, 19 June 2015 21:53 UTC

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References: <557FEA01.7070207@isode.com> <557FE6E4.3040509@isode.com> <20150619062752.3506.qmail@cr.yp.to> <CAA4PzX3Toc+Ev6rp38rU73rinygxGPE7_FLXOWrRMh+N4SPyYQ@mail.gmail.com> <CAMfhd9Ua=fV_MKMfj1T8dApM6fA7Ko4y8-_uu03dd_WpmK4VvQ@mail.gmail.com> <D1AA03C5.1AD55%uri@ll.mit.edu>
Date: Fri, 19 Jun 2015 14:53:06 -0700
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From: Adam Langley <agl@imperialviolet.org>
To: "Blumenthal, Uri - 0553 - MITLL" <uri@ll.mit.edu>
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Subject: Re: [Cfrg] Summary of the poll: Elliptic Curves - signature scheme: friendliness to low memory implementations (ends on June 3rd)
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On Fri, Jun 19, 2015 at 2:40 PM, Blumenthal, Uri - 0553 - MITLL
<uri@ll.mit.edu> wrote:
> Good point. But doesn’t that imply the ability to create collisions in H()
> at will?

No, it's just a hash-cash problem: find x such that the first byte of
H(x) is one, and such that a couple of other bytes in H(x) have
certain values. Even if the hash function is perfect, trying 256
different values of x should give you one where H(x) starts with a
particular byte.


Cheers

AGL

-- 
Adam Langley agl@imperialviolet.org https://www.imperialviolet.org

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