Re: [Cfrg] [saag] A proposal for compact representation of an elliptic curve point (ECC point compression)

Hi Andrey:

One can already implement the x-coordinate only representation of an 
elliptic curve point simply by converting the affine representation into 
compressed representation and randomizing the compression "bit". The 
reverse operation then yields the point or its inverse (which have the 
same x-coordinate).

To my knowledge, this does not require any changes to data formatting 
(nor additional bytes).

Best regards,

Rene

On 12/11/2012 6:37 PM, Andrey Jivsov wrote:
> On 12/11/2012 03:15 PM, Peter Gutmann wrote:
>> Andrey Jivsov <openpgp@brainhub.org> writes:
>>
>>> I thought that it would be useful for the Internet community to have 
>>> an IETF
>>> document that describes how to encode an ECC point.
>>
>> Maybe I'm missing something here, but wouldn't this just consist of:
>>
>> -- Snip --
>>
>> See [1].
>>
>> [1] X9.62-2005, "Public Key Cryptography for the Financial Services 
>> Industry:
>> The Elliptic Curve Digital Signature Standard (ECDSA)", November, 2005.
>>
>> -- Snip --
>>
>> That's what every existing RFC that uses ECC seems to be using.
>>
>> Peter.
>>
>
> Hello Peter.
>
> "X9.62-2005" in the search engine lends me on a page that asks for 
> $100. I think http://www.secg.org/collateral/sec1_final.pdf [SEC1] is 
> more popular as a reference (assuming they are identical regarding the 
> point compression method).
>
> I claim that what I submitted is better in many respects than SEC1.
>
> Let me expand on one of the benefits not covered in the spec. It's 
> very likely that an employee of a commercial company thinking about 
> using [SEC1] compression with any ECC method would get an order from 
> the legal department to stay away from compression. The fact that 
> somebody on the Internet posted something to the contrary has little 
> weight for them. My contribution is an attempt towards a compact 
> representation that is actually usable in practice. It's the most 
> direct extension to the 1985 idea by [Miller] (see my document for 
> details).
>
> Thank you.
>
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