secp224r1 not working with pointFromX

[dcousens]

As can be seen in the tests we currently skip secp224r1 in the tests because it is not fully supported.
This appears to be because we are using a curve specific optimization in curve.js: https://github.com/cryptocoinjs/ecurve/blob/master/lib/curve.js#L22.

Porting over to bn.js does resolve this issue, but because we aren't using the reduction contexts all the way through, it has a huge performance hit.

For now, it seems better to just flag this as obvious as possible and keep building up tests around the library.

[jprichardson]

How about we just remove secp224r1 curve?

[dcousens]

I think that would be a responsible decision, but maybe also a note in the README that this implementation is only tested for the included curves and contains specific optimizations as such.

[dcousens]

Found a source for the optimization: http://eprint.iacr.org/2012/309.pdf.
Ref 2.3 Point Compression.

[dcousens]

Ok, this is simply because the prime chosen in secp224 is not congruent to 3 (mod 4), and is easily verified by checking the below code against all fields.

console.log(curve.p.and(new BigInteger('3')).toString())

This is mentioned as a pre-condition in the paper referenced above.
This fast case can be seen in bn.js.

I don't see any easy way of getting around this in bigi without introducing new code.

[jprichardson]

OK, I'd be in favor of getting rid of the curve. I doubt many will use it
anyways and if that changes, we can cross that bridge then.

Thoughts?

On Mon, Jun 23, 2014 at 10:52 PM, Daniel Cousens [email protected]
wrote:

Ok, this is simply because the prime chosen in secp224 is not congruent
to 3 (mod 4), and is easily verified by checking the below code against
all fields.

console.log(curve.p.and(new BigInteger('3')).toString())

This is mentioned as a pre-condition in the paper referenced above.
This fast case can be seen in bn.js
https://github.com/indutny/bn.js/blob/master/lib/bn.js#L1607-L1615.

I don't see any easy way of getting around this in bigi without
introducing significant new code.

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[dcousens]

Now that we're aware of the underlying issue, I'm perfectly OK with removing the curve and just making a note, at least until a better solution is found.

[jprichardson]

Removed the curve in 1.0.0.