[Cryptography] Edwards curves are just ellipses - and why ECC works

[Bill Cox]

On Sun, Oct 4, 2015 at 9:18 AM, Bill Cox <waywardgeek at gmail.com> wrote:

> Edwards form:
>
>     sn3 = (sn1(cn2/dn2) + sn2)/(1 + d*sn1(cn1/sn1)sn2(cn2/dn2)
>     cn3/dn3 = ((cn1/dn1)(cn2/dn2) - sn1*sn2)/(1 -
> d*sn1(cn1/dn1)sn2(cn2/dn2))
>

I left out one factor.  The Edwards form of the ellipse point addition law
is:

    sn3 = (sn1(cn2/dn2) + sn2(cn1/dn1))/(1 + d*sn1(cn1/sn1)sn2(cn2/dn2)
    cn3/dn3 = ((cn1/dn1)(cn2/dn2) - sn1*sn2)/(1 - d*sn1(cn1/sn1)sn2(cn2/dn2)

Bill
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