Hi

I use this exemple: http://www.royalforkblog.com/2014/09/04/ecc/

elliptic curve: y^2 = x^3 - 3x + 4 (mod 29)

I want to find y (=9) coordinate from x (=17) coordinate for the point 
(17,9)

x^3 - 3x + 4 (mod 29) = 17^3 - 3*17 + 4 mod 29 = 4866 mod 29 = 23

if I compute the multiplicative inverse of 23, I find 24:

24 * 23 mod 29 = 552 mod 29 = 1

Then I can multiply both sides by 23:

23 * 24 * 23 mod 29 = 12696 mod 29 = 23

But this number is not the square of another number: y^2 /= 12696

My question: how do I find y such that

y^2 mod 29 = 23

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