# How to represent point-at-infinity in affine coordinate

In projective coordinates point-at-infinity can be identified with z=0. How to identify the point-at-infinity in affine coordinate.

Whether x=0 and y=0 can be considered as point-at-infinity in affine coordinate?

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Does crypto.stackexchange.com/questions/6156/… help, by any chance? –  Thomas Feb 25 '13 at 5:58
@Thomas: I went through the link you posted. My question is not related to encoding of the point-at-infinity. In our implementation after EC operation such as EC point addition we return the point "x=0, y=0" when we encounter point-at-infinity. So I wanted to check is it safe in doing this? Is there a remote possibility of obtaining a valid point with x=0,y=0 when working with standard EC curves? –  Andy Feb 26 '13 at 4:15
Well, clearly (0,0) is a valid point for the curve y^2=x^3+x which is in the standard reduced Weierstrass form. If you want a simple encoding that can be unambiguous, why not use (p,0) where p is the cardinality of the field of definition ? –  minar Jul 3 '13 at 22:27