# ECC point compression trick

*From*: "Tom St Denis" <tomstdenis@xxxxxxxxx>*Date*: 28 Jun 2006 07:14:34 -0700

Think about what mm said ... why can't we just always use one of the

roots?

e.g. you have

y == +/- sqrt(x^3 - 3x + b)

Why not always just use the positive root [adjusting your secret

multiplier as required since (-k)P == k(-P)].

You still have to compute the root to find y but now you don't even

send the one bit. You just send x.

This halves the key space but I don't see how that causes any practical

problems. You're still going to have to cycle find it.

Tom

.

**Follow-Ups**:**Re: ECC point compression trick***From:*Pubkeybreaker

**Re: ECC point compression trick***From:*Paul Rubin

**Re: ECC point compression trick***From:*Tom St Denis

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