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I'm using bouncycastle which uses X and Y coordinates for public keys.

An EC public key is more compactly represented by the X coordinate and the sign of the Y coordinate.

How do I use bouncycastle to transform X and Y into X and Y-sign, and vice versa. (The curve is secp256k1 if that makes any difference.)

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  • $\begingroup$ Do you want to know how this is done mathematically ("point compression") or do you want to know how to do this with BouncyCastle? $\endgroup$ – SEJPM Oct 20 '15 at 12:11
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    $\begingroup$ I think the above should answer this. If the problem is how to do it using BC APIs, that's more of a programming question that should be asked somewhere else. $\endgroup$ – otus Oct 20 '15 at 13:19
  • $\begingroup$ Yes, it is a duplicate, I will delete this question. $\endgroup$ – Thomas Von Panom Oct 20 '15 at 14:57

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