Quote from: pooya87 on August 01, 2019, 05:00:53 AM

Quote from: BurtW on July 31, 2019, 12:46:11 PM

The x coordinate and y coordinate are both binary numbers in the range 2²⁵⁶.

the max is also a little bit less than 2²⁵⁶ but unlike private keys the max is defined by P (the prime) not N (the curve order)

Quote from: BurtW on July 31, 2019, 12:46:11 PM

For the curve used for Bitcoin public keys it turns out that for every x coordinate there are two possible y coordinates.

that doesn't depend on which curve is used, as long as it is an elliptic curve it will be symmetrical about the x-axis so for each x there are 2 y values. which is due to the formula being y²=...

Quote from: BurtW on July 31, 2019, 12:46:11 PM

A compressed public key give you the x coordinate and the sign of the y coordinate so in order to convert it to a full public key you have to calculate the correct y coordinate from the x coordinate.

that is not exactly the "sign", the first byte being 2 or 3 indicates if y is even or odd respectively.
we don't actually use any signs in elliptic curve calculations since we are using modular arithmetic. for example if prime is 7 then we have
4 ≡ 11 ≡ 18 ≡ -3 ≡ -10 (mod 7)
by a "contract" we only use the smallest positive number meaning "4"

Thanks, I was trying to be a little less technical for zeilar since he is a total noob - I did not want to overwhelm him.

You points are all well taken. Very good information for the more technical savvy in the audience.

Quote from: zielar on July 31, 2019, 10:28:11 PM

Thank you very much! I do not yet understand, however, where these values consisting of more than 150 SAME numbers come from. Converting hex to dec gives me a string of 77 characters. I could transform the logic to combine the DEC result from the first and the second and it will come out just right :-) but it probably does not work, because these strings usually also appear twice.

I have absolutely no idea how to decipher your post so I cannot help you. Good luck!