From the ECDH demo here http://www-cs-students.stanford.edu/~tjw/jsbn/ecdh.html
If I generate a private key for alice I can get
P = 1175846487558108474218546536054752289210804601041
Which gives the following public key point.
X = 583857549063195252150226340830731484791130788759 Y = 1195037839477751118658084226553581900533276838164
For ECDSA public key compression the above coordinates would be prepended by 02 and the X coordinate would be used. So the compressed key for the above (based on X9.62) is...
If I only have the compressed key given above, how would I derive Y i.e. the uncompressed point.