http://i3xi5qxvnvtjk3am4vkw3xvfecjitic3brox4tfgl6mxqyzctqudscqd.onion/dir-spec/converting-to-ed25519.html
Thus, we need the sign of the x-coordinate
to do this operation; otherwise, we'll have two possible
x-coordinates that might have correspond to the ed25519 public key. To get the sign, the easiest way is to take the corresponding
private key, feed it to the ed25519 public key generation
algorithm, and see what the sign is. [Recomputing the sign bit from the private key every time sounds
rather strange and inefficient to me… —isis] Note that in addition to its coordinates,...