An interface for an elliptic curve public key as defined by RFC 7748. These keys are distinct from the keys represented by
ECPublicKey, and they are intended for use with algorithms based on RFC 7748 such as the XDH
KeyAgreementalgorithm. An XEC public key is a particular point on the curve, which is represented using only its u-coordinate as described in RFC 7748. A u-coordinate is an element of the field of integers modulo some value that is determined by the algorithm parameters. This field element is represented by a BigInteger which may hold any value. That is, the BigInteger is not restricted to the range of canonical field elements.