+/*
+ * NIST SP800-56A co-factor ECDH tests.
+ * KATs taken from NIST documents with parameters:
+ *
+ * - (QCAVSx,QCAVSy) is the public key for CAVS.
+ * - dIUT is the private key for IUT.
+ * - (QIUTx,QIUTy) is the public key for IUT.
+ * - ZIUT is the shared secret KAT.
+ *
+ * CAVS: Cryptographic Algorithm Validation System
+ * IUT: Implementation Under Test
+ *
+ * This function tests two things:
+ *
+ * 1. dIUT * G = (QIUTx,QIUTy)
+ * i.e. public key for IUT computes correctly.
+ * 2. x-coord of cofactor * dIUT * (QCAVSx,QCAVSy) = ZIUT
+ * i.e. co-factor ECDH key computes correctly.
+ *
+ * returns zero on failure or unsupported curve. One otherwise.
+ */