[Nils Gura and Douglas Stebila (Sun Microsystems Laboratories)]
*) Add ECDH in new directory crypto/ecdh/.
+TODO: more general interface (return x coordinate, not its hash)
+TODO: bug: pad x with leading zeros if necessary
[Douglas Stebila (Sun Microsystems Laboratories)]
*) Let BN_rand_range() abort with an error after 100 iterations