Clarify u2f registration public key encoding

ldap/compositetypes/composite_types.go

@@ -103,7 +103,8 @@ func UnmarshalEncryptedKey(s string) (*EncryptedKey, error) {
 //
 // The serialized format follows part of the U2F standard and just
 // stores 64 bytes of the public key immediately followed by the key
-// handle data, with no encoding.
+// handle data, with no encoding. Note that the public key itself is a
+// serialization of the elliptic curve parameters.
 //
 // The data in U2FRegistration is still encoded, but it can be turned
 // into a usable form (github.com/tstranex/u2f.Registration) later.