Validates the payload received from the other participant during round 3.
See {@link JPAKEParticipant} for more details on round 3.
After execution, the {@link #getState() state} will be {@link #STATE_ROUND_3_VALIDATED}.
@param keyingMaterial The keying material as returned from {@link #calculateKeyingMaterial()}.
@throws CryptoException if validation fails.
@throws IllegalStateException if called prior to {@link #calculateKeyingMaterial()}, or multiple times