Definition msg_eqb (msg1 msg2:HMAC_Abstract.Message PARS.P): bool.
destruct msg1 as [m1 M1].
destruct msg2 as [m2 M2].
apply (list_EqDec bool_EqDec). apply m1. apply m2.
Defined.

Lemma Message_eqdec: EqDec (HMAC_Abstract.Message PARS.P).
apply (Build_EqDec msg_eqb).