intuition.
unfold GHMAC_2K, HMAC_spec.GHMAC_2K, GNMAC, HMAC_spec.GNMAC, b, HMAC_spec.b.
remember (splitVector (c + p) (c + p) k) as z.
destruct z.
rewrite splitVector_append.
unfold app_fpad, hash_words.
simpl.
trivial.
Qed.
Definition HMAC_RKA_A : OracleComp (Bvector b * Bvector c) (Bvector c) bool :=
k_Out <--$ OC_Query _ (opad, iv);
k_In <--$ OC_Query _ (ipad, iv);
[b, _] <--$2 $ A _ _ (f_oracle GNMAC _ (Vector.append k_Out k_In)) tt;
$ ret b.
Local Opaque evalDist.

Theorem A_HMAC_RKA_equiv :
Pr[A_HMAC] == Pr[RKA_G0 _ (Rnd b) (dual_f h) (BVxor b) HMAC_RKA_A].