Extend mlkem_top with a runtime op_i select (0=KeyGen, 1=Encaps) and the
first Encaps stages, reusing the shared keccak_core and the ST_H multi-block
SHA3-256 machinery:
ST_ENC_H: H(ek) over preloaded ek_bram (same FSM as KeyGen ST_H)
ST_ENC_G: (K,r) = G(m||H(ek)) via new 64-byte single-block SHA3-512
- sha3_top_shared: add mode=2'b11 = SHA3-512 over a full 512-bit message
(g512_pad). Standalone tb_sha3_g512 confirms it byte-exact.
- mlkem_top: new ports op_i, msg_i, ek_in_{we,addr,byte} (ek preload), ss_o,
dbg_ct_*, dbg_r_o/dbg_hek_o. st widened 4->5 bits; ST_ENC_* states added.
Renamed message port to msg_i to avoid collision with ST_M counter m_i.
- TB tb_mlkem_enc_katK + gen_encaps_vectors.py (per-byte ek/m/ct/ss vectors).
Verified ss==KAT.ss for K=2/3/4, cases 0-2 (all PASS). KeyGen unaffected
(K=2 c0 still ek==pk, dk==sk byte-exact).
KeyGen's Keccak consumers (G/H via sha3, A via SampleNTT, C via CBD) run in
disjoint top-FSM phases, so one keccak_core suffices. Add sha3_top_shared
(keccak_core externalised as kc_* ports, like the existing sample_*_shared
variants); mlkem_top now instantiates one keccak_core and a phase mux that
routes kc_state_i/kc_valid_i from the active consumer and gates kc_valid_o
per consumer (inactive samplers latch squeeze state unconditionally).
Cuts the KeyGen datapath from 4 keccak_core (1600-bit state + 24-round logic
each) to 1 -- the dominant ASIC area win. 11/11 KAT PASS (K=2 c0-4, K=3/4
c0-2), byte-exact, 0 file-not-found.
