circomlib/circuits/smt/smtverifiersm.circom
2018-12-16 11:27:29 +01:00

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/*
Copyright 2018 0KIMS association.
This file is part of circom (Zero Knowledge Circuit Compiler).
circom is a free software: you can redistribute it and/or modify it
under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
circom is distributed in the hope that it will be useful, but WITHOUT
ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public
License for more details.
You should have received a copy of the GNU General Public License
along with circom. If not, see <https://www.gnu.org/licenses/>.
*/
/*
Each level in the SMTVerifier has a state.
This is the state machine.
The signals are
levIns: 1 if we are in the level where the insertion should happen
xor: 1 if the bitKey of the old and new keys are different in this level
is0: Input that indicates that the oldKey is 0
fnc: 0 -> VERIFY INCLUSION
1 -> VERIFY NOT INCLUSION
err state is not a state itself. It's a lack of state.
The end of the last level will have to be `na`
levIns=0 any
┌────┐ ┌────┐
│ │ │ │
│ ▼ levIns=1 ▼ │
│ ########### is0=1 ########### ########### │
│ # # fnc=1 # # any # # │
└──# top # ─────────────────────▶# i0 #───────────────▶# na #──┘
## ## ──────────┐ ## ## ┌───────▶## ##
########─────────────┐│ ######### │┌────────▶#########
││ levIns=1 ││
││ is0=0 ########### ││
││ fnc=1 # # any│
│└──────────▶ # iold #────────┘│
│ ## ## │
│ ######### │
│ │
│ levIns=1 ########### │
│ fnc=0 # # any
└────────────▶# inew #─────────┘
## ##
#########
*/
template SMTVerifierSM() {
signal input is0;
signal input levIns;
signal input fnc;
signal input prev_top;
signal input prev_i0;
signal input prev_iold;
signal input prev_inew;
signal input prev_na;
signal output st_top;
signal output st_i0;
signal output st_iold;
signal output st_inew;
signal output st_na;
signal prev_top_lev_ins;
signal prev_top_lev_ins_fnc;
prev_top_lev_ins <== prev_top * levIns;
prev_top_lev_ins_fnc <== prev_top_lev_ins*fnc; // prev_top * levIns * fnc
// st_top = prev_top * (1-levIns)
// = + prev_top
// - prev_top * levIns
st_top <== prev_top - prev_top_lev_ins;
// st_inew = prev_top * levIns * (1-fnc)
// = + prev_top * levIns
// - prev_top * levIns * fnc
st_inew <== prev_top_lev_ins - prev_top_lev_ins_fnc;
// st_iold = prev_top * levIns * (1-is0)*fnc
// = + prev_top * levIns * fnc
// - prev_top * levIns * fnc * is0
st_iold <== prev_top_lev_ins_fnc * (1 - is0);
// st_i0 = prev_top * levIns * is0
// = + prev_top * levIns * is0
st_i0 <== prev_top_lev_ins * is0;
st_na <== prev_na + prev_inew + prev_iold + prev_i0;
}