Fgc Protocol 3.1 - Step 3.

bmr/network.go

@@ -14,5 +14,6 @@ type Operand byte
 // Network protocol messages.
 const (
 	OpInit Operand = iota
-	OpFx
+	OpFxLambda
+	OpFxR
 )

bmr/peer.go

@@ -9,7 +9,9 @@ package bmr
 import (
 	"fmt"
 	"io"
+	"math/big"
 
+	"github.com/markkurossi/mpc/circuit"
 	"github.com/markkurossi/mpc/ot"
 	"github.com/markkurossi/text/superscript"
 )
@@ -83,12 +85,12 @@ func (peer *Peer) consumerMsgLoop(id string) error {
 			if err != nil {
 				return err
 			}
-		case OpFx:
+		case OpFxLambda:
 			gid, err := peer.from.ReceiveUint32()
 			if err != nil {
 				return err
 			}
-			peer.this.Debugf("%s: %s: id=%v\n", id, op, gid)
+			peer.this.Debugf("%s: %s: gid=%v\n", id, op, gid)
 			gate := peer.this.circ.Gates[gid]
 			lv := peer.this.lambda.Bit(int(gate.Input1))
 
@@ -101,13 +103,50 @@ func (peer *Peer) consumerMsgLoop(id string) error {
 			v ^= xb
 			peer.this.luv.SetBit(peer.this.luv, gid, v)
 			peer.this.completions++
-			if peer.this.completions == peer.this.circ.NumGates {
+			if peer.this.completions == peer.this.syncBarrier(1) {
+				peer.this.c.Signal()
+			}
+			peer.this.m.Unlock()
+
+		case OpFxR:
+			gid, err := peer.from.ReceiveUint32()
+			if err != nil {
+				return err
+			}
+			peer.this.Debugf("%s: %s: gid=%v\n", id, op, gid)
+			gate := peer.this.circ.Gates[gid]
+			luvws := []*big.Int{
+				peer.this.luvw0,
+				peer.this.luvw1,
+				peer.this.luvw2,
+				peer.this.luvw3,
+			}
+			// XXX patch luvws based on gate.Op
+			switch gate.Op {
+			case circuit.AND:
+			default:
+				return fmt.Errorf("gate %v not implemented yet", gate.Op)
+			}
+			var xbs []Label
+			for _, luvw := range luvws {
+				xb, err := FxkReceive(peer.otReceiver, luvw.Bit(gid))
+				if err != nil {
+					return err
+				}
+				xbs = append(xbs, xb)
+			}
+			peer.this.m.Lock()
+			for i := 0; i < len(xbs); i++ {
+				peer.this.rj[gid][i].Xor(xbs[i])
+			}
+			peer.this.completions++
+			if peer.this.completions == peer.this.syncBarrier(2) {
 				peer.this.c.Signal()
 			}
 			peer.this.m.Unlock()
 
 		default:
-			return fmt.Errorf("%s: %s: not implemented\n", id, op)
+			return fmt.Errorf("%s: %s: not implemented", id, op)
 		}
 
 		peer.to.Flush()

bmr/player.go

@@ -43,6 +43,9 @@ type Player struct {
 	luvw1 *big.Int
 	luvw2 *big.Int
 	luvw3 *big.Int
+
+	// The XOR shares of Rj matching ρij,α,β
+	rj [][]Label
 }
 
 // NewPlayer creates a new multi-party player.
@@ -99,6 +102,17 @@ func (p *Player) Play() error {
 			count, p.numPlayers-1)
 	}
 
+	// Init circuit-dependent fields.
+	p.rj = make([][]Label, p.circ.NumGates)
+	for i := 0; i < p.circ.NumGates; i++ {
+		switch p.circ.Gates[i].Op {
+		case circuit.AND:
+			p.rj[i] = make([]Label, 4)
+		default:
+			return fmt.Errorf("gate %v not implemented yet", p.circ.Gates[i].Op)
+		}
+	}
+
 	p.Debugf("BMR: #gates=%v\n", p.circ.NumGates)
 
 	p.Debugf("Offline Phase...\n")
@@ -216,6 +230,10 @@ func (p *Player) offlinePhase() error {
 	return nil
 }
 
+func (p *Player) syncBarrier(nth int) int {
+	return p.circ.NumGates * (len(p.peers) - 1) * nth
+}
+
 // fgc computes the multiparty garbled circuit (3.1.2 The Protocol for
 // Fgc - Page 7).
 func (p *Player) fgc() (err error) {
@@ -238,7 +256,7 @@ func (p *Player) fgc() (err error) {
 				if peer == nil {
 					continue
 				}
-				err = peer.to.SendByte(byte(OpFx))
+				err = peer.to.SendByte(byte(OpFxLambda))
 				if err != nil {
 					return err
 				}
@@ -261,8 +279,7 @@ func (p *Player) fgc() (err error) {
 
 	p.m.Lock()
 	p.luv.Xor(p.luv, luv)
-
-	for p.completions < p.circ.NumGates {
+	for p.completions < p.syncBarrier(1) {
 		p.c.Wait()
 	}
 	p.m.Unlock()
@@ -297,7 +314,6 @@ func (p *Player) fgc() (err error) {
 			return fmt.Errorf("gate %v not implemented yet", gate.Op)
 		}
 	}
-
 	fmt.Printf("Player%s: %cuvw=%v\n", p.IDString(), symbols.Lambda,
 		lambda(p.luvw0, p.circ.NumGates))
 	fmt.Printf("Player%s: %cuv̄w=%v\n", p.IDString(), symbols.Lambda,
@@ -307,6 +323,48 @@ func (p *Player) fgc() (err error) {
 	fmt.Printf("Player%s: %cūv̄w=%v\n", p.IDString(), symbols.Lambda,
 		lambda(p.luvw3, p.circ.NumGates))
 
+	// Step 3: for i!=j, run Fxk(R,luvw)
+	for gid := 0; gid < p.circ.NumGates; gid++ {
+		for _, peer := range p.peers {
+			if peer == nil {
+				continue
+			}
+			err = peer.to.SendByte(byte(OpFxR))
+			if err != nil {
+				return err
+			}
+			err = peer.to.SendUint32(gid)
+			if err != nil {
+				return err
+			}
+			for n := 0; n < len(p.rj[gid]); n++ {
+				r, err := FxkSend(peer.otSender, p.r)
+				if err != nil {
+					return err
+				}
+				p.m.Lock()
+				p.rj[gid][n].Xor(r)
+				p.m.Unlock()
+			}
+		}
+	}
+	p.m.Lock()
+	for p.completions < p.syncBarrier(2) {
+		p.c.Wait()
+	}
+	p.m.Unlock()
+
+	for gid := 0; gid < p.circ.NumGates; gid++ {
+		p.Debugf("Player%s: rj[%v]:\t", p.IDString(), gid)
+		for idx, l := range p.rj[gid] {
+			if idx > 0 {
+				p.Debugf(" ")
+			}
+			p.Debugf("%v", l)
+		}
+		p.Debugf("\n")
+	}
+
 	return nil
 }