Some more refactoring

cmd/handin6/main.go

@@ -36,8 +36,11 @@ func (alice *Party) RunAlice(x int, priv *homomorphic.PrivateKey) (result bool,
 
 	// Send encoded input ints to bob
 	for i := 0; i < 3; i++ {
-		alice.conn <- homomorphic.Encrypt(xval[i], &priv.PublicKey)
-		// alice.conn <- *alice.HEProt.Encode(xval[i])
+		c, err := homomorphic.Encrypt(rand.Reader, xval[i], &priv.PublicKey)
+		if err != nil {
+			return false, err
+		}
+		alice.conn <- c
 	}
 
 	//Receive and decode result from bob
@@ -53,7 +56,10 @@ func (bob *Party) RunBob(y int, pub *homomorphic.PublicKey) (err error) {
 		if val {
 			bit = 1
 		}
-		c_y[i] = homomorphic.Encrypt(bit, pub)
+		c_y[i], err = homomorphic.Encrypt(rand.Reader, bit, pub)
+		if err != nil {
+			return
+		}
 		// c_y[i] = bob.HEProt.Encode(bit)
 	}
 
@@ -63,9 +69,30 @@ func (bob *Party) RunBob(y int, pub *homomorphic.PublicKey) (err error) {
 		c_x[i] = <-bob.conn
 	}
 
-	bob.conn <- homomorphic.Evaluate(c_x, c_y, pub)
+	c, err := evaluate(c_x, c_y, pub)
+	if err != nil {
+		return
+	}
+	bob.conn <- c
 	// bob.conn <- *bob.HEProt.Eval(c_x, c_y)
-	return nil
+	return
+}
+
+func evaluate(x, y []*big.Int, pub *homomorphic.PublicKey) (result *big.Int, err error) {
+	one, err := homomorphic.Encrypt(rand.Reader, 1, pub)
+	if err != nil {
+		return
+	}
+	tmp := make([]*big.Int, 3)
+
+	for i := 0; i < 3; i++ {
+		v := new(big.Int).Mul(x[i], y[i])
+		tmp[i] = v.Add(v, one)
+	}
+
+	result = new(big.Int).Mul(tmp[0], tmp[1])
+	result.Mul(result, tmp[2])
+	return
 }
 
 // RunProtocol runs the protocol between receiving blood type x and donor blood

internal/crypto/homomorphic/dhe.go

@@ -4,7 +4,6 @@ import (
 	"crycomp/internal/crypto/util"
 	"io"
 	"math/big"
-	mRand "math/rand"
 )
 
 var two = big.NewInt(2)
@@ -69,15 +68,19 @@ func GenerateKey(random io.Reader, pLen, qLen, rLen, n int) (priv *PrivateKey, e
 	return
 }
 
-func Encrypt(m int, pub *PublicKey) (c *big.Int) {
+func Encrypt(random io.Reader, m int, pub *PublicKey) (c *big.Int, err error) {
+	// Sample random subset S of [0...n]
 	S := make([]int, pub.n)
 	for i := 0; i < pub.n; i++ {
 		S[i] = i
 	}
+	util.Shuffle(pub.n, func(i, j int) { S[i], S[j] = S[j], S[i] })
+	sLen, err := util.RandIntn(random, big.NewInt(int64(pub.n)))
+	if err != nil {
+		return
+	}
+	S = S[:sLen.Int64()]
 
-	// TODO crypto rand
-	mRand.Shuffle(pub.n, func(i, j int) { S[i], S[j] = S[j], S[i] })
-	S = S[:pub.n]
 	c = big.NewInt(int64(m))
 	for i := range S {
 		c = c.Add(c, pub.y[S[i]])
@@ -90,17 +93,3 @@ func Decrypt(c *big.Int, priv *PrivateKey) int {
 	m.Mod(m, two)
 	return int(m.Int64())
 }
-
-func Evaluate(x, y []*big.Int, pub *PublicKey) (result *big.Int) {
-	one := Encrypt(1, pub)
-	tmp := make([]*big.Int, 3)
-
-	for i := 0; i < 3; i++ {
-		v := new(big.Int).Mul(x[i], y[i])
-		tmp[i] = v.Add(v, one)
-	}
-
-	result = new(big.Int).Mul(tmp[0], tmp[1])
-	result.Mul(result, tmp[2])
-	return
-}

internal/crypto/util/util.go

@@ -81,6 +81,10 @@ func Perm(n int) []int {
 	return mRand.New(&cryptoSource{}).Perm(n)
 }
 
+func Shuffle(n int, swap func(i, j int)) {
+	mRand.New(&cryptoSource{}).Shuffle(n, swap)
+}
+
 func (s *cryptoSource) Int63() int64 {
 	_, err := cRand.Read(s[:])
 	if err != nil {