diff --git a/crypto/mta/proofs.go b/crypto/mta/proofs.go
index 1656e49b..4a7147c4 100644
--- a/crypto/mta/proofs.go
+++ b/crypto/mta/proofs.go
@@ -45,6 +45,8 @@ func ProveBobWC(ec elliptic.Curve, pk *paillier.PublicKey, NTilde, h1, h2, c1, c
 	q := ec.Params().N
 	q3 := new(big.Int).Mul(q, q)
 	q3 = new(big.Int).Mul(q, q3)
+	q7 := new(big.Int).Mul(q3, q3)
+	q7 = new(big.Int).Mul(q7, q)
 	qNTilde := new(big.Int).Mul(q, NTilde)
 	q3NTilde := new(big.Int).Mul(q3, NTilde)
 
@@ -62,7 +64,8 @@ func ProveBobWC(ec elliptic.Curve, pk *paillier.PublicKey, NTilde, h1, h2, c1, c
 
 	// 4.
 	beta := common.GetRandomPositiveRelativelyPrimeInt(pk.N)
-	gamma := common.GetRandomPositiveRelativelyPrimeInt(pk.N)
+
+	gamma := common.GetRandomPositiveInt(q7)
 
 	// 5.
 	u := crypto.NewECPointNoCurveCheck(ec, zero, zero) // initialization suppresses an IDE warning