diff --git a/cmd/cmd.go b/cmd/cmd.go
index 28f244b..570ed0e 100644
--- a/cmd/cmd.go
+++ b/cmd/cmd.go
@@ -17,7 +17,8 @@ import (
 
 func main() {
 	fmt.Println("eth-kzg-ceremony-alt")
-	fmt.Printf("====================\n\n")
+	fmt.Printf("====================\n")
+	fmt.Printf("            https://github.com/arnaucube/eth-kzg-ceremony-alt\n\n")
 
 	redB := color.New(color.FgRed, color.Bold)
 	cyan := color.New(color.FgCyan)
@@ -29,7 +30,7 @@ func main() {
 	var randomness string
 	var sleepTime uint64
 	flag.StringVarP(&sequencerURL, "url", "u",
-		"https://kzg-ceremony-sequencer-dev.fly.dev", "sequencer url")
+		"https://sequencer.ceremony.ethereum.org", "sequencer url")
 	flag.StringVarP(&randomness, "rand", "r",
 		"", fmt.Sprintf("randomness, needs to be bigger than %d", kzgceremony.MinRandomnessLen))
 	flag.Uint64VarP(&sleepTime, "sleeptime", "s",
diff --git a/go.mod b/go.mod
index 3aaedc3..ee0f583 100644
--- a/go.mod
+++ b/go.mod
@@ -7,6 +7,7 @@ require (
 	github.com/frankban/quicktest v1.14.4
 	github.com/kilic/bls12-381 v0.1.0
 	github.com/spf13/pflag v1.0.5
+	golang.org/x/crypto v0.4.0
 )
 
 require (
@@ -16,5 +17,5 @@ require (
 	github.com/mattn/go-colorable v0.1.12 // indirect
 	github.com/mattn/go-isatty v0.0.14 // indirect
 	github.com/rogpeppe/go-internal v1.9.0 // indirect
-	golang.org/x/sys v0.0.0-20220520151302-bc2c85ada10a // indirect
+	golang.org/x/sys v0.3.0 // indirect
 )
diff --git a/go.sum b/go.sum
index 1d77765..c556350 100644
--- a/go.sum
+++ b/go.sum
@@ -22,10 +22,12 @@ github.com/rogpeppe/go-internal v1.9.0 h1:73kH8U+JUqXU8lRuOHeVHaa/SZPifC7BkcraZV
 github.com/rogpeppe/go-internal v1.9.0/go.mod h1:WtVeX8xhTBvf0smdhujwtBcq4Qrzq/fJaraNFVN+nFs=
 github.com/spf13/pflag v1.0.5 h1:iy+VFUOCP1a+8yFto/drg2CJ5u0yRoB7fZw3DKv/JXA=
 github.com/spf13/pflag v1.0.5/go.mod h1:McXfInJRrz4CZXVZOBLb0bTZqETkiAhM9Iw0y3An2Bg=
+golang.org/x/crypto v0.4.0 h1:UVQgzMY87xqpKNgb+kDsll2Igd33HszWHFLmpaRMq/8=
+golang.org/x/crypto v0.4.0/go.mod h1:3quD/ATkf6oY+rnes5c3ExXTbLc8mueNue5/DoinL80=
 golang.org/x/sys v0.0.0-20200116001909-b77594299b42/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20200223170610-d5e6a3e2c0ae/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20201101102859-da207088b7d1/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20210630005230-0f9fa26af87c/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.0.0-20210927094055-39ccf1dd6fa6/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
-golang.org/x/sys v0.0.0-20220520151302-bc2c85ada10a h1:dGzPydgVsqGcTRVwiLJ1jVbufYwmzD3LfVPLKsKg+0k=
-golang.org/x/sys v0.0.0-20220520151302-bc2c85ada10a/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+golang.org/x/sys v0.3.0 h1:w8ZOecv6NaNa/zC8944JTU3vz4u6Lagfk4RPQxv92NQ=
+golang.org/x/sys v0.3.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
diff --git a/powersoftau.go b/powersoftau.go
index cb69260..b450cf4 100644
--- a/powersoftau.go
+++ b/powersoftau.go
@@ -4,6 +4,8 @@ import (
 	"fmt"
 	"math/big"
 
+	"golang.org/x/crypto/blake2b"
+
 	bls12381 "github.com/kilic/bls12-381"
 )
 
@@ -81,7 +83,7 @@ func (cs *State) Contribute(randomness []byte) (*State, error) {
 		ns.Transcripts[i].NumG1Powers = cs.Transcripts[i].NumG1Powers
 		ns.Transcripts[i].NumG2Powers = cs.Transcripts[i].NumG2Powers
 
-		newSRS, proof, err := Contribute(cs.Transcripts[i].PowersOfTau, randomness)
+		newSRS, proof, err := Contribute(cs.Transcripts[i].PowersOfTau, i, randomness)
 		if err != nil {
 			return nil, err
 		}
@@ -109,7 +111,7 @@ func (pb *BatchContribution) Contribute(randomness []byte) (*BatchContribution,
 		nb.Contributions[i].NumG1Powers = pb.Contributions[i].NumG1Powers
 		nb.Contributions[i].NumG2Powers = pb.Contributions[i].NumG2Powers
 
-		newSRS, proof, err := Contribute(pb.Contributions[i].PowersOfTau, randomness)
+		newSRS, proof, err := Contribute(pb.Contributions[i].PowersOfTau, i, randomness)
 		if err != nil {
 			return nil, err
 		}
@@ -135,9 +137,10 @@ func newEmptySRS(nG1, nG2 int) *SRS {
 	return &SRS{g1s, g2s}
 }
 
-func tau(randomness []byte) *toxicWaste {
+func tau(round int, randomness []byte) *toxicWaste {
+	val := blake2b.Sum256(randomness)
 	tau := new(big.Int).Mod(
-		new(big.Int).SetBytes(randomness),
+		new(big.Int).SetBytes(val[:]),
 		g2.Q())
 	tau_Fr := bls12381.NewFr().FromBytes(tau.Bytes())
 	TauG2 := g2.New()
@@ -176,12 +179,12 @@ func genProof(toxicWaste *toxicWaste, prevSRS, newSRS *SRS) *Proof {
 
 // Contribute takes as input the previous SRS and a random
 // byte slice, and returns the new SRS together with the Proof
-func Contribute(prevSRS *SRS, randomness []byte) (*SRS, *Proof, error) {
+func Contribute(prevSRS *SRS, round int, randomness []byte) (*SRS, *Proof, error) {
 	if len(randomness) < MinRandomnessLen {
 		return nil, nil, fmt.Errorf("err randomness") // WIP
 	}
 	// set tau from randomness
-	tw := tau(randomness)
+	tw := tau(round, randomness)
 
 	newSRS := computeContribution(tw, prevSRS)
 
diff --git a/powersoftau_test.go b/powersoftau_test.go
index a9c92d4..1441cc5 100644
--- a/powersoftau_test.go
+++ b/powersoftau_test.go
@@ -13,13 +13,13 @@ func TestContribution(t *testing.T) {
 
 	srs_0 := newEmptySRS(10, 10)
 
-	srs_1, proof_1, err := Contribute(srs_0,
+	srs_1, proof_1, err := Contribute(srs_0, 0,
 		[]byte("1111111111111111111111111111111111111111111111111111111111111111"))
 	c.Assert(err, qt.IsNil)
 
 	c.Assert(Verify(srs_0, srs_1, proof_1), qt.IsTrue)
 
-	srs_2, proof_2, err := Contribute(srs_1,
+	srs_2, proof_2, err := Contribute(srs_1, 0,
 		[]byte("2222222222222222222222222222222222222222222222222222222222222222"))
 	c.Assert(err, qt.IsNil)
 	c.Assert(Verify(srs_1, srs_2, proof_2), qt.IsTrue)