add Poseidon multihash ([]*big.Int), add HashBytes for MiMC7 & Poseidon

mimc7/mimc7.go

@@ -127,3 +127,21 @@ func Hash(arr []*big.Int, key *big.Int) (*big.Int, error) {
 	}
 	return r, nil
 }
+
+// HashBytes hashes a msg byte slice by blocks of 31 bytes encoded as
+// little-endian
+func HashBytes(b []byte) (*big.Int, error) {
+	n := 31
+	bElems := make([]*big.Int, 0, len(b)/n+1)
+	for i := 0; i < len(b)/n; i++ {
+		v := new(big.Int)
+		utils.SetBigIntFromLEBytes(v, b[n*i:n*(i+1)])
+		bElems = append(bElems, v)
+	}
+	if len(b)%n != 0 {
+		v := new(big.Int)
+		utils.SetBigIntFromLEBytes(v, b[(len(b)/n)*n:])
+		bElems = append(bElems, v)
+	}
+	return Hash(bElems, nil)
+}

mimc7/mimc7_test.go

@@ -77,6 +77,11 @@ func TestMIMC7(t *testing.T) {
 	assert.Nil(t, err)
 	// same hash value than the iden3js and circomlib tests:
 	assert.Equal(t, "0x"+hex.EncodeToString((*big.Int)(h4).Bytes()), "0x284bc1f34f335933a23a433b6ff3ee179d682cd5e5e2fcdd2d964afa85104beb")
+
+	msg := []byte("Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.")
+	hmsg, err := HashBytes(msg)
+	assert.Nil(t, err)
+	assert.Equal(t, "16855787120419064316734350414336285711017110414939748784029922801367685456065", hmsg.String())
 }
 
 func BenchmarkMIMC7(b *testing.B) {