diff --git a/cmd/update.go b/cmd/update.go
new file mode 100644
index 0000000..ce94cee
--- /dev/null
+++ b/cmd/update.go
@@ -0,0 +1,43 @@
+package cmd
+
+import (
+	"bytes"
+	"io"
+	"io/ioutil"
+	"log"
+	"os"
+	"path/filepath"
+	"strings"
+
+	"lukechampine.com/blake3"
+)
+
+func CreateCheckSumFile(writePath string, filename string, reader io.ReadCloser) {
+	fileExtBlake3 := addBlakeExtension(filename)
+	file, _ := os.Create(filepath.Join(writePath, fileExtBlake3))
+	var fileBytes []byte
+	fileBytes, _ = ioutil.ReadAll(reader)
+	byteHash := blake3.Sum256(fileBytes)
+
+	hashReader := bytes.NewReader(byteHash[:])
+
+	if _, err := io.Copy(file, hashReader); err != nil { // that side effect I mentioned in the above for loop makes this possible to do out of loop.
+		log.Fatal(err)
+	}
+}
+
+func isEqualFiles(writePath string, filename string, reader io.ReadCloser) bool {
+	fileExtBlake3 := addBlakeExtension(filename)
+	previousHash, _ := ioutil.ReadFile(filepath.Join(writePath, fileExtBlake3))
+	var fileBytes []byte
+	fileBytes, _ = ioutil.ReadAll(reader)
+	newHash := blake3.Sum256(fileBytes)
+	return bytes.Equal(previousHash, newHash[:])
+}
+
+func addBlakeExtension(fileName string) string {
+	if pos := strings.LastIndexByte(fileName, '.'); pos != -1 {
+		return fileName[:pos] + ".blake3"
+	}
+	return fileName + ".blake3"
+}
diff --git a/cmd/update_test.go b/cmd/update_test.go
new file mode 100644
index 0000000..0691aa3
--- /dev/null
+++ b/cmd/update_test.go
@@ -0,0 +1,19 @@
+package cmd
+
+import (
+	"fmt"
+	"log"
+	"net/http"
+)
+
+func ExampleIsEqualFiles() {
+	response, err := http.Get("https://ftp.expasy.org/databases/rhea/rdf/rhea.rdf.gz")
+
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	defer response.Body.Close()
+	fmt.Println(isEqualFiles("../data/build", "rhea.rdf.gz", response.Body))
+	//Output: true
+}
diff --git a/data/build/rhea.rdf.blake3 b/data/build/rhea.rdf.blake3
new file mode 100644
index 0000000..a3057f7
--- /dev/null
+++ b/data/build/rhea.rdf.blake3
@@ -0,0 +1,2 @@
+�䊰*Mg�T5p2
+k�-��||">�T�!�ro:
\ No newline at end of file
diff --git a/go.mod b/go.mod
index c646280..1bdc0f8 100644
--- a/go.mod
+++ b/go.mod
@@ -22,4 +22,5 @@ require (
 	golang.org/x/xerrors v0.0.0-20200804184101-5ec99f83aff1 // indirect
 	gopkg.in/ini.v1 v1.62.0 // indirect
 	gopkg.in/yaml.v3 v3.0.0-20210107192922-496545a6307b // indirect
+	lukechampine.com/blake3 v1.0.0 // indirect
 )