diff --git a/internal/client/browsers/browser.go b/internal/client/browsers/browser.go
new file mode 100644
index 0000000..3e89875
--- /dev/null
+++ b/internal/client/browsers/browser.go
@@ -0,0 +1,41 @@
+package browsers
+
+import "encoding/binary"
+
+type ClientHelloFields struct {
+	Random         []byte
+	SessionId      []byte
+	X25519KeyShare []byte
+	ServerName     string
+}
+
+// Browser represents the signature of a browser at a particular version
+type Browser interface {
+	// ComposeClientHello produces the ClientHello message (without TLS record layer) as the mimicking browser would
+	ComposeClientHello(ClientHelloFields) []byte
+}
+
+// addExtensionRecord, add type, length to extension data
+func addExtRec(typ []byte, data []byte) []byte {
+	length := make([]byte, 2)
+	binary.BigEndian.PutUint16(length, uint16(len(data)))
+	ret := make([]byte, 2+2+len(data))
+	copy(ret[0:2], typ)
+	copy(ret[2:4], length)
+	copy(ret[4:], data)
+	return ret
+}
+
+func generateSNI(serverName string) []byte {
+	serverNameListLength := make([]byte, 2)
+	binary.BigEndian.PutUint16(serverNameListLength, uint16(len(serverName)+3))
+	serverNameType := []byte{0x00} // host_name
+	serverNameLength := make([]byte, 2)
+	binary.BigEndian.PutUint16(serverNameLength, uint16(len(serverName)))
+	ret := make([]byte, 2+1+2+len(serverName))
+	copy(ret[0:2], serverNameListLength)
+	copy(ret[2:3], serverNameType)
+	copy(ret[3:5], serverNameLength)
+	copy(ret[5:], serverName)
+	return ret
+}