Added more random options

Merge github.com:ahhh/respounder into add-computernames
A random number in a random position will be placed in the
getComputerName function. A function to create a random length string
between 16 and 32 characters will be created and then filled with
either a number or character. These options have been added to the
command line options.

Author: jamesbcook

computernames.go

@@ -10,22 +10,45 @@ var (
 	firstName    = []string{"alice", "bob", "john"}
 	lastName     = []string{"smith", "johnson", "williams"}
 	jobName      = []string{"dev", "qa", "ops", "hr"}
+	alph         = []string{"a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l", "m", "n", "o", "p", "q", "r", "s", "t", "u", "v", "w", "x", "y", "z"}
+	num          = []string{"0", "1", "2", "3", "4", "5", "6", "7", "8", "9"}
 )
 
 func getRandomNumber(length int) int {
 	return rand.Intn(length)
 }
 
+func getRandomNumberBetween(min, max int) int {
+	return rand.Intn(max-min) + min
+}
+
 func getComputerName() string {
-	dstSlice := make([]string, 4)
-	srcSlice := make([]string, 4)
+	dstSlice := make([]string, 5)
+	srcSlice := make([]string, 5)
 	srcSlice[0] = computerName[getRandomNumber(len(computerName))]
 	srcSlice[1] = firstName[getRandomNumber(len(firstName))]
 	srcSlice[2] = lastName[getRandomNumber(len(lastName))]
 	srcSlice[3] = jobName[getRandomNumber(len(jobName))]
-	perm := rand.Perm(4)
+	srcSlice[4] = num[getRandomNumber(len(num))]
+	perm := rand.Perm(5)
 	for i, v := range perm {
 		dstSlice[v] = srcSlice[i]
 	}
 	return strings.Join(dstSlice[:], "")
 }
+
+func randomString() string {
+	strLen := getRandomNumberBetween(16, 32)
+	compName := make([]string, strLen)
+	var numOrStr int
+	for x := 0; x < strLen; x++ {
+		numOrStr = getRandomNumber(2)
+		switch numOrStr {
+		case 0:
+			compName[x] = num[getRandomNumber(len(num))]
+		case 1:
+			compName[x] = alph[getRandomNumber(len(alph))]
+		}
+	}
+	return strings.Join(compName, "")
+}

respounder.go

@@ -30,6 +30,13 @@ const (
 	LLMNRPort  = 5355
 )
 
+const (
+	def     = 0x00
+	newComp = 0x01
+	randCom = 0x02
+	randStr = 0x03
+)
+
 var (
 	// stdout is default output
 	outFile = os.Stdout
@@ -40,10 +47,18 @@ var (
 	// argument flags
 	jsonPtr = flag.Bool("json", false,
 		`Prints a JSON to STDOUT if a responder is detected on
-	network. Other text is sent to STDERR`)
+		network. Other text is sent to STDERR`)
 
 	debugPtr = flag.Bool("debug", false,
 		`Creates a debug.log file with a trace of the program`)
+
+	compPtr = flag.String("computername", "aweirdcomputername",
+		`Overrides the default computer name, requires at least 16 charcter hostname`)
+	randCompPtr = flag.Bool("rcomputername", false,
+		`Overrides the default computer name, with a random choice of words`)
+	randStrPtr = flag.Bool("rstring", false,
+		`Overrides the default computer name, with a completely random string`)
+	comNameType byte
 )
 
 func init() {
@@ -52,6 +67,17 @@ func init() {
 
 func main() {
 	initFlags()
+	flag.Parse()
+
+	if *compPtr != "aweirdcomputername" {
+		comNameType = newComp
+	} else if *randCompPtr {
+		comNameType = randCom
+	} else if *randStrPtr {
+		comNameType = randStr
+	} else {
+		comNameType = def
+	}
 
 	fmt.Fprintln(os.Stderr, Banner)
 
@@ -109,12 +135,22 @@ func checkResponderOnInterface(inf net.Interface) map[string]string {
 
 // Creates and sends a LLMNR request to the UDP multicast address.
 func sendLLMNRProbe(ip net.IP) string {
+	var cName string
 	responderIP := ""
 	// 2 byte random transaction id eg. 0x8e53
 	randomTransactionID := fmt.Sprintf("%04x", rand.Intn(65535))
-	computerName := getComputerName()
-	cNameLen := fmt.Sprintf("%2x", len(computerName))
-	encCName := hex.EncodeToString([]byte(computerName))
+	switch comNameType {
+	case def:
+		cName = string(*compPtr)
+	case newComp:
+		cName = string(*compPtr)
+	case randCom:
+		cName = getComputerName()
+	case randStr:
+		cName = randomString()
+	}
+	cNameLen := fmt.Sprintf("%2x", len(cName))
+	encCName := hex.EncodeToString([]byte(cName))
 	// LLMNR request in raw bytes
 	llmnrRequest := randomTransactionID +
 		"00000001000000000000" + cNameLen + encCName + "0000010001"
@@ -162,7 +198,7 @@ func getValidIPv4Addr(addrs []net.Addr) net.IP {
 func initFlags() {
 	flag.Usage = func() {
 		fmt.Fprintf(os.Stderr, "Respounder version %1.1f\n", Version)
-		fmt.Fprintf(os.Stderr, "Usage: $ respounder [-json] [-debug]")
+		fmt.Fprintf(os.Stderr, "Usage: $ respounder [-json] [-debug] [-computername anewcomputername! | -rcomputername | -rstring]")
 		fmt.Fprintf(os.Stderr, "\n\nFlags:\n")
 		flag.PrintDefaults()
 	}