challenge: do challenge 34 part ii

1 files changed, 252 insertions, 17 deletions

diff --git a/challenge/c34.go b/challenge/c34.go
index 5a0f109..86a40b8 100644
--- a/challenge/c34.go
+++ b/challenge/c34.go
@@ -14,11 +14,15 @@ import (
 )
 
 func C34(args []string) {
-	if len(args) != 2 {
-		fmt.Println("Usage: cryptopals -c 34 ENTITY PORT")
+	if len(args) < 2 {
+		fmt.Println("Usage: cryptopals -c 34 ENTITY PORT [S-PORT]")
 		return
 	}
 	entity := args[0]
+	if entity == "attacker" && len(args) != 3 {
+		fmt.Println("Usage: cryptopals -c 34 attacker PORT S-PORT")
+		return
+	}
 	port, err := lib.StrToNum(args[1])
 	if err != nil {
 		fmt.Println("Port invalid")
@@ -28,6 +32,18 @@ func C34(args []string) {
 		fmt.Println("Error: port number must be >= 12000")
 		return
 	}
+	sport := 0
+	if entity == "attacker" {
+		sport, err = lib.StrToNum(args[2])
+		if err != nil {
+			fmt.Println("S-Port invalid")
+			return
+		}
+		if sport < 12000 {
+			fmt.Println("Error: port number must be >= 12000")
+			return
+		}
+	}
 
 	// Cipher functions.
 	//
@@ -47,7 +63,12 @@ func C34(args []string) {
 	// Encipher using AES-CBC.
 	encipher := func(skey *big.Int, msg string) (string, error) {
 		// Make key out of DH sesssion key.
-		k := skey.Bytes()[0:16]
+		skeyb := skey.Bytes()
+		if len(skeyb) < 16 {
+			// Pad it to 16 bytes.
+			skeyb = append(skeyb, make([]byte, 16-len(skeyb))...)
+		}
+		k := skeyb[0:16]
 
 		// Make initialization vector.
 		iv, err := lib.RandomBytes(16)
@@ -68,7 +89,12 @@ func C34(args []string) {
 	// Decipher using AES-CBC.
 	decipher := func(skey *big.Int, packet string) (string, error) {
 		// Make key out of DH sesssion key.
-		k := skey.Bytes()[0:16]
+		skeyb := skey.Bytes()
+		if len(skeyb) < 16 {
+			// Pad it to 16 bytes.
+			skeyb = append(skeyb, make([]byte, 16-len(skeyb))...)
+		}
+		k := skeyb[0:16]
 
 		// Decode packet
 		cipher, iv := cipherPacketDecode(packet)
@@ -118,11 +144,14 @@ func C34(args []string) {
 	}
 	// Handle connection from a client.
 	serverHandleConn := func(conn net.Conn) {
+		defer conn.Close()
+
 		// Do DH handshake.
 		skey, err := serverDHHandshake(conn)
 		if err != nil {
 			fmt.Printf("DH Handshake failed [%v]: %v\n",
 				conn.RemoteAddr(), err)
+			return
 		}
 		fmt.Printf("Made secure connection with %v\n", conn.RemoteAddr())
 
@@ -146,6 +175,9 @@ func C34(args []string) {
 			}
 			fmt.Printf("Received from [%v]: '%v'\n", conn.RemoteAddr(), msg)
 
+			// Make msg to client.
+			msg = fmt.Sprintf("-> %s", msg)
+
 			// Encrypt and echo back message.
 			cpacket, err := encipher(skey, msg)
 			if err != nil {
@@ -230,9 +262,10 @@ func C34(args []string) {
 		// Make a secure connection to server.
 		conn, skey, err := clientSecureConnToServer()
 		if err != nil {
-			fmt.Printf("Unable to establish secure connection: %v", err)
+			fmt.Printf("Unable to establish secure connection: %v\n", err)
 			return
 		}
+		defer conn.Close()
 		fmt.Printf("Made secure connection with %v\n", conn.RemoteAddr())
 
 		// Enter write loop.
@@ -273,12 +306,174 @@ func C34(args []string) {
 				return
 			}
 			// Barf server's response.
-			fmt.Printf("Server: %s\n", smsg)
+			fmt.Printf("%s\n", smsg)
+		}
+	}
+	// Attacker handling.
+	//
+	// Slurp DH params from client.
+	attackerSlurpDHParams := func(conn net.Conn) ([]string, error) {
+		// Read DH packet from client.
+		packet, err := bufio.NewReader(conn).ReadString('\n')
+		if err != nil {
+			return []string{}, err
+		}
+		// Remove newline character from packet.
+		packet = packet[:len(packet)-1]
+
+		// Try to read DH paramters from packet.
+		params := lib.StrSplitAt('+', packet)
+		if len(params) != 3 {
+			return []string{}, lib.CPError{"DH paramters invalid"}
+		}
+
+		// Try make a DH from params.
+		_, ok := lib.NewDH(params[0], params[1])
+		if !ok {
+			return []string{}, lib.CPError{"DH initialization failed"}
+		}
+		return params, nil
+	}
+	// Forward initial DH request to server. Initial "parameter"
+	// injection happens here (p+g+p).
+	attackerConnectToServer := func(p, g string) (net.Conn, error) {
+		// Try to connect to server.
+		addr := fmt.Sprintf(":%d", sport)
+		conn, err := net.Dial("tcp", addr)
+		if err != nil {
+			return conn, err
+		}
+
+		// Make DH packet: p+g+p
+		pub, ok := new(big.Int).SetString(lib.StripSpaceChars(p), 16)
+		if !ok {
+			return conn, lib.CPError{"Unable to parse p"}
+		}
+		packet := fmt.Sprintf("%v+%v+%v", p, g, pub)
+
+		// Sent DH packet to server.
+		fmt.Fprintf(conn, "%s\n", packet)
+
+		// Wait and try to get server's DH public key.
+		_, err = bufio.NewReader(conn).ReadString('\n')
+		if err != nil {
+			return conn, err
+		}
+
+		// Return server connection.
+		return conn, nil
+	}
+	// Handle connection from a client.
+	attackerHandleConn := func(conn net.Conn) {
+		defer conn.Close()
+
+		// Read DH params from client.
+		dhParams, err := attackerSlurpDHParams(conn)
+		if err != nil {
+			fmt.Printf("Error: %v\n", err)
+			return
+		}
+
+		// Forward request to server with p+g+p.
+		// connServer: connection to server.
+		connServer, err := attackerConnectToServer(
+			dhParams[0],
+			dhParams[1],
+		)
+		if err != nil {
+			fmt.Printf("Error: %v\n", err)
+			return
+		}
+		defer connServer.Close()
+
+		// Respond to client with p as the public key.
+		pub, ok := new(big.Int).SetString(lib.StripSpaceChars(dhParams[0]), 16)
+		if !ok {
+			fmt.Printf("Error: Unable to parse p\n")
+			return
+		}
+		fmt.Fprintf(conn, "%v\n", pub)
+
+		// Enter loop.
+		skey := new(big.Int).SetInt64(0) // Session key is zero.
+		for {
+			// Read from client.
+			packet, err := bufio.NewReader(conn).ReadString('\n')
+			if err != nil {
+				fmt.Printf("Closed connection to [%v]\n",
+					conn.RemoteAddr())
+				return
+			}
+			// Remove newline character.
+			packet = packet[:len(packet)-1]
+
+			// Decipher packet.
+			msg, err := decipher(skey, packet)
+			if err != nil {
+				fmt.Printf("Message decryption failed for [%v]: %v\n",
+					conn.RemoteAddr(), err)
+				return
+			}
+			fmt.Printf("Received from client [%v]: '%v'\n",
+				conn.RemoteAddr(), msg)
+
+			// Encrypt and forward message to server.
+			spacket, err := encipher(skey, msg)
+			if err != nil {
+				fmt.Printf("Message encryption failed for [%v]: %v\n",
+					connServer.RemoteAddr(), err)
+				return
+			}
+			// Send message to server.
+			fmt.Fprintf(connServer, "%s\n", spacket)
+
+			// Read encrypted message from server.
+			spacket, err = bufio.NewReader(connServer).ReadString('\n')
+			if err != nil {
+				fmt.Printf("Closed connection to [%v]\n",
+					connServer.RemoteAddr())
+				return
+			}
+			// Remove newline character.
+			spacket = spacket[:len(spacket)-1]
+
+			// Decipher packet.
+			msg, err = decipher(skey, spacket)
+			if err != nil {
+				fmt.Printf("Message decryption failed for [%v]: %v\n",
+					connServer.RemoteAddr(), err)
+				return
+			}
+			fmt.Printf("Received from server [%v]: '%v'\n",
+				connServer.RemoteAddr(), msg)
+
+			// Encrypt and echo back message.
+			cpacket, err := encipher(skey, msg)
+			if err != nil {
+				fmt.Printf("Message encryption failed for [%v]: %v\n",
+					conn.RemoteAddr(), err)
+				return
+			}
+			// Send message to client.
+			fmt.Fprintf(conn, "%s\n", cpacket)
 		}
 	}
-	// Attacker
+	// Start (mitm) attacker server.
 	attackerSpawn := func() {
-		// Stub for now.
+		p := fmt.Sprintf(":%d", port)
+		ln, err := net.Listen("tcp", p)
+		if err != nil {
+			fmt.Printf("Attacker listen error: %v\n", err)
+			return
+		}
+		for {
+			fmt.Println("Waiting for connection...")
+			conn, err := ln.Accept()
+			if err != nil {
+				fmt.Printf("Attacker accept error: %v", err)
+			}
+			go attackerHandleConn(conn)
+		}
 	}
 
 	// Take action based on entity.
@@ -296,20 +491,60 @@ func C34(args []string) {
 
 // Output:
 //
-// Part I:
+// https://ricketyspace.net/cryptopals/c34.webm
+//
+//  Part I:
 //
 // $ ./cryptopals -c 34 server 12000
 // Waiting for connection...
 // Waiting for connection...
-// Made secure connection with 127.0.0.1:1698
-// Received from [127.0.0.1:1698]: 'ice ice baby'
-// Received from [127.0.0.1:1698]: 'vip'
-// Closed connection to [127.0.0.1:1698]
+// Made secure connection with 127.0.0.1:6546
+// Received from [127.0.0.1:6546]: 'Books are such a drudgery.'
+// Closed connection to [127.0.0.1:6546]
 //
 // $ ./cryptopals -c 34 client 12000
 // Made secure connection with 127.0.0.1:12000
-// > ice ice baby
-// Server: ice ice baby
-// > vip
-// Server: vip
+// > Books are such a drudgery.
+// -> Books are such a drudgery.
+// > ^C
+//
+// Part II:
+//
+// $ ./cryptopals -c 34 server 12000
+// Waiting for connection...
+// Made secure connection with 127.0.0.1:46128
+// Received from [127.0.0.1:46128]: 'When I have fears that I may cease to be'
+// Received from [127.0.0.1:46128]: 'Before my pen has glean'd my teeming brain,'
+// Received from [127.0.0.1:46128]: 'Before high piled books, in charactry,'
+// Received from [127.0.0.1:46128]: 'Hold like rich garners the full ripen'd grain;'
+// Received from [127.0.0.1:46128]: '...'
+// Closed connection to [127.0.0.1:46128]
+//
+// $ ./cryptopals -c 34 attacker 12001 12000
+// Waiting for connection...
+// Waiting for connection...
+// Received from client [127.0.0.1:9186]: 'When I have fears that I may cease to be'
+// Received from server [127.0.0.1:12000]: '-> When I have fears that I may cease to be'
+// Received from client [127.0.0.1:9186]: 'Before my pen has glean'd my teeming brain,'
+// Received from server [127.0.0.1:12000]: '-> Before my pen has glean'd my teeming brain,'
+// Received from client [127.0.0.1:9186]: 'Before high piled books, in charactry,'
+// Received from server [127.0.0.1:12000]: '-> Before high piled books, in charactry,'
+// Received from client [127.0.0.1:9186]: 'Hold like rich garners the full ripen'd grain;'
+// Received from server [127.0.0.1:12000]: '-> Hold like rich garners the full ripen'd grain;'
+// Received from client [127.0.0.1:9186]: '...'
+// Received from server [127.0.0.1:12000]: '-> ...'
+// Closed connection to [127.0.0.1:9186]
+//
+// $ ./cryptopals -c 34 client 12001
+// Made secure connection with 127.0.0.1:12001
+// > When I have fears that I may cease to be
+// -> When I have fears that I may cease to be
+// > Before my pen has glean'd my teeming brain,
+// -> Before my pen has glean'd my teeming brain,
+// > Before high piled books, in charactry,
+// -> Before high piled books, in charactry,
+// > Hold like rich garners the full ripen'd grain;
+// -> Hold like rich garners the full ripen'd grain;
+// > ...
+// -> ...
 // > ^C