challenge: do challenge 35 - part ii

1 files changed, 339 insertions, 1 deletions

diff --git a/challenge/c35.go b/challenge/c35.go
index cb2d166..b266e47 100644
--- a/challenge/c35.go
+++ b/challenge/c35.go
@@ -15,10 +15,15 @@ import (
 
 func C35(args []string) {
 	if len(args) < 2 {
-		fmt.Println("Usage: cryptopals -c 35 ENTITY PORT")
+		fmt.Println("Usage: cryptopals -c 35 ENTITY PORT [S-PORT] [G]")
 		return
 	}
 	entity := args[0]
+	if entity == "attacker" && len(args) != 4 {
+		fmt.Println("Usage: cryptopals -c 35 attacker PORT S-PORT G")
+		fmt.Println("\n       G should be '1', 'p' or 'p-1'")
+		return
+	}
 	port, err := lib.StrToNum(args[1])
 	if err != nil {
 		fmt.Println("Port invalid")
@@ -28,6 +33,24 @@ func C35(args []string) {
 		fmt.Println("Error: port number must be >= 12000")
 		return
 	}
+	sport := 0
+	gtype := ""
+	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
+		}
+		gtype = lib.StripSpaceChars(args[3])
+		if gtype != "1" && gtype != "p" && gtype != "p-1" {
+			fmt.Println("Error: G is invalid")
+			return
+		}
+	}
 
 	// Cipher functions.
 	//
@@ -325,6 +348,257 @@ func C35(args []string) {
 			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) != 2 {
+			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
+	}
+	// Return DH param `g` based on gtype.
+	attackerGetDHG := func(p string) (string, *big.Int, bool) {
+		if gtype == "1" {
+			return "1", new(big.Int).SetInt64(1), true
+		}
+
+		// Convert string `p` to big.Int.
+		pi, ok := new(big.Int).SetString(p, 16)
+		if !ok {
+			return "", nil, false
+		}
+
+		if gtype == "p" {
+			return p, pi, true
+		}
+
+		if gtype != "p-1" {
+			return "", nil, false
+		}
+
+		// gtype is "p-1"; make it.
+		pi.Sub(pi, new(big.Int).SetInt64(1))
+		return fmt.Sprintf("%x", pi), pi, true
+	}
+	// Try to make a connection with the server using DH and
+	// return serve'rs DH public key.
+	attackerSecureConnToServer := func(p, g string) (net.Conn, *big.Int, error) {
+		// Try to connect to server.
+		addr := fmt.Sprintf(":%d", sport)
+		conn, err := net.Dial("tcp", addr)
+		if err != nil {
+			return conn, nil, err
+		}
+
+		// Initialize DH.
+		dh, ok := lib.NewDH(p, g)
+		if !ok {
+			return conn, nil, lib.CPError{"DH initialization failed"}
+		}
+
+		// Make DH packet: p+g
+		packet := fmt.Sprintf("%v+%v", p, g)
+
+		// Sent DH packet to server.
+		fmt.Fprintf(conn, "%s\n", packet)
+
+		// Wait and try to get ACK from server.
+		spacket, err := bufio.NewReader(conn).ReadString('\n')
+		if err != nil {
+			return conn, nil, err
+		}
+		// Remove newline character.
+		spacket = spacket[:len(spacket)-1]
+		if spacket != "ACK" {
+			return conn, nil, lib.CPError{"ACK failed"}
+		}
+
+		// Send DH public key to server.
+		fmt.Fprintf(conn, "%v\n", dh.Pub())
+
+		// Get server's DH public key.
+		spacket, err = bufio.NewReader(conn).ReadString('\n')
+		if err != nil {
+			return conn, nil, err
+		}
+		// Remove newline character.
+		spacket = spacket[:len(spacket)-1]
+
+		// Parse server's DH public key.
+		sPub, ok := new(big.Int).SetString(lib.StripSpaceChars(spacket), 10)
+		if !ok {
+			return conn, nil, lib.CPError{"Server's DH key invalid"}
+		}
+
+		// Return server connection and server's DH public key.
+		return conn, dh.SharedSecret(sPub), 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
+		}
+
+		// DH params for the server.
+		p := dhParams[0]
+		g, gi, ok := attackerGetDHG(p)
+		if !ok {
+			fmt.Println("Error: Unable to get DH param 'g'")
+			return
+		}
+		sconn, skey, err := attackerSecureConnToServer(p, g)
+		if err != nil {
+			fmt.Printf("Error: %v\n", err)
+			return
+		}
+		defer sconn.Close()
+
+		// Send ACK to client.
+		fmt.Fprintf(conn, "ACK\n")
+
+		// Wait and get client's DH public key
+		packet, err := bufio.NewReader(conn).ReadString('\n')
+		if err != nil {
+			fmt.Println("Error: Unable to read client's DH public key")
+			return
+		}
+		// Remove newline character.
+		packet = packet[:len(packet)-1]
+
+		// Parse client's DH public key.
+		_, ok = new(big.Int).SetString(lib.StripSpaceChars(packet), 10)
+		if !ok {
+			fmt.Println("Error: client DH public key invalid")
+			return
+		}
+
+		// Send server's session key as public key to client.
+		fmt.Fprintf(conn, "%v\n", skey)
+
+		// Client session key.
+		ckey := new(big.Int).Set(skey)
+		ckeyAlt := new(big.Int)
+		ckeyConfirmed := true
+		if gtype == "p-1" {
+			// ckey can be 1 or p-1. Set ckeyAlt to p-1 if
+			// ckey is 1; 1 otherwise.
+			ckeyConfirmed = false
+			if ckey.Cmp(new(big.Int).SetInt64(1)) == 0 {
+				ckeyAlt.Set(gi)
+			} else {
+				ckeyAlt.Set(new(big.Int).SetInt64(1))
+			}
+		}
+
+		// Enter mitm loop
+		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.
+			if !ckeyConfirmed {
+				_, err = decipher(ckey, packet)
+				if err != nil {
+					ckey = ckeyAlt
+					ckeyConfirmed = true
+				}
+			}
+			msg, err := decipher(ckey, 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",
+					sconn.RemoteAddr(), err)
+				return
+			}
+			// Send message to server.
+			fmt.Fprintf(sconn, "%s\n", spacket)
+
+			// Read encrypted message from server.
+			spacket, err = bufio.NewReader(sconn).ReadString('\n')
+			if err != nil {
+				fmt.Printf("Closed connection to [%v]\n",
+					sconn.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",
+					sconn.RemoteAddr(), err)
+				return
+			}
+			fmt.Printf("Received from server [%v]: '%v'\n",
+				sconn.RemoteAddr(), msg)
+
+			// Encrypt and echo back message.
+			cpacket, err := encipher(ckey, 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)
+		}
+	}
+	// Start (mitm) attacker server.
+	attackerSpawn := func() {
+		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.
 	switch {
@@ -332,6 +606,8 @@ func C35(args []string) {
 		serverSpawn()
 	case entity == "client":
 		clientSpawn()
+	case entity == "attacker":
+		attackerSpawn()
 	default:
 		fmt.Println("Error: Uknown entity")
 	}
@@ -356,3 +632,65 @@ func C35(args []string) {
 // -> Kara Swisher's Sway.
 // > ^C
 //
+// Part II:
+//
+// https://ricketyspace.net/cryptopals/c35.webm
+//
+// $ ./cryptopals -c 35 server 12000
+// Waiting for connection...
+// Waiting for connection...
+// Made secure connection with 127.0.0.1:27477
+// Received from [127.0.0.1:27477]: 'If the red slayer think he slays,'
+// Closed connection to [127.0.0.1:27477]
+// Waiting for connection...
+// Made secure connection with 127.0.0.1:46947
+// Received from [127.0.0.1:46947]: 'Or if the slain think he is slain,'
+// Closed connection to [127.0.0.1:46947]
+// Waiting for connection...
+// Made secure connection with 127.0.0.1:42735
+// Received from [127.0.0.1:42735]: 'They know not well the subtle ways'
+// Received from [127.0.0.1:42735]: 'I keep, and pass, and turn again.'
+// Closed connection to [127.0.0.1:42735]
+// ^C
+//
+// $ ./cryptopals -c 35 attacker 12001 12000 1
+// Waiting for connection...
+// Waiting for connection...
+// Received from client [127.0.0.1:12597]: 'If the red slayer think he slays,'
+// Received from server [127.0.0.1:12000]: '-> If the red slayer think he slays,'
+// Closed connection to [127.0.0.1:12597]
+// ^C
+// ada$ ./cryptopals -c 35 attacker 12001 12000 p
+// Waiting for connection...
+// Waiting for connection...
+// Received from client [127.0.0.1:47227]: 'Or if the slain think he is slain,'
+// Received from server [127.0.0.1:12000]: '-> Or if the slain think he is slain,'
+// Closed connection to [127.0.0.1:47227]
+// ^C
+// ada$ ./cryptopals -c 35 attacker 12001 12000 p-1
+// Waiting for connection...
+// Waiting for connection...
+// Received from client [127.0.0.1:9193]: 'They know not well the subtle ways'
+// Received from server [127.0.0.1:12000]: '-> They know not well the subtle ways'
+// Received from client [127.0.0.1:9193]: 'I keep, and pass, and turn again.'
+// Received from server [127.0.0.1:12000]: '-> I keep, and pass, and turn again.'
+// Closed connection to [127.0.0.1:9193]
+// ^C
+//
+// $ ./cryptopals -c 35 client 12001
+// Made secure connection with 127.0.0.1:12001
+// > If the red slayer think he slays,
+// -> If the red slayer think he slays,
+// > ^C
+// ada$ ./cryptopals -c 35 client 12001
+// Made secure connection with 127.0.0.1:12001
+// > Or if the slain think he is slain,
+// -> Or if the slain think he is slain,
+// > ^C
+// ada$ ./cryptopals -c 35 client 12001
+// Made secure connection with 127.0.0.1:12001
+// > They know not well the subtle ways
+// -> They know not well the subtle ways
+// > I keep, and pass, and turn again.
+// -> I keep, and pass, and turn again.
+// > ^C