challenge: c38: implement simplified srp

2 files changed, 452 insertions, 0 deletions

diff --git a/challenge/c38.go b/challenge/c38.go
new file mode 100644
index 0000000..79681da
--- /dev/null
+++ b/challenge/c38.go
@@ -0,0 +1,450 @@
+// Copyright © 2022 siddharth ravikumar <s@ricketyspace.net>
+// SPDX-License-Identifier: ISC
+
+package challenge
+
+import (
+	"bufio"
+	"fmt"
+	"math/big"
+	"net"
+	"os"
+
+	"ricketyspace.net/cryptopals/lib"
+)
+
+func C38(args []string) {
+	if len(args) < 2 {
+		fmt.Println("Usage: cryptopals -c 36 [ client | server ] PORT")
+		return
+	}
+	entity := args[0]
+	port, err := lib.StrToNum(args[1])
+	if err != nil {
+		fmt.Println("port invalid")
+		return
+	}
+	if port < 12000 {
+		fmt.Println("port number must be >= 12000")
+		return
+	}
+
+	// Register user on the server.
+	serverRegisterUser := func(server *lib.SRPServer, info []string) error {
+		if len(info) != 5 {
+			return fmt.Errorf("regiser user: info valid")
+		}
+		n := info[0]
+		g := info[1]
+		k := info[2]
+		ident := info[3]
+		pass := info[4]
+		user, err := lib.NewSRPUser(n, g, k, ident, pass)
+		if err != nil {
+			return fmt.Errorf("register user: %v", err)
+		}
+		if err = server.RegisterUser(user); err != nil {
+			return fmt.Errorf("register user: %v", err)
+		}
+		return nil
+	}
+	// Login user on the server.
+	serverLoginUser := func(server *lib.SRPServer, info []string,
+		conn net.Conn) error {
+		if len(info) != 2 {
+			return fmt.Errorf("login user: info valid")
+		}
+		ident := info[0]
+		user, err := server.GetUser(ident)
+		if err != nil {
+			return fmt.Errorf("get user: %v", err)
+		}
+		if user.LoggedIn() {
+			return fmt.Errorf("user already has a session open")
+		}
+		clientPub := new(big.Int).SetBytes(lib.HexStrToBytes(info[1]))
+		if clientPub.Cmp(big.NewInt(0)) == 0 {
+			return fmt.Errorf("user public key invalid")
+		}
+
+		user.EphemeralKeyGen() // Generate server pub key for user.
+		serverPub, err := user.EphemeralKeyPubSimple()
+		if err != nil {
+			return fmt.Errorf("server pub key: %v", err)
+		}
+
+		// Generate scrambling param.
+		err = user.SetScramblingParamSimple()
+		if err != nil {
+			return fmt.Errorf("setting scrambling param: %v", err)
+		}
+		sParam := user.GetScramblingParam()
+
+		// Make ACK packet
+		packet := fmt.Sprintf("%s+%s+%s", lib.BytesToHexStr(user.Salt()),
+			lib.BytesToHexStr(serverPub.Bytes()),
+			lib.BytesToHexStr(sParam))
+
+		// Send packet to client.
+		_, err = fmt.Fprintf(conn, "%s\n", packet)
+		if err != nil {
+			return fmt.Errorf("sending packet to client: %v", err)
+		}
+
+		// Compute session key.
+		err = user.ComputeSessionKey(clientPub)
+		if err != nil {
+			return fmt.Errorf("computing session key: %v", err)
+		}
+
+		// Wait and try to read hmac from client.
+		cpacket, err := bufio.NewReader(conn).ReadString('\n')
+		if err != nil {
+			return fmt.Errorf("hmac recv: %v", err)
+		}
+		hmac := []byte(cpacket[:len(cpacket)-1])
+		if !user.SessionKeyMacVerify(hmac) {
+			return fmt.Errorf("hmac verification failed")
+		}
+		// Login user.
+		user.LogIn()
+
+		return nil
+	}
+	// Logout user on the server.
+	serverLogoutUser := func(server *lib.SRPServer, ident string,
+		conn net.Conn) error {
+		user, err := server.GetUser(ident)
+		if err != nil {
+			return fmt.Errorf("get user: %v", err)
+		}
+		if !user.LoggedIn() {
+			return fmt.Errorf("user not logged in")
+		}
+		// Logout user.
+		user.LogOut()
+		return nil
+	}
+	// Handle connection from a client.
+	serverHandleConn := func(server *lib.SRPServer, conn net.Conn) {
+		defer conn.Close()
+		fmt.Printf("Got connection from %v\n", conn.RemoteAddr())
+
+		// Read packet from client.
+		packet, err := bufio.NewReader(conn).ReadString('\n')
+		if err != nil {
+			fmt.Printf("Unable to read from client %v\n",
+				conn.RemoteAddr())
+			return
+		}
+
+		// Remove newline character from packet.
+		packet = packet[:len(packet)-1]
+
+		parts := lib.StrSplitAt('+', packet)
+		if len(parts) < 2 {
+			fmt.Fprintf(conn, "invalid request\n")
+			return
+		}
+
+		switch {
+		case parts[0] == "register":
+			err = serverRegisterUser(server, parts[1:])
+			if err != nil {
+				fmt.Fprintf(conn, "%v\n", err)
+				return
+			} else {
+				fmt.Fprintf(conn, "OK\n")
+			}
+			return
+		case parts[0] == "login":
+			err = serverLoginUser(server, parts[1:], conn)
+			if err != nil {
+				fmt.Fprintf(conn, "%v\n", err)
+			} else {
+				fmt.Fprintf(conn, "OK\n")
+			}
+			return
+		case parts[0] == "logout":
+			err = serverLogoutUser(server, parts[1], conn)
+			if err != nil {
+				fmt.Fprintf(conn, "%v\n", err)
+			} else {
+				fmt.Fprintf(conn, "OK\n")
+			}
+			return
+		default:
+			fmt.Fprintf(conn, "invalid action")
+			return
+		}
+
+	}
+	// Start SRP server.
+	serverSpawn := func() {
+		server := new(lib.SRPServer)
+
+		p := fmt.Sprintf(":%d", port)
+		ln, err := net.Listen("tcp", p)
+		if err != nil {
+			fmt.Printf("server listen error: %v\n", err)
+			return
+		}
+		for {
+			fmt.Println("Waiting for connection...")
+			conn, err := ln.Accept()
+			if err != nil {
+				fmt.Printf("server accept error: %v\n", err)
+			}
+			go serverHandleConn(server, conn)
+		}
+	}
+	// Register user with server.
+	clientRegisterUser := func(client *lib.SRPClient, ident string) error {
+		n := lib.StripSpaceChars(
+			`ffffffffffffffffc90fdaa22168c234c4c6628b80dc1cd129024
+                         e088a67cc74020bbea63b139b22514a08798e3404ddef9519b3cd
+                         3a431b302b0a6df25f14374fe1356d6d51c245e485b576625e7ec
+                         6f44c42e9a637ed6b0bff5cb6f406b7edee386bfb5a899fa5ae9f
+                         24117c4b1fe649286651ece45b3dc2007cb8a163bf0598da48361
+                         c55d39a69163fa8fd24cf5f83655d23dca3ad961c62f356208552
+                         bb9ed529077096966d670c354e4abc9804f1746c08ca237327fff
+                         fffffffffffff`)
+		g := "2"
+		k := "3"
+
+		// Prompt for password.
+		fmt.Printf("password> ")
+		pass, err := bufio.NewReader(os.Stdin).ReadString('\n')
+		if err != nil {
+			return fmt.Errorf("unable to read password: %v", err)
+		}
+
+		// Create session for user.
+		client.Session, err = lib.NewSRPClientSession(n, g, k, ident)
+		if err != nil {
+			return fmt.Errorf("unable to create session: %v", err)
+		}
+
+		// Make SRP registration packet.
+		packet := fmt.Sprintf("%s+%s+%s+%s+%s+%s", "register",
+			n, g, k, ident, pass)
+
+		// Try to connect to server.
+		conn, err := net.Dial("tcp", fmt.Sprintf(":%d", port))
+		if err != nil {
+			return fmt.Errorf("unable connect to server: %v", err)
+		}
+		defer conn.Close()
+
+		// Send packet to server.
+		_, err = fmt.Fprintf(conn, "%s", packet)
+		if err != nil {
+			return fmt.Errorf("unable communicate with server: %v", err)
+		}
+
+		// Wait and try to get registration ACK from server.
+		spacket, err := bufio.NewReader(conn).ReadString('\n')
+		if err != nil {
+			return fmt.Errorf("server did not respond: %v", err)
+		}
+		// Remove newline character.
+		spacket = spacket[:len(spacket)-1]
+		if spacket != "OK" {
+			return fmt.Errorf("server registration failed: %s", spacket)
+		}
+		return nil
+	}
+	// Login user into the server.
+	clientLoginUser := func(client *lib.SRPClient, ident string) error {
+		n := lib.StripSpaceChars(
+			`ffffffffffffffffc90fdaa22168c234c4c6628b80dc1cd129024
+                         e088a67cc74020bbea63b139b22514a08798e3404ddef9519b3cd
+                         3a431b302b0a6df25f14374fe1356d6d51c245e485b576625e7ec
+                         6f44c42e9a637ed6b0bff5cb6f406b7edee386bfb5a899fa5ae9f
+                         24117c4b1fe649286651ece45b3dc2007cb8a163bf0598da48361
+                         c55d39a69163fa8fd24cf5f83655d23dca3ad961c62f356208552
+                         bb9ed529077096966d670c354e4abc9804f1746c08ca237327fff
+                         fffffffffffff`)
+		g := "2"
+		k := "3"
+
+		// Prompt for password.
+		fmt.Printf("password> ")
+		pass, err := bufio.NewReader(os.Stdin).ReadString('\n')
+		if err != nil {
+			return fmt.Errorf("unable to read password: %v", err)
+		}
+		pass = pass[:len(pass)-1]
+
+		// Create session for user.
+		client.Session, err = lib.NewSRPClientSession(n, g, k, ident)
+		if err != nil {
+			return fmt.Errorf("unable to create session: %v", err)
+		}
+
+		// Get session pub key.
+		pub, err := client.Session.EphemeralKeyPub()
+		if err != nil {
+			return fmt.Errorf("unable to get pub key: %v", err)
+		}
+
+		// Make SRP login packet.
+		packet := fmt.Sprintf("%s+%s+%s", "login",
+			ident, lib.BytesToHexStr(pub.Bytes()))
+
+		// Try to connect to server.
+		conn, err := net.Dial("tcp", fmt.Sprintf(":%d", port))
+		if err != nil {
+			return fmt.Errorf("unable connect to server: %v", err)
+		}
+		defer conn.Close()
+
+		// Send login packet to server.
+		_, err = fmt.Fprintf(conn, "%s\n", packet)
+		if err != nil {
+			return fmt.Errorf("unable communicate with server: %v", err)
+		}
+
+		// Wait and try to get registration ACK from server.
+		spacket, err := bufio.NewReader(conn).ReadString('\n')
+		if err != nil {
+			return fmt.Errorf("server did not respond: %v", err)
+		}
+		// Remove newline character.
+		spacket = spacket[:len(spacket)-1]
+
+		if !lib.StrHas(spacket, "+") {
+			return fmt.Errorf("pub exchange: %s", spacket)
+		}
+		parts := lib.StrSplitAt('+', spacket)
+		if len(parts) < 3 {
+			return fmt.Errorf("server login response invalid")
+		}
+		salt := lib.HexStrToBytes(parts[0])
+		serverPub := new(big.Int).SetBytes(lib.HexStrToBytes(parts[1]))
+		sParam := lib.HexStrToBytes(parts[2])
+
+		// Compute session key.
+		err = client.Session.SetScramblingParamSimple(sParam)
+		if err != nil {
+			return fmt.Errorf("setting scrambling param: %v", err)
+		}
+		err = client.Session.ComputeSessionKeySimple(salt, pass, serverPub)
+		if err != nil {
+			return fmt.Errorf("computing session key: %v", err)
+		}
+
+		// Compute session key hmac
+		hmac, err := client.Session.SessionKeyMac(salt)
+		if err != nil {
+			return fmt.Errorf("sesion key hmac: %v", err)
+		}
+
+		// Send hmac to server.
+		_, err = fmt.Fprintf(conn, "%s\n", hmac)
+		if err != nil {
+			return fmt.Errorf("sending hmac: %v", err)
+		}
+
+		// Wait and try to get registration ACK from server.
+		spacket, err = bufio.NewReader(conn).ReadString('\n')
+		if err != nil {
+			return fmt.Errorf("server did not respond: %v", err)
+		}
+		// Remove newline character.
+		spacket = spacket[:len(spacket)-1]
+		if spacket != "OK" {
+			return fmt.Errorf("login failed: %s", spacket)
+		}
+		// Login user.
+		client.LogIn()
+		return nil
+	}
+	// Logout user.
+	clientLogoutUser := func(client *lib.SRPClient) error {
+		// Make logout packet.
+		packet := fmt.Sprintf("%s+%s", "logout", client.Ident())
+
+		// Try to connect to server.
+		conn, err := net.Dial("tcp", fmt.Sprintf(":%d", port))
+		if err != nil {
+			return fmt.Errorf("unable connect to server: %v", err)
+		}
+		defer conn.Close()
+
+		// Send login packet to server.
+		_, err = fmt.Fprintf(conn, "%s\n", packet)
+		if err != nil {
+			return fmt.Errorf("logout send: %v", err)
+		}
+
+		// Wait and try to get logout ACK from server.
+		spacket, err := bufio.NewReader(conn).ReadString('\n')
+		if err != nil {
+			return fmt.Errorf("logout recv: %v", err)
+		}
+		// Remove newline character.
+		spacket = spacket[:len(spacket)-1]
+		if spacket != "OK" {
+			return fmt.Errorf("logout ack: %s", spacket)
+		}
+
+		// Logout user.
+		client.Session = nil
+
+		return nil
+	}
+	// Start SRP client.
+	clientSpawn := func() {
+		client := new(lib.SRPClient)
+		// Enter repl.
+		for {
+			// Read message from stdin.
+			fmt.Printf("%s> ", client.Ident())
+			msg, err := bufio.NewReader(os.Stdin).ReadString('\n')
+			if err != nil {
+				fmt.Printf("read error: %v\n", err)
+				return
+			}
+			// Remove newline character.
+			msg = msg[:len(msg)-1]
+
+			msg_parts := lib.StrSplitAt(' ', msg)
+			switch {
+			case !client.LoggedIn() && msg_parts[0] == "register" &&
+				len(msg_parts) == 2:
+				err := clientRegisterUser(client, msg_parts[1])
+				if err != nil {
+					fmt.Printf("Registration failed: %v\n", err)
+				} else {
+					fmt.Printf("Registered!\n")
+				}
+			case !client.LoggedIn() && msg_parts[0] == "login" &&
+				len(msg_parts) == 2:
+				err := clientLoginUser(client, msg_parts[1])
+				if err != nil {
+					fmt.Printf("Login failed: %v\n", err)
+				} else {
+					fmt.Printf("Logged in!\n")
+				}
+			case client.LoggedIn() && msg_parts[0] == "logout":
+				err := clientLogoutUser(client)
+				if err != nil {
+					fmt.Printf("Logout failed: %v\n", err)
+				} else {
+					fmt.Printf("Logged out!\n")
+				}
+			}
+		}
+	}
+
+	// Take action based on entity.
+	switch {
+	case entity == "server":
+		serverSpawn()
+	case entity == "client":
+		clientSpawn()
+	default:
+		fmt.Println("uknown entity")
+	}
+}
diff --git a/cryptopals.go b/cryptopals.go
index 0bb909b..82627e0 100644
--- a/cryptopals.go
+++ b/cryptopals.go
@@ -94,5 +94,7 @@ func main() {
 		challenge.C36(flag.Args())
 	case 37:
 		challenge.C37(flag.Args())
+	case 38:
+		challenge.C38(flag.Args())
 	}
 }