diff options
| -rw-r--r-- | challenge/c36.go | 186 |
1 files changed, 184 insertions, 2 deletions
diff --git a/challenge/c36.go b/challenge/c36.go index dc4456b..80c231a 100644 --- a/challenge/c36.go +++ b/challenge/c36.go @@ -6,6 +6,7 @@ package challenge import ( "bufio" "fmt" + "math/big" "net" "os" @@ -49,6 +50,65 @@ func C36(args []string) { } 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.EphemeralKeyPub() + if err != nil { + return fmt.Errorf("server pub key: %v", err) + } + + // Make ACK packet + packet := fmt.Sprintf("%s+%s", lib.BytesToHexStr(user.Salt()), + lib.BytesToHexStr(serverPub.Bytes())) + + // 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.SetScramblingParam(clientPub) + if err != nil { + return fmt.Errorf("setting scrambling param: %v", err) + } + 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: %v", hmac) + } + // Login user. + user.LogIn() + + return nil + } // Handle connection from a client. serverHandleConn := func(server *lib.SRPServer, conn net.Conn) { defer conn.Close() @@ -81,6 +141,14 @@ func C36(args []string) { 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 default: fmt.Fprintf(conn, "invalid action") return @@ -162,13 +230,118 @@ func C36(args []string) { } 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) < 2 { + return fmt.Errorf("server login response invalid") + } + salt := lib.HexStrToBytes(parts[0]) + serverPub := new(big.Int).SetBytes(lib.HexStrToBytes(parts[1])) + + // Compute session key. + err = client.Session.SetScramblingParam(serverPub) + if err != nil { + return fmt.Errorf("setting scrambling param: %v", err) + } + err = client.Session.ComputeSessionKey(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 + } // Start SRP client. clientSpawn := func() { client := new(lib.SRPClient) // Enter repl. for { // Read message from stdin. - fmt.Printf("> ") + fmt.Printf("%s> ", client.Ident()) msg, err := bufio.NewReader(os.Stdin).ReadString('\n') if err != nil { fmt.Printf("read error: %v\n", err) @@ -179,13 +352,22 @@ func C36(args []string) { msg_parts := lib.StrSplitAt(' ', msg) switch { - case msg_parts[0] == "register" && len(msg_parts) == 2: + 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") + } } } } |