Implement mTLS (frozen version for audit)

README.md

@@ -131,11 +131,16 @@ application.
 The application implements the [Tella Nearby Sharing protocol](https://github.com/Horizontal-org/Tella-P2P-Protocol) with the following endpoints:
 
 - Default Port: 53320
-- `POST /api/v1/ping` - Initial handshake for manual connections
-- `POST /api/v1/register` - Device registration with PIN authentication
-- `POST /api/v1/prepare-upload` - Prepare file transfer session
-- `PUT /api/v1/upload` - File upload with binary data
-* `POST /api/v1/close-connection`
+- `POST /api/v2/ping` - Initial handshake for manual connections
+- `POST /api/v2/register` - Device registration with PIN authentication
+- `POST /api/v2/prepare-upload` - Prepare file transfer session
+- `PUT /api/v2/upload` - File upload with binary data
+- `POST /api/v2/close-connection`
+
+Legacy routes (transition to v2 is incompatible with v1):
+
+- `POST /api/v1/ping` - returns 400 Client error
+- `POST /api/v1/register` - returns 403 Rejected
 
 ## Platform-Specific Notes
 

backend/app/app.go

@@ -112,6 +112,15 @@ func (a *App) ConfirmRegistration() error {
 	return a.registrationHandler.ConfirmRegistration()
 }
 
+// called as part of manual connection, when the receiver has confirmed the "receiver cert hash verification" by
+// pressing button "confirm and continue"
+func (a *App) ManualConfirmationReceiverForReceiver() error {
+	if a.registrationHandler == nil {
+		return errRegistrationNotInit
+	}
+	return a.registrationHandler.SendPingResponse()
+}
+
 func (a *App) RejectRegistration() error {
 	if a.registrationHandler == nil {
 		return errRegistrationNotInit

backend/core/modules/registration/handler.go

@@ -32,6 +32,7 @@ type Handler struct {
 	service             Service
 	ctx                 context.Context
 	pendingRegistration *PendingRegistration
+	pendingPingResponse chan struct{}
 	mu                  sync.RWMutex
 }
 
@@ -42,27 +43,65 @@ func NewHandler(service Service, ctx context.Context) *Handler {
 	}
 }
 
+func (h *Handler) Reset() {
+	h.mu.Lock()
+	if h.pendingPingResponse != nil {
+		close(h.pendingPingResponse)
+	}
+	h.pendingPingResponse = nil
+	h.pendingRegistration = nil
+	h.mu.Unlock()
+}
+
 func (h *Handler) HandlePing(w http.ResponseWriter, r *http.Request) {
 	if r.Method != http.MethodPost {
 		w.WriteHeader(http.StatusMethodNotAllowed)
 		return
 	}
 
-	runtime.EventsEmit(h.ctx, "ping-received", map[string]interface{}{
-		"timestamp": time.Now().Unix(),
-		"message":   "Device attempting to connect",
-		"state":     "waiting",
-	})
+	// we only react & respond to the first ping request we receive.
+	//
+	// TODO (2026-06-22): would like to tie the confirmation action to the ip doing the ip request, so that we
+	// can selectively only respond to that ping request. the current frontend structure makes this a bit difficult / fraught.
+	// 
+	// barring that we decide to only react & respond to the first received ping request. this is also inline with the
+	// "single connection"-centric model of tella's p2p protocol. i.e. we only respond to ping if sender not
+	// registered/registration not in progress.
+	if h.pendingPingResponse == nil {
+		h.pendingPingResponse = make(chan struct{})
+		runtime.EventsEmit(h.ctx, "ping-received", map[string]interface{}{
+			"timestamp": time.Now().Unix(),
+			"message":   "Device attempting to connect",
+			"state":     "waiting",
+		})
+	}
 
+	// NOTE (2026-06-22): this style of solution only handles one ping response at a time: the first ping received
+	<-h.pendingPingResponse
 	w.Header().Set("Content-Type", "application/json")
-	json.NewEncoder(w).Encode(struct {
-		Status string `json:"status"`
-	}{
-		Status: "ok",
-	})
+	json.NewEncoder(w).Encode(map[string]bool{"senderShowHash": true})
 }
 
-func (h *Handler) HandleRegister(w http.ResponseWriter, r *http.Request) {
+func (h *Handler) SendPingResponse() error {
+	// channel should never be nil here, but then again sometimes 'never' does happen :)
+	if h.pendingPingResponse != nil {
+		h.pendingPingResponse <- struct{}{}
+	}
+	return nil
+}
+
+// rememberSenderFingerprint pins the sender certificate hash. calling changes tls config of package server, making it stricter in terms
+// of requiring tls client certs. the tls config change requires restarting the https server instance.
+//
+// lockAndGetSenderFingerprintCandidate locks the current candidate for sender fingerprint,
+// preventing it from being changed without discarding the session and starting over. 
+// this locking behaviour is intended to limit the attack surface and prevent mismatches in what is presented to a user
+// and what may be pinned. 
+//
+// we lock after authorisation to limit attacks that are intended to sabotage the connection
+// establishment by prematurely forcing the fingerprint to be locked and thus would prevent an authentic sender from
+// having their fingerprint from being chosen.
+func (h *Handler) HandleRegister(w http.ResponseWriter, r *http.Request, rememberSenderFingerprint func (string) error, lockAndGetSenderFingerprintCandidate func() string) {
 	if r.Method != http.MethodPost {
 		w.WriteHeader(http.StatusMethodNotAllowed)
 		return
@@ -92,7 +131,27 @@ func (h *Handler) HandleRegister(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	// Store the pending registration
+	if authorised, err := h.service.IsAuthorised(request.PIN, request.Nonce); !authorised {
+		if errors.Is(err, ErrPinInvalid) {
+			http.Error(w, "Invalid PIN", http.StatusUnauthorized)
+		} 
+		if errors.Is(err, ErrTooManyAttempts) {
+			http.Error(w, "Too many requests", http.StatusTooManyRequests)
+		}
+		return
+	}
+
+	// do this after authorisation (PIN / nonce check) because getSenderFingerprintCandidate locks the current candidate,
+	// preventing it from being changed without discarding the session and starting over. this locking behaviour is to limit the attack
+	// surface of what is presented to a user and what may be pinned
+	// 
+	// it's only a claimed sender until verification has been mutually confirmed
+	certificateHashClaimedSender := lockAndGetSenderFingerprintCandidate()
+	if len(certificateHashClaimedSender) != 64 {
+		http.Error(w, "Missing required parameters", http.StatusBadRequest)
+		return
+	}
+
 	h.mu.Lock()
 	h.pendingRegistration = &PendingRegistration{
 		PIN:      request.PIN,
@@ -107,6 +166,7 @@ func (h *Handler) HandleRegister(w http.ResponseWriter, r *http.Request) {
 		"timestamp": time.Now().Unix(),
 		"message":   "Sender is requesting to register",
 		"state":     "confirm",
+		"senderCertificateHash": certificateHashClaimedSender,
 	})
 
 	// Wait for user confirmation or timeout
@@ -117,6 +177,19 @@ func (h *Handler) HandleRegister(w http.ResponseWriter, r *http.Request) {
 
 		h.mu.Lock()
 		h.pendingRegistration = nil
+		// if we're sending a successful response it was because the pin was valid!
+		// since PIN was valid, we can now save the sender's certificate hash and restart the server
+		// note: since `rememberSenderFingerprint` requires a restart of the https server, we likely have to send the
+		// response before restarting?
+		err = rememberSenderFingerprint(certificateHashClaimedSender)
+		// TODO cblgh(2026-03-15): figure out something less catastrophic for the app than just panic here. but https
+		// handler is a hard place to recover from the death of the https server ^^'
+		//
+		// maybe emit some kind of event to frontend to signal catastrophic failure && need to restart?
+		// runtime.EventsEmit(h.ctx, "register-request-received", map[string]interface{}{
+		if err != nil {
+			panic(err)
+		}
 		h.mu.Unlock()
 
 	case err := <-h.pendingRegistration.Error:

backend/core/modules/registration/ports.go

@@ -1,6 +1,7 @@
 package registration
 
 type Service interface {
+	IsAuthorised(pin, nonce string) (bool, error)
 	CreateSession(pin string, nonce string) (string, error)
 	SetPINCode(pinCode string)
 	ForgetSession(sessionID string)

backend/core/modules/registration/service.go

@@ -32,16 +32,26 @@ func NewService(ctx context.Context) Service {
 	}
 }
 
-func (s *service) CreateSession(pin, nonce string) (string, error) {
+var ErrTooManyAttempts = errors.New("Too many invalid attempts")
+var ErrPinInvalid = errors.New("Invalid PIN")
+
+func (s *service) IsAuthorised(pin, nonce string) (bool, error) {
 	// TODO cblgh(2026-02-17): guard ratelimiter with mutex alt. use sync.Map to prevent crash from malicious behaviour?
 	// TODO cblgh(2026-03-11) change this rate limiter to not be on the nonce any more?
 	if s.rateLimiter[nonce] >= 3 { // check this with the team
-		return "", errors.New("too many invalid attempts")
+		return false, ErrTooManyAttempts
 	}
 
 	if pin != s.pinCode {
 		s.rateLimiter[nonce]++
-		return "", errors.New("Invalid pin")
+		return false, ErrPinInvalid
+	}
+	return true, nil
+}
+
+func (s *service) CreateSession(pin, nonce string) (string, error) {
+	if authorised, err := s.IsAuthorised(pin, nonce); !authorised {
+		return "", err
 	}
 
 	sessionID := uuid.New().String()

backend/core/modules/server/handler.go

@@ -24,10 +24,26 @@ func NewHandler(
 	}
 }
 
-func (h *Handler) SetupRoutes() {
-	h.mux.HandleFunc("/api/v1/ping", h.registrationHandler.HandlePing)
-	h.mux.HandleFunc("/api/v1/register", h.registrationHandler.HandleRegister)
-	h.mux.HandleFunc("/api/v1/prepare-upload", h.transferHandler.HandlePrepare)
-	h.mux.HandleFunc("/api/v1/upload", h.transferHandler.HandleUpload)
-	h.mux.HandleFunc("/api/v1/close-connection", h.transferHandler.HandleCloseConnection)
+// TODO (2026-06-15): keep /api/v1/ping /api/v1/register around and serve legacy responses to sent queries there
+func (h *Handler) SetupRoutes(pinFingerprint func (string) error, getSenderFingerprintCandidate func () string) {
+	h.mux.HandleFunc("/api/v2/ping", h.registrationHandler.HandlePing)
+	h.mux.HandleFunc("/api/v2/register", func(res http.ResponseWriter, req *http.Request) {
+		h.registrationHandler.HandleRegister(res, req, pinFingerprint, getSenderFingerprintCandidate)
+	})
+	h.mux.HandleFunc("/api/v2/prepare-upload", h.transferHandler.HandlePrepare)
+	h.mux.HandleFunc("/api/v2/upload", h.transferHandler.HandleUpload)
+	h.mux.HandleFunc("/api/v2/close-connection", h.transferHandler.HandleCloseConnection)
+
+	// handle v1 legacy routes
+	h.mux.HandleFunc("/api/v1/ping", func (res http.ResponseWriter, req *http.Request) {
+		// TODO (2026-06-18): collectively decide what to respond to old v1-pings. Will 400 crash clients or is it OK?
+		http.Error(res, "Bad request", http.StatusBadRequest)
+	})
+	h.mux.HandleFunc("/api/v1/register", func(res http.ResponseWriter, req *http.Request) {
+		http.Error(res, "Rejected", http.StatusForbidden)
+	})
+
+	h.mux.HandleFunc("/", func (res http.ResponseWriter, req *http.Request) {
+		http.Error(res, "Not found", http.StatusNotFound)
+	})
 }