Handle SAS verification by exposing an endpoint where the SAS can be sent to be verified

Signed-off-by: Nikos Filippakis <me@nfil.dev>

README.md

@@ -13,6 +13,7 @@ Go-NEB is a [Matrix](https://matrix.org) bot written in Go. It is the successor
     * [Configuring clients](#configuring-clients)
     * [Configuring services](#configuring-services)
     * [Configuring realms](#configuring-realms)
+    * [SAS verification](#sas-verification)
  * [Developing](#developing)
     * [Architecture](#architecture)
     * [API Docs](#viewing-the-api-docs)
@@ -178,6 +179,22 @@ Authentication via the config file:
  - [Github](https://matrix-org.github.io/go-neb/pkg/github.com/matrix-org/go-neb/realms/github/index.html#Session)
  - [JIRA](https://matrix-org.github.io/go-neb/pkg/github.com/matrix-org/go-neb/realms/jira/index.html#Session)
 
+## SAS verification
+Go-NEB supports SAS verification using the decimal method. Another user can start a verification transaction with Go-NEB using their client, and it will be accepted. In order to confirm the devices, the 3 SAS integers must then be sent to Go-NEB, to the endpoint '/verifySAS' so that it can mark the device as trusted.
+
+For example, if your user ID is `@user:localhost` and your device ID is `ABCD`, you start a SAS verification with Go-NEB and get the SAS "1111 2222 3333". You can perform the following curl request to let Go-NEB know the SAS integers so that it can match them with its own:
+
+```bash
+curl -X POST --header 'Content-Type: application/json' -d '{
+    "UserID": "@neb:localhost",
+    "OtherUserID": "@user:localhost",
+    "OtherDeviceID": "ABCD",
+    "SAS": [1111,2222,3333]
+}' 'http://localhost:4050/verifySAS'
+```
+
+If the SAS match and you also confirm that via the other device's client, the verification should finish successfully.
+
 # Contributing
 
 Before submitting pull requests, please read the [Matrix.org contribution guidelines](https://github.com/matrix-org/synapse/blob/develop/CONTRIBUTING.md#sign-off) regarding sign-off of your work.

api/api.go

@@ -80,6 +80,18 @@ type ClientConfig struct {
 	DisplayName string
 }
 
+// A IncomingDecimalSAS contains the decimal SAS as displayed on another device. The SAS consists of three numbers.
+type IncomingDecimalSAS struct {
+	// The matrix User ID of the user that Neb uses in the verification process. E.g. @alice:matrix.org
+	UserID id.UserID
+	// The three numbers that the SAS consists of.
+	SAS [3]uint
+	// The matrix User ID of the other user whose device is being verified.
+	OtherUserID id.UserID
+	// The matrix Device ID of the other device that is being verified.
+	OtherDeviceID id.DeviceID
+}
+
 // Session contains the complete auth session information for a given user on a given realm.
 // They are created for use with ConfigFile.
 type Session struct {
@@ -132,6 +144,14 @@ func (c *ClientConfig) Check() error {
 	return nil
 }
 
+// Check that the received SAS data contains the correct fields.
+func (c *IncomingDecimalSAS) Check() error {
+	if c.UserID == "" || c.OtherUserID == "" || c.OtherDeviceID == "" {
+		return errors.New(`Must supply a "UserID", an "OtherUserID", and an "OtherDeviceID"`)
+	}
+	return nil
+}
+
 // Check that the request is valid.
 func (r *RequestAuthSessionRequest) Check() error {
 	if r.UserID == "" || r.RealmID == "" || r.Config == nil {

api/handlers/client.go

@@ -7,6 +7,7 @@ import (
 	"github.com/matrix-org/go-neb/api"
 	"github.com/matrix-org/go-neb/clients"
 	"github.com/matrix-org/util"
+	"maunium.net/go/mautrix/crypto"
 )
 
 // ConfigureClient represents an HTTP handler capable of processing /admin/configureClient requests.
@@ -67,3 +68,55 @@ func (s *ConfigureClient) OnIncomingRequest(req *http.Request) util.JSONResponse
 		}{oldClient, body},
 	}
 }
+
+// VerifySAS represents an HTTP handler capable of processing /verifySAS requests.
+type VerifySAS struct {
+	Clients *clients.Clients
+}
+
+// OnIncomingRequest handles POST requests to /verifySAS. The JSON object provided
+// is of type "api.IncomingDecimalSAS".
+//
+// The request should contain the three decimal SAS numbers as displayed on the other device that is being verified,
+// as well as that device's user and device ID.
+// It should also contain the user ID that Go-NEB's client is using.
+//
+// Request:
+//  POST /verifySAS
+//  {
+//      "UserID": "@my_bot:localhost", // Neb's user ID
+//      "OtherUserID": "@user:localhost", // User ID of device we're verifying with
+//      "OtherDeviceID": "ABCDEFG", // Device ID of device we're verifying with
+//      "SAS": [1111, 2222, 3333] // SAS displayed on device we're verifying with
+//  }
+//
+// Response:
+//  HTTP/1.1 200 OK
+//  {}
+func (s *VerifySAS) OnIncomingRequest(req *http.Request) util.JSONResponse {
+	if req.Method != "POST" {
+		return util.MessageResponse(405, "Unsupported Method")
+	}
+
+	var body api.IncomingDecimalSAS
+	if err := json.NewDecoder(req.Body).Decode(&body); err != nil {
+		return util.MessageResponse(400, "Error parsing request JSON")
+	}
+
+	if err := body.Check(); err != nil {
+		return util.MessageResponse(400, "Error parsing client config")
+	}
+
+	client, err := s.Clients.Client(body.UserID)
+	if err != nil {
+		util.GetLogger(req.Context()).WithError(err).WithField("body", body).Error("Failed to load client")
+		return util.MessageResponse(500, "Error storing SAS")
+	}
+
+	client.SubmitDecimalSAS(body.OtherUserID, body.OtherDeviceID, crypto.DecimalSASData(body.SAS))
+
+	return util.JSONResponse{
+		Code: 200,
+		JSON: struct{}{},
+	}
+}

clients/bot_client.go

@@ -1,6 +1,7 @@
 package clients
 
 import (
+	"sync"
 	"time"
 
 	"github.com/matrix-org/go-neb/api"
@@ -9,6 +10,7 @@ import (
 	log "github.com/sirupsen/logrus"
 	"maunium.net/go/mautrix"
 	"maunium.net/go/mautrix/crypto"
+	"maunium.net/go/mautrix/event"
 	mevt "maunium.net/go/mautrix/event"
 	"maunium.net/go/mautrix/id"
 )
@@ -21,6 +23,7 @@ type BotClient struct {
 	config          api.ClientConfig
 	olmMachine      *crypto.OlmMachine
 	stateStore      *NebStateStore
+	verificationSAS *sync.Map
 }
 
 // InitOlmMachine initializes a BotClient's internal OlmMachine given a client object and a Neb store,
@@ -54,6 +57,9 @@ func (botClient *BotClient) InitOlmMachine(client *mautrix.Client, nebStore *mat
 
 	botClient.stateStore = &NebStateStore{&nebStore.InMemoryStore}
 	olmMachine := crypto.NewOlmMachine(client, cryptoLogger, cryptoStore, botClient.stateStore)
+	olmMachine.AcceptVerificationFrom = func(_ string, _ *crypto.DeviceIdentity) (crypto.VerificationRequestResponse, crypto.VerificationHooks) {
+		return crypto.AcceptRequest, botClient
+	}
 	if err = olmMachine.Load(); err != nil {
 		return
 	}
@@ -142,3 +148,69 @@ func (botClient *BotClient) Sync() {
 		}
 	}
 }
+
+// VerifySASMatch returns whether the received SAS matches the SAS that the bot generated.
+// It retrieves the SAS of the other device from the bot client's SAS sync map, where it was stored by the `SubmitDecimalSAS` function.
+func (botClient *BotClient) VerifySASMatch(otherDevice *crypto.DeviceIdentity, sas crypto.SASData) bool {
+	log.WithFields(log.Fields{
+		"otherUser":   otherDevice.UserID,
+		"otherDevice": otherDevice.DeviceID,
+	}).Infof("Waiting for SAS")
+	if sas.Type() != event.SASDecimal {
+		log.Warnf("Unsupported SAS type: %v", sas.Type())
+		return false
+	}
+	key := otherDevice.UserID.String() + ":" + otherDevice.DeviceID.String()
+	sasChan, loaded := botClient.verificationSAS.LoadOrStore(key, make(chan crypto.DecimalSASData))
+	if !loaded {
+		// if we created the chan, delete it after the timeout duration
+		defer botClient.verificationSAS.Delete(key)
+	}
+	select {
+	case otherSAS := <-sasChan.(chan crypto.DecimalSASData):
+		ourSAS := sas.(crypto.DecimalSASData)
+		log.WithFields(log.Fields{
+			"otherUser":   otherDevice.UserID,
+			"otherDevice": otherDevice.DeviceID,
+		}).Warnf("Our SAS: %v, Received SAS: %v, Match: %v", ourSAS, otherSAS, ourSAS == otherSAS)
+		return ourSAS == otherSAS
+	case <-time.After(botClient.olmMachine.DefaultSASTimeout):
+		log.Warnf("Timed out while waiting for SAS from device %v", otherDevice.DeviceID)
+	}
+	return false
+}
+
+// SubmitDecimalSAS stores the received decimal SAS from another device to compare to the local one.
+// It stores the SAS in the bot client's SAS sync map to be retrieved from the `VerifySASMatch` function.
+func (botClient *BotClient) SubmitDecimalSAS(otherUser id.UserID, otherDevice id.DeviceID, sas crypto.DecimalSASData) {
+	key := otherUser.String() + ":" + otherDevice.String()
+	sasChan, loaded := botClient.verificationSAS.LoadOrStore(key, make(chan crypto.DecimalSASData))
+	go func() {
+		if !loaded {
+			// if we created the chan, delete it after the timeout duration
+			defer botClient.verificationSAS.Delete(key)
+		}
+		// insert to channel in goroutine to avoid blocking if we are not expecting a SAS for this user/device right now
+		select {
+		case sasChan.(chan crypto.DecimalSASData) <- crypto.DecimalSASData(sas):
+		case <-time.After(botClient.olmMachine.DefaultSASTimeout):
+			log.Warnf("Timed out while trying to send SAS for device %v", otherDevice)
+		}
+	}()
+}
+
+// VerificationMethods returns the supported SAS verification methods.
+// As a bot we only support decimal as it's easier to understand.
+func (botClient *BotClient) VerificationMethods() []crypto.VerificationMethod {
+	return []crypto.VerificationMethod{
+		crypto.VerificationMethodDecimal{},
+	}
+}
+
+// OnCancel is called when a SAS verification is canceled.
+func (botClient *BotClient) OnCancel(cancelledByUs bool, reason string, reasonCode event.VerificationCancelCode) {
+}
+
+// OnSuccess is called when a SAS verification is successful.
+func (botClient *BotClient) OnSuccess() {
+}

clients/clients.go

@@ -340,6 +340,7 @@ func (c *Clients) initClient(botClient *BotClient) error {
 		log.Warn("Device ID is not set which will result in E2E encryption/decryption not working")
 	}
 	botClient.Client = client
+	botClient.verificationSAS = &sync.Map{}
 
 	syncer := client.Syncer.(*mautrix.DefaultSyncer)
 

clients/clients_test.go

@@ -4,11 +4,14 @@ import (
 	"fmt"
 	"net/http"
 	"reflect"
+	"sync"
 	"testing"
+	"time"
 
 	"github.com/matrix-org/go-neb/database"
 	"github.com/matrix-org/go-neb/types"
 	"maunium.net/go/mautrix"
+	"maunium.net/go/mautrix/crypto"
 	mevt "maunium.net/go/mautrix/event"
 	"maunium.net/go/mautrix/id"
 )
@@ -103,3 +106,48 @@ func TestCommandParsing(t *testing.T) {
 	}
 
 }
+
+func TestSASVerificationHandling(t *testing.T) {
+	botClient := BotClient{verificationSAS: &sync.Map{}}
+	botClient.olmMachine = &crypto.OlmMachine{
+		DefaultSASTimeout: time.Minute,
+	}
+	otherUserID := id.UserID("otherUser")
+	otherDeviceID := id.DeviceID("otherDevice")
+	otherDevice := &crypto.DeviceIdentity{
+		UserID:   otherUserID,
+		DeviceID: otherDeviceID,
+	}
+	botClient.SubmitDecimalSAS(otherUserID, otherDeviceID, crypto.DecimalSASData([3]uint{4, 5, 6}))
+	matched := botClient.VerifySASMatch(otherDevice, crypto.DecimalSASData([3]uint{1, 2, 3}))
+	if matched {
+		t.Error("SAS matched when they shouldn't have")
+	}
+
+	botClient.SubmitDecimalSAS(otherUserID, otherDeviceID, crypto.DecimalSASData([3]uint{1, 2, 3}))
+	matched = botClient.VerifySASMatch(otherDevice, crypto.DecimalSASData([3]uint{1, 2, 3}))
+	if !matched {
+		t.Error("Expected SAS to match but they didn't")
+	}
+
+	botClient.SubmitDecimalSAS(otherUserID+"wrong", otherDeviceID, crypto.DecimalSASData([3]uint{4, 5, 6}))
+	finished := make(chan bool)
+	go func() {
+		matched := botClient.VerifySASMatch(otherDevice, crypto.DecimalSASData([3]uint{1, 2, 3}))
+		finished <- true
+		if !matched {
+			t.Error("SAS didn't match when it should have (receiving SAS after calling verification func)")
+		}
+	}()
+	select {
+	case <-finished:
+		t.Error("Verification finished before receiving the SAS from the correct user")
+	default:
+	}
+	botClient.SubmitDecimalSAS(otherUserID, otherDeviceID, crypto.DecimalSASData([3]uint{1, 2, 3}))
+	select {
+	case <-finished:
+	case <-time.After(10 * time.Second):
+		t.Error("Verification did not finish after receiving the SAS from the correct user")
+	}
+}

go.mod

@@ -51,5 +51,5 @@ require (
 	gopkg.in/alecthomas/kingpin.v2 v2.2.6 // indirect
 	gopkg.in/check.v1 v1.0.0-20190902080502-41f04d3bba15 // indirect
 	gopkg.in/yaml.v2 v2.3.0
-	maunium.net/go/mautrix v0.6.0
+	maunium.net/go/mautrix v0.7.0
 )

goneb.go

@@ -189,6 +189,8 @@ func setup(e envVars, mux *http.ServeMux, matrixClient *http.Client) {
 	rh := &handlers.RealmRedirect{db}
 	mux.HandleFunc("/realms/redirects/", prometheus.InstrumentHandlerFunc("realmRedirectHandler", util.Protect(rh.Handle)))
 
+	mux.Handle("/verifySAS", prometheus.InstrumentHandler("verifySAS", util.MakeJSONAPI(&handlers.VerifySAS{matrixClients})))
+
 	// Read exclusively from the config file if one was supplied.
 	// Otherwise, add HTTP listeners for new Services/Sessions/Clients/etc.
 	if e.ConfigFile != "" {