crypto: Replace cryptoMode with DeviceIsolationMode concept (#4429)

* crypto: Replace cryptoMode with DeviceIsolationMode concept

* use enum instead of string for the IsolationMode kind

* Code review - Cleaning, renaming

* review: unneeded @see in doc

* review: Rename IsolationMode with better names

* review: quick cleaning and doc

spec/integ/crypto/crypto.spec.ts

@@ -82,11 +82,13 @@ import { SecretStorageKeyDescription } from "../../../src/secret-storage";
 import {
     CrossSigningKey,
     CryptoCallbacks,
-    CryptoMode,
     DecryptionFailureCode,
+    DeviceIsolationMode,
     EventShieldColour,
     EventShieldReason,
     KeyBackupInfo,
+    AllDevicesIsolationMode,
+    OnlySignedDevicesIsolationMode,
 } from "../../../src/crypto-api";
 import { E2EKeyResponder } from "../../test-utils/E2EKeyResponder";
 import { IKeyBackup } from "../../../src/crypto/backup";
@@ -747,9 +749,34 @@ describe.each(Object.entries(CRYPTO_BACKENDS))("crypto (%s)", (backend: string,
             );
         });
 
+        describe("IsolationMode decryption tests", () => {
             newBackendOnly(
-            "fails with an error when cross-signed sender is required but sender is not cross-signed",
+                "OnlySigned mode - fails with an error when cross-signed sender is required but sender is not cross-signed",
                 async () => {
+                    const decryptedEvent = await setUpTestAndDecrypt(new OnlySignedDevicesIsolationMode());
+
+                    // It will error as an unknown device because we haven't fetched
+                    // the sender's device keys.
+                    expect(decryptedEvent.isDecryptionFailure()).toBe(true);
+                    expect(decryptedEvent.decryptionFailureReason).toEqual(DecryptionFailureCode.UNKNOWN_SENDER_DEVICE);
+                },
+            );
+
+            newBackendOnly(
+                "NoIsolation mode - Decrypts with warning when cross-signed sender is required but sender is not cross-signed",
+                async () => {
+                    const decryptedEvent = await setUpTestAndDecrypt(new AllDevicesIsolationMode(false));
+
+                    expect(decryptedEvent.isDecryptionFailure()).toBe(false);
+
+                    expect(await aliceClient.getCrypto()!.getEncryptionInfoForEvent(decryptedEvent)).toEqual({
+                        shieldColour: EventShieldColour.RED,
+                        shieldReason: EventShieldReason.UNKNOWN_DEVICE,
+                    });
+                },
+            );
+
+            async function setUpTestAndDecrypt(isolationMode: DeviceIsolationMode): Promise<MatrixEvent> {
                 // This tests that a message will not be decrypted if the sender
                 // is not sufficiently trusted according to the selected crypto
                 // mode.
@@ -760,7 +787,7 @@ describe.each(Object.entries(CRYPTO_BACKENDS))("crypto (%s)", (backend: string,
                 expectAliceKeyQuery({ device_keys: { "@alice:localhost": {} }, failures: {} });
 
                 // Start by using Invisible crypto mode
-                aliceClient.getCrypto()!.setCryptoMode(CryptoMode.Invisible);
+                aliceClient.getCrypto()!.setDeviceIsolationMode(isolationMode);
 
                 await startClientAndAwaitFirstSync();
 
@@ -807,26 +834,9 @@ describe.each(Object.entries(CRYPTO_BACKENDS))("crypto (%s)", (backend: string,
                 expect(event.isEncrypted()).toBe(true);
 
                 // it probably won't be decrypted yet, because it takes a while to process the olm keys
-                const decryptedEvent = await testUtils.awaitDecryption(event);
-                // It will error as an unknown device because we haven't fetched
-                // the sender's device keys.
-                expect(decryptedEvent.decryptionFailureReason).toEqual(DecryptionFailureCode.UNKNOWN_SENDER_DEVICE);
-
-                // Next, try decrypting in transition mode, which should also
-                // fail for the same reason
-                aliceClient.getCrypto()!.setCryptoMode(CryptoMode.Transition);
-
-                await event.attemptDecryption(aliceClient["cryptoBackend"]!);
-                expect(decryptedEvent.decryptionFailureReason).toEqual(DecryptionFailureCode.UNKNOWN_SENDER_DEVICE);
-
-                // Decrypting in legacy mode should succeed since it doesn't
-                // care about device trust.
-                aliceClient.getCrypto()!.setCryptoMode(CryptoMode.Legacy);
-
-                await event.attemptDecryption(aliceClient["cryptoBackend"]!);
-                expect(decryptedEvent.decryptionFailureReason).toEqual(null);
-            },
-        );
+                return await testUtils.awaitDecryption(event);
+            }
+        });
 
         it("Decryption fails with Unable to decrypt for other errors", async () => {
             expectAliceKeyQuery({ device_keys: { "@alice:localhost": {} }, failures: {} });

src/crypto-api/index.ts

@@ -41,11 +41,9 @@ export interface CryptoApi {
     globalBlacklistUnverifiedDevices: boolean;
 
     /**
-     * The cryptography mode to use.
-     *
-     * @see CryptoMode
+     * The {@link DeviceIsolationMode} mode to use.
      */
-    setCryptoMode(cryptoMode: CryptoMode): void;
+    setDeviceIsolationMode(isolationMode: DeviceIsolationMode): void;
 
     /**
      * Return the current version of the crypto module.
@@ -667,38 +665,59 @@ export enum DecryptionFailureCode {
     UNKNOWN_ENCRYPTION_ALGORITHM = "UNKNOWN_ENCRYPTION_ALGORITHM",
 }
 
-/**
- * The cryptography mode.  Affects how messages are encrypted and decrypted.
- * Only supported by Rust crypto.
- */
-export enum CryptoMode {
-    /**
-     * Message encryption keys are shared with all devices in the room, except for
-     * blacklisted devices, or unverified devices if
-     * `globalBlacklistUnverifiedDevices` is set.  Events from all senders are
-     * decrypted.
-     */
-    Legacy,
+/** Base {@link DeviceIsolationMode} kind. */
+export enum DeviceIsolationModeKind {
+    AllDevicesIsolationMode,
+    OnlySignedDevicesIsolationMode,
+}
 
 /**
-     * Events are encrypted as with `Legacy` mode, but encryption will throw an error if a
-     * verified user has an unsigned device, or if a verified user replaces
-     * their identity.  Events are decrypted only if they come from cross-signed
-     * devices, or devices that existed before the Rust crypto SDK started
-     * tracking device trust: other events will result in a decryption failure. (To access the failure
-     * reason, see {@link MatrixEvent.decryptionFailureReason}.)
+ * A type of {@link DeviceIsolationMode}.
+ *
+ * Message encryption keys are shared with all devices in the room, except in case of
+ * verified user problems (see {@link errorOnVerifiedUserProblems}).
+ *
+ * Events from all senders are always decrypted (and should be decorated with message shields in case
+ * of authenticity warnings, see {@link EventEncryptionInfo}).
  */
-    Transition,
+export class AllDevicesIsolationMode {
+    public readonly kind = DeviceIsolationModeKind.AllDevicesIsolationMode;
 
     /**
+     *
+     * @param errorOnVerifiedUserProblems - Behavior when sharing keys to remote devices.
+     *
+     * If set to `true`, sharing keys will fail (i.e. message sending will fail) with an error if:
+     *   - The user was previously verified but is not anymore, or:
+     *   - A verified user has some unverified devices (not cross-signed).
+     *
+     * If `false`, the keys will be distributed as usual. In this case, the client UX should display
+     * warnings to inform the user about problematic devices/users, and stop them hitting this case.
+     */
+    public constructor(public readonly errorOnVerifiedUserProblems: boolean) {}
+}
+
+/**
+ * A type of {@link DeviceIsolationMode}.
+ *
  * Message encryption keys are only shared with devices that have been cross-signed by their owner.
-     * Encryption will throw an error if a verified user replaces their identity.  Events are
-     * decrypted only if they come from a cross-signed device other events will result in a decryption
+ * Encryption will throw an error if a verified user replaces their identity.
+ *
+ * Events are decrypted only if they come from a cross-signed device. Other events will result in a decryption
  * failure. (To access the failure reason, see {@link MatrixEvent.decryptionFailureReason}.)
  */
-    Invisible,
+export class OnlySignedDevicesIsolationMode {
+    public readonly kind = DeviceIsolationModeKind.OnlySignedDevicesIsolationMode;
 }
 
+/**
+ * DeviceIsolationMode represents the mode of device isolation used when encrypting or decrypting messages.
+ * It can be one of two types: {@link AllDevicesIsolationMode} or {@link OnlySignedDevicesIsolationMode}.
+ *
+ * Only supported by rust Crypto.
+ */
+export type DeviceIsolationMode = AllDevicesIsolationMode | OnlySignedDevicesIsolationMode;
+
 /**
  * Options object for `CryptoApi.bootstrapCrossSigning`.
  */

src/crypto/index.ts

@@ -88,9 +88,9 @@ import {
     BootstrapCrossSigningOpts,
     CrossSigningKeyInfo,
     CrossSigningStatus,
-    CryptoMode,
     decodeRecoveryKey,
     DecryptionFailureCode,
+    DeviceIsolationMode,
     DeviceVerificationStatus,
     encodeRecoveryKey,
     EventEncryptionInfo,
@@ -650,12 +650,11 @@ export class Crypto extends TypedEventEmitter<CryptoEvent, CryptoEventHandlerMap
     }
 
     /**
-     * Implementation of {@link Crypto.CryptoApi#setCryptoMode}.
+     * Implementation of {@link Crypto.CryptoApi#setDeviceIsolationMode}.
      */
-    public setCryptoMode(cryptoMode: CryptoMode): void {
+    public setDeviceIsolationMode(isolationMode: DeviceIsolationMode): void {
         throw new Error("Not supported");
     }
-
     /**
      * Implementation of {@link Crypto.CryptoApi#getVersion}.
      */

src/rust-crypto/rust-crypto.ts

@@ -45,7 +45,6 @@ import {
     CrossSigningStatus,
     CryptoApi,
     CryptoCallbacks,
-    CryptoMode,
     Curve25519AuthData,
     DecryptionFailureCode,
     DeviceVerificationStatus,
@@ -61,6 +60,9 @@ import {
     VerificationRequest,
     encodeRecoveryKey,
     deriveRecoveryKeyFromPassphrase,
+    DeviceIsolationMode,
+    AllDevicesIsolationMode,
+    DeviceIsolationModeKind,
 } from "../crypto-api/index.ts";
 import { deviceKeysToDeviceMap, rustDeviceToJsDevice } from "./device-converter.ts";
 import { IDownloadKeyResult, IQueryKeysRequest } from "../client.ts";
@@ -107,7 +109,7 @@ export class RustCrypto extends TypedEventEmitter<RustCryptoEvents, RustCryptoEv
     private readonly RECOVERY_KEY_DERIVATION_ITERATIONS = 500000;
 
     private _trustCrossSignedDevices = true;
-    private cryptoMode = CryptoMode.Legacy;
+    private deviceIsolationMode: DeviceIsolationMode = new AllDevicesIsolationMode(false);
 
     /** whether {@link stop} has been called */
     private stopped = false;
@@ -259,7 +261,7 @@ export class RustCrypto extends TypedEventEmitter<RustCryptoEvents, RustCryptoEv
             // through decryptEvent and hence get rid of this case.
             throw new Error("to-device event was not decrypted in preprocessToDeviceMessages");
         }
-        return await this.eventDecryptor.attemptEventDecryption(event, this.cryptoMode);
+        return await this.eventDecryptor.attemptEventDecryption(event, this.deviceIsolationMode);
     }
 
     /**
@@ -370,10 +372,10 @@ export class RustCrypto extends TypedEventEmitter<RustCryptoEvents, RustCryptoEv
     }
 
     /**
-     * Implementation of {@link Crypto.CryptoApi#setCryptoMode}.
+     * Implementation of {@link CryptoApi#setDeviceIsolationMode}.
      */
-    public setCryptoMode(cryptoMode: CryptoMode): void {
-        this.cryptoMode = cryptoMode;
+    public setDeviceIsolationMode(isolationMode: DeviceIsolationMode): void {
+        this.deviceIsolationMode = isolationMode;
     }
 
     /**
@@ -1776,7 +1778,10 @@ class EventDecryptor {
         private readonly perSessionBackupDownloader: PerSessionKeyBackupDownloader,
     ) {}
 
-    public async attemptEventDecryption(event: MatrixEvent, cryptoMode: CryptoMode): Promise<IEventDecryptionResult> {
+    public async attemptEventDecryption(
+        event: MatrixEvent,
+        isolationMode: DeviceIsolationMode,
+    ): Promise<IEventDecryptionResult> {
         // add the event to the pending list *before* attempting to decrypt.
         // then, if the key turns up while decryption is in progress (and
         // decryption fails), we will schedule a retry.
@@ -1784,16 +1789,14 @@ class EventDecryptor {
         this.addEventToPendingList(event);
 
         let trustRequirement;
-        switch (cryptoMode) {
-            case CryptoMode.Legacy:
+
+        switch (isolationMode.kind) {
+            case DeviceIsolationModeKind.AllDevicesIsolationMode:
                 trustRequirement = RustSdkCryptoJs.TrustRequirement.Untrusted;
                 break;
-            case CryptoMode.Transition:
+            case DeviceIsolationModeKind.OnlySignedDevicesIsolationMode:
                 trustRequirement = RustSdkCryptoJs.TrustRequirement.CrossSignedOrLegacy;
                 break;
-            case CryptoMode.Invisible:
-                trustRequirement = RustSdkCryptoJs.TrustRequirement.CrossSigned;
-                break;
         }
 
         try {