diff --git a/Riot/Modules/Application/LegacyAppDelegate.m b/Riot/Modules/Application/LegacyAppDelegate.m
index 236fd2cdd..4ed6ddf02 100644
--- a/Riot/Modules/Application/LegacyAppDelegate.m
+++ b/Riot/Modules/Application/LegacyAppDelegate.m
@@ -3753,7 +3753,7 @@ NSString *const AppDelegateUniversalLinkDidChangeNotification = @"AppDelegateUni
 
 - (void)keyVerificationCoordinatorBridgePresenterDelegateDidComplete:(KeyVerificationCoordinatorBridgePresenter *)coordinatorBridgePresenter otherUserId:(NSString * _Nonnull)otherUserId otherDeviceId:(NSString * _Nonnull)otherDeviceId
 {
-    MXCrypto *crypto = coordinatorBridgePresenter.session.crypto;
+    id<MXCrypto> crypto = coordinatorBridgePresenter.session.crypto;
     if (!crypto.backup.hasPrivateKeyInCryptoStore || !crypto.backup.enabled)
     {
         MXLogDebug(@"[AppDelegate][MXKeyVerification] requestAllPrivateKeys: Request key backup private keys");
@@ -3998,7 +3998,7 @@ NSString *const AppDelegateUniversalLinkDidChangeNotification = @"AppDelegateUni
 
 - (void)registerUserDidSignInOnNewDeviceNotificationForSession:(MXSession*)session
 {
-    MXCrossSigning *crossSigning = session.crypto.crossSigning;
+    id<MXCrossSigning> crossSigning = session.crypto.crossSigning;
     
     if (!crossSigning)
     {
@@ -4089,7 +4089,7 @@ NSString *const AppDelegateUniversalLinkDidChangeNotification = @"AppDelegateUni
 
 - (void)registerDidChangeCrossSigningKeysNotificationForSession:(MXSession*)session
 {
-    MXCrossSigning *crossSigning = session.crypto.crossSigning;
+    id<MXCrossSigning> crossSigning = session.crypto.crossSigning;
     
     if (!crossSigning)
     {
diff --git a/Riot/Modules/MatrixKit/Models/Account/MXKAccount.m b/Riot/Modules/MatrixKit/Models/Account/MXKAccount.m
index 128e9b161..cec79f31c 100644
--- a/Riot/Modules/MatrixKit/Models/Account/MXKAccount.m
+++ b/Riot/Modules/MatrixKit/Models/Account/MXKAccount.m
@@ -1743,8 +1743,18 @@ static NSArray<NSNumber*> *initialSyncSilentErrorsHTTPStatusCodes;
         return;
     }
     
+    if (![mxSession.crypto.crossSigning isKindOfClass:[MXLegacyCrossSigning class]]) {
+        MXLogFailure(@"Device dehydratation is currently only supported by legacy cross signing, add support to all implementations");
+        if (failure)
+        {
+            failure(nil);
+        }
+        return;
+    }
+    MXLegacyCrossSigning *crossSigning = (MXLegacyCrossSigning *)mxSession.crypto.crossSigning;;
+    
     MXLogDebug(@"[MXKAccount] attemptDeviceDehydrationWithRetry: starting device dehydration");
-    [[MXKAccountManager sharedManager].dehydrationService dehydrateDeviceWithMatrixRestClient:mxRestClient crypto:mxSession.crypto dehydrationKey:keyData success:^(NSString *deviceId) {
+    [[MXKAccountManager sharedManager].dehydrationService dehydrateDeviceWithMatrixRestClient:mxRestClient crossSigning:crossSigning dehydrationKey:keyData success:^(NSString *deviceId) {
         MXLogDebug(@"[MXKAccount] attemptDeviceDehydrationWithRetry: device successfully dehydrated");
         
         if (success)
diff --git a/Riot/Modules/Settings/Security/SecurityViewController.m b/Riot/Modules/Settings/Security/SecurityViewController.m
index 2e7993c38..f76b891cb 100644
--- a/Riot/Modules/Settings/Security/SecurityViewController.m
+++ b/Riot/Modules/Settings/Security/SecurityViewController.m
@@ -627,7 +627,7 @@ TableViewSectionsDelegate>
 
 - (void)loadCrossSigning
 {
-    MXCrossSigning *crossSigning = self.mainSession.crypto.crossSigning;
+    id<MXCrossSigning> crossSigning = self.mainSession.crypto.crossSigning;
     
     [crossSigning refreshStateWithSuccess:^(BOOL stateUpdated) {
         if (stateUpdated)
@@ -643,7 +643,7 @@ TableViewSectionsDelegate>
 {
     NSInteger numberOfRowsInCrossSigningSection;
     
-    MXCrossSigning *crossSigning = self.mainSession.crypto.crossSigning;
+    id<MXCrossSigning> crossSigning = self.mainSession.crypto.crossSigning;
     switch (crossSigning.state)
     {
         case MXCrossSigningStateNotBootstrapped:                // Action: Bootstrap
@@ -661,7 +661,7 @@ TableViewSectionsDelegate>
 
 - (NSAttributedString*)crossSigningInformation
 {
-    MXCrossSigning *crossSigning = self.mainSession.crypto.crossSigning;
+    id<MXCrossSigning> crossSigning = self.mainSession.crypto.crossSigning;
     
     NSString *crossSigningInformation;
     switch (crossSigning.state)
@@ -708,7 +708,7 @@ TableViewSectionsDelegate>
     buttonCell.mxkButton.accessibilityIdentifier = nil;
     
     // And customise it
-    MXCrossSigning *crossSigning = self.mainSession.crypto.crossSigning;
+    id<MXCrossSigning> crossSigning = self.mainSession.crypto.crossSigning;
     switch (crossSigning.state)
     {
         case MXCrossSigningStateNotBootstrapped:                // Action: Bootstrap
diff --git a/RiotTests/UserSessionsDataProviderTests.swift b/RiotTests/UserSessionsDataProviderTests.swift
index 85459347e..df504a992 100644
--- a/RiotTests/UserSessionsDataProviderTests.swift
+++ b/RiotTests/UserSessionsDataProviderTests.swift
@@ -111,7 +111,7 @@ private class MockSession: MXSession {
 }
 
 /// A mock `MXCrypto` that can override the `canCrossSign` state.
-private class MockCrypto: MXCrypto {
+private class MockCrypto: MXLegacyCrypto {
     let canCrossSign: Bool
     override var crossSigning: MXCrossSigning! { MockCrossSigning(canCrossSign: canCrossSign) }
     
@@ -123,7 +123,7 @@ private class MockCrypto: MXCrypto {
 }
 
 /// A mock `MXCrossSigning` with an overridden `canCrossSign` property.
-private class MockCrossSigning: MXCrossSigning {
+private class MockCrossSigning: MXLegacyCrossSigning {
     let canCrossSignMock: Bool
     override var canCrossSign: Bool { canCrossSignMock }
     
diff --git a/changelog.d/pr-6943.change b/changelog.d/pr-6943.change
new file mode 100644
index 000000000..6e35736b1
--- /dev/null
+++ b/changelog.d/pr-6943.change
@@ -0,0 +1 @@
+Crypto: Define MXCrypto and MXCrossSigning as protocols