diff --git a/keyserver/src/push/encrypted-notif-utils-api.js b/keyserver/src/push/encrypted-notif-utils-api.js
index 39ad0b0ba..9235e881c 100644
--- a/keyserver/src/push/encrypted-notif-utils-api.js
+++ b/keyserver/src/push/encrypted-notif-utils-api.js
@@ -1,59 +1,59 @@
 // @flow
 
 import type { EncryptResult } from '@commapp/olm';
 
 import type { EncryptedNotifUtilsAPI } from 'lib/types/notif-types.js';
 
 import { blobServiceUpload } from './utils.js';
 import { encryptAndUpdateOlmSession } from '../updaters/olm-session-updater.js';
 import { getOlmUtility } from '../utils/olm-utils.js';
 
 const encryptedNotifUtilsAPI: EncryptedNotifUtilsAPI = {
   encryptSerializedNotifPayload: async (
     cryptoID: string,
     unencryptedPayload: string,
     encryptedPayloadSizeValidator?: (
       encryptedPayload: string,
       type: '1' | '0',
     ) => boolean,
   ) => {
     let dbPersistCondition;
     if (encryptedPayloadSizeValidator) {
       dbPersistCondition = ({
         serializedPayload,
       }: {
         +[string]: EncryptResult,
       }) =>
         encryptedPayloadSizeValidator(
           serializedPayload.body,
           serializedPayload.type ? '1' : '0',
         );
     }
 
     const {
       encryptedMessages: { serializedPayload },
       dbPersistConditionViolated,
       encryptionOrder,
     } = await encryptAndUpdateOlmSession(
       cryptoID,
       'notifications',
       {
         serializedPayload: unencryptedPayload,
       },
       dbPersistCondition,
     );
 
     return {
       encryptedData: serializedPayload,
       sizeLimitViolated: dbPersistConditionViolated,
       encryptionOrder,
     };
   },
   uploadLargeNotifPayload: blobServiceUpload,
   getNotifByteSize: (serializedPayload: string) =>
     Buffer.byteLength(serializedPayload),
-  getEncryptedNotifHash: (serializedNotification: string) =>
+  getEncryptedNotifHash: async (serializedNotification: string) =>
     getOlmUtility().sha256(serializedNotification),
 };
 
 export default encryptedNotifUtilsAPI;
diff --git a/lib/push/crypto.js b/lib/push/crypto.js
index 49a358e7a..08ab18e2d 100644
--- a/lib/push/crypto.js
+++ b/lib/push/crypto.js
@@ -1,619 +1,621 @@
 // @flow
 
 import invariant from 'invariant';
 
 import type {
   PlainTextWebNotification,
   PlainTextWebNotificationPayload,
   WebNotification,
   PlainTextWNSNotification,
   WNSNotification,
   AndroidVisualNotification,
   AndroidVisualNotificationPayload,
   AndroidBadgeOnlyNotification,
   AndroidNotificationRescind,
   NotificationTargetDevice,
   SenderDeviceDescriptor,
   EncryptedNotifUtilsAPI,
   APNsVisualNotification,
   APNsNotificationRescind,
   APNsBadgeOnlyNotification,
 } from '../types/notif-types.js';
 
 async function encryptAndroidNotificationPayload<T>(
   encryptedNotifUtilsAPI: EncryptedNotifUtilsAPI,
   cryptoID: string,
   senderDeviceDescriptor: SenderDeviceDescriptor,
   unencryptedPayload: T,
   payloadSizeValidator?: (
     | T
     | $ReadOnly<{
         ...SenderDeviceDescriptor,
         +encryptedPayload: string,
         +type: '1' | '0',
       }>,
   ) => boolean,
 ): Promise<{
   +resultPayload:
     | T
     | $ReadOnly<{
         ...SenderDeviceDescriptor,
         +encryptedPayload: string,
         +type: '1' | '0',
       }>,
   +payloadSizeExceeded: boolean,
   +encryptionOrder?: number,
 }> {
   try {
     const unencryptedSerializedPayload = JSON.stringify(unencryptedPayload);
     if (!unencryptedSerializedPayload) {
       return {
         resultPayload: unencryptedPayload,
         payloadSizeExceeded: payloadSizeValidator
           ? payloadSizeValidator(unencryptedPayload)
           : false,
       };
     }
 
     let dbPersistCondition;
     if (payloadSizeValidator) {
       dbPersistCondition = (serializedPayload: string, type: '1' | '0') =>
         payloadSizeValidator({
           encryptedPayload: serializedPayload,
           type,
           ...senderDeviceDescriptor,
         });
     }
 
     const {
       encryptedData: serializedPayload,
       sizeLimitViolated: dbPersistConditionViolated,
       encryptionOrder,
     } = await encryptedNotifUtilsAPI.encryptSerializedNotifPayload(
       cryptoID,
       unencryptedSerializedPayload,
       dbPersistCondition,
     );
 
     return {
       resultPayload: {
         ...senderDeviceDescriptor,
         encryptedPayload: serializedPayload.body,
         type: serializedPayload.type ? '1' : '0',
       },
       payloadSizeExceeded: !!dbPersistConditionViolated,
       encryptionOrder,
     };
   } catch (e) {
     console.log('Notification encryption failed: ' + e);
     const resultPayload = {
       encryptionFailed: '1',
       ...unencryptedPayload,
     };
     return {
       resultPayload,
       payloadSizeExceeded: payloadSizeValidator
         ? payloadSizeValidator(resultPayload)
         : false,
     };
   }
 }
 
 async function encryptAPNsVisualNotification(
   encryptedNotifUtilsAPI: EncryptedNotifUtilsAPI,
   cryptoID: string,
   senderDeviceDescriptor: SenderDeviceDescriptor,
   notification: APNsVisualNotification,
   notificationSizeValidator?: APNsVisualNotification => boolean,
   codeVersion?: ?number,
   blobHolder?: ?string,
 ): Promise<{
   +notification: APNsVisualNotification,
   +payloadSizeExceeded: boolean,
   +encryptedPayloadHash?: string,
   +encryptionOrder?: number,
 }> {
   const {
     id,
     headers,
     aps: { badge, alert, sound },
     ...rest
   } = notification;
 
   invariant(
     !headers['apns-collapse-id'],
     `Collapse ID can't be directly stored in APNsVisualNotification object due ` +
       `to security reasons. Please put it in payload property`,
   );
 
   let unencryptedPayload = {
     ...rest,
     aps: { sound },
     merged: alert,
     badge,
   };
 
   if (blobHolder) {
     unencryptedPayload = { ...unencryptedPayload, blobHolder };
   }
 
   try {
     const unencryptedSerializedPayload = JSON.stringify(unencryptedPayload);
 
     let encryptedNotifAps = { 'mutable-content': 1 };
     if (codeVersion && codeVersion >= 254 && codeVersion % 2 === 0) {
       encryptedNotifAps = {
         ...encryptedNotifAps,
         alert: { body: 'ENCRYPTED' },
       };
     }
 
     let dbPersistCondition;
     if (notificationSizeValidator) {
       dbPersistCondition = (encryptedPayload: string, type: '0' | '1') =>
         notificationSizeValidator({
           ...senderDeviceDescriptor,
           id,
           headers,
           encryptedPayload,
           type,
           aps: encryptedNotifAps,
         });
     }
 
     const {
       encryptedData: serializedPayload,
       sizeLimitViolated: dbPersistConditionViolated,
       encryptionOrder,
     } = await encryptedNotifUtilsAPI.encryptSerializedNotifPayload(
       cryptoID,
       unencryptedSerializedPayload,
       dbPersistCondition,
     );
 
-    const encryptedPayloadHash = encryptedNotifUtilsAPI.getEncryptedNotifHash(
-      serializedPayload.body,
-    );
+    const encryptedPayloadHash =
+      await encryptedNotifUtilsAPI.getEncryptedNotifHash(
+        serializedPayload.body,
+      );
 
     return {
       notification: {
         ...senderDeviceDescriptor,
         id,
         headers,
         encryptedPayload: serializedPayload.body,
         type: serializedPayload.type ? '1' : '0',
         aps: encryptedNotifAps,
       },
       payloadSizeExceeded: !!dbPersistConditionViolated,
       encryptedPayloadHash,
       encryptionOrder,
     };
   } catch (e) {
     console.log('Notification encryption failed: ' + e);
     const unencryptedNotification = { ...notification, encryptionFailed: '1' };
     return {
       notification: unencryptedNotification,
       payloadSizeExceeded: notificationSizeValidator
         ? notificationSizeValidator(unencryptedNotification)
         : false,
     };
   }
 }
 
 async function encryptAPNsSilentNotification(
   encryptedNotifUtilsAPI: EncryptedNotifUtilsAPI,
   cryptoID: string,
   senderDeviceDescriptor: SenderDeviceDescriptor,
   notification: APNsNotificationRescind | APNsBadgeOnlyNotification,
   codeVersion?: ?number,
 ): Promise<{
   +notification: APNsNotificationRescind | APNsBadgeOnlyNotification,
   +encryptedPayloadHash?: string,
   +encryptionOrder?: number,
 }> {
   const {
     headers,
     aps: { badge },
     ...rest
   } = notification;
 
   let unencryptedPayload = {
     ...rest,
   };
 
   if (badge !== null && badge !== undefined) {
     unencryptedPayload = { ...unencryptedPayload, badge, aps: {} };
   }
 
   try {
     const unencryptedSerializedPayload = JSON.stringify(unencryptedPayload);
 
     let encryptedNotifAps = { 'mutable-content': 1 };
     if (codeVersion && codeVersion >= 254 && codeVersion % 2 === 0) {
       encryptedNotifAps = {
         ...encryptedNotifAps,
         alert: { body: 'ENCRYPTED' },
       };
     }
 
     const { encryptedData: serializedPayload, encryptionOrder } =
       await encryptedNotifUtilsAPI.encryptSerializedNotifPayload(
         cryptoID,
         unencryptedSerializedPayload,
       );
 
-    const encryptedPayloadHash = encryptedNotifUtilsAPI.getEncryptedNotifHash(
-      serializedPayload.body,
-    );
+    const encryptedPayloadHash =
+      await encryptedNotifUtilsAPI.getEncryptedNotifHash(
+        serializedPayload.body,
+      );
 
     return {
       notification: {
         ...senderDeviceDescriptor,
         headers,
         encryptedPayload: serializedPayload.body,
         type: serializedPayload.type ? '1' : '0',
         aps: encryptedNotifAps,
       },
       encryptedPayloadHash,
       encryptionOrder,
     };
   } catch (e) {
     console.log('Notification encryption failed: ' + e);
     const unencryptedNotification = { ...notification, encryptionFailed: '1' };
     return {
       notification: unencryptedNotification,
     };
   }
 }
 
 async function encryptAndroidVisualNotification(
   encryptedNotifUtilsAPI: EncryptedNotifUtilsAPI,
   senderDeviceDescriptor: SenderDeviceDescriptor,
   cryptoID: string,
   notification: AndroidVisualNotification,
   notificationSizeValidator?: AndroidVisualNotification => boolean,
   blobHolder?: ?string,
 ): Promise<{
   +notification: AndroidVisualNotification,
   +payloadSizeExceeded: boolean,
   +encryptionOrder?: number,
 }> {
   const { id, ...rest } = notification.data;
 
   let unencryptedData = {};
   if (id) {
     unencryptedData = { id };
   }
 
   let unencryptedPayload = rest;
   if (blobHolder) {
     unencryptedPayload = { ...unencryptedPayload, blobHolder };
   }
 
   let payloadSizeValidator;
   if (notificationSizeValidator) {
     payloadSizeValidator = (
       payload:
         | AndroidVisualNotificationPayload
         | $ReadOnly<{
             ...SenderDeviceDescriptor,
             +encryptedPayload: string,
             +type: '0' | '1',
           }>,
     ) => {
       return notificationSizeValidator({
         data: { ...unencryptedData, ...payload },
       });
     };
   }
   const { resultPayload, payloadSizeExceeded, encryptionOrder } =
     await encryptAndroidNotificationPayload(
       encryptedNotifUtilsAPI,
       cryptoID,
       senderDeviceDescriptor,
       unencryptedPayload,
       payloadSizeValidator,
     );
   return {
     notification: {
       data: {
         ...unencryptedData,
         ...resultPayload,
       },
     },
     payloadSizeExceeded,
     encryptionOrder,
   };
 }
 
 async function encryptAndroidSilentNotification(
   encryptedNotifUtilsAPI: EncryptedNotifUtilsAPI,
   cryptoID: string,
   senderDeviceDescriptor: SenderDeviceDescriptor,
   notification: AndroidNotificationRescind | AndroidBadgeOnlyNotification,
 ): Promise<AndroidNotificationRescind | AndroidBadgeOnlyNotification> {
   // We don't validate payload size for rescind
   // since they are expected to be small and
   // never exceed any FCM limit
   const { ...unencryptedPayload } = notification.data;
   const { resultPayload } = await encryptAndroidNotificationPayload(
     encryptedNotifUtilsAPI,
     cryptoID,
     senderDeviceDescriptor,
     unencryptedPayload,
   );
   if (resultPayload.encryptedPayload) {
     return {
       data: { ...resultPayload },
     };
   }
 
   if (resultPayload.rescind) {
     return {
       data: { ...resultPayload },
     };
   }
 
   return {
     data: {
       ...resultPayload,
     },
   };
 }
 
 async function encryptBasicPayload<T>(
   encryptedNotifUtilsAPI: EncryptedNotifUtilsAPI,
   cryptoID: string,
   senderDeviceDescriptor: SenderDeviceDescriptor,
   basicPayload: T,
 ): Promise<
   | $ReadOnly<{
       ...SenderDeviceDescriptor,
       +encryptedPayload: string,
       +type: '1' | '0',
       +encryptionOrder?: number,
     }>
   | { ...T, +encryptionFailed: '1' },
 > {
   const unencryptedSerializedPayload = JSON.stringify(basicPayload);
 
   if (!unencryptedSerializedPayload) {
     return { ...basicPayload, encryptionFailed: '1' };
   }
 
   try {
     const { encryptedData: serializedPayload, encryptionOrder } =
       await encryptedNotifUtilsAPI.encryptSerializedNotifPayload(
         cryptoID,
         unencryptedSerializedPayload,
       );
 
     return {
       ...senderDeviceDescriptor,
       encryptedPayload: serializedPayload.body,
       type: serializedPayload.type ? '1' : '0',
       encryptionOrder,
     };
   } catch (e) {
     console.log('Notification encryption failed: ' + e);
     return {
       ...basicPayload,
       encryptionFailed: '1',
     };
   }
 }
 
 async function encryptWebNotification(
   encryptedNotifUtilsAPI: EncryptedNotifUtilsAPI,
   cryptoID: string,
   senderDeviceDescriptor: SenderDeviceDescriptor,
   notification: PlainTextWebNotification,
 ): Promise<{ +notification: WebNotification, +encryptionOrder?: number }> {
   const { id, ...payloadSansId } = notification;
   const { encryptionOrder, ...encryptionResult } =
     await encryptBasicPayload<PlainTextWebNotificationPayload>(
       encryptedNotifUtilsAPI,
       cryptoID,
       senderDeviceDescriptor,
       payloadSansId,
     );
 
   return {
     notification: { id, ...encryptionResult },
     encryptionOrder,
   };
 }
 
 async function encryptWNSNotification(
   encryptedNotifUtilsAPI: EncryptedNotifUtilsAPI,
   cryptoID: string,
   senderDeviceDescriptor: SenderDeviceDescriptor,
   notification: PlainTextWNSNotification,
 ): Promise<{ +notification: WNSNotification, +encryptionOrder?: number }> {
   const { encryptionOrder, ...encryptionResult } =
     await encryptBasicPayload<PlainTextWNSNotification>(
       encryptedNotifUtilsAPI,
       cryptoID,
       senderDeviceDescriptor,
       notification,
     );
   return {
     notification: { ...encryptionResult },
     encryptionOrder,
   };
 }
 
 function prepareEncryptedAPNsVisualNotifications(
   encryptedNotifUtilsAPI: EncryptedNotifUtilsAPI,
   senderDeviceDescriptor: SenderDeviceDescriptor,
   devices: $ReadOnlyArray<NotificationTargetDevice>,
   notification: APNsVisualNotification,
   codeVersion?: ?number,
   notificationSizeValidator?: APNsVisualNotification => boolean,
 ): Promise<
   $ReadOnlyArray<{
     +cryptoID: string,
     +deliveryID: string,
     +notification: APNsVisualNotification,
     +payloadSizeExceeded: boolean,
     +encryptedPayloadHash?: string,
     +encryptionOrder?: number,
   }>,
 > {
   const notificationPromises = devices.map(
     async ({ cryptoID, deliveryID, blobHolder }) => {
       const notif = await encryptAPNsVisualNotification(
         encryptedNotifUtilsAPI,
         cryptoID,
         senderDeviceDescriptor,
         notification,
         notificationSizeValidator,
         codeVersion,
         blobHolder,
       );
       return { cryptoID, deliveryID, ...notif };
     },
   );
   return Promise.all(notificationPromises);
 }
 
 function prepareEncryptedAPNsSilentNotifications(
   encryptedNotifUtilsAPI: EncryptedNotifUtilsAPI,
   senderDeviceDescriptor: SenderDeviceDescriptor,
   devices: $ReadOnlyArray<NotificationTargetDevice>,
   notification: APNsNotificationRescind | APNsBadgeOnlyNotification,
   codeVersion?: ?number,
 ): Promise<
   $ReadOnlyArray<{
     +cryptoID: string,
     +deliveryID: string,
     +notification: APNsNotificationRescind | APNsBadgeOnlyNotification,
   }>,
 > {
   const notificationPromises = devices.map(async ({ deliveryID, cryptoID }) => {
     const { notification: notif } = await encryptAPNsSilentNotification(
       encryptedNotifUtilsAPI,
       cryptoID,
       senderDeviceDescriptor,
       notification,
       codeVersion,
     );
     return { cryptoID, deliveryID, notification: notif };
   });
   return Promise.all(notificationPromises);
 }
 
 function prepareEncryptedAndroidVisualNotifications(
   encryptedNotifUtilsAPI: EncryptedNotifUtilsAPI,
   senderDeviceDescriptor: SenderDeviceDescriptor,
   devices: $ReadOnlyArray<NotificationTargetDevice>,
   notification: AndroidVisualNotification,
   notificationSizeValidator?: (
     notification: AndroidVisualNotification,
   ) => boolean,
 ): Promise<
   $ReadOnlyArray<{
     +cryptoID: string,
     +deliveryID: string,
     +notification: AndroidVisualNotification,
     +payloadSizeExceeded: boolean,
     +encryptionOrder?: number,
   }>,
 > {
   const notificationPromises = devices.map(
     async ({ deliveryID, cryptoID, blobHolder }) => {
       const notif = await encryptAndroidVisualNotification(
         encryptedNotifUtilsAPI,
         senderDeviceDescriptor,
         cryptoID,
         notification,
         notificationSizeValidator,
         blobHolder,
       );
       return { deliveryID, cryptoID, ...notif };
     },
   );
   return Promise.all(notificationPromises);
 }
 
 function prepareEncryptedAndroidSilentNotifications(
   encryptedNotifUtilsAPI: EncryptedNotifUtilsAPI,
   senderDeviceDescriptor: SenderDeviceDescriptor,
   devices: $ReadOnlyArray<NotificationTargetDevice>,
   notification: AndroidNotificationRescind | AndroidBadgeOnlyNotification,
 ): Promise<
   $ReadOnlyArray<{
     +cryptoID: string,
     +deliveryID: string,
     +notification: AndroidNotificationRescind | AndroidBadgeOnlyNotification,
     +encryptionOrder?: number,
   }>,
 > {
   const notificationPromises = devices.map(async ({ deliveryID, cryptoID }) => {
     const notif = await encryptAndroidSilentNotification(
       encryptedNotifUtilsAPI,
       cryptoID,
       senderDeviceDescriptor,
       notification,
     );
     return { deliveryID, cryptoID, notification: notif };
   });
   return Promise.all(notificationPromises);
 }
 
 function prepareEncryptedWebNotifications(
   encryptedNotifUtilsAPI: EncryptedNotifUtilsAPI,
   senderDeviceDescriptor: SenderDeviceDescriptor,
   devices: $ReadOnlyArray<NotificationTargetDevice>,
   notification: PlainTextWebNotification,
 ): Promise<
   $ReadOnlyArray<{
     +deliveryID: string,
     +notification: WebNotification,
     +encryptionOrder?: number,
   }>,
 > {
   const notificationPromises = devices.map(async ({ deliveryID, cryptoID }) => {
     const notif = await encryptWebNotification(
       encryptedNotifUtilsAPI,
       cryptoID,
       senderDeviceDescriptor,
       notification,
     );
     return { ...notif, deliveryID };
   });
   return Promise.all(notificationPromises);
 }
 
 function prepareEncryptedWNSNotifications(
   encryptedNotifUtilsAPI: EncryptedNotifUtilsAPI,
   senderDeviceDescriptor: SenderDeviceDescriptor,
   devices: $ReadOnlyArray<NotificationTargetDevice>,
   notification: PlainTextWNSNotification,
 ): Promise<
   $ReadOnlyArray<{
     +deliveryID: string,
     +notification: WNSNotification,
     +encryptionOrder?: number,
   }>,
 > {
   const notificationPromises = devices.map(async ({ deliveryID, cryptoID }) => {
     const notif = await encryptWNSNotification(
       encryptedNotifUtilsAPI,
       cryptoID,
       senderDeviceDescriptor,
       notification,
     );
     return { ...notif, deliveryID };
   });
   return Promise.all(notificationPromises);
 }
 
 export {
   prepareEncryptedAPNsVisualNotifications,
   prepareEncryptedAPNsSilentNotifications,
   prepareEncryptedAndroidVisualNotifications,
   prepareEncryptedAndroidSilentNotifications,
   prepareEncryptedWebNotifications,
   prepareEncryptedWNSNotifications,
 };
diff --git a/lib/types/notif-types.js b/lib/types/notif-types.js
index 6c5945525..5b71ce9d6 100644
--- a/lib/types/notif-types.js
+++ b/lib/types/notif-types.js
@@ -1,400 +1,400 @@
 // @flow
 
 import type { EncryptResult } from '@commapp/olm';
 import t, { type TInterface, type TUnion } from 'tcomb';
 
 import type { Platform } from './device-types.js';
 import type { EntityText, ThreadEntity } from '../utils/entity-text.js';
 import { tShape } from '../utils/validation-utils.js';
 
 export type NotifTexts = {
   +merged: string | EntityText,
   +body: string | EntityText,
   +title: string | ThreadEntity,
   +prefix?: string | EntityText,
 };
 
 export type ResolvedNotifTexts = {
   +merged: string,
   +body: string,
   +title: string,
   +prefix?: string,
 };
 export const resolvedNotifTextsValidator: TInterface<ResolvedNotifTexts> =
   tShape<ResolvedNotifTexts>({
     merged: t.String,
     body: t.String,
     title: t.String,
     prefix: t.maybe(t.String),
   });
 
 export type SenderDeviceDescriptor =
   | { +keyserverID: string }
   | { +senderDeviceID: string };
 
 export const senderDeviceDescriptorValidator: TUnion<SenderDeviceDescriptor> =
   t.union([
     tShape({ keyserverID: t.String }),
     tShape({ senderDeviceID: t.String }),
   ]);
 
 // Web notifs types
 export type PlainTextWebNotificationPayload = {
   +body: string,
   +prefix?: string,
   +title: string,
   +unreadCount?: number,
   +threadID: string,
   +encryptionFailed?: '1',
 };
 
 export type PlainTextWebNotification = $ReadOnly<{
   +id: string,
   ...PlainTextWebNotificationPayload,
 }>;
 
 export type EncryptedWebNotification = $ReadOnly<{
   ...SenderDeviceDescriptor,
   +id: string,
   +encryptedPayload: string,
   +type: '0' | '1',
 }>;
 
 export type WebNotification =
   | PlainTextWebNotification
   | EncryptedWebNotification;
 
 // WNS notifs types
 export type PlainTextWNSNotification = {
   +body: string,
   +prefix?: string,
   +title: string,
   +unreadCount?: number,
   +threadID: string,
   +encryptionFailed?: '1',
 };
 
 export type EncryptedWNSNotification = $ReadOnly<{
   ...SenderDeviceDescriptor,
   +encryptedPayload: string,
   +type: '0' | '1',
 }>;
 
 export type WNSNotification =
   | PlainTextWNSNotification
   | EncryptedWNSNotification;
 
 // Android notifs types
 export type AndroidVisualNotificationPayloadBase = $ReadOnly<{
   +badge?: string,
   +body: string,
   +title: string,
   +prefix?: string,
   +threadID: string,
   +collapseID?: string,
   +badgeOnly?: '0' | '1',
   +encryptionFailed?: '1',
 }>;
 
 type AndroidSmallVisualNotificationPayload = $ReadOnly<{
   ...AndroidVisualNotificationPayloadBase,
   +messageInfos?: string,
 }>;
 
 type AndroidLargeVisualNotificationPayload = $ReadOnly<{
   ...AndroidVisualNotificationPayloadBase,
   +blobHash: string,
   +encryptionKey: string,
 }>;
 
 export type AndroidVisualNotificationPayload =
   | AndroidSmallVisualNotificationPayload
   | AndroidLargeVisualNotificationPayload;
 
 type EncryptedThinThreadPayload = {
   +keyserverID: string,
   +encryptedPayload: string,
   +type: '0' | '1',
 };
 
 type EncryptedThickThreadPayload = {
   +senderDeviceID: string,
   +encryptedPayload: string,
   +type: '0' | '1',
 };
 
 export type AndroidVisualNotification = {
   +data: $ReadOnly<{
     +id?: string,
     ...
       | AndroidSmallVisualNotificationPayload
       | AndroidLargeVisualNotificationPayload
       | EncryptedThinThreadPayload
       | EncryptedThickThreadPayload,
   }>,
 };
 
 type AndroidThinThreadRescindPayload = {
   +badge: string,
   +rescind: 'true',
   +rescindID?: string,
   +setUnreadStatus: 'true',
   +threadID: string,
   +encryptionFailed?: string,
 };
 
 type AndroidThickThreadRescindPayload = {
   +rescind: 'true',
   +setUnreadStatus: 'true',
   +threadID: string,
   +encryptionFailed?: string,
 };
 
 export type AndroidNotificationRescind = {
   +data:
     | AndroidThinThreadRescindPayload
     | AndroidThickThreadRescindPayload
     | EncryptedThinThreadPayload
     | EncryptedThickThreadPayload,
 };
 
 type AndroidKeyserverBadgeOnlyPayload = {
   +badge: string,
   +badgeOnly: '1',
   +encryptionFailed?: string,
 };
 
 type AndroidThickThreadBadgeOnlyPayload = {
   +threadID: string,
   +badgeOnly: '1',
   +encryptionFailed?: string,
 };
 
 export type AndroidBadgeOnlyNotification = {
   +data:
     | AndroidKeyserverBadgeOnlyPayload
     | AndroidThickThreadBadgeOnlyPayload
     | EncryptedThinThreadPayload
     | EncryptedThickThreadPayload,
 };
 
 type AndroidNotificationWithPriority =
   | {
       +notification: AndroidVisualNotification,
       +priority: 'high',
     }
   | {
       +notification: AndroidBadgeOnlyNotification | AndroidNotificationRescind,
       +priority: 'normal',
     };
 
 // APNs notifs types
 export type APNsNotificationTopic =
   | 'app.comm.macos'
   | 'app.comm'
   | 'org.squadcal.app';
 
 export type APNsNotificationHeaders = {
   +'apns-priority'?: 1 | 5 | 10,
   +'apns-id'?: string,
   +'apns-expiration'?: number,
   +'apns-topic': APNsNotificationTopic,
   +'apns-collapse-id'?: string,
   +'apns-push-type': 'background' | 'alert' | 'voip',
 };
 
 export type EncryptedAPNsSilentNotification = $ReadOnly<{
   ...SenderDeviceDescriptor,
   +headers: APNsNotificationHeaders,
   +encryptedPayload: string,
   +type: '1' | '0',
   +aps: { +'mutable-content': number, +'alert'?: { body: 'ENCRYPTED' } },
 }>;
 
 export type EncryptedAPNsVisualNotification = $ReadOnly<{
   ...EncryptedAPNsSilentNotification,
   +id: string,
 }>;
 
 type APNsVisualNotificationPayloadBase = {
   +aps: {
     +'badge'?: string | number,
     +'alert'?: string | { +body?: string, ... },
     +'thread-id': string,
     +'mutable-content'?: number,
     +'sound'?: string,
   },
   +body: string,
   +title: string,
   +prefix?: string,
   +threadID: string,
   +collapseID?: string,
   +encryptionFailed?: '1',
 };
 
 type APNsSmallVisualNotificationPayload = $ReadOnly<{
   ...APNsVisualNotificationPayloadBase,
   +messageInfos?: string,
 }>;
 
 type APNsLargeVisualNotificationPayload = $ReadOnly<{
   ...APNsVisualNotificationPayloadBase,
   +blobHash: string,
   +encryptionKey: string,
 }>;
 
 export type APNsVisualNotification =
   | $ReadOnly<{
       +headers: APNsNotificationHeaders,
       +id: string,
       ...
         | APNsSmallVisualNotificationPayload
         | APNsLargeVisualNotificationPayload,
     }>
   | EncryptedAPNsVisualNotification;
 
 type APNsLegacyRescindPayload = {
   +backgroundNotifType: 'CLEAR',
   +notificationId: string,
   +setUnreadStatus: true,
   +threadID: string,
   +aps: {
     +'badge': string | number,
     +'content-available': number,
   },
 };
 
 type APNsKeyserverRescindPayload = {
   +backgroundNotifType: 'CLEAR',
   +notificationId: string,
   +setUnreadStatus: true,
   +threadID: string,
   +aps: {
     +'badge': string | number,
     +'mutable-content': number,
   },
 };
 
 type APNsThickThreadRescindPayload = {
   +backgroundNotifType: 'CLEAR',
   +setUnreadStatus: true,
   +threadID: string,
   +aps: {
     +'mutable-content': number,
   },
 };
 
 export type APNsNotificationRescind =
   | $ReadOnly<{
       +headers: APNsNotificationHeaders,
       +encryptionFailed?: '1',
       ...
         | APNsLegacyRescindPayload
         | APNsKeyserverRescindPayload
         | APNsThickThreadRescindPayload,
     }>
   | EncryptedAPNsSilentNotification;
 
 type APNsLegacyBadgeOnlyNotification = {
   +aps: {
     +badge: string | number,
   },
 };
 
 type APNsKeyserverBadgeOnlyNotification = {
   +aps: {
     +'badge': string | number,
     +'mutable-content': number,
   },
 };
 
 type APNsThickThreadBadgeOnlyNotification = {
   +aps: {
     +'mutable-content': number,
   },
   +threadID: string,
 };
 
 export type APNsBadgeOnlyNotification =
   | $ReadOnly<{
       +headers: APNsNotificationHeaders,
       +encryptionFailed?: '1',
       ...
         | APNsLegacyBadgeOnlyNotification
         | APNsKeyserverBadgeOnlyNotification
         | APNsThickThreadBadgeOnlyNotification,
     }>
   | EncryptedAPNsSilentNotification;
 
 export type APNsNotification =
   | APNsVisualNotification
   | APNsNotificationRescind
   | APNsBadgeOnlyNotification;
 
 export type TargetedAPNsNotification = {
   +notification: APNsNotification,
   +deliveryID: string,
   +encryptedPayloadHash?: string,
   +encryptionOrder?: number,
 };
 
 export type TargetedAndroidNotification = $ReadOnly<{
   ...AndroidNotificationWithPriority,
   +deliveryID: string,
   +encryptionOrder?: number,
 }>;
 
 export type TargetedWebNotification = {
   +notification: WebNotification,
   +deliveryID: string,
   +encryptionOrder?: number,
 };
 
 export type TargetedWNSNotification = {
   +notification: WNSNotification,
   +deliveryID: string,
   +encryptionOrder?: number,
 };
 
 export type NotificationTargetDevice = {
   +cryptoID: string,
   +deliveryID: string,
   +blobHolder?: string,
 };
 
 export type TargetedNotificationWithPlatform = {
   +platform: Platform,
   +targetedNotification:
     | TargetedAPNsNotification
     | TargetedWNSNotification
     | TargetedWebNotification
     | TargetedAndroidNotification,
 };
 
 export type EncryptedNotifUtilsAPI = {
   +encryptSerializedNotifPayload: (
     cryptoID: string,
     unencryptedPayload: string,
     encryptedPayloadSizeValidator?: (
       encryptedPayload: string,
       type: '1' | '0',
     ) => boolean,
   ) => Promise<{
     +encryptedData: EncryptResult,
     +sizeLimitViolated?: boolean,
     +encryptionOrder?: number,
   }>,
   +uploadLargeNotifPayload: (
     payload: string,
     numberOfHolders: number,
   ) => Promise<
     | {
         +blobHolders: $ReadOnlyArray<string>,
         +blobHash: string,
         +encryptionKey: string,
       }
     | { +blobUploadError: string },
   >,
   +getNotifByteSize: (serializedNotification: string) => number,
-  +getEncryptedNotifHash: (serializedNotification: string) => string,
+  +getEncryptedNotifHash: (serializedNotification: string) => Promise<string>,
 };
diff --git a/native/push/encrypted-notif-utils-api.js b/native/push/encrypted-notif-utils-api.js
new file mode 100644
index 000000000..5315f7bd4
--- /dev/null
+++ b/native/push/encrypted-notif-utils-api.js
@@ -0,0 +1,42 @@
+// @flow
+
+import type { EncryptedNotifUtilsAPI } from 'lib/types/notif-types.js';
+
+import { commUtilsModule } from '../native-modules.js';
+
+const encryptedNotifUtilsAPI: EncryptedNotifUtilsAPI = {
+  encryptSerializedNotifPayload: async (
+    cryptoID: string,
+    unencryptedPayload: string,
+    encryptedPayloadSizeValidator?: (
+      encryptedPayload: string,
+      type: '1' | '0',
+    ) => boolean,
+  ) => {
+    // The "mock" implementation below will be replaced with proper
+    // implementation after olm notif sessions initialization is
+    // implemented. for now it is actually beneficial to return
+    // original string as encrypted string since it allows for
+    // better testing as we can verify which data are encrypted
+    // and which aren't.
+    return {
+      encryptedData: { body: unencryptedPayload, type: 1 },
+      sizeLimitViolated: encryptedPayloadSizeValidator
+        ? !encryptedPayloadSizeValidator(unencryptedPayload, '1')
+        : false,
+    };
+  },
+  uploadLargeNotifPayload: async () => ({ blobUploadError: 'not_implemented' }),
+  getNotifByteSize: (serializedNotification: string) => {
+    return commUtilsModule.encodeStringToUTF8ArrayBuffer(serializedNotification)
+      .byteLength;
+  },
+  getEncryptedNotifHash: async (serializedNotification: string) => {
+    const notifAsArrayBuffer = commUtilsModule.encodeStringToUTF8ArrayBuffer(
+      serializedNotification,
+    );
+    return commUtilsModule.sha256(notifAsArrayBuffer);
+  },
+};
+
+export default encryptedNotifUtilsAPI;
diff --git a/web/push-notif/encrypted-notif-utils-api.js b/web/push-notif/encrypted-notif-utils-api.js
new file mode 100644
index 000000000..f5dd3df4b
--- /dev/null
+++ b/web/push-notif/encrypted-notif-utils-api.js
@@ -0,0 +1,38 @@
+// @flow
+
+import type { EncryptedNotifUtilsAPI } from 'lib/types/notif-types.js';
+
+const encryptedNotifUtilsAPI: EncryptedNotifUtilsAPI = {
+  encryptSerializedNotifPayload: async (
+    cryptoID: string,
+    unencryptedPayload: string,
+    encryptedPayloadSizeValidator?: (
+      encryptedPayload: string,
+      type: '1' | '0',
+    ) => boolean,
+  ) => {
+    // The "mock" implementation below will be replaced with proper
+    // implementation after olm notif sessions initialization is
+    // implemented. for now it is actually beneficial to return
+    // original string as encrypted string since it allows for
+    // better testing as we can verify which data are encrypted
+    // and which aren't.
+    return {
+      encryptedData: { body: unencryptedPayload, type: 1 },
+      sizeLimitViolated: encryptedPayloadSizeValidator
+        ? !encryptedPayloadSizeValidator(unencryptedPayload, '1')
+        : false,
+    };
+  },
+  uploadLargeNotifPayload: async () => ({ blobUploadError: 'not_implemented' }),
+  getNotifByteSize: (serializedNotification: string) => {
+    return new Blob([serializedNotification]).size;
+  },
+  getEncryptedNotifHash: async (serializedNotification: string) => {
+    const notificationBytes = new TextEncoder().encode(serializedNotification);
+    const hashBytes = await crypto.subtle.digest('SHA-256', notificationBytes);
+    return btoa(String.fromCharCode(...new Uint8Array(hashBytes)));
+  },
+};
+
+export default encryptedNotifUtilsAPI;