diff --git a/keyserver/flow-typed/npm/@commapp/olm_vx.x.x.js b/keyserver/flow-typed/npm/@commapp/olm_vx.x.x.js
index f365eecbc..21f35119f 100644
--- a/keyserver/flow-typed/npm/@commapp/olm_vx.x.x.js
+++ b/keyserver/flow-typed/npm/@commapp/olm_vx.x.x.js
@@ -1,182 +1,183 @@
 // flow-typed signature: 085f002da86534cfd8cee47ffa99dd67
 // flow-typed version: <<STUB>>/@commapp/olm_v3.2.4/flow_v0.182.0
 
 declare module '@commapp/olm' {
 
 /*
 Copyright 2020 The Matrix.org Foundation C.I.C.
 
 Licensed under the Apache License, Version 2.0 (the "License");
 you may not use this file except in compliance with the License.
 You may obtain a copy of the License at
 
     http://www.apache.org/licenses/LICENSE-2.0
 
 Unless required by applicable law or agreed to in writing, software
 distributed under the License is distributed on an "AS IS" BASIS,
 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 See the License for the specific language governing permissions and
 limitations under the License.
 */
 
   declare export class Account {
     constructor(): void;
     free(): void;
     create(): void;
     identity_keys(): string;
     sign(message: string | Uint8Array): string;
     one_time_keys(): string;
     mark_keys_as_published(): void;
     max_number_of_one_time_keys(): number;
     generate_one_time_keys(number_of_keys: number): void;
     remove_one_time_keys(session: Session): void;
     generate_prekey(): void;
     prekey(): string;
     unpublished_prekey(): ?string;
     prekey_signature(): ?string;
     forget_old_prekey(): void;
     mark_prekey_as_published(): void;
     last_prekey_publish_time(): number;
     generate_fallback_key(): void;
     fallback_key(): string;
     unpublished_fallback_key(): string;
     forget_old_fallback_key(): void;
     pickle(key: string | Uint8Array): string;
     unpickle(key: string | Uint8Array, pickle: string): void;
   }
 
   declare export type EncryptResult = {
     +type: 0 | 1, // 0: PreKey, 1: Message
     +body: string,
   };
   declare export class Session {
     constructor(): void;
     free(): void;
     pickle(key: string | Uint8Array): string;
     unpickle(key: string | Uint8Array, pickle: string): void;
     create_outbound(
       account: Account,
       their_identity_key: string,
       their_signing_key: string,
       their_prekey: string,
       their_prekey_signature: string,
       their_one_time_key: string,
     ): void;
     create_inbound(account: Account, one_time_key_message: string): void;
     create_inbound_from(
       account: Account,
       identity_key: string,
       one_time_key_message: string,
     ): void;
     session_id(): string;
     has_received_message(): boolean;
     matches_inbound(one_time_key_message: string): boolean;
     matches_inbound_from(
       identity_key: string,
       one_time_key_message: string,
     ): boolean;
     encrypt(plaintext: string): EncryptResult;
     decrypt(message_type: number, message: string): string;
+    decrypt_sequential(message_type: number, message: string): string;
     describe(): string;
   }
 
   declare export class Utility {
     constructor(): void;
     free(): void;
     sha256(input: string | Uint8Array): string;
     ed25519_verify(
       key: string,
       message: string | Uint8Array,
       signature: string,
     ): void;
   }
 
   declare export type DecryptResult = {
     +message_index: string,
     +plaintext: string,
   };
 
   declare export class InboundGroupSession {
     constructor(): void;
     free(): void;
     pickle(key: string | Uint8Array): string;
     unpickle(key: string | Uint8Array, pickle: string): void;
     create(session_key: string): string;
     import_session(session_key: string): string;
     decrypt(message: string): DecryptResult;
     session_id(): string;
     first_known_index(): number;
     export_session(message_index: number): string;
   }
 
   declare export class OutboundGroupSession {
     constructor(): void;
     free(): void;
     pickle(key: string | Uint8Array): string;
     unpickle(key: string | Uint8Array, pickle: string): void;
     create(): void;
     encrypt(plaintext: string): string;
     session_id(): string;
     session_key(): string;
     message_index(): number;
   }
 
   declare export type PkEncryptionEncryptResult = {
     +ciphertext: string,
     +mac: string,
     +ephemeral: string,
   };
 
   declare export class PkEncryption {
     constructor(): void;
     free(): void;
     set_recipient_key(key: string): void;
     encrypt(plaintext: string): PkEncryptionEncryptResult;
   }
 
   declare export class PkDecryption {
     constructor(): void;
     free(): void;
     init_with_private_key(key: Uint8Array): string;
     generate_key(): string;
     get_private_key(): Uint8Array;
     pickle(key: string | Uint8Array): string;
     unpickle(key: string | Uint8Array, pickle: string): string;
     decrypt(ephemeral_key: string, mac: string, ciphertext: string): string;
   }
 
   declare export class PkSigning {
     constructor(): void;
     free(): void;
     init_with_seed(seed: Uint8Array): string;
     generate_seed(): Uint8Array;
     sign(message: string): string;
   }
 
   declare export class SAS {
     constructor(): void;
     free(): void;
     get_pubkey(): string;
     set_their_key(their_key: string): void;
     generate_bytes(info: string, length: number): Uint8Array;
     calculate_mac(input: string, info: string): string;
     calculate_mac_fixed_base64(input: string, info: string): string;
     calculate_mac_long_kdf(input: string, info: string): string;
   }
 
   declare export function init(opts?: Object): Promise<void>;
 
   declare export function get_library_version(): [number, number, number];
 
   declare export var PRIVATE_KEY_LENGTH: number;
 
   declare export default {
     init: typeof init,
     get_library_version: typeof get_library_version,
     PRIVATE_KEY_LENGTH: typeof PRIVATE_KEY_LENGTH,
     Account: typeof Account,
     Utility: typeof Utility,
     Session: typeof Session,
   };
 
 }
diff --git a/keyserver/src/utils/olm-utils.test.js b/keyserver/src/utils/olm-utils.test.js
index 1eabe968f..e498877c0 100644
--- a/keyserver/src/utils/olm-utils.test.js
+++ b/keyserver/src/utils/olm-utils.test.js
@@ -1,223 +1,309 @@
 // @flow
 
 import olm from '@commapp/olm';
 
 import { getOlmUtility } from '../utils/olm-utils.js';
 
 describe('olm.Account', () => {
   const alphabet =
     'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789 ';
 
   const randomString = (length: number) =>
     Array.from(
       { length },
       () => alphabet[Math.floor(Math.random() * alphabet.length)],
     ).join('');
 
   const initAccount = (mark_prekey_published: boolean = true) => {
     const account = new olm.Account();
     account.create();
     account.generate_prekey();
     account.generate_one_time_keys(1);
     if (mark_prekey_published) {
       account.mark_prekey_as_published();
     }
     return account;
   };
 
   const createSession = (
     aliceSession: olm.Session,
     aliceAccount: olm.Account,
     bobAccount: olm.Account,
     regen: boolean = false,
     forget: boolean = false,
     invalid_sign: boolean = false,
   ) => {
     const bobOneTimeKeys = JSON.parse(bobAccount.one_time_keys()).curve25519;
     bobAccount.mark_keys_as_published();
     const otk_id = Object.keys(bobOneTimeKeys)[0];
 
     if (regen) {
       bobAccount.generate_prekey();
       if (forget) {
         bobAccount.forget_old_prekey();
       }
     }
 
     if (invalid_sign) {
       try {
         aliceSession.create_outbound(
           aliceAccount,
           JSON.parse(bobAccount.identity_keys()).curve25519,
           JSON.parse(bobAccount.identity_keys()).ed25519,
           String(Object.values(JSON.parse(bobAccount.prekey()).curve25519)[0]),
           bobAccount.sign(randomString(32)),
           bobOneTimeKeys[otk_id],
         );
       } catch (error) {
         expect(error.message).toBe('OLM.BAD_SIGNATURE');
         return false;
       }
 
       try {
         aliceSession.create_outbound(
           aliceAccount,
           JSON.parse(bobAccount.identity_keys()).curve25519,
           JSON.parse(bobAccount.identity_keys()).ed25519,
           String(Object.values(JSON.parse(bobAccount.prekey()).curve25519)[0]),
           randomString(43),
           bobOneTimeKeys[otk_id],
         );
       } catch (error) {
         expect(error.message).toBe('OLM.INVALID_BASE64');
         return false;
       }
     }
 
     aliceSession.create_outbound(
       aliceAccount,
       JSON.parse(bobAccount.identity_keys()).curve25519,
       JSON.parse(bobAccount.identity_keys()).ed25519,
       String(Object.values(JSON.parse(bobAccount.prekey()).curve25519)[0]),
       String(bobAccount.prekey_signature()),
       bobOneTimeKeys[otk_id],
     );
 
     return aliceSession;
   };
 
   const testRatchet = (
     aliceSession: olm.Session,
     bobSession: olm.Session,
     bobAccount: olm.Account,
     num_msg: number = 1,
   ) => {
     let test_text = randomString(40);
     let encrypted = aliceSession.encrypt(test_text);
     expect(encrypted.type).toEqual(0);
 
     try {
       bobSession.create_inbound(bobAccount, encrypted.body);
     } catch (error) {
       expect(error.message).toBe('OLM.BAD_MESSAGE_KEY_ID');
       return false;
     }
 
     bobAccount.remove_one_time_keys(bobSession);
     let decrypted = bobSession.decrypt(encrypted.type, encrypted.body);
     expect(decrypted).toEqual(test_text);
 
     test_text = randomString(40);
     encrypted = bobSession.encrypt(test_text);
     expect(encrypted.type).toEqual(1);
     decrypted = aliceSession.decrypt(encrypted.type, encrypted.body);
     expect(decrypted).toEqual(test_text);
 
+    const aliceEncrypted = aliceSession.encrypt(test_text);
+    expect(() =>
+      aliceSession.decrypt(aliceEncrypted.type, aliceEncrypted.body),
+    ).toThrow('OLM.BAD_MESSAGE_MAC');
+
     for (let index = 1; index < num_msg; index++) {
       test_text = randomString(40);
       encrypted = aliceSession.encrypt(test_text);
       expect(encrypted.type).toEqual(1);
       decrypted = bobSession.decrypt(encrypted.type, encrypted.body);
       expect(decrypted).toEqual(test_text);
 
       test_text = randomString(40);
       encrypted = bobSession.encrypt(test_text);
       expect(encrypted.type).toEqual(1);
       decrypted = aliceSession.decrypt(encrypted.type, encrypted.body);
       expect(decrypted).toEqual(test_text);
     }
 
+    expect(() =>
+      aliceSession.decrypt_sequential(encrypted.type, encrypted.body),
+    ).toThrow('OLM.OLM_ALREADY_DECRYPTED_OR_KEYS_SKIPPED');
+
+    return true;
+  };
+
+  const testRatchetSequential = (
+    aliceSession: olm.Session,
+    bobSession: olm.Session,
+    bobAccount: olm.Account,
+  ) => {
+    let test_text = randomString(40);
+    let encrypted = aliceSession.encrypt(test_text);
+    expect(encrypted.type).toEqual(0);
+
+    try {
+      bobSession.create_inbound(bobAccount, encrypted.body);
+    } catch (error) {
+      expect(error.message).toBe('OLM.BAD_MESSAGE_KEY_ID');
+      return false;
+    }
+
+    bobAccount.remove_one_time_keys(bobSession);
+    let decrypted = bobSession.decrypt(encrypted.type, encrypted.body);
+    expect(decrypted).toEqual(test_text);
+
+    test_text = randomString(40);
+    encrypted = bobSession.encrypt(test_text);
+    expect(encrypted.type).toEqual(1);
+    decrypted = aliceSession.decrypt(encrypted.type, encrypted.body);
+    expect(decrypted).toEqual(test_text);
+
+    const testText1 = 'message1';
+    const encrypted1 = bobSession.encrypt(testText1);
+    const testText2 = 'message2';
+    const encrypted2 = bobSession.encrypt(testText2);
+
+    // encrypt message using alice session and trying to decrypt with
+    // the same session => `BAD_MESSAGE_MAC`
+    const aliceEncrypted = aliceSession.encrypt(test_text);
+    expect(() =>
+      aliceSession.decrypt_sequential(aliceEncrypted.type, aliceEncrypted.body),
+    ).toThrow('OLM.BAD_MESSAGE_MAC');
+
+    // decrypting encrypted2 before encrypted1 using
+    // decrypt_sequential() => OLM_MESSAGE_OUT_OF_ORDER
+    expect(() =>
+      aliceSession.decrypt_sequential(encrypted2.type, encrypted2.body),
+    ).toThrow('OLM.OLM_MESSAGE_OUT_OF_ORDER');
+
+    // test correct order
+    const decrypted1 = aliceSession.decrypt_sequential(
+      encrypted1.type,
+      encrypted1.body,
+    );
+    expect(decrypted1).toEqual(testText1);
+    const decrypted2 = aliceSession.decrypt_sequential(
+      encrypted2.type,
+      encrypted2.body,
+    );
+    expect(decrypted2).toEqual(testText2);
+
+    // try to decrypt second time
+    // the same message => OLM_ALREADY_DECRYPTED_OR_KEYS_SKIPPED
+    expect(() =>
+      aliceSession.decrypt_sequential(encrypted2.type, encrypted2.body),
+    ).toThrow('OLM.OLM_ALREADY_DECRYPTED_OR_KEYS_SKIPPED');
+
     return true;
   };
 
   it('should get Olm Utility', async () => {
     await olm.init();
     const utility = getOlmUtility();
     expect(utility).toBeDefined();
   });
 
   it('should generate, regenerate, forget, and publish prekey', async () => {
     await olm.init();
     const account = initAccount(false);
 
     expect(account.last_prekey_publish_time()).toEqual(0);
     expect(account.prekey()).toBeDefined();
     expect(account.unpublished_prekey()).toBeDefined();
     account.mark_prekey_as_published();
     const last_published = account.last_prekey_publish_time();
     expect(last_published).toBeGreaterThan(0);
 
     try {
       console.log(account.unpublished_prekey());
     } catch (error) {
       expect(error.message).toContain('NO_UNPUBLISHED_PREKEY');
     }
     account.forget_old_prekey();
 
     account.generate_prekey();
     expect(account.prekey()).toBeDefined();
     expect(account.unpublished_prekey()).toBeDefined();
 
     expect(account.last_prekey_publish_time()).toEqual(last_published);
     account.mark_prekey_as_published();
     expect(account.last_prekey_publish_time()).toBeGreaterThanOrEqual(
       last_published,
     );
     account.forget_old_prekey();
   });
 
   it('should encrypt and decrypt', async () => {
     await olm.init();
     const aliceAccount = initAccount();
     const bobAccount = initAccount();
     const aliceSession = new olm.Session();
     const bobSession = new olm.Session();
 
     createSession(aliceSession, aliceAccount, bobAccount);
     expect(testRatchet(aliceSession, bobSession, bobAccount)).toBeTrue;
   });
 
+  it('should encrypt and decrypt sequential', async () => {
+    await olm.init();
+    const aliceAccount = initAccount();
+    const bobAccount = initAccount();
+    const aliceSession = new olm.Session();
+    const bobSession = new olm.Session();
+
+    createSession(aliceSession, aliceAccount, bobAccount);
+    expect(testRatchetSequential(aliceSession, bobSession, bobAccount))
+      .toBeTrue;
+  });
+
   it('should encrypt and decrypt, even after a prekey is rotated', async () => {
     await olm.init();
     const aliceAccount = initAccount();
     const bobAccount = initAccount();
     const aliceSession = new olm.Session();
     const bobSession = new olm.Session();
 
     createSession(aliceSession, aliceAccount, bobAccount, true);
     expect(testRatchet(aliceSession, bobSession, bobAccount)).toBeTrue;
   });
 
   it('should not encrypt and decrypt, after the old prekey is forgotten', async () => {
     await olm.init();
     const aliceAccount = initAccount();
     const bobAccount = initAccount();
     const aliceSession = new olm.Session();
     const bobSession = new olm.Session();
 
     createSession(aliceSession, aliceAccount, bobAccount, true, true);
     expect(testRatchet(aliceSession, bobSession, bobAccount)).toBeFalse;
   });
 
   it('should encrypt and decrypt repeatedly', async () => {
     await olm.init();
     const aliceAccount = initAccount();
     const bobAccount = initAccount();
     const aliceSession = new olm.Session();
     const bobSession = new olm.Session();
 
     createSession(aliceSession, aliceAccount, bobAccount, false, false);
     expect(testRatchet(aliceSession, bobSession, bobAccount, 100)).toBeTrue;
   });
 
   it('should not encrypt and decrypt if prekey is not signed correctly', async () => {
     await olm.init();
     const aliceAccount = initAccount();
     const bobAccount = initAccount();
     const aliceSession = new olm.Session();
 
     expect(
       createSession(aliceSession, aliceAccount, bobAccount, false, false, true),
     ).toBeFalse;
   });
 });
diff --git a/lib/flow-typed/npm/@commapp/olm_vx.x.x.js b/lib/flow-typed/npm/@commapp/olm_vx.x.x.js
index f365eecbc..21f35119f 100644
--- a/lib/flow-typed/npm/@commapp/olm_vx.x.x.js
+++ b/lib/flow-typed/npm/@commapp/olm_vx.x.x.js
@@ -1,182 +1,183 @@
 // flow-typed signature: 085f002da86534cfd8cee47ffa99dd67
 // flow-typed version: <<STUB>>/@commapp/olm_v3.2.4/flow_v0.182.0
 
 declare module '@commapp/olm' {
 
 /*
 Copyright 2020 The Matrix.org Foundation C.I.C.
 
 Licensed under the Apache License, Version 2.0 (the "License");
 you may not use this file except in compliance with the License.
 You may obtain a copy of the License at
 
     http://www.apache.org/licenses/LICENSE-2.0
 
 Unless required by applicable law or agreed to in writing, software
 distributed under the License is distributed on an "AS IS" BASIS,
 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 See the License for the specific language governing permissions and
 limitations under the License.
 */
 
   declare export class Account {
     constructor(): void;
     free(): void;
     create(): void;
     identity_keys(): string;
     sign(message: string | Uint8Array): string;
     one_time_keys(): string;
     mark_keys_as_published(): void;
     max_number_of_one_time_keys(): number;
     generate_one_time_keys(number_of_keys: number): void;
     remove_one_time_keys(session: Session): void;
     generate_prekey(): void;
     prekey(): string;
     unpublished_prekey(): ?string;
     prekey_signature(): ?string;
     forget_old_prekey(): void;
     mark_prekey_as_published(): void;
     last_prekey_publish_time(): number;
     generate_fallback_key(): void;
     fallback_key(): string;
     unpublished_fallback_key(): string;
     forget_old_fallback_key(): void;
     pickle(key: string | Uint8Array): string;
     unpickle(key: string | Uint8Array, pickle: string): void;
   }
 
   declare export type EncryptResult = {
     +type: 0 | 1, // 0: PreKey, 1: Message
     +body: string,
   };
   declare export class Session {
     constructor(): void;
     free(): void;
     pickle(key: string | Uint8Array): string;
     unpickle(key: string | Uint8Array, pickle: string): void;
     create_outbound(
       account: Account,
       their_identity_key: string,
       their_signing_key: string,
       their_prekey: string,
       their_prekey_signature: string,
       their_one_time_key: string,
     ): void;
     create_inbound(account: Account, one_time_key_message: string): void;
     create_inbound_from(
       account: Account,
       identity_key: string,
       one_time_key_message: string,
     ): void;
     session_id(): string;
     has_received_message(): boolean;
     matches_inbound(one_time_key_message: string): boolean;
     matches_inbound_from(
       identity_key: string,
       one_time_key_message: string,
     ): boolean;
     encrypt(plaintext: string): EncryptResult;
     decrypt(message_type: number, message: string): string;
+    decrypt_sequential(message_type: number, message: string): string;
     describe(): string;
   }
 
   declare export class Utility {
     constructor(): void;
     free(): void;
     sha256(input: string | Uint8Array): string;
     ed25519_verify(
       key: string,
       message: string | Uint8Array,
       signature: string,
     ): void;
   }
 
   declare export type DecryptResult = {
     +message_index: string,
     +plaintext: string,
   };
 
   declare export class InboundGroupSession {
     constructor(): void;
     free(): void;
     pickle(key: string | Uint8Array): string;
     unpickle(key: string | Uint8Array, pickle: string): void;
     create(session_key: string): string;
     import_session(session_key: string): string;
     decrypt(message: string): DecryptResult;
     session_id(): string;
     first_known_index(): number;
     export_session(message_index: number): string;
   }
 
   declare export class OutboundGroupSession {
     constructor(): void;
     free(): void;
     pickle(key: string | Uint8Array): string;
     unpickle(key: string | Uint8Array, pickle: string): void;
     create(): void;
     encrypt(plaintext: string): string;
     session_id(): string;
     session_key(): string;
     message_index(): number;
   }
 
   declare export type PkEncryptionEncryptResult = {
     +ciphertext: string,
     +mac: string,
     +ephemeral: string,
   };
 
   declare export class PkEncryption {
     constructor(): void;
     free(): void;
     set_recipient_key(key: string): void;
     encrypt(plaintext: string): PkEncryptionEncryptResult;
   }
 
   declare export class PkDecryption {
     constructor(): void;
     free(): void;
     init_with_private_key(key: Uint8Array): string;
     generate_key(): string;
     get_private_key(): Uint8Array;
     pickle(key: string | Uint8Array): string;
     unpickle(key: string | Uint8Array, pickle: string): string;
     decrypt(ephemeral_key: string, mac: string, ciphertext: string): string;
   }
 
   declare export class PkSigning {
     constructor(): void;
     free(): void;
     init_with_seed(seed: Uint8Array): string;
     generate_seed(): Uint8Array;
     sign(message: string): string;
   }
 
   declare export class SAS {
     constructor(): void;
     free(): void;
     get_pubkey(): string;
     set_their_key(their_key: string): void;
     generate_bytes(info: string, length: number): Uint8Array;
     calculate_mac(input: string, info: string): string;
     calculate_mac_fixed_base64(input: string, info: string): string;
     calculate_mac_long_kdf(input: string, info: string): string;
   }
 
   declare export function init(opts?: Object): Promise<void>;
 
   declare export function get_library_version(): [number, number, number];
 
   declare export var PRIVATE_KEY_LENGTH: number;
 
   declare export default {
     init: typeof init,
     get_library_version: typeof get_library_version,
     PRIVATE_KEY_LENGTH: typeof PRIVATE_KEY_LENGTH,
     Account: typeof Account,
     Utility: typeof Utility,
     Session: typeof Session,
   };
 
 }
diff --git a/web/flow-typed/npm/@commapp/olm_vx.x.x.js b/web/flow-typed/npm/@commapp/olm_vx.x.x.js
index f365eecbc..21f35119f 100644
--- a/web/flow-typed/npm/@commapp/olm_vx.x.x.js
+++ b/web/flow-typed/npm/@commapp/olm_vx.x.x.js
@@ -1,182 +1,183 @@
 // flow-typed signature: 085f002da86534cfd8cee47ffa99dd67
 // flow-typed version: <<STUB>>/@commapp/olm_v3.2.4/flow_v0.182.0
 
 declare module '@commapp/olm' {
 
 /*
 Copyright 2020 The Matrix.org Foundation C.I.C.
 
 Licensed under the Apache License, Version 2.0 (the "License");
 you may not use this file except in compliance with the License.
 You may obtain a copy of the License at
 
     http://www.apache.org/licenses/LICENSE-2.0
 
 Unless required by applicable law or agreed to in writing, software
 distributed under the License is distributed on an "AS IS" BASIS,
 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 See the License for the specific language governing permissions and
 limitations under the License.
 */
 
   declare export class Account {
     constructor(): void;
     free(): void;
     create(): void;
     identity_keys(): string;
     sign(message: string | Uint8Array): string;
     one_time_keys(): string;
     mark_keys_as_published(): void;
     max_number_of_one_time_keys(): number;
     generate_one_time_keys(number_of_keys: number): void;
     remove_one_time_keys(session: Session): void;
     generate_prekey(): void;
     prekey(): string;
     unpublished_prekey(): ?string;
     prekey_signature(): ?string;
     forget_old_prekey(): void;
     mark_prekey_as_published(): void;
     last_prekey_publish_time(): number;
     generate_fallback_key(): void;
     fallback_key(): string;
     unpublished_fallback_key(): string;
     forget_old_fallback_key(): void;
     pickle(key: string | Uint8Array): string;
     unpickle(key: string | Uint8Array, pickle: string): void;
   }
 
   declare export type EncryptResult = {
     +type: 0 | 1, // 0: PreKey, 1: Message
     +body: string,
   };
   declare export class Session {
     constructor(): void;
     free(): void;
     pickle(key: string | Uint8Array): string;
     unpickle(key: string | Uint8Array, pickle: string): void;
     create_outbound(
       account: Account,
       their_identity_key: string,
       their_signing_key: string,
       their_prekey: string,
       their_prekey_signature: string,
       their_one_time_key: string,
     ): void;
     create_inbound(account: Account, one_time_key_message: string): void;
     create_inbound_from(
       account: Account,
       identity_key: string,
       one_time_key_message: string,
     ): void;
     session_id(): string;
     has_received_message(): boolean;
     matches_inbound(one_time_key_message: string): boolean;
     matches_inbound_from(
       identity_key: string,
       one_time_key_message: string,
     ): boolean;
     encrypt(plaintext: string): EncryptResult;
     decrypt(message_type: number, message: string): string;
+    decrypt_sequential(message_type: number, message: string): string;
     describe(): string;
   }
 
   declare export class Utility {
     constructor(): void;
     free(): void;
     sha256(input: string | Uint8Array): string;
     ed25519_verify(
       key: string,
       message: string | Uint8Array,
       signature: string,
     ): void;
   }
 
   declare export type DecryptResult = {
     +message_index: string,
     +plaintext: string,
   };
 
   declare export class InboundGroupSession {
     constructor(): void;
     free(): void;
     pickle(key: string | Uint8Array): string;
     unpickle(key: string | Uint8Array, pickle: string): void;
     create(session_key: string): string;
     import_session(session_key: string): string;
     decrypt(message: string): DecryptResult;
     session_id(): string;
     first_known_index(): number;
     export_session(message_index: number): string;
   }
 
   declare export class OutboundGroupSession {
     constructor(): void;
     free(): void;
     pickle(key: string | Uint8Array): string;
     unpickle(key: string | Uint8Array, pickle: string): void;
     create(): void;
     encrypt(plaintext: string): string;
     session_id(): string;
     session_key(): string;
     message_index(): number;
   }
 
   declare export type PkEncryptionEncryptResult = {
     +ciphertext: string,
     +mac: string,
     +ephemeral: string,
   };
 
   declare export class PkEncryption {
     constructor(): void;
     free(): void;
     set_recipient_key(key: string): void;
     encrypt(plaintext: string): PkEncryptionEncryptResult;
   }
 
   declare export class PkDecryption {
     constructor(): void;
     free(): void;
     init_with_private_key(key: Uint8Array): string;
     generate_key(): string;
     get_private_key(): Uint8Array;
     pickle(key: string | Uint8Array): string;
     unpickle(key: string | Uint8Array, pickle: string): string;
     decrypt(ephemeral_key: string, mac: string, ciphertext: string): string;
   }
 
   declare export class PkSigning {
     constructor(): void;
     free(): void;
     init_with_seed(seed: Uint8Array): string;
     generate_seed(): Uint8Array;
     sign(message: string): string;
   }
 
   declare export class SAS {
     constructor(): void;
     free(): void;
     get_pubkey(): string;
     set_their_key(their_key: string): void;
     generate_bytes(info: string, length: number): Uint8Array;
     calculate_mac(input: string, info: string): string;
     calculate_mac_fixed_base64(input: string, info: string): string;
     calculate_mac_long_kdf(input: string, info: string): string;
   }
 
   declare export function init(opts?: Object): Promise<void>;
 
   declare export function get_library_version(): [number, number, number];
 
   declare export var PRIVATE_KEY_LENGTH: number;
 
   declare export default {
     init: typeof init,
     get_library_version: typeof get_library_version,
     PRIVATE_KEY_LENGTH: typeof PRIVATE_KEY_LENGTH,
     Account: typeof Account,
     Utility: typeof Utility,
     Session: typeof Session,
   };
 
 }