diff --git a/js/modules/data.d.ts b/js/modules/data.d.ts
index 92441555f..c70fd17e1 100644
--- a/js/modules/data.d.ts
+++ b/js/modules/data.d.ts
@@ -179,7 +179,7 @@ export function updateGuardNodes(nodes: Array<string>): Promise<void>;
 
 // Storage Items
 export function createOrUpdateItem(data: StorageItem): Promise<void>;
-export function getItemById(id: string): Promise<StorageItem>;
+export function getItemById(id: string): Promise<StorageItem | undefined>;
 export function getAlItems(): Promise<Array<StorageItem>>;
 export function bulkAddItems(array: Array<StorageItem>): Promise<void>;
 export function removeItemById(id: string): Promise<void>;
diff --git a/js/modules/metadata/SecretSessionCipher.d.ts b/js/modules/metadata/SecretSessionCipher.d.ts
new file mode 100644
index 000000000..1375167fd
--- /dev/null
+++ b/js/modules/metadata/SecretSessionCipher.d.ts
@@ -0,0 +1,23 @@
+import { SignalService } from '../../../ts/protobuf';
+import {
+  BinaryString,
+  CipherTextObject,
+} from '../../../libtextsecure/libsignal-protocol';
+
+export declare class SecretSessionCipher {
+  constructor(storage: any);
+  encrypt(
+    destinationPubkey: string,
+    senderCertificate: SignalService.SenderCertificate,
+    innerEncryptedMessage: CipherTextObject
+  ): Promise<ArrayBuffer>;
+  decrypt(
+    cipherText: ArrayBuffer,
+    me: { number: string; deviceId: number }
+  ): Promise<{
+    isMe?: boolean;
+    sender: string;
+    content: ArrayBuffer;
+    type: SignalService.Envelope.Type;
+  }>;
+}
diff --git a/js/modules/signal.d.ts b/js/modules/signal.d.ts
new file mode 100644
index 000000000..f395f30a6
--- /dev/null
+++ b/js/modules/signal.d.ts
@@ -0,0 +1,9 @@
+import { SecretSessionCipher } from './metadata/SecretSessionCipher';
+
+interface Metadata {
+  SecretSessionCipher: typeof SecretSessionCipher;
+}
+
+export interface SignalInterface {
+  Metadata: Metadata;
+}
diff --git a/ts/session/crypto/MessageEncrypter.ts b/ts/session/crypto/MessageEncrypter.ts
index d58a11f2f..f19a3bbfa 100644
--- a/ts/session/crypto/MessageEncrypter.ts
+++ b/ts/session/crypto/MessageEncrypter.ts
@@ -1,12 +1,10 @@
 import { EncryptionType } from '../types/EncryptionType';
 import { SignalService } from '../../protobuf';
-import { libloki, libsignal, textsecure } from '../../window';
-import {
-  CipherTextObject,
-  SignalProtocolAddress,
-} from '../../../libtextsecure/libsignal-protocol';
+import { libloki, libsignal, Signal, textsecure } from '../../window';
+import { CipherTextObject } from '../../../libtextsecure/libsignal-protocol';
+import { UserUtil } from '../../util';
 
-function padPlainTextBuffer(messageBuffer: Uint8Array): Uint8Array {
+export function padPlainTextBuffer(messageBuffer: Uint8Array): Uint8Array {
   const plaintext = new Uint8Array(
     getPaddedMessageLength(messageBuffer.byteLength + 1) - 1
   );
@@ -53,31 +51,49 @@ export async function encrypt(
     throw new Error('Encryption is not yet supported');
   }
 
-  let cipherText: CipherTextObject;
+  let innerCipherText: CipherTextObject;
   if (encryptionType === EncryptionType.SessionReset) {
     const cipher = new libloki.crypto.FallBackSessionCipher(address);
-    cipherText = await cipher.encrypt(plainText.buffer);
+    innerCipherText = await cipher.encrypt(plainText.buffer);
   } else {
     const cipher = new libsignal.SessionCipher(
       textsecure.storage.protocol,
       address
     );
-    cipherText = await cipher.encrypt(plainText.buffer);
+    innerCipherText = await cipher.encrypt(plainText.buffer);
   }
 
-  return encryptUsingSealedSender(address, cipherText);
+  return encryptUsingSealedSender(device, innerCipherText);
 }
 
 async function encryptUsingSealedSender(
-  address: SignalProtocolAddress,
-  cipherText: CipherTextObject
+  device: string,
+  innerCipherText: CipherTextObject
 ): Promise<{
   envelopeType: SignalService.Envelope.Type;
   cipherText: Base64String;
 }> {
-  // TODO: Do stuff here
+  const ourNumber = await UserUtil.getCurrentDevicePubKey();
+  if (!ourNumber) {
+    throw new Error('Failed to fetch current device public key.');
+  }
+
+  const certificate = SignalService.SenderCertificate.create({
+    sender: ourNumber,
+    senderDevice: 1,
+  });
+
+  const cipher = new Signal.Metadata.SecretSessionCipher(
+    textsecure.storage.protocol
+  );
+  const cipherTextBuffer = await cipher.encrypt(
+    device,
+    certificate,
+    innerCipherText
+  );
+
   return {
     envelopeType: SignalService.Envelope.Type.UNIDENTIFIED_SENDER,
-    cipherText: 'implement me!',
+    cipherText: Buffer.from(cipherTextBuffer).toString('base64'),
   };
 }
diff --git a/ts/util/index.ts b/ts/util/index.ts
index ec0ca2e21..8416f8630 100644
--- a/ts/util/index.ts
+++ b/ts/util/index.ts
@@ -4,6 +4,7 @@ import { isFileDangerous } from './isFileDangerous';
 import { missingCaseError } from './missingCaseError';
 import { migrateColor } from './migrateColor';
 import { makeLookup } from './makeLookup';
+import * as UserUtil from './user';
 
 export {
   arrayBufferToObjectURL,
@@ -12,4 +13,5 @@ export {
   makeLookup,
   migrateColor,
   missingCaseError,
+  UserUtil,
 };
diff --git a/ts/util/user.ts b/ts/util/user.ts
new file mode 100644
index 000000000..cea991b17
--- /dev/null
+++ b/ts/util/user.ts
@@ -0,0 +1,17 @@
+import { getItemById } from '../../js/modules/data';
+import { KeyPair } from '../../libtextsecure/libsignal-protocol';
+
+export async function getCurrentDevicePubKey(): Promise<string | undefined> {
+  const item = await getItemById('number_id');
+  if (!item || !item.value) {
+    return undefined;
+  }
+
+  return item.value.split('.')[0];
+}
+
+export async function getIdentityKeyPair(): Promise<KeyPair | undefined> {
+  const item = await getItemById('identityKey');
+
+  return item?.value;
+}
diff --git a/ts/window.ts b/ts/window.ts
index cc5a28be3..1cfa81639 100644
--- a/ts/window.ts
+++ b/ts/window.ts
@@ -1,5 +1,6 @@
 import { LocalizerType } from './types/Util';
 import { LibsignalProtocol } from '../libtextsecure/libsignal-protocol';
+import { SignalInterface } from '../js/modules/signal';
 
 interface WindowInterface extends Window {
   seedNodeList: any;
@@ -37,7 +38,7 @@ interface WindowInterface extends Window {
   libloki: any;
   displayNameRegex: any;
 
-  Signal: any;
+  Signal: SignalInterface;
   Whisper: any;
   ConversationController: any;