diff --git a/lib/types/grpc-types.js b/lib/types/grpc-types.js
new file mode 100644
--- /dev/null
+++ b/lib/types/grpc-types.js
@@ -0,0 +1,139 @@
+// @flow
+
+export interface GetUserPublicKeyRequest {
+  userID?: string;
+  deviceID?: string;
+}
+export interface GetUserPublicKeyResponse__Output {
+  publicKey: string;
+}
+
+export type MetadataValue = string | Buffer;
+
+export interface MetadataOptions {
+  idempotentRequest?: boolean;
+  waitForReady?: boolean;
+  cacheableRequest?: boolean;
+  corked?: boolean;
+}
+export type MetadataObject = Map<string, MetadataValue[]>;
+
+declare export class Metadata {
+  internalRepr: MetadataObject;
+  constructor(options: MetadataOptions): this;
+
+  set(key: string, value: MetadataValue): void;
+
+  add(key: string, value: MetadataValue): void;
+
+  remove(key: string): void;
+
+  get(key: string): MetadataValue[];
+
+  getMap(): {
+    [key: string]: MetadataValue,
+    ...
+  };
+
+  clone(): Metadata;
+
+  merge(other: Metadata): void;
+  setOptions(options: MetadataOptions): void;
+  getOptions(): MetadataOptions;
+
+  toHttp2Headers(): mixed;
+
+  toJSON(): void;
+
+  static fromHttp2Headers(headers: mixed): Metadata;
+}
+
+declare export var Status: {
+  +OK: 0, // 0
+  +CANCELLED: 1, // 1
+  +UNKNOWN: 2, // 2
+  +INVALID_ARGUMENT: 3, // 3
+  +DEADLINE_EXCEEDED: 4, // 4
+  +NOT_FOUND: 5, // 5
+  +ALREADY_EXISTS: 6, // 6
+  +PERMISSION_DENIED: 7, // 7
+  +RESOURCE_EXHAUSTED: 8, // 8
+  +FAILED_PRECONDITION: 9, // 9
+  +ABORTED: 10, // 10
+  +OUT_OF_RANGE: 11, // 11
+  +UNIMPLEMENTED: 12, // 12
+  +INTERNAL: 13, // 13
+  +UNAVAILABLE: 14, // 14
+  +DATA_LOSS: 15, // 15
+  +UNAUTHENTICATED: 16, // 16
+};
+
+export interface WriteCallback {
+  (error?: Error | null): void;
+}
+export interface MessageContext {
+  callback?: WriteCallback;
+  flags?: number;
+}
+
+export interface StatusObject {
+  code: typeof Status;
+  details: string;
+  metadata: Metadata;
+}
+
+export interface InterceptingListener {
+  onReceiveMetadata(metadata: Metadata): void;
+  onReceiveMessage(message: mixed): void;
+  onReceiveStatus(status: StatusObject): void;
+}
+
+export interface InterceptingCallInterface {
+  cancelWithStatus(status: typeof Status, details: string): void;
+  getPeer(): string;
+  start(
+    metadata: Metadata,
+    listener?: $Rest<InterceptingListener, { ... }>,
+  ): void;
+  sendMessageWithContext(context: MessageContext, message: mixed): void;
+  sendMessage(message: mixed): void;
+  startRead(): void;
+  halfClose(): void;
+}
+
+export interface EmitterAugmentation1<Name: string | Symbol, Arg> {
+  addListener(event: Name, listener: (arg1: Arg) => void): ClientUnaryCall;
+  emit(event: Name, arg1: Arg): boolean;
+  on(event: Name, listener: (arg1: Arg) => void): ClientUnaryCall;
+  once(event: Name, listener: (arg1: Arg) => void): ClientUnaryCall;
+  prependListener(event: Name, listener: (arg1: Arg) => void): ClientUnaryCall;
+  prependOnceListener(
+    event: Name,
+    listener: (arg1: Arg) => void,
+  ): ClientUnaryCall;
+  removeListener(event: Name, listener: (arg1: Arg) => void): ClientUnaryCall;
+}
+
+export type ClientUnaryCall = {
+  ...{
+    call?: InterceptingCallInterface,
+    cancel(): void,
+    getPeer(): string,
+    ...
+  },
+  ...EmitterAugmentation1<'metadata', Metadata>,
+  ...EmitterAugmentation1<'status', StatusObject>,
+  ...any,
+};
+
+export interface RequestCallback<ResponseType> {
+  (err: Error | null, value?: ResponseType): void;
+}
+
+export type IdentityServiceClient = {
+  getUserPublicKey(
+    argument: GetUserPublicKeyRequest,
+    callback: RequestCallback<GetUserPublicKeyResponse__Output>,
+  ): ClientUnaryCall,
+  ...
+};