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 +1,141 @@
+// @flow
+
+export type GetUserPublicKeyRequest = {
+  +userID?: string,
+  +deviceID?: string,
+};
+
+export type GetUserPublicKeyResponse__Output = {
+  +publicKey: string,
+};
+
+export type MetadataValue = string | Buffer;
+
+export type 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(): { [key: string]: MetadataValue[] };
+
+  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 type WriteCallback = (error?: Error | null) => void;
+export type MessageContext = {
+  +callback?: WriteCallback,
+  +flags?: number,
+};
+
+export type StatusObject = {
+  +code: typeof Status,
+  +details: string,
+  +metadata: Metadata,
+};
+
+export type InterceptingListener = {
+  +onReceiveMetadata: (metadata: Metadata) => void,
+  +onReceiveMessage: (message: mixed) => void,
+  +onReceiveStatus: (status: StatusObject) => void,
+};
+
+export type InterceptingCallInterface = {
+  +cancelWithStatus: (status: typeof Status, details: string) => void,
+  +getPeer: () => string,
+  +start: (metadata: Metadata, listener?: $Exact<InterceptingListener>) => void,
+  +sendMessageWithContext: (context: MessageContext, message: mixed) => void,
+  +sendMessage: (message: mixed) => void,
+  +startRead: () => void,
+  +halfClose: () => void,
+};
+
+export type EmitterAugmentation1<Name: string | Symbol, Arg> = {
+  +addListener: (event: Name, listener: (arg1: Arg) => void) => ClientUnaryCall,
+  +emit: (event: Name, arg1: Arg) => boolean,
+  +on: (event: Name, listener: (arg1: Arg) => void) => ClientUnaryCall,
+  +once: (event: Name, listener: (arg1: Arg) => void) => ClientUnaryCall,
+  +prependListener: (
+    event: Name,
+    listener: (arg1: Arg) => void,
+  ) => ClientUnaryCall,
+  +prependOnceListener: (
+    event: Name,
+    listener: (arg1: Arg) => void,
+  ) => ClientUnaryCall,
+  +removeListener: (
+    event: Name,
+    listener: (arg1: Arg) => void,
+  ) => ClientUnaryCall,
+};
+
+export type ClientUnaryCall = {
+  ...{
+    +call?: InterceptingCallInterface,
+    +cancel: () => void,
+    +getPeer: () => string,
+  },
+  ...EmitterAugmentation1<'metadata', Metadata>,
+  ...EmitterAugmentation1<'status', StatusObject>,
+  ...
+} & events$EventEmitter;
+
+export type RequestCallback<ResponseType> = (
+  err: Error | null,
+  value?: ResponseType,
+) => void;
+
+export type IdentityServiceClient = {
+  getUserPublicKey(
+    argument: GetUserPublicKeyRequest,
+    callback: RequestCallback<GetUserPublicKeyResponse__Output>,
+  ): ClientUnaryCall,
+  ...
+};