diff --git a/api/rest.py b/api/rest.py
index d1fef98..06b6375 100644
--- a/api/rest.py
+++ b/api/rest.py
@@ -5,6 +5,8 @@ The REST endpoints.
 """
 
 from aiohttp import web
+import asyncio
+from concurrent.futures import ProcessPoolExecutor
 import datetime
 import logging
 import os
@@ -12,8 +14,9 @@ import pkg_resources
 import typing as T
 
 from aiohttp_session import get_session, Session
+from passlib.hash import bcrypt
 
-from bot_z.async_operator import AsyncOperator
+from bot_z.async_operator import AsyncOperator, push_to_loop
 from api.async_bot import login, logout, checkin, checkout, status
 from api import BASE_URI, DEBUG
 
@@ -22,6 +25,28 @@ alog = logging.getLogger("api")
 routes = web.RouteTableDef()
 OPERATORS = {}  # type: T.Dict[T.Text, AsyncOperator]
 BASE_PATH = pkg_resources.resource_filename(__name__, "assets")
+EXECUTOR = ProcessPoolExecutor()
+# WARN: the default il 12 rounds; both the server and the client shall compute
+# this hash. The target client is a smartphone with poor performance on
+# crypto computations, so we should keep this low, as the verification step
+# is optionally enforced by the client.
+ROUNDS = 6
+
+
+def _reckon_token_response(base_uri: T.Text) -> T.Text:
+    return bcrypt.using(rounds=ROUNDS, truncate_error=True).hash(base_uri)
+
+
+async def reckon_token_response(
+    base_uri: T.Text, loop: asyncio.AbstractEventLoop
+) -> T.Text:
+    """
+    A client and the server should agree if the pairing is adequate.
+    This could be accomplished calculating on both sides an cryptographic
+    secret. The current implementation uses bcrypt to compute the hash on
+    server side and the client should verify the secret on its side.
+    """
+    return await push_to_loop(loop, EXECUTOR, _reckon_token_response, base_uri)
 
 
 async def get_set_operator(
@@ -75,6 +100,14 @@ async def routing_handler(request: web.Request) -> web.Response:
     return web.json_response({"logged_in": _logged_in})
 
 
+@routes.get("/api/ping")
+async def ping_handler(request: web.Request) -> web.Response:
+    alog.debug("pinged on %s", request.path)
+    resp_data = await reckon_token_response(request.app["base_uri"], request.app.loop)
+    alog.debug("ping response: %s", resp_data)
+    return web.json_response({"hash": resp_data})
+
+
 @routes.post("/api/login")
 async def login_handler(request: web.Request) -> web.Response:
     data = await request.json()
@@ -82,7 +115,7 @@ async def login_handler(request: web.Request) -> web.Response:
     password = data.get("password")
     if not user or not password:
         alog.debug("login - missing username or password: %s", data)
-        return web.json_response({"error": "Missing username or password"}, status=403)
+        return web.json_response({"error": "Missing username or password"}, status=401)
     op, session = await get_set_operator(request, user, password)
     alog.debug("login - user: %s, password: %s", user, password)
     res = await login(op, user, password)
@@ -101,7 +134,7 @@ async def logout_handler(request: web.Request) -> web.Response:
     op = OPERATORS.get(op_key)
     if not op:
         return web.json_response(
-            {"error": "No session", "logged_in": False}, status=403
+            {"error": "No session", "logged_in": False}, status=401
         )
     res = await logout(op)
     alog.debug("logout result: %s", res)
@@ -117,7 +150,7 @@ async def checkin_handler(request: web.Request) -> web.Response:
     op = OPERATORS.get(session.get("async_operator"))
     if not op:
         return web.json_response(
-            {"error": "No session", "logged_in": False}, status=403
+            {"error": "No session", "logged_in": False}, status=401
         )
     res = await checkin(op)
     alog.debug("checkin result: %s", res)
@@ -131,7 +164,7 @@ async def checkout_handler(request: web.Request) -> web.Response:
     op = OPERATORS.get(session.get("async_operator"))
     if not op:
         return web.json_response(
-            {"error": "No session", "logged_in": False}, status=403
+            {"error": "No session", "logged_in": False}, status=401
         )
     res = await checkout(op)
     alog.debug("checkout result: %s", res)
@@ -145,7 +178,7 @@ async def movements_handle(request: web.Request) -> web.Response:
     op = OPERATORS.get(session.get("async_operator"))
     if not op:
         return web.json_response(
-            {"error": "No session", "logged_in": False}, status=403
+            {"error": "No session", "logged_in": False}, status=401
         )
     res = await status(op)
     alog.debug("movements result: %s", res)
diff --git a/setup.py b/setup.py
index 3592514..700736b 100644
--- a/setup.py
+++ b/setup.py
@@ -53,6 +53,8 @@ requirements = [
     "aiohttp-session==2.7.0",
     "cryptography==2.7",
     "PyYAML==5.1.2",
+    "passlib>=1.7.1, <2.0.0",
+    "bcrypt==0.1.1",
 ]
 
 setup_requirements = []  # type: T.List[str]