diff --git a/apps/cli/__init__.py b/apps/cli/__init__.py
index f6d347c..58be430 100644
--- a/apps/cli/__init__.py
+++ b/apps/cli/__init__.py
@@ -13,6 +13,8 @@ APPOINTMENTS_FOLDER_NAME = "appointments"
 SUPPORTED_HASH_FUNCTIONS = ["SHA256"]
 SUPPORTED_CIPHERS = ["AES-GCM-128"]
 
+CLI_PUBLIC_KEY = "cli_pk.pem"
+CLI_PRIVATE_KEY = "cli_sk.pem"
 PISA_PUBLIC_KEY = "pisa_pk.pem"
 
 # Configure logging
diff --git a/apps/cli/pisa_cli.py b/apps/cli/pisa_cli.py
index 2d1da6c..12213dd 100644
--- a/apps/cli/pisa_cli.py
+++ b/apps/cli/pisa_cli.py
@@ -6,21 +6,28 @@ import requests
 import time
 from sys import argv
 from hashlib import sha256
-from binascii import unhexlify
+from binascii import hexlify, unhexlify
 from getopt import getopt, GetoptError
 from requests import ConnectTimeout, ConnectionError
 from uuid import uuid4
 
 from cryptography.hazmat.backends import default_backend
 from cryptography.hazmat.primitives import hashes
-from cryptography.hazmat.primitives.serialization import load_pem_public_key
+from cryptography.hazmat.primitives.serialization import load_pem_public_key, load_pem_private_key
 from cryptography.hazmat.primitives.asymmetric import ec
 from cryptography.exceptions import InvalidSignature, UnsupportedAlgorithm
 
 from apps.cli.blob import Blob
 from apps.cli.help import help_add_appointment, help_get_appointment
-from apps.cli import DEFAULT_PISA_API_SERVER, DEFAULT_PISA_API_PORT, PISA_PUBLIC_KEY, APPOINTMENTS_FOLDER_NAME
-from apps.cli import logger
+from apps.cli import (
+    DEFAULT_PISA_API_SERVER,
+    DEFAULT_PISA_API_PORT,
+    CLI_PUBLIC_KEY,
+    CLI_PRIVATE_KEY,
+    PISA_PUBLIC_KEY,
+    APPOINTMENTS_FOLDER_NAME,
+    logger,
+)
 
 
 HTTP_OK = 200
@@ -48,21 +55,42 @@ def generate_dummy_appointment():
     print("\nData stored in dummy_appointment_data.json")
 
 
-# Loads and returns Pisa's public key from disk.
-# Will raise NotFoundError or IOError if the attempts to open and read the public key file fail.
-# Will raise ValueError if it the public key file was present but it failed to be deserialized.
-def load_pisa_public_key():
+def sign_appointment(sk, appointment):
+    data = json.dumps(appointment, sort_keys=True, separators=(",", ":")).encode("utf-8")
+    return hexlify(sk.sign(data, ec.ECDSA(hashes.SHA256()))).decode("utf-8")
+
+
+# Loads and returns Pisa keys from disk
+def load_key_file_data(file_name):
     try:
-        with open(PISA_PUBLIC_KEY, "r") as key_file:
-            pubkey_pem = key_file.read().encode("utf-8")
-            pisa_public_key = load_pem_public_key(pubkey_pem, backend=default_backend())
-            return pisa_public_key
+        with open(file_name, "r") as key_file:
+            key_pem = key_file.read().encode("utf-8")
+        return key_pem
+
+    except FileNotFoundError:
+        raise FileNotFoundError("File not found.")
+
+
+# Deserialize public key from pem data.
+def load_public_key(pk_pem):
+    try:
+        pisa_pk = load_pem_public_key(pk_pem, backend=default_backend())
+        return pisa_pk
 
     except UnsupportedAlgorithm:
         raise ValueError("Could not deserialize the public key (unsupported algorithm).")
 
 
-# Verifies that the appointment signature is a valid signature with public key `pk`,
+# Deserialize private key from pem data.
+def load_private_key(sk_pem):
+    try:
+        cli_sk = load_pem_private_key(sk_pem, None, backend=default_backend())
+        return cli_sk
+
+    except UnsupportedAlgorithm:
+        raise ValueError("Could not deserialize the private key (unsupported algorithm).")
+
+
 # returning True or False accordingly.
 def is_appointment_signature_valid(appointment, signature, pk):
     try:
@@ -143,7 +171,38 @@ def add_appointment(args):
         appointment_data.get("end_time"),
         appointment_data.get("dispute_delta"),
     )
-    appointment_json = json.dumps(appointment, sort_keys=True, separators=(",", ":"))
+
+    try:
+        sk_pem = load_key_file_data(CLI_PRIVATE_KEY)
+        cli_sk = load_private_key(sk_pem)
+
+    except ValueError:
+        logger.error("Failed to deserialize the public key. It might be in an unsupported format.")
+        return False
+
+    except FileNotFoundError:
+        logger.error("Client's private key file not found. Please check your settings.")
+        return False
+
+    except IOError as e:
+        logger.error("I/O error({}): {}".format(e.errno, e.strerror))
+        return False
+
+    signature = sign_appointment(cli_sk, appointment)
+    try:
+        cli_pk_pem = load_key_file_data(CLI_PUBLIC_KEY)
+
+    except FileNotFoundError:
+        logger.error("Client's private key file not found. Please check your settings.")
+        return False
+
+    except IOError as e:
+        logger.error("I/O error({}): {}".format(e.errno, e.strerror))
+        return False
+
+    data = {"appointment": appointment, "signature": signature, "public_key": cli_pk_pem.decode("utf-8")}
+
+    appointment_json = json.dumps(data, sort_keys=True, separators=(",", ":"))
 
     logger.info("Sending appointment to PISA")
 
@@ -181,7 +240,8 @@ def add_appointment(args):
     signature = response_json["signature"]
     # verify that the returned signature is valid
     try:
-        pk = load_pisa_public_key()
+        pk_pem = load_key_file_data(PISA_PUBLIC_KEY)
+        pk = load_public_key(pk_pem)
         is_sig_valid = is_appointment_signature_valid(appointment, signature, pk)
 
     except ValueError:
diff --git a/pisa/api.py b/pisa/api.py
index 562386f..29a33e4 100644
--- a/pisa/api.py
+++ b/pisa/api.py
@@ -32,7 +32,9 @@ def add_appointment():
     # Check content type once if properly defined
     request_data = json.loads(request.get_json())
     inspector = Inspector()
-    appointment = inspector.inspect(request_data)
+    appointment = inspector.inspect(
+        request_data.get("appointment"), request_data.get("signature"), request_data.get("public_key")
+    )
 
     error = None
     response = None
diff --git a/pisa/errors.py b/pisa/errors.py
index ad2baf4..275e097 100644
--- a/pisa/errors.py
+++ b/pisa/errors.py
@@ -8,6 +8,7 @@ APPOINTMENT_FIELD_TOO_BIG = -6
 APPOINTMENT_WRONG_FIELD = -7
 APPOINTMENT_CIPHER_NOT_SUPPORTED = -8
 APPOINTMENT_HASH_FUNCTION_NOT_SUPPORTED = -9
+APPOINTMENT_INVALID_SIGNATURE = -10
 
 # Custom RPC errors
 RPC_TX_REORGED_AFTER_BROADCAST = -98
diff --git a/pisa/inspector.py b/pisa/inspector.py
index 68ac698..4d20503 100644
--- a/pisa/inspector.py
+++ b/pisa/inspector.py
@@ -1,4 +1,12 @@
+import json
 import re
+from binascii import unhexlify
+
+from cryptography.hazmat.backends import default_backend
+from cryptography.hazmat.primitives.asymmetric import ec
+from cryptography.hazmat.primitives import hashes
+from cryptography.hazmat.primitives.serialization import load_pem_public_key
+from cryptography.exceptions import InvalidSignature
 
 from pisa import errors
 import pisa.conf as conf
@@ -15,14 +23,14 @@ logger = Logger("Inspector")
 
 
 class Inspector:
-    def inspect(self, data):
-        locator = data.get("locator")
-        start_time = data.get("start_time")
-        end_time = data.get("end_time")
-        dispute_delta = data.get("dispute_delta")
-        encrypted_blob = data.get("encrypted_blob")
-        cipher = data.get("cipher")
-        hash_function = data.get("hash_function")
+    def inspect(self, appt, signature, public_key):
+        locator = appt.get("locator")
+        start_time = appt.get("start_time")
+        end_time = appt.get("end_time")
+        dispute_delta = appt.get("dispute_delta")
+        encrypted_blob = appt.get("encrypted_blob")
+        cipher = appt.get("cipher")
+        hash_function = appt.get("hash_function")
 
         block_height = BlockProcessor.get_block_count()
 
@@ -41,6 +49,8 @@ class Inspector:
                 rcode, message = self.check_cipher(cipher)
             if rcode == 0:
                 rcode, message = self.check_hash_function(hash_function)
+            if rcode == 0:
+                rcode, message = self.check_appointment_signature(appt, signature, public_key)
 
             if rcode == 0:
                 r = Appointment(locator, start_time, end_time, dispute_delta, encrypted_blob, cipher, hash_function)
@@ -245,3 +255,24 @@ class Inspector:
             logger.error(message)
 
         return rcode, message
+
+    @staticmethod
+    # Verifies that the appointment signature is a valid signature with public key
+    def check_appointment_signature(appointment, signature, pk_pem):
+        message = None
+        rcode = 0
+
+        if signature is None:
+            rcode = errors.APPOINTMENT_EMPTY_FIELD
+            message = "empty signature received"
+
+        try:
+            sig_bytes = unhexlify(signature.encode("utf-8"))
+            client_pk = load_pem_public_key(pk_pem.encode("utf-8"), backend=default_backend())
+            data = json.dumps(appointment, sort_keys=True, separators=(",", ":")).encode("utf-8")
+            client_pk.verify(sig_bytes, data, ec.ECDSA(hashes.SHA256()))
+
+        except InvalidSignature:
+            rcode = errors.APPOINTMENT_INVALID_SIGNATURE
+
+        return rcode, message
diff --git a/test/apps/cli/test_pisa_cli.py b/test/apps/cli/test_pisa_cli.py
index caf2e91..8390b25 100644
--- a/test/apps/cli/test_pisa_cli.py
+++ b/test/apps/cli/test_pisa_cli.py
@@ -50,7 +50,7 @@ def test_is_appointment_signature_valid():
     assert not pisa_cli.is_appointment_signature_valid(dummy_appointment, other_signature, pisa_pk)
 
 
-def get_dummy_pisa_pk():
+def get_dummy_pisa_pk(pem_data):
     return pisa_pk
 
 
@@ -60,7 +60,7 @@ def test_add_appointment(monkeypatch):
     # and the return value is True
 
     # make sure the test uses the right dummy key instead of loading it from disk
-    monkeypatch.setattr(pisa_cli, "load_pisa_public_key", get_dummy_pisa_pk)
+    monkeypatch.setattr(pisa_cli, "load_public_key", get_dummy_pisa_pk)
 
     response = {"locator": dummy_appointment["locator"], "signature": sign_appointment(pisa_sk, dummy_appointment)}
 
@@ -81,7 +81,7 @@ def test_add_appointment_with_invalid_signature(monkeypatch):
     # make sure that the right endpoint is requested, but the return value is False
 
     # make sure the test uses the right dummy key instead of loading it from disk
-    monkeypatch.setattr(pisa_cli, "load_pisa_public_key", get_dummy_pisa_pk)
+    monkeypatch.setattr(pisa_cli, "load_public_key", get_dummy_pisa_pk)
 
     response = {
         "locator": dummy_appointment["locator"],
diff --git a/test/unit/conftest.py b/test/unit/conftest.py
index 4f27d60..2027673 100644
--- a/test/unit/conftest.py
+++ b/test/unit/conftest.py
@@ -1,3 +1,4 @@
+import json
 import pytest
 import random
 import requests
@@ -5,7 +6,12 @@ from time import sleep
 from shutil import rmtree
 from threading import Thread
 from hashlib import sha256
-from binascii import unhexlify
+from binascii import hexlify, unhexlify
+
+from cryptography.hazmat.backends import default_backend
+from cryptography.hazmat.primitives import hashes
+from cryptography.hazmat.primitives.asymmetric import ec
+from cryptography.hazmat.primitives import serialization
 
 from pisa.conf import DB_PATH
 from apps.cli.blob import Blob
@@ -48,6 +54,18 @@ def prng_seed():
     random.seed(0)
 
 
+@pytest.fixture(scope="module")
+def generate_keypair():
+    client_sk = ec.generate_private_key(ec.SECP256K1, default_backend())
+    client_pk = (
+        client_sk.public_key()
+        .public_bytes(encoding=serialization.Encoding.PEM, format=serialization.PublicFormat.SubjectPublicKeyInfo)
+        .decode("utf-8")
+    )
+
+    return client_sk, client_pk
+
+
 @pytest.fixture(scope="module")
 def db_manager():
     manager = DBManager("test_db")
@@ -73,6 +91,11 @@ def generate_blocks(n):
         generate_block()
 
 
+def sign_appointment(sk, appointment):
+    data = json.dumps(appointment, sort_keys=True, separators=(",", ":")).encode("utf-8")
+    return hexlify(sk.sign(data, ec.ECDSA(hashes.SHA256()))).decode("utf-8")
+
+
 def generate_dummy_appointment_data(start_time_offset=5, end_time_offset=30):
     current_height = bitcoin_cli().getblockcount()
 
@@ -91,6 +114,14 @@ def generate_dummy_appointment_data(start_time_offset=5, end_time_offset=30):
     cipher = "AES-GCM-128"
     hash_function = "SHA256"
 
+    # dummy keys for this test
+    client_sk = ec.generate_private_key(ec.SECP256K1, default_backend())
+    client_pk = (
+        client_sk.public_key()
+        .public_bytes(encoding=serialization.Encoding.PEM, format=serialization.PublicFormat.SubjectPublicKeyInfo)
+        .decode("utf-8")
+    )
+
     locator = sha256(unhexlify(dispute_txid)).hexdigest()
     blob = Blob(dummy_appointment_data.get("tx"), cipher, hash_function)
 
@@ -107,7 +138,11 @@ def generate_dummy_appointment_data(start_time_offset=5, end_time_offset=30):
         "triggered": False,
     }
 
-    return appointment_data, dispute_tx
+    signature = sign_appointment(client_sk, appointment_data)
+
+    data = {"appointment": appointment_data, "signature": signature, "public_key": client_pk}
+
+    return data, dispute_tx
 
 
 def generate_dummy_appointment(start_time_offset=5, end_time_offset=30):
@@ -115,7 +150,7 @@ def generate_dummy_appointment(start_time_offset=5, end_time_offset=30):
         start_time_offset=start_time_offset, end_time_offset=end_time_offset
     )
 
-    return Appointment.from_dict(appointment_data), dispute_tx
+    return Appointment.from_dict(appointment_data["appointment"]), dispute_tx
 
 
 def generate_dummy_job():
diff --git a/test/unit/test_api.py b/test/unit/test_api.py
index 14c0c3f..32e4724 100644
--- a/test/unit/test_api.py
+++ b/test/unit/test_api.py
@@ -17,40 +17,40 @@ locator_dispute_tx_map = {}
 
 
 @pytest.fixture
-def new_appointment():
-    appointment, dispute_tx = generate_dummy_appointment_data()
-    locator_dispute_tx_map[appointment["locator"]] = dispute_tx
+def new_appt_data():
+    appt_data, dispute_tx = generate_dummy_appointment_data()
+    locator_dispute_tx_map[appt_data["appointment"]["locator"]] = dispute_tx
 
-    return appointment
+    return appt_data
 
 
-def add_appointment(appointment):
-    r = requests.post(url=PISA_API, json=json.dumps(appointment), timeout=5)
+def add_appointment(new_appt_data):
+    r = requests.post(url=PISA_API, json=json.dumps(new_appt_data), timeout=5)
 
     if r.status_code == 200:
-        appointments.append(appointment)
+        appointments.append(new_appt_data["appointment"])
 
     return r
 
 
-def test_add_appointment(run_api, run_bitcoind, new_appointment):
+def test_add_appointment(run_api, run_bitcoind, new_appt_data):
     # Properly formatted appointment
-    r = add_appointment(new_appointment)
+    r = add_appointment(new_appt_data)
     assert r.status_code == 200
 
     # Incorrect appointment
-    new_appointment["dispute_delta"] = 0
-    r = add_appointment(new_appointment)
+    new_appt_data["appointment"]["dispute_delta"] = 0
+    r = add_appointment(new_appt_data)
     assert r.status_code == 400
 
 
-def test_request_appointment(new_appointment):
+def test_request_appointment(new_appt_data):
     # First we need to add an appointment
-    r = add_appointment(new_appointment)
+    r = add_appointment(new_appt_data)
     assert r.status_code == 200
 
     # Next we can request it
-    r = requests.get(url=PISA_API + "/get_appointment?locator=" + new_appointment["locator"])
+    r = requests.get(url=PISA_API + "/get_appointment?locator=" + new_appt_data["appointment"]["locator"])
     assert r.status_code == 200
 
     # Each locator may point to multiple appointments, check them all
@@ -60,7 +60,7 @@ def test_request_appointment(new_appointment):
     appointment_status = [appointment.pop("status") for appointment in received_appointments]
 
     # Check that the appointment is within the received appoints
-    assert new_appointment in received_appointments
+    assert new_appt_data["appointment"] in received_appointments
 
     # Check that all the appointments are being watched
     assert all([status == "being_watched" for status in appointment_status])
@@ -76,28 +76,28 @@ def test_request_random_appointment():
     assert all([status == "not_found" for status in appointment_status])
 
 
-def test_add_appointment_multiple_times(new_appointment, n=MULTIPLE_APPOINTMENTS):
+def test_add_appointment_multiple_times(new_appt_data, n=MULTIPLE_APPOINTMENTS):
     # Multiple appointments with the same locator should be valid
     # DISCUSS: #34-store-identical-appointments
     for _ in range(n):
-        r = add_appointment(new_appointment)
+        r = add_appointment(new_appt_data)
         assert r.status_code == 200
 
 
-def test_request_multiple_appointments_same_locator(new_appointment, n=MULTIPLE_APPOINTMENTS):
+def test_request_multiple_appointments_same_locator(new_appt_data, n=MULTIPLE_APPOINTMENTS):
     for _ in range(n):
-        r = add_appointment(new_appointment)
+        r = add_appointment(new_appt_data)
         assert r.status_code == 200
 
-    test_request_appointment(new_appointment)
+    test_request_appointment(new_appt_data)
 
 
-def test_add_too_many_appointment(new_appointment):
+def test_add_too_many_appointment(new_appt_data):
     for _ in range(MAX_APPOINTMENTS - len(appointments)):
-        r = add_appointment(new_appointment)
+        r = add_appointment(new_appt_data)
         assert r.status_code == 200
 
-    r = add_appointment(new_appointment)
+    r = add_appointment(new_appt_data)
     assert r.status_code == 503
 
 
diff --git a/test/unit/test_inspector.py b/test/unit/test_inspector.py
index 30b272d..297642c 100644
--- a/test/unit/test_inspector.py
+++ b/test/unit/test_inspector.py
@@ -1,11 +1,18 @@
-from binascii import unhexlify
+import json
+from binascii import hexlify, unhexlify
 
+from cryptography.hazmat.backends import default_backend
+from cryptography.hazmat.primitives import hashes
+from cryptography.hazmat.primitives.asymmetric import ec
+
+from apps.cli.pisa_cli import build_appointment
 from pisa import c_logger
 from pisa.errors import *
 from pisa.inspector import Inspector
 from pisa.appointment import Appointment
 from pisa.block_processor import BlockProcessor
 from test.unit.conftest import get_random_value_hex
+
 from pisa.conf import MIN_DISPUTE_DELTA, SUPPORTED_CIPHERS, SUPPORTED_HASH_FUNCTIONS
 
 c_logger.disabled = True
@@ -18,6 +25,11 @@ WRONG_TYPES = [[], "", get_random_value_hex(32), 3.2, 2.0, (), object, {}, " " *
 WRONG_TYPES_NO_STR = [[], unhexlify(get_random_value_hex(32)), 3.2, 2.0, (), object, {}, object()]
 
 
+def sign_appointment(sk, appointment):
+    data = json.dumps(appointment, sort_keys=True, separators=(",", ":")).encode("utf-8")
+    return hexlify(sk.sign(data, ec.ECDSA(hashes.SHA256()))).decode("utf-8")
+
+
 def test_check_locator():
     # Right appointment type, size and format
     locator = get_random_value_hex(32)
@@ -189,13 +201,42 @@ def test_check_hash_function():
     assert Inspector.check_hash_function(hash_function)[0] == APPOINTMENT_EMPTY_FIELD
 
 
-def test_inspect(run_bitcoind):
+def test_check_appointment_signature(generate_keypair):
+    client_sk, client_pk = generate_keypair
+
+    dummy_appointment_request = {
+        "tx": get_random_value_hex(192),
+        "tx_id": get_random_value_hex(32),
+        "start_time": 1500,
+        "end_time": 50000,
+        "dispute_delta": 200,
+    }
+    dummy_appointment = build_appointment(**dummy_appointment_request)
+
+    # Verify that an appointment signed by the client is valid
+    signature = sign_appointment(client_sk, dummy_appointment)
+    assert Inspector.check_appointment_signature(dummy_appointment, signature, client_pk)
+
+    fake_sk = ec.generate_private_key(ec.SECP256K1, default_backend())
+
+    # Create a bad signature to make sure inspector rejects it
+    bad_signature = sign_appointment(fake_sk, dummy_appointment)
+    assert (
+        Inspector.check_appointment_signature(dummy_appointment, bad_signature, client_pk)[0]
+        == APPOINTMENT_INVALID_SIGNATURE
+    )
+
+
+def test_inspect(run_bitcoind, generate_keypair):
     # At this point every single check function has been already tested, let's test inspect with an invalid and a valid
     # appointments.
 
+    client_sk, client_pk = generate_keypair
+
     # Invalid appointment, every field is empty
     appointment_data = dict()
-    appointment = inspector.inspect(appointment_data)
+    signature = sign_appointment(client_sk, appointment_data)
+    appointment = inspector.inspect(appointment_data, signature, client_pk)
     assert type(appointment) == tuple and appointment[0] != 0
 
     # Valid appointment
@@ -217,7 +258,9 @@ def test_inspect(run_bitcoind):
         "hash_function": hash_function,
     }
 
-    appointment = inspector.inspect(appointment_data)
+    signature = sign_appointment(client_sk, appointment_data)
+
+    appointment = inspector.inspect(appointment_data, signature, client_pk)
 
     assert (
         type(appointment) == Appointment