Make it possible to customize SSL ciphers (#3212) (#3214)

Given that Python 3.10 changed the default list of TLS ciphers, it is a
good idea to allow customization of the list of ciphers when using
Redis with TLS. In some situations the client is unusable right now
with older servers and Python >= 3.10.

redis/asyncio/client.py

@@ -226,6 +226,7 @@ def __init__(
         ssl_ca_data: Optional[str] = None,
         ssl_check_hostname: bool = False,
         ssl_min_version: Optional[ssl.TLSVersion] = None,
+        ssl_ciphers: Optional[str] = None,
         max_connections: Optional[int] = None,
         single_connection_client: bool = False,
         health_check_interval: int = 0,
@@ -333,6 +334,7 @@ def __init__(
                             "ssl_ca_data": ssl_ca_data,
                             "ssl_check_hostname": ssl_check_hostname,
                             "ssl_min_version": ssl_min_version,
+                            "ssl_ciphers": ssl_ciphers,
                         }
                     )
             # This arg only used if no pool is passed in

redis/asyncio/cluster.py

@@ -273,6 +273,7 @@ def __init__(
         ssl_check_hostname: bool = False,
         ssl_keyfile: Optional[str] = None,
         ssl_min_version: Optional[ssl.TLSVersion] = None,
+        ssl_ciphers: Optional[str] = None,
         protocol: Optional[int] = 2,
         address_remap: Optional[Callable[[str, int], Tuple[str, int]]] = None,
         cache_enabled: bool = False,
@@ -347,6 +348,7 @@ def __init__(
                     "ssl_check_hostname": ssl_check_hostname,
                     "ssl_keyfile": ssl_keyfile,
                     "ssl_min_version": ssl_min_version,
+                    "ssl_ciphers": ssl_ciphers,
                 }
             )
 

redis/asyncio/connection.py

@@ -836,6 +836,7 @@ def __init__(
         ssl_ca_data: Optional[str] = None,
         ssl_check_hostname: bool = False,
         ssl_min_version: Optional[ssl.TLSVersion] = None,
+        ssl_ciphers: Optional[str] = None,
         **kwargs,
     ):
         self.ssl_context: RedisSSLContext = RedisSSLContext(
@@ -846,6 +847,7 @@ def __init__(
             ca_data=ssl_ca_data,
             check_hostname=ssl_check_hostname,
             min_version=ssl_min_version,
+            ciphers=ssl_ciphers,
         )
         super().__init__(**kwargs)
 
@@ -893,6 +895,7 @@ class RedisSSLContext:
         "context",
         "check_hostname",
         "min_version",
+        "ciphers",
     )
 
     def __init__(
@@ -904,6 +907,7 @@ def __init__(
         ca_data: Optional[str] = None,
         check_hostname: bool = False,
         min_version: Optional[ssl.TLSVersion] = None,
+        ciphers: Optional[str] = None,
     ):
         self.keyfile = keyfile
         self.certfile = certfile
@@ -924,6 +928,7 @@ def __init__(
         self.ca_data = ca_data
         self.check_hostname = check_hostname
         self.min_version = min_version
+        self.ciphers = ciphers
         self.context: Optional[ssl.SSLContext] = None
 
     def get(self) -> ssl.SSLContext:
@@ -937,6 +942,8 @@ def get(self) -> ssl.SSLContext:
                 context.load_verify_locations(cafile=self.ca_certs, cadata=self.ca_data)
             if self.min_version is not None:
                 context.minimum_version = self.min_version
+            if self.ciphers is not None:
+                context.set_ciphers(self.ciphers)
             self.context = context
         return self.context
 

redis/client.py

@@ -204,6 +204,7 @@ def __init__(
         ssl_ocsp_context=None,
         ssl_ocsp_expected_cert=None,
         ssl_min_version=None,
+        ssl_ciphers=None,
         max_connections=None,
         single_connection_client=False,
         health_check_interval=0,
@@ -318,6 +319,7 @@ def __init__(
                             "ssl_ocsp_context": ssl_ocsp_context,
                             "ssl_ocsp_expected_cert": ssl_ocsp_expected_cert,
                             "ssl_min_version": ssl_min_version,
+                            "ssl_ciphers": ssl_ciphers,
                         }
                     )
             connection_pool = ConnectionPool(**kwargs)

redis/connection.py

@@ -776,6 +776,7 @@ def __init__(
         ssl_ocsp_context=None,
         ssl_ocsp_expected_cert=None,
         ssl_min_version=None,
+        ssl_ciphers=None,
         **kwargs,
     ):
         """Constructor
@@ -795,6 +796,7 @@ def __init__(
             ssl_ocsp_context: A fully initialized OpenSSL.SSL.Context object to be used in verifying the ssl_ocsp_expected_cert
             ssl_ocsp_expected_cert: A PEM armoured string containing the expected certificate to be returned from the ocsp verification service.
             ssl_min_version: The lowest supported SSL version. It affects the supported SSL versions of the SSLContext. None leaves the default provided by ssl module.
+            ssl_ciphers: A string listing the ciphers that are allowed to be used. Defaults to None, which means that the default ciphers are used. See https://docs.python.org/3/library/ssl.html#ssl.SSLContext.set_ciphers for more information.
 
         Raises:
             RedisError
@@ -828,6 +830,7 @@ def __init__(
         self.ssl_ocsp_context = ssl_ocsp_context
         self.ssl_ocsp_expected_cert = ssl_ocsp_expected_cert
         self.ssl_min_version = ssl_min_version
+        self.ssl_ciphers = ssl_ciphers
         super().__init__(**kwargs)
 
     def _connect(self):
@@ -852,6 +855,8 @@ def _connect(self):
             )
         if self.ssl_min_version is not None:
             context.minimum_version = self.ssl_min_version
+        if self.ssl_ciphers:
+            context.set_ciphers(self.ssl_ciphers)
         sslsock = context.wrap_socket(sock, server_hostname=self.host)
         if self.ssl_validate_ocsp is True and CRYPTOGRAPHY_AVAILABLE is False:
             raise RedisError("cryptography is not installed.")

tests/test_asyncio/test_cluster.py

@@ -1,6 +1,7 @@
 import asyncio
 import binascii
 import datetime
+import ssl
 import warnings
 from typing import Any, Awaitable, Callable, Dict, List, Optional, Type, Union
 from urllib.parse import urlparse
@@ -2961,6 +2962,59 @@ async def test_ssl_connection(
         async with await create_client(ssl=True, ssl_cert_reqs="none") as rc:
             assert await rc.ping()
 
+    @pytest.mark.parametrize(
+        "ssl_ciphers",
+        [
+            "AES256-SHA:DHE-RSA-AES256-SHA:AES128-SHA:DHE-RSA-AES128-SHA",
+            "ECDHE-ECDSA-AES256-GCM-SHA384",
+            "ECDHE-RSA-AES128-GCM-SHA256",
+        ],
+    )
+    async def test_ssl_connection_tls12_custom_ciphers(
+        self, ssl_ciphers, create_client: Callable[..., Awaitable[RedisCluster]]
+    ) -> None:
+        async with await create_client(
+            ssl=True,
+            ssl_cert_reqs="none",
+            ssl_min_version=ssl.TLSVersion.TLSv1_2,
+            ssl_ciphers=ssl_ciphers,
+        ) as rc:
+            assert await rc.ping()
+
+    async def test_ssl_connection_tls12_custom_ciphers_invalid(
+        self, create_client: Callable[..., Awaitable[RedisCluster]]
+    ) -> None:
+        async with await create_client(
+            ssl=True,
+            ssl_cert_reqs="none",
+            ssl_min_version=ssl.TLSVersion.TLSv1_2,
+            ssl_ciphers="foo:bar",
+        ) as rc:
+            with pytest.raises(RedisClusterException) as e:
+                assert await rc.ping()
+            assert "Redis Cluster cannot be connected" in str(e.value)
+
+    @pytest.mark.parametrize(
+        "ssl_ciphers",
+        [
+            "TLS_CHACHA20_POLY1305_SHA256",
+            "TLS_AES_256_GCM_SHA384:TLS_CHACHA20_POLY1305_SHA256",
+        ],
+    )
+    async def test_ssl_connection_tls13_custom_ciphers(
+        self, ssl_ciphers, create_client: Callable[..., Awaitable[RedisCluster]]
+    ) -> None:
+        # TLSv1.3 does not support changing the ciphers
+        async with await create_client(
+            ssl=True,
+            ssl_cert_reqs="none",
+            ssl_min_version=ssl.TLSVersion.TLSv1_2,
+            ssl_ciphers=ssl_ciphers,
+        ) as rc:
+            with pytest.raises(RedisClusterException) as e:
+                assert await rc.ping()
+            assert "Redis Cluster cannot be connected" in str(e.value)
+
     async def test_validating_self_signed_certificate(
         self, create_client: Callable[..., Awaitable[RedisCluster]]
     ) -> None:

tests/test_asyncio/test_connect.py

@@ -50,6 +50,32 @@ async def test_uds_connect(uds_address):
     await _assert_connect(conn, path)
 
 
+@pytest.mark.ssl
+@pytest.mark.parametrize(
+    "ssl_ciphers",
+    [
+        "AES256-SHA:DHE-RSA-AES256-SHA:AES128-SHA:DHE-RSA-AES128-SHA",
+        "ECDHE-ECDSA-AES256-GCM-SHA384",
+        "ECDHE-RSA-AES128-GCM-SHA256",
+    ],
+)
+async def test_tcp_ssl_tls12_custom_ciphers(tcp_address, ssl_ciphers):
+    host, port = tcp_address
+    certfile = get_ssl_filename("server-cert.pem")
+    keyfile = get_ssl_filename("server-key.pem")
+    conn = SSLConnection(
+        host=host,
+        port=port,
+        client_name=_CLIENT_NAME,
+        ssl_ca_certs=certfile,
+        socket_timeout=10,
+        ssl_min_version=ssl.TLSVersion.TLSv1_2,
+        ssl_ciphers=ssl_ciphers,
+    )
+    await _assert_connect(conn, tcp_address, certfile=certfile, keyfile=keyfile)
+    await conn.disconnect()
+
+
 @pytest.mark.ssl
 @pytest.mark.parametrize(
     "ssl_min_version",

tests/test_connect.py

@@ -71,6 +71,31 @@ def test_tcp_ssl_connect(tcp_address, ssl_min_version):
     _assert_connect(conn, tcp_address, certfile=certfile, keyfile=keyfile)
 
 
+@pytest.mark.ssl
+@pytest.mark.parametrize(
+    "ssl_ciphers",
+    [
+        "AES256-SHA:DHE-RSA-AES256-SHA:AES128-SHA:DHE-RSA-AES128-SHA",
+        "ECDHE-ECDSA-AES256-GCM-SHA384",
+        "ECDHE-RSA-AES128-GCM-SHA256",
+    ],
+)
+def test_tcp_ssl_tls12_custom_ciphers(tcp_address, ssl_ciphers):
+    host, port = tcp_address
+    certfile = get_ssl_filename("server-cert.pem")
+    keyfile = get_ssl_filename("server-key.pem")
+    conn = SSLConnection(
+        host=host,
+        port=port,
+        client_name=_CLIENT_NAME,
+        ssl_ca_certs=certfile,
+        socket_timeout=10,
+        ssl_min_version=ssl.TLSVersion.TLSv1_2,
+        ssl_ciphers=ssl_ciphers,
+    )
+    _assert_connect(conn, tcp_address, certfile=certfile, keyfile=keyfile)
+
+
 @pytest.mark.ssl
 @pytest.mark.skipif(not ssl.HAS_TLSv1_3, reason="requires TLSv1.3")
 def test_tcp_ssl_version_mismatch(tcp_address):

tests/test_ssl.py

@@ -78,6 +78,68 @@ def test_validating_self_signed_string_certificate(self, request):
         assert r.ping()
         r.close()
 
+    @pytest.mark.parametrize(
+        "ssl_ciphers",
+        [
+            "AES256-SHA:DHE-RSA-AES256-SHA:AES128-SHA:DHE-RSA-AES128-SHA",
+            "DHE-RSA-AES256-GCM-SHA384",
+            "ECDHE-RSA-AES256-SHA384:ECDHE-ECDSA-CHACHA20-POLY1305",
+        ],
+    )
+    def test_ssl_connection_tls12_custom_ciphers(self, request, ssl_ciphers):
+        ssl_url = request.config.option.redis_ssl_url
+        p = urlparse(ssl_url)[1].split(":")
+        r = redis.Redis(
+            host=p[0],
+            port=p[1],
+            ssl=True,
+            ssl_cert_reqs="none",
+            ssl_min_version=ssl.TLSVersion.TLSv1_3,
+            ssl_ciphers=ssl_ciphers,
+        )
+        assert r.ping()
+        r.close()
+
+    def test_ssl_connection_tls12_custom_ciphers_invalid(self, request):
+        ssl_url = request.config.option.redis_ssl_url
+        p = urlparse(ssl_url)[1].split(":")
+        r = redis.Redis(
+            host=p[0],
+            port=p[1],
+            ssl=True,
+            ssl_cert_reqs="none",
+            ssl_min_version=ssl.TLSVersion.TLSv1_2,
+            ssl_ciphers="foo:bar",
+        )
+        with pytest.raises(RedisError) as e:
+            r.ping()
+        assert "No cipher can be selected" in str(e)
+        r.close()
+
+    @pytest.mark.parametrize(
+        "ssl_ciphers",
+        [
+            "TLS_CHACHA20_POLY1305_SHA256",
+            "TLS_AES_256_GCM_SHA384:TLS_CHACHA20_POLY1305_SHA256",
+        ],
+    )
+    def test_ssl_connection_tls13_custom_ciphers(self, request, ssl_ciphers):
+        # TLSv1.3 does not support changing the ciphers
+        ssl_url = request.config.option.redis_ssl_url
+        p = urlparse(ssl_url)[1].split(":")
+        r = redis.Redis(
+            host=p[0],
+            port=p[1],
+            ssl=True,
+            ssl_cert_reqs="none",
+            ssl_min_version=ssl.TLSVersion.TLSv1_2,
+            ssl_ciphers=ssl_ciphers,
+        )
+        with pytest.raises(RedisError) as e:
+            r.ping()
+        assert "No cipher can be selected" in str(e)
+        r.close()
+
     def _create_oscp_conn(self, request):
         ssl_url = request.config.option.redis_ssl_url
         p = urlparse(ssl_url)[1].split(":")