Remove ability to use configurations without TLS by default

OpenVPN 2.6 already warned about this feature being removed. OpenVPN 2.7 will with this change no longer accept these configurations without having a --allow-deprecated-insecure-static-crypto added to the command line or the configuration itself. This will serve as a last and final warning for people who missed the warning message in OpenVPN 2.6. This commit also removes the documentation for --secret and the static key mode. Change-Id: I4f29953b91cf8e8daf2c9503da44073ad96d0ff5 Signed-off-by: Arne Schwabe <[email protected]> Acked-by: Frank Lichtenheld <[email protected]> Message-Id: <[email protected]> URL: https://www.mail-archive.com/[email protected]/msg27194.html Signed-off-by: Gert Doering <[email protected]>
OpenVPN · Oct 13, 2023 · 392da5b · 392da5b
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diff --git a/Changes.rst b/Changes.rst
@@ -1,3 +1,15 @@
+Overview of changes in 2.7
+==========================
+``secret`` support has been removed by default.
+    static key mode (non-TLS) is no longer considered "good and secure enough"
+    for today's requirements.  Use TLS mode instead.  If deploying a PKI CA
+    is considered "too complicated", using ``--peer-fingerprint`` makes
+    TLS mode about as easy as using ``--secret``.
+
+    This mode can still be enabled by using
+    ``--allow-deprecated-insecure-static-crypto`` but will be removed in
+    OpenVPN 2.8.
+
 Overview of changes in 2.6
 ==========================
 

diff --git a/doc/man-sections/encryption-options.rst b/doc/man-sections/encryption-options.rst
@@ -69,20 +69,20 @@ Generating key material
      $ openvpn --tls-crypt-v2 v2crypt-server.key --genkey tls-crypt-v2-client v2crypt-client-1.key
 
   * Generating *Shared Secret Keys*
-    Generate a shared secret, for use with the ``--secret``, ``--tls-auth``
+    Generate a shared secret, for use with the ``--tls-auth``
     or ``--tls-crypt`` options.
 
     Syntax:
     ::
 
-       $ openvpn --genkey secret|tls-crypt|tls-auth keyfile
+       $ openvpn --genkey tls-crypt|tls-auth keyfile
 
-    The key is saved in ``keyfile``. All three variants (``--secret``,
-    ``tls-crypt`` and ``tls-auth``) generate the same type of key. The
-    aliases are added for convenience.
+    The key is saved in ``keyfile``. Both variants (``tls-crypt`` and
+    ``tls-auth``) generate the same type of key. The aliases are added for
+    convenience.
 
-    If using this for ``--secret``, this file must be shared with the peer
-    over a pre-existing secure channel such as ``scp``\(1).
+    This file must be shared with the peer over a pre-existing secure
+    channel such as ``scp``\(1).
 
   * Generating *TLS Crypt v2 Server key*
     Generate a ``--tls-crypt-v2`` key to be used by an OpenVPN server.

diff --git a/doc/man-sections/inline-files.rst b/doc/man-sections/inline-files.rst
@@ -3,7 +3,7 @@ INLINE FILE SUPPORT
 
 OpenVPN allows including files in the main configuration for the ``--ca``,
 ``--cert``, ``--dh``, ``--extra-certs``, ``--key``, ``--pkcs12``,
-``--secret``, ``--crl-verify``, ``--http-proxy-user-pass``, ``--tls-auth``,
+``--crl-verify``, ``--http-proxy-user-pass``, ``--tls-auth``,
 ``--auth-gen-token-secret``, ``--peer-fingerprint``, ``--tls-crypt``,
 ``--tls-crypt-v2`` and ``--verify-hash`` options.
 

diff --git a/doc/man-sections/link-options.rst b/doc/man-sections/link-options.rst
@@ -226,10 +226,7 @@ the local and the remote host.
   Ping remote over the TCP/UDP control channel if no packets have been
   sent for at least ``n`` seconds (specify ``--ping`` on both peers to
   cause ping packets to be sent in both directions since OpenVPN ping
-  packets are not echoed like IP ping packets). When used in one of
-  OpenVPN's secure modes (where ``--secret``, ``--tls-server`` or
-  ``--tls-client`` is specified), the ping packet will be
-  cryptographically secure.
+  packets are not echoed like IP ping packets).
 
   This option has two intended uses:
 
@@ -427,8 +424,7 @@ the local and the remote host.
   received by the prior session.
 
   This option only makes sense when replay protection is enabled (the
-  default) and you are using either ``--secret`` (shared-secret key mode)
-  or TLS mode with ``--tls-auth``.
+  default) and you are using TLS mode with ``--tls-auth``.
 
 --session-timeout n
   Raises :code:`SIGTERM` for the client instance after ``n`` seconds since

diff --git a/doc/man-sections/protocol-options.rst b/doc/man-sections/protocol-options.rst
@@ -73,9 +73,7 @@ configured in a compatible way between both the local and remote side.
   configured on the data channel, however, later versions usually
   ignored this directive in favour of a negotiated cipher.
   Starting with 2.6.0, this option is always ignored in TLS mode
-  when it comes to configuring the cipher and will only control the
-  cipher for ``--secret`` pre-shared-key mode (note: this mode is
-  deprecated and strictly not recommended).
+  when it comes to configuring the cipher.
 
   If you wish to specify the cipher to use on the data channel,
   please see ``--data-ciphers`` (for regular negotiation) and
@@ -182,7 +180,7 @@ configured in a compatible way between both the local and remote side.
 
 --key-direction
   Alternative way of specifying the optional direction parameter for the
-  ``--tls-auth`` and ``--secret`` options. Useful when using inline files
+  ``--tls-auth`` option. Useful when using inline files
   (See section on inline files).
 
 --data-ciphers cipher-list
@@ -234,54 +232,10 @@ configured in a compatible way between both the local and remote side.
   have been configured with ``--enable-small``
   (typically used on routers or other embedded devices).
 
---secret args
-  **DEPRECATED** Enable Static Key encryption mode (non-TLS). Use pre-shared secret
-  ``file`` which was generated with ``--genkey``.
 
-  Valid syntaxes:
-  ::
-
-     secret file
-     secret file direction
-
-  The optional ``direction`` parameter enables the use of 4 distinct keys
-  (HMAC-send, cipher-encrypt, HMAC-receive, cipher-decrypt), so that each
-  data flow direction has a different set of HMAC and cipher keys. This
-  has a number of desirable security properties including eliminating
-  certain kinds of DoS and message replay attacks.
-
-  When the ``direction`` parameter is omitted, 2 keys are used
-  bidirectionally, one for HMAC and the other for encryption/decryption.
-
-  The ``direction`` parameter should always be complementary on either
-  side of the connection, i.e. one side should use :code:`0` and the other
-  should use :code:`1`, or both sides should omit it altogether.
-
-  The ``direction`` parameter requires that ``file`` contains a 2048 bit
-  key. While pre-1.5 versions of OpenVPN generate 1024 bit key files, any
-  version of OpenVPN which supports the ``direction`` parameter, will also
-  support 2048 bit key file generation using the ``--genkey`` option.
-
-  Static key encryption mode has certain advantages, the primary being
-  ease of configuration.
-
-  There are no certificates or certificate authorities or complicated
-  negotiation handshakes and protocols. The only requirement is that you
-  have a pre-existing secure channel with your peer (such as ``ssh``) to
-  initially copy the key. This requirement, along with the fact that your
-  key never changes unless you manually generate a new one, makes it
-  somewhat less secure than TLS mode (see below). If an attacker manages
-  to steal your key, everything that was ever encrypted with it is
-  compromised. Contrast that to the perfect forward secrecy features of
-  TLS mode (using Diffie Hellman key exchange), where even if an attacker
-  was able to steal your private key, he would gain no information to help
-  him decrypt past sessions.
-
-  Another advantageous aspect of Static Key encryption mode is that it is
-  a handshake-free protocol without any distinguishing signature or
-  feature (such as a header or protocol handshake sequence) that would
-  mark the ciphertext packets as being generated by OpenVPN. Anyone
-  eavesdropping on the wire would see nothing but random-looking data.
+--allow-deprecated-insecure-static-crypto
+   **DEPRECATED** This allow using OpenVPN without TLS. This is deprecated
+   and will be removed in OpenVPN 2.8.
 
 --tran-window n
   Transition window -- our old key can live this many seconds after a new

diff --git a/doc/man-sections/server-options.rst b/doc/man-sections/server-options.rst
@@ -406,7 +406,7 @@ fast hardware. SSL/TLS authentication must be used in this mode.
   Options that will be compared for compatibility include ``dev-type``,
   ``link-mtu``, ``tun-mtu``, ``proto``, ``ifconfig``,
   ``comp-lzo``, ``fragment``, ``keydir``, ``cipher``,
-  ``auth``, ``keysize``, ``secret``,
+  ``auth``, ``keysize``,
   ``tls-auth``, ``key-method``, ``tls-server``
   and ``tls-client``.
 

diff --git a/doc/man-sections/tls-options.rst b/doc/man-sections/tls-options.rst
@@ -295,8 +295,24 @@ certificates and keys: https://github.com/OpenVPN/easy-rsa
   Older versions (up to OpenVPN 2.3) supported a freeform passphrase file.
   This is no longer supported in newer versions (v2.4+).
 
-  See the ``--secret`` option for more information on the optional
-  ``direction`` parameter.
+  The optional ``direction`` parameter enables the use of 2 distinct keys
+  (HMAC-send, HMAC-receive), so that each
+  data flow direction has a different HMAC key. This has a number of desirable
+  security properties including eliminating certain kinds of DoS and message
+  replay attacks.
+
+  When the ``direction`` parameter is omitted, the same key is used
+  bidirectionally.
+
+  The ``direction`` parameter should always be complementary on either
+  side of the connection, i.e. one side should use :code:`0` and the other
+  should use :code:`1`, or both sides should omit it altogether.
+
+  The ``direction`` parameter requires that ``file`` contains a 2048 bit
+  key. While pre-1.5 versions of OpenVPN generate 1024 bit key files, any
+  version of OpenVPN which supports the ``direction`` parameter, will also
+  support 2048 bit key file generation using the ``--genkey`` option.
+
 
   ``--tls-auth`` is recommended when you are running OpenVPN in a mode
   where it is listening for packets from any IP address, such as when

diff --git a/src/openvpn/options.c b/src/openvpn/options.c
@@ -531,12 +531,6 @@ static const char usage_message[] =
     "\n"
     "Data Channel Encryption Options (must be compatible between peers):\n"
     "(These options are meaningful for both Static Key & TLS-mode)\n"
-    "--secret f [d]  : (DEPRECATED) Enable Static Key encryption mode (non-TLS).\n"
-    "                  Use shared secret file f, generate with --genkey.\n"
-    "                  The optional d parameter controls key directionality.\n"
-    "                  If d is specified, use separate keys for each\n"
-    "                  direction, set d=0 on one side of the connection,\n"
-    "                  and d=1 on the other side.\n"
     "--auth alg      : Authenticate packets with HMAC using message\n"
     "                  digest algorithm alg (default=%s).\n"
     "                  (usually adds 16 or 20 bytes per packet)\n"
@@ -619,14 +613,12 @@ static const char usage_message[] =
     "                  control channel to protect against attacks on the TLS stack\n"
     "                  and DoS attacks.\n"
     "                  f (required) is a shared-secret key file.\n"
-    "                  The optional d parameter controls key directionality,\n"
-    "                  see --secret option for more info.\n"
+    "                  The optional d parameter controls key directionality.\n"
     "--tls-crypt key : Add an additional layer of authenticated encryption on top\n"
     "                  of the TLS control channel to hide the TLS certificate,\n"
     "                  provide basic post-quantum security and protect against\n"
     "                  attacks on the TLS stack and DoS attacks.\n"
     "                  key (required) provides the pre-shared key file.\n"
-    "                  see --secret option for more info.\n"
     "--tls-crypt-v2 key : For clients: use key as a client-specific tls-crypt key.\n"
     "                  For servers: use key to decrypt client-specific keys.  For\n"
     "                  key generation (--genkey tls-crypt-v2-client): use key to\n"
@@ -759,8 +751,8 @@ static const char usage_message[] =
 #endif /* ifdef _WIN32 */
     "\n"
     "Generate a new key :\n"
-    "--genkey secret file   : Generate a new random key of type and write to file\n"
-    "                         (for use with --secret, --tls-auth or --tls-crypt)."
+    "--genkey tls-auth file   : Generate a new random key of type and write to file\n"
+    "                         (for use with --tls-auth or --tls-crypt)."
 #ifdef ENABLE_FEATURE_TUN_PERSIST
     "\n"
     "Tun/tap config mode (available with linux 2.4+):\n"
@@ -2823,11 +2815,21 @@ options_postprocess_verify_ce(const struct options *options,
 
     if (!options->tls_server && !options->tls_client)
     {
-        msg(M_INFO, "DEPRECATION: No tls-client or tls-server option in "
-            "configuration detected. OpenVPN 2.7 will remove the "
+        int msglevel = M_USAGE;
+        if (options->allow_deprecated_insecure_static_crypto)
+        {
+            msglevel = M_INFO;
+        }
+
+        msg(msglevel, "DEPRECATION: No tls-client or tls-server option in "
+            "configuration detected. OpenVPN 2.8 will remove the "
             "functionality to run a VPN without TLS. "
             "See the examples section in the manual page for "
-            "examples of a similar quick setup with peer-fingerprint.");
+            "examples of a similar quick setup with peer-fingerprint."
+            "OpenVPN 2.7 allows using this configuration when using "
+            "--allow-deprecated-insecure-static-crypto but you should move"
+            "to a proper configuration using TLS as soon as possible."
+            );
     }
 
     if (options->ssl_flags & (SSLF_CLIENT_CERT_NOT_REQUIRED|SSLF_CLIENT_CERT_OPTIONAL))
@@ -8515,6 +8517,12 @@ add_option(struct options *options,
             }
         }
     }
+    else if (streq(p[0], "allow-deprecated-insecure-static-crypto"))
+    {
+        VERIFY_PERMISSION(OPT_P_GENERAL);
+        options->allow_deprecated_insecure_static_crypto = true;
+
+    }
     else if (streq(p[0], "genkey") && !p[4])
     {
         VERIFY_PERMISSION(OPT_P_GENERAL);

diff --git a/src/openvpn/options.h b/src/openvpn/options.h
@@ -552,6 +552,7 @@ struct options
     /* Cipher parms */
     const char *shared_secret_file;
     bool shared_secret_file_inline;
+    bool allow_deprecated_insecure_static_crypto;
     int key_direction;
     const char *ciphername;
     bool enable_ncp_fallback;      /**< If defined fall back to

diff --git a/tests/t_lpback.sh b/tests/t_lpback.sh
@@ -97,7 +97,7 @@ set +e
 for cipher in ${CIPHERS}
 do
     test_start "Testing cipher ${cipher}... "
-    ( "${openvpn}" --test-crypto --secret key.$$ --cipher ${cipher} ) >log.$$ 2>&1
+    ( "${openvpn}" --test-crypto --secret key.$$  --allow-deprecated-insecure-static-crypto --cipher ${cipher} ) >log.$$ 2>&1
     test_end $? log.$$
 done