From patchwork Tue Aug 11 22:54:12 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Arne Schwabe X-Patchwork-Id: 1376 Return-Path: Delivered-To: patchwork@openvpn.net Delivered-To: patchwork@openvpn.net Received: from director12.mail.ord1d.rsapps.net ([172.27.255.53]) by backend30.mail.ord1d.rsapps.net with LMTP id 6Hp8Km+5M1/mIgAAIUCqbw for ; Wed, 12 Aug 2020 05:42:07 -0400 Received: from proxy5.mail.iad3a.rsapps.net ([172.27.255.53]) by director12.mail.ord1d.rsapps.net with LMTP id AIBCKW+5M19zSwAAIasKDg (envelope-from ) for ; Wed, 12 Aug 2020 05:42:07 -0400 Received: from smtp25.gate.iad3a ([172.27.255.53]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) by proxy5.mail.iad3a.rsapps.net with LMTP id 8OLSIm+5M19DBgAAhn5joQ ; Wed, 12 Aug 2020 05:42:07 -0400 X-Spam-Threshold: 95 X-Spam-Score: 0 X-Spam-Flag: NO X-Virus-Scanned: OK X-Orig-To: openvpnslackdevel@openvpn.net X-Originating-Ip: [216.105.38.7] Authentication-Results: smtp25.gate.iad3a.rsapps.net; iprev=pass policy.iprev="216.105.38.7"; spf=pass smtp.mailfrom="openvpn-devel-bounces@lists.sourceforge.net" smtp.helo="lists.sourceforge.net"; dkim=fail (signature verification failed) header.d=sourceforge.net; dkim=fail (signature verification failed) header.d=sf.net; dmarc=none (p=nil; dis=none) header.from=rfc2549.org X-Suspicious-Flag: YES X-Classification-ID: 15bb5784-dc80-11ea-85fe-52540086a678-1-1 Received: from [216.105.38.7] ([216.105.38.7:35648] helo=lists.sourceforge.net) by smtp25.gate.iad3a.rsapps.net (envelope-from ) (ecelerity 4.2.38.62370 r(:)) with ESMTPS (cipher=DHE-RSA-AES256-GCM-SHA384) id D2/29-31503-F69B33F5; Wed, 12 Aug 2020 05:42:07 -0400 Received: from [127.0.0.1] (helo=sfs-ml-4.v29.lw.sourceforge.com) by sfs-ml-4.v29.lw.sourceforge.com with esmtp (Exim 4.90_1) (envelope-from ) id 1k5nG2-0001c4-2V; Wed, 12 Aug 2020 09:41:18 +0000 Received: from [172.30.20.202] (helo=mx.sourceforge.net) by sfs-ml-4.v29.lw.sourceforge.com with esmtps (TLSv1.2:ECDHE-RSA-AES256-GCM-SHA384:256) (Exim 4.90_1) (envelope-from ) id 1k5nG0-0001bo-DK for openvpn-devel@lists.sourceforge.net; Wed, 12 Aug 2020 09:41:16 +0000 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=sourceforge.net; s=x; h=Message-Id:Date:Subject:To:From:Sender:Reply-To:Cc: MIME-Version:Content-Type:Content-Transfer-Encoding:Content-ID: Content-Description:Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc :Resent-Message-ID:In-Reply-To:References:List-Id:List-Help:List-Unsubscribe: List-Subscribe:List-Post:List-Owner:List-Archive; bh=A46QBg2LUe9wWK6gh+efHybGINMYmi77F2B7lrH7Ntw=; b=hPlLask2gkc/oxAX4iM8lDWnDH YQXfHPQwiJFN8RGeK0tWL6ytF+PYuz8hhvYorvJazd3uGVmjDpk/PAS3SHyqv/DPtpeJZ0yTzjMLY 0CMpkyjEKKOFVOk1EZHAAQ2oJhSvCyOsZDPQOJspaT+S6N4h7gwCI8hx5kLpk5AHtotk=; DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=sf.net; s=x ; h=Message-Id:Date:Subject:To:From:Sender:Reply-To:Cc:MIME-Version: Content-Type:Content-Transfer-Encoding:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: In-Reply-To:References:List-Id:List-Help:List-Unsubscribe:List-Subscribe: List-Post:List-Owner:List-Archive; bh=A46QBg2LUe9wWK6gh+efHybGINMYmi77F2B7lrH7Ntw=; b=N3V8UzEpo7BN6dcrKQhsa8jlEO QolZCbhNdQ7kPoqwefHpKgc2DpdZCmrs5neneo1svSTwQLpaydDZeZGa7oJH1KRDesO3Ei/8OPPZF 3T+i6dgkEiJ4LVN+PXsFZzLQ7HXcCutEaiEdRlzBzVdHqtsi5ocogokdlGznM7Rq17tM=; Received: from mail.blinkt.de ([192.26.174.232]) by sfi-mx-4.v28.lw.sourceforge.com with esmtps (TLSv1.2:ECDHE-RSA-AES256-GCM-SHA384:256) (Exim 4.92.2) id 1k5nFw-00Ab61-Fo for openvpn-devel@lists.sourceforge.net; Wed, 12 Aug 2020 09:41:16 +0000 Received: from kamera.blinkt.de ([2001:638:502:390:20c:29ff:fec8:535c]) by mail.blinkt.de with smtp (Exim 4.94 (FreeBSD)) (envelope-from ) id 1k5nFi-000AR8-S3 for openvpn-devel@lists.sourceforge.net; Wed, 12 Aug 2020 11:40:58 +0200 Received: (nullmailer pid 19223 invoked by uid 10006); Wed, 12 Aug 2020 08:54:12 -0000 From: Arne Schwabe To: openvpn-devel@lists.sourceforge.net Date: Wed, 12 Aug 2020 10:54:12 +0200 Message-Id: <20200812085412.19178-1-arne@rfc2549.org> X-Mailer: git-send-email 2.17.1 X-Spam-Report: Spam Filtering performed by mx.sourceforge.net. See http://spamassassin.org/tag/ for more details. 0.0 URIBL_BLOCKED ADMINISTRATOR NOTICE: The query to URIBL was blocked. See http://wiki.apache.org/spamassassin/DnsBlocklists#dnsbl-block for more information. [URIs: rfc2549.org] 0.0 HEADER_FROM_DIFFERENT_DOMAINS From and EnvelopeFrom 2nd level mail domains are different 0.0 SPF_NONE SPF: sender does not publish an SPF Record 0.0 SPF_HELO_NONE SPF: HELO does not publish an SPF Record X-Headers-End: 1k5nFw-00Ab61-Fo Subject: [Openvpn-devel] [PATCH] Improve sections about older OpenVPN clients in cipher-negotiation.rst X-BeenThere: openvpn-devel@lists.sourceforge.net X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , MIME-Version: 1.0 Errors-To: openvpn-devel-bounces@lists.sourceforge.net X-getmail-retrieved-from-mailbox: Inbox - Explain the IV_NCP=2 client situation in 2.4 a bit better. - Make more clear what exact versions are meant in the old client section - add a missing - in a heading Thanks to Richard Bohnhomme for initial proof reading. Signed-off-by: Arne Schwabe Acked-by: Gert Doering --- doc/man-sections/cipher-negotiation.rst | 34 ++++++++++++++----------- 1 file changed, 19 insertions(+), 15 deletions(-) diff --git a/doc/man-sections/cipher-negotiation.rst b/doc/man-sections/cipher-negotiation.rst index 46c9d7cf..b2c20241 100644 --- a/doc/man-sections/cipher-negotiation.rst +++ b/doc/man-sections/cipher-negotiation.rst @@ -22,14 +22,18 @@ it is automatically added to this list. If both options are unset the default is OpenVPN 2.4 clients ------------------- -The negotiation support in OpenVPN 2.4 was a first implementation and still had some -quirks. Its main goal was "upgrade to AES-256-GCM when possible". +The negotiation support in OpenVPN 2.4 was the first iteration of the implementation +and still had some quirks. Its main goal was "upgrade to AES-256-GCM when possible". An OpenVPN 2.4 client that is built against a crypto library that supports AES in GCM mode and does not have ``--ncp-disable`` will always announce support for -`AES-256-GCM` and `AES-128-GCM` even if the ``--ncp-ciphers`` option does not include -those two ciphers. It is therefore recommended to add `AES-256-GCM` and `AES-128-GCM` -to the ``--ncp-ciphers`` options to workaround this bug. +`AES-256-GCM` and `AES-128-GCM` to a server by sending :code:`IV_NCP=2`. +This only causes a problem if ``--ncp-ciphers`` option has been changed from the +default of :code:`AES-256-GCM:AES-128-GCM` to a value that does not include +these two ciphers. When a OpenVPN servers try to use `AES-256-GCM` or +`AES-128-GCM` the connection will then fail. It is therefore recommended to +always have the `AES-256-GCM` and `AES-128-GCM` ciphers to the ``--ncp-ciphers`` +options to avoid this behaviour. OpenVPN 3 clients ----------------- @@ -42,7 +46,7 @@ To support OpenVPN 3.x based clients at least one of these ciphers needs to be included in the server's ``--data-ciphers`` option. -OpenVPN 2.3 clients and older (and clients with ``--ncp-disable``) +OpenVPN 2.3 and older clients (and clients with ``--ncp-disable``) ------------------------------------------------------------------ When a client without cipher negotiation support connects to a server the cipher specified with the ``--cipher`` option in the client configuration @@ -50,10 +54,10 @@ must be included in the ``--data-ciphers`` option of the server to allow the client to connect. Otherwise the client will be sent the ``AUTH_FAILED`` message that indicates no shared cipher. -If the client has been configured with the ``--enable-small`` -:code:``./configure`` argument, using ``data-ciphers-fallback cipher`` -in the server config file with the explicit cipher used by the client -is necessary. +If the client is 2.3 or older and has been configured with the +``--enable-small`` :code:`./configure` argument, using +``data-ciphers-fallback cipher`` in the server config file with the explicit +cipher used by the client is necessary. OpenVPN 2.4 server ------------------ @@ -66,7 +70,7 @@ adding `AES-128-GCM` and `AES-256-GCM` to the client's ``--data-ciphers`` option is required. OpenVPN 2.5+ will only announce the ``IV_NCP=2`` flag if those ciphers are present. -OpenVPN 2.3 and older servers (and servers with ``-ncp-disable``) +OpenVPN 2.3 and older servers (and servers with ``--ncp-disable``) ----------------------------------------------------------------- The cipher used by the server must be included in ``--data-ciphers`` to allow the client connecting to a server without cipher negotiation @@ -74,10 +78,10 @@ support. (For compatibility OpenVPN 2.5 will also accept the cipher set with ``--cipher``) -If the server has been configured with the ``--enable-small`` -:code:``./configure` argument, adding ``data-ciphers-fallback cipher`` -to the client config with the explicit cipher used by the server -is necessary. +If the server is 2.3 or older and has been configured with the +``--enable-small`` :code:`./configure` argument, adding +``data-ciphers-fallback cipher`` to the client config with the explicit +cipher used by the server is necessary. Blowfish in CBC mode (BF-CBC) deprecation ------------------------------------------