From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:50570) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aoByC-0004tk-GZ for qemu-devel@nongnu.org; Thu, 07 Apr 2016 11:35:49 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1aoBy7-0005Z8-NI for qemu-devel@nongnu.org; Thu, 07 Apr 2016 11:35:44 -0400 Received: from mx1.redhat.com ([209.132.183.28]:57919) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aoBy7-0005Z3-Fc for qemu-devel@nongnu.org; Thu, 07 Apr 2016 11:35:39 -0400 References: <1460028959-59091-1-git-send-email-alex@alex.org.uk> <20160407115159.GE19932@redhat.com> <4B431A9F-94A5-4F35-BE43-8C1E5767D0E3@alex.org.uk> <97F7DE7A-30CA-49C0-8122-51B3FD71B7E3@alex.org.uk> From: Eric Blake Message-ID: <57067E49.8010608@redhat.com> Date: Thu, 7 Apr 2016 09:35:37 -0600 MIME-Version: 1.0 In-Reply-To: <97F7DE7A-30CA-49C0-8122-51B3FD71B7E3@alex.org.uk> Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="20MNShVs3WI5F3MRCWGOog9939Pb3McvI" Subject: Re: [Qemu-devel] [PATCH] Improve documentation for TLS List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Alex Bligh , "Daniel P. Berrange" Cc: "nbd-general@lists.sourceforge.net" , Wouter Verhelst , "qemu-devel@nongnu.org" This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --20MNShVs3WI5F3MRCWGOog9939Pb3McvI Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable On 04/07/2016 06:36 AM, Alex Bligh wrote: >=20 > On 7 Apr 2016, at 13:13, Alex Bligh wrote: >=20 >> I guess it's worth documenting >> this, though I thought it was obvious. >=20 > The next version will have this section: >=20 > ### Downgrade attacks >=20 > A danger inherent in any scheme relying on the negotiation too much space > of whether TLS should be employed is downgrade attacks. >=20 > There are two main dangers: >=20 > * A Man-in-the-Middle (MitM) hijacks a session and impersonates > the server (possibly by proxying it) claiming not to support > TLS. In this manner, the client is confused into operating > in a plain-text manner with the MitM (with the session possibly > being proxied in plain-text to the server using the method > below). looks like too much space is a problem in general in this rough draft; I'll quit pointing it out and assume you will reflow before final submission. >=20 > * The MitM hijacks a session and impersonates the client > (possibly by proxying it) claiming not to support TLS. In > this manner the server is confused into oeprating in a plain-text s/oeprating/operating/ > manner with the MitM (with the session being possibly > proxied to the server with the method above). s/server/client/ >=20 > With regard to the first, any client that does not wish > to be subject to potential downgrade attack SHOULD ensure > that if a TLS endpoint is specified by the client, it > ensures that TLS is negotiated prior to sending or > requesting sensitive data. To recap, yhe client MAY send s/yhe/the/ > `NBD_OPT_STARTTLS` at any point during option haggling, > and MAY disconnect the session if `NBD_REP_ACK` is not > provided. Probably want to add: "but the client SHOULD strongly consider sending `NBD_OPT_STARTTLS` as its first option" >=20 > With regard to the second, any server that does not wish > to be subject to a potential downgrade attack SHOULD either > used FORCEDTLS mode, or should force TLS on those exports > it is concerned about using SELECTIVE mode and TLS-only > exports. It is not possible to avoid downgrade attacks > on exports which are may be served either via TLS or > in plain text. Probably want to add: "OPTIONALTLS mode SHOULD NOT be used if there is a potential for man-in-the-middle attacks" --=20 Eric Blake eblake redhat com +1-919-301-3266 Libvirt virtualization library http://libvirt.org --20MNShVs3WI5F3MRCWGOog9939Pb3McvI Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v2 Comment: Public key at http://people.redhat.com/eblake/eblake.gpg Comment: Using GnuPG with Thunderbird - http://www.enigmail.net/ iQEcBAEBCAAGBQJXBn5JAAoJEKeha0olJ0NqSgAH/31zXkpfwJvbfOIb4m+/JnW8 /wlGf/bZZOZrL/tRq+EzN1nUxZsutvJJahQvfDhNI7b8StII71KhIzzS6FdgJMfV +IyLCbCqPgnSCkYA17Nwq1XWu1mQvtL7JNDUTRaJBu4q5rlW1FUwmSPWAjarPWBQ FjaVfpj/qPSG0RmdORv7fvLFP/my045zLoiiD5FaYstQ2cUW0sTFjyDsQG+95A09 ZE4ha0NeHH/Ds2t02a/n1VE1AT+nF2E+SwLQLgRXnt85lqxGnmLBNNvNXFAGtS4g UNK0GkEq25GYdIW6XZlnOhQS6BCVmpq/tiaJMwrY/rTICaKfsmjei+luJWSIdAg= =HIsJ -----END PGP SIGNATURE----- --20MNShVs3WI5F3MRCWGOog9939Pb3McvI--