Re: [TLS] Consensus Call on Removing GMT from the Handshake
"Dan Harkins" <dharkins@lounge.org> Mon, 16 June 2014 19:10 UTC
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Date: Mon, 16 Jun 2014 12:10:46 -0700
From: Dan Harkins <dharkins@lounge.org>
To: Robert Ransom <rransom.8774@gmail.com>
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Subject: Re: [TLS] Consensus Call on Removing GMT from the Handshake
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On Mon, June 16, 2014 1:28 am, Robert Ransom wrote: > On 6/16/14, Dan Harkins <dharkins@lounge.org> wrote: >> >> On Sun, June 15, 2014 6:52 pm, Watson Ladd wrote: >>> On Sun, Jun 15, 2014 at 9:52 PM, Dan Harkins <dharkins@lounge.org> >>> wrote: >>>> >>>> On Sat, June 14, 2014 6:31 am, Jacob Appelbaum wrote: >>>>> On 6/13/14, Joseph Salowey (jsalowey) <jsalowey@cisco.com> wrote: >>>>>> There appears to be significant support for the removal of GMT from >>>>>> the >>>>>> client >>>>>> and server random values in TLS. The chairs would like to ask two >>>>>> questions: >>>>>> >>>>>> - Should we remove the GMT values from the client and server values >>>>>> in >>>>>> TLS >>>>>> 1.3? >>>>>> >>>>> >>>>> I would request that the language in 1.3 be MUST for clients to avoid >>>>> client fingerprinting by a passive or active adversary. For servers, >>>>> I >>>>> would request that they servers SHOULD make it random. I would also >>>>> request that for 1.3 that it isn't a requirement (MUST) to make it >>>>> random. >>>> >>>> I see no value in retaining the GMT value in the server random. >>>> Making >>>> it optional requires some justification. Care to share it? >>> >>> Tails currently uses the gmt time from servers to figure out what time >>> it is. Making it optional lets them ween off. >> >> I don't know what "Tails" is but deciding what time it is based on the >> value of a field that you have no guarantee that you'll find in a >> received >> packet sounds like a really bad idea. And since this is a consensus call >> for removing the GMT value from random in a new version of TLS then >> "Tails" can figure out some other way to determine time when it >> negotiates this new version.There is no weening possible or needed. > > 'Tails' (<https://tails.boum.org/>) is a live CD which, roughly, > routes all of a user's traffic through Tor. I don't remember whether > it still uses 'tlsdate' (they put considerable effort into switching > to learning the system time from Tor's directory documents), but it > used a small set of servers for tlsdate and it did enough sanity > checking on tlsdate's results that it wouldn't have been confused by > random values in that protocol field. Very cool! > The more important (widely deployed) use of tlsdate is in Google's > ChromeOS, which is probably why Adam Langley wants to not immediately > turn off that timestamp field on Google's servers. Since Google > controls both the client software and the servers used for tlsdate in > ChromeOS, their use of tlsdate should be completely safe. In both of these cases, the client seems to know when it's talking to a like instance of TLS-- either a Tails client connecting to a Tor server or a ChromeOS client connecting to a Google server-- so this can be supported proprietarily. Think of "random" as a covert channel and tlsdate as the data to transfer through it. Neither of these are a really justification for making it optional in the standard to include GMT in the server random. Dan.
- [TLS] Consensus Call on Removing GMT from the Han… Joseph Salowey (jsalowey)
- Re: [TLS] Consensus Call on Removing GMT from the… Martin Thomson
- Re: [TLS] Consensus Call on Removing GMT from the… Adam Langley
- Re: [TLS] Consensus Call on Removing GMT from the… Jacob Appelbaum
- Re: [TLS] Consensus Call on Removing GMT from the… Michael Staubermann
- Re: [TLS] Consensus Call on Removing GMT from the… Russ Housley
- Re: [TLS] Consensus Call on Removing GMT from the… Dan Harkins
- Re: [TLS] Consensus Call on Removing GMT from the… Watson Ladd
- Re: [TLS] Consensus Call on Removing GMT from the… Dan Harkins
- Re: [TLS] Consensus Call on Removing GMT from the… Robert Ransom
- Re: [TLS] Consensus Call on Removing GMT from the… Nick Mathewson
- Re: [TLS] Consensus Call on Removing GMT from the… Dan Harkins
- Re: [TLS] Consensus Call on Removing GMT from the… Jacob Appelbaum
- Re: [TLS] Consensus Call on Removing GMT from the… Jacob Appelbaum