Re: [TLS] New drafts: adding input to the TLS master secret
Martin Rex <mrex@sap.com> Wed, 03 February 2010 02:17 UTC
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From: Martin Rex <mrex@sap.com>
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To: marsh@extendedsubset.com
Date: Wed, 03 Feb 2010 03:18:06 +0100
In-Reply-To: <4B68D672.2060609@extendedsubset.com> from "Marsh Ray" at Feb 2, 10 07:50:42 pm
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Cc: paul.hoffman@vpnc.org, tls@ietf.org
Subject: Re: [TLS] New drafts: adding input to the TLS master secret
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Marsh Ray wrote: > > Paul Hoffman wrote: > > > > This proposed protocol change is only relevant to scenarios where > > there is a cryptographic reason to mix inherently non-sensitive data > > passed before the change_cipher_spec message into the master secret. > > You said the data is "not sensitive" and it is sent in plain text. So an > attacker has it as soon as the endpoints do. > > What does this accomplish over just hashing your extra data into the 28 > byte random field? (which would not require a new protocol structure) I had the same thought. Have the endpoints hash it into the random fields that are sent in the ClientHellos. Adding extra data onto every TLS handshake that will _only_ be used during full handshake and completely useless for all session resumptions seems like a waste. (For large&busy servers, a session resumption rate of >95% is desired). > > 224 bits of from each endpoint ... is 448 bits really not enough entropy > somehow? 448 bits ought to be enough for anybody :-) > > It looks to me (but IANAC) like the PRF maxes out at 672 bits of entropy > doing key block expansion (master_secret[48]*8 + 128md5 + 160sha), so > you can only effectively add 224 bits (only 50% more) from any source. The PRF will have to do some kind of compression of all the entropy from the inputs. > > How big were you planning to make those symmetric keys anyway? I would prefer to _not_ call anything "key" that is going to travel in the clear. Personally, I always think of "keys" being secret or even private information. I would prefer the term "random" or "entropy". -Martin
- Re: [TLS] New drafts: adding input to the TLS mas… Stefan Santesson
- [TLS] New drafts: adding input to the TLS master … Paul Hoffman
- Re: [TLS] New drafts: adding input to the TLS mas… Paul Hoffman
- Re: [TLS] New drafts: adding input to the TLS mas… Dean Anderson
- Re: [TLS] New drafts: adding input to the TLS mas… Paul Hoffman
- Re: [TLS] New drafts: adding input to the TLS mas… Simon Josefsson
- Re: [TLS] New drafts: adding input to the TLS mas… Paul Hoffman
- Re: [TLS] New drafts: adding input to the TLS mas… Simon Josefsson
- Re: [TLS] New drafts: adding input to the TLS mas… Brian Smith
- Re: [TLS] New drafts: adding input to the TLS mas… Paul Hoffman
- Re: [TLS] New drafts: adding input to the TLS mas… Brian Smith
- Re: [TLS] New drafts: adding input to the TLS mas… Martin Rex
- Re: [TLS] New drafts: adding input to the TLS mas… Paul Hoffman
- Re: [TLS] New drafts: adding input to the TLS mas… Marsh Ray
- Re: [TLS] New drafts: adding input to the TLS mas… Martin Rex
- Re: [TLS] New drafts: adding input to the TLS mas… Paul Hoffman
- Re: [TLS] New drafts: adding input to the TLS mas… Marsh Ray
- Re: [TLS] New drafts: adding input to the TLS mas… Martin Rex
- Re: [TLS] New drafts: adding input to the TLS mas… Paul Hoffman
- Re: [TLS] New drafts: adding input to the TLS mas… Marsh Ray
- Re: [TLS] New drafts: adding input to the TLS mas… Paul Hoffman
- Re: [TLS] New drafts: adding input to the TLS mas… Bill Frantz
- Re: [TLS] New drafts: adding input to the TLS mas… Marsh Ray
- Re: [TLS] New drafts: adding input to the TLS mas… Paul Hoffman
- Re: [TLS] New drafts: adding input to the TLS mas… Paul Hoffman
- Re: [TLS] New drafts: adding input to the TLS mas… Marsh Ray
- Re: [TLS] New drafts: adding input to the TLS mas… Paul Hoffman
- Re: [TLS] New drafts: adding input to the TLS mas… Eric Rescorla
- Re: [TLS] New drafts: adding input to the TLS mas… Dean Anderson
- Re: [TLS] New drafts: adding input to the TLS mas… Eric Rescorla
- Re: [TLS] New drafts: adding input to the TLS mas… Dean Anderson
- Re: [TLS] New drafts: adding input to the TLS mas… Jeffrey A. Williams
- Re: [TLS] New drafts: adding input to the TLS mas… Eric Rescorla
- Re: [TLS] New drafts: adding input to the TLS mas… Eric Rescorla
- Re: [TLS] New drafts: adding input to the TLS mas… Martin Rex
- Re: [TLS] New drafts: adding input to the TLS mas… Dean Anderson
- Re: [TLS] New drafts: adding input to the TLS mas… Dean Anderson
- Re: [TLS] New drafts: adding input to the TLS mas… Marsh Ray
- Re: [TLS] New drafts: adding input to the TLS mas… Eric Rescorla
- Re: [TLS] New drafts: adding input to the TLS mas… Eric Rescorla
- Re: [TLS] New drafts: adding input to the TLS mas… Eric Rescorla
- Re: [TLS] New drafts: adding input to the TLS mas… Martin Rex
- Re: [TLS] New drafts: adding input to the TLS mas… Eric Rescorla
- Re: [TLS] New drafts: adding input to the TLS mas… Marsh Ray
- Re: [TLS] New drafts: adding input to the TLS mas… Dean Anderson
- Re: [TLS] New drafts: adding input to the TLS mas… Marsh Ray
- Re: [TLS] New drafts: adding input to the TLS mas… Dean Anderson
- Re: [TLS] New drafts: adding input to the TLS mas… Martin Rex
- Re: [TLS] New drafts: adding input to the TLS mas… James Manger