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Re: [TLS] RFC4492bis - Removing ECDH

Ilari Liusvaara <ilari.liusvaara@elisanet.fi> Sun, 11 January 2015 05:14 UTC

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Date: Sun, 11 Jan 2015 07:14:21 +0200
From: Ilari Liusvaara <ilari.liusvaara@elisanet.fi>
To: Michael Clark <michael@metaparadigm.com>
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Subject: Re: [TLS] RFC4492bis - Removing ECDH
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On Sun, Jan 11, 2015 at 10:17:09AM +0800, Michael Clark wrote:
> 
> There is a more subtle pass through case where handshake messages can be
> tampered with (without access to a CA, just an Internet coffee bucks
> WiFi tap). Allows attacks such as editing cipher lists and any other
> associated handshake metadata (curve format extensions, switching on
> compression) that are not properly authenticated. Until I am certain
> they are completely mitigated I remain skeptical.

This attack won't work.

- TLS 1.3: The messages are hashed into hMS, so you can't decrypt the
  rest of the handshake due to having wrong keys.
- TLS 1.0-1.2 w/o false start: The Finished values will fail to verify.
- TLS 1.0-1.2 /w false start: The selected crypto must be strong, or
  endpoints won't enage in false start.


-Ilari

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