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Re: [TLS] TLS 1.2 Long-term Support Profile draft posted

Dave Garrett <davemgarrett@gmail.com> Sat, 19 March 2016 23:30 UTC

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From: Dave Garrett <davemgarrett@gmail.com>
To: tls@ietf.org, Peter Gutmann <pgut001@cs.auckland.ac.nz>
Date: Sat, 19 Mar 2016 19:30:35 -0400
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Subject: Re: [TLS] TLS 1.2 Long-term Support Profile draft posted
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https://tools.ietf.org/html/draft-gutmann-tls-lts-01#section-3.2

>   TLS-LTS adds a hash of the domain parameters into the master secret
>   to protect against the use of manipulated curves/domain parameters:
>
>   o  TLS-LTS implementations MUST include a SHA-256 hash of the EDH or
>      ECDH parameters in the master secret computation by concatenating
>      the hash to the pre_master_secret value.  In the case of EDH, the
>      value that's hashed is the ServerDHParams structure.  In the case
>      of ECDH the value that's hashed is the ServerECDHParams structure.
>      This means that the master_secret computation becomes:
>
>   master_secret = PRF(pre_master_secret || param_hash, "master secret",
>                       ClientHello.random + ServerHello.random)
>                       [0..47];

It would be a lot simpler, safer, and interoperable to just mandate use of the Extended Master Secret Extension [RFC 7627].

https://tools.ietf.org/html/rfc7627


Dave

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