Re: [TLS] New drafts: adding input to the TLS master secret

Simon Josefsson <> Tue, 02 February 2010 19:27 UTC

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From: Simon Josefsson <>
To: Paul Hoffman <>
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Date: Tue, 02 Feb 2010 20:28:00 +0100
In-Reply-To: <p06240813c78e116da3f6@[]> (Paul Hoffman's message of "Tue\, 2 Feb 2010 09\:38\:11 -0800")
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Subject: Re: [TLS] New drafts: adding input to the TLS master secret
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Paul Hoffman <> writes:

>>There is one thing in draft-hoffman-tls-additional-random-ext-00.txt
>>that bothers me: There is no requirement that additional random data is
>>generated using cryptographic principles.  This means the extension can
>>be used as a general-purpose extension mechanism to exchange data that
>>has meaning to, for example, some middle-ware that sits between the
>>client and server.
>>Is this the intention?  I'm assuming no, and that the
>>additional_random_value actually are intended to be, well, just an
>>additional random value.
> Correct. That's why the document says:
>    The recipient of an additional_random extension MUST NOT try to parse
>    the additional_random_value.

I noticed that, but as I (perhaps incorrectly) interpreted "recipient"
to mean "client or server", I was left with an uncertainty whether or
not the extension was intended for transporting data (e.g.,
authorization information) intended for middle-ware.

>>Therefor, I would suggest that a new requirement is added:
>>   The client and server MUST generate the additional_random_value data
>>   using a secure random number generator.  [RANDOM] provides guidance
>>   on the generation of random values.
>>   [RANDOM]   Eastlake, D., 3rd, Schiller, J., and S. Crocker,
>>              "Randomness Requirements for Security", BCP 106, RFC 4086,
>>              June 2005.
> This is a great addition, thanks. It will be in the -01.

That solves my issues with two documents, and I support their