Re: [TLS] Protocol version for inappropriate_fallback alerts

Watson Ladd <watsonbladd@gmail.com> Fri, 14 November 2014 17:42 UTC

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Date: Fri, 14 Nov 2014 09:42:22 -0800
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From: Watson Ladd <watsonbladd@gmail.com>
To: "mrex@sap.com" <mrex@sap.com>
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Cc: Florian Weimer <fweimer@redhat.com>, "tls@ietf.org" <tls@ietf.org>
Subject: Re: [TLS] Protocol version for inappropriate_fallback alerts
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On Fri, Nov 14, 2014 at 9:31 AM, Martin Rex <mrex@sap.com> wrote:
> Ben Laurie wrote:
>> Martin Rex <mrex@sap.com> wrote:
>>
>>> Keep in mind that there is the general IETF rule
>>>
>>> "Be liberal in what you accept, be conservative in what you send",
>>
>> This "rule" is terrible for security and absolutely should not be followed.
>
> You seem to have missed it, but what we were discussing here
> is a guidance for the server which protocol version the server should
> use at the record layer when returning the fatal invalid_fallback
> alert to the client.

I'm confused. The record layers in all versions of TLS are the same,
except for the version number, until encryption is turned on, and we
have a version negotiation mechanism. Why shouldn't the server send
the alert using the version that version negotiation would produce?

Sincerely,
Watson Ladd

>
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