Re: [TLS] Question about TLS_RSA_WITH_3DES_EDE_CBC_SHA

Adam Langley <agl@google.com> Fri, 01 July 2011 13:20 UTC

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Date: Fri, 1 Jul 2011 09:20:06 -0400
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From: Adam Langley <agl@google.com>
To: Stefan Winter <stefan.winter@restena.lu>
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Subject: Re: [TLS] Question about TLS_RSA_WITH_3DES_EDE_CBC_SHA
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On Fri, Jul 1, 2011 at 7:58 AM, Stefan Winter <stefan.winter@restena.lu> wrote:
> I'm not sure whether TLS_RSA_WITH_3DES_EDE_CBC_SHA is a two-key or a three-key 3DES algorithm. This condition would be the only one that could downgrade the I-D in question from "unconditionally compliant" to "conditionally compliant".

I believe it's the 3-key algorithm. RFC 5246, App B covers this:

"DES can also be operated in a mode [3DES] where three independent
keys and three encryptions are used for each block of data; this uses
168 bits of key (24 bytes in the TLS key generation method) and
provides the equivalent of 112 bits of security."


Cheers

AGL