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Re: [TLS] Encryption of TLS 1.3 content type

Juho Vähä-Herttua <juhovh@iki.fi> Mon, 28 July 2014 21:23 UTC

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From: Juho Vähä-Herttua <juhovh@iki.fi>
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Date: Tue, 29 Jul 2014 00:23:50 +0300
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To: Colm MacCárthaigh <colm@allcosts.net>
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Subject: Re: [TLS] Encryption of TLS 1.3 content type
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> On 29.7.2014, at 0.15, Colm MacCárthaigh <colm@allcosts.net> wrote:
> 
> On Mon, Jul 28, 2014 at 8:14 AM, Nikos Mavrogiannopoulos
> <nmav@redhat.com> wrote:
>> On the contrary, all _new_ ciphers are stream (GCM, CCM)
> 
> Now you've got me scratching my head, because both GCM and CCM are
> authentication modes for block ciphers, not stream.

They are both authenticated counter modes for block ciphers, which means they behave like stream ciphers. Even though the output from the cipher comes in blocks, all redundant bytes in the end can be dropped, unlike in CBC mode. 

Therefore 2 byte alert encrypted with GCM or CCM is still 2 bytes plus the authentication tag. I believe this is what Nikos meant.


Juho

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