Re: [tcpinc] Resumption safety (was "Eric Rescorla's Discuss on draft-ietf-tcpinc-tcpcrypt-09: (with DISCUSS and COMMENT)")

Eric Rescorla <ekr@rtfm.com> Sat, 02 December 2017 00:09 UTC

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From: Eric Rescorla <ekr@rtfm.com>
Date: Fri, 1 Dec 2017 16:08:40 -0800
Message-ID: <CABcZeBPN_XQc8np3CWi_-AtDUafW4ZPc8EnRje8yj57Rv-vxyw@mail.gmail.com>
To: Valery Smyslov <svanru@gmail.com>
Cc: "Black, David" <David.Black@dell.com>, tcpinc <tcpinc@ietf.org>, Kyle Rose <krose@krose.org>, "Mirja Kuehlewind (IETF)" <ietf@kuehlewind.net>
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Subject: Re: [tcpinc] Resumption safety (was "Eric Rescorla's Discuss on draft-ietf-tcpinc-tcpcrypt-09: (with DISCUSS and COMMENT)")
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On Thu, Nov 30, 2017 at 10:54 PM, Valery Smyslov <svanru@gmail.com>; wrote:

> Hi,
>
> > Black, David writes:
> > > 2)      Copying a running virtual machine, including memory, which
> creates a
> > > copy of the session secrets.  Such copies are routinely stored on
> non-volatile
> > > storage, from which the VM can be resumed.
>
> [...]
>
> > > An additional reason for concern is that the encryption provided by
> the mandatory
> >> AEAD algorithm for tcpcrypt, AEAD_AES_128_GCM, is a stream cipher (AES
> GCM),
> >> for which reuse of a <nonce, key> pair is catastrophic - XOR-ing the
> two ciphertexts removes encryption.
>
> This is not tcpcrypt problem. The same problem applies to any
> security protocol (IPsec, TLS, etc.) that uses counter based cipher modes
> (GCM, CCM, etc.).
> Switch to nonce-misuse resistant modes.
>

Actually, the problem here is unique to tcpcrypt because it doesn't use a
nonce during resumption, so
reuse of the resumption key causes failure. That does not happen in TLS or
(I believe) IKE.

-Ekr


> Regards,
> Valery Smyslov.
>
>
>