RE: Packet Number Encryption outside of AEAD

"Deval, Manasi" <manasi.deval@intel.com> Fri, 27 July 2018 22:11 UTC

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From: "Deval, Manasi" <manasi.deval@intel.com>
To: Christian Huitema <huitema@huitema.net>, Kazuho Oku <kazuhooku@gmail.com>, =?utf-8?B?TWlra2VsIEZhaG7DuGUgSsO4cmdlbnNlbg==?= <mikkelfj@gmail.com>
CC: IETF QUIC WG <quic@ietf.org>
Subject: RE: Packet Number Encryption outside of AEAD
Thread-Topic: Packet Number Encryption outside of AEAD
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Date: Fri, 27 Jul 2018 22:11:31 +0000
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About the issue of Packet Number Encryption outside of AEAD - We agree it simplifies both hardware and software logic. It also allows the2 encryption operations to run mostly in parallel, so it is a welcome modification.

Thanks,
Manasi


-----Original Message-----
From: QUIC [mailto:quic-bounces@ietf.org] On Behalf Of Christian Huitema
Sent: Friday, July 27, 2018 6:43 AM
To: Kazuho Oku <kazuhooku@gmail.com>; Mikkel Fahnøe Jørgensen <mikkelfj@gmail.com>
Cc: IETF QUIC WG <quic@ietf.org>
Subject: Re: Packet Number Encryption outside of AEAD



On 7/26/2018 9:14 PM, Kazuho Oku wrote:
> Consider the case where a sender encodes a packet number using 4
> octets even when just using 1 octet is enough.
>
> An on-path attacker rewrites the packet by applying XOR 0x80 to the
> first octet of the encrypted PN, and trimming the latter three octets
> of the encrypted PN.
That attack does not work, because the encoding of the PN is big-endian.
The actual packet number is in the fourth octet. Or rather, it only
works in the special case where the PN is 0.

-- Christian Huitema