Re: AES MAC security question

From: David Taylor (davidt-news_at_yadt.co.uk)
Date: 07/03/05


Date: Sun, 3 Jul 2005 00:10:08 +0000 (UTC)

Rein Anders Apeland <apeland@mivu.no> wrote on Sun, 03 Jul 2005 00:58:48 +0200:
> [-- text/plain, encoding quoted-printable, charset: ISO-8859-1, 49 lines --]
>
> On Sat, 2005-07-02 at 22:19 +0000, Andrew Swallow wrote:
>> Kristian Gj?steen wrote:
>>
>> > Andrew Swallow <am.swallow@btopenworld.com> wrote:
>> >
>> >>For a packet size of 128 bits and a 5 megabit rate
>> >
>> >
>> > Who on earth would allow his car to process commands at a rate
>> > of 5 megabit?
>> >
>> That depends on what sort of receiver you are using.
>>
>> Andrew Swallow
>
> Thanks for your comments.
>
> Some more details on my system:
>
> - The data rate for the system is 10 kbaud.
> - Each and every transmitter has its unique key.
> - The receiver would reject all used counter values, which means that
> if transmitter X transmits a packet with counter value 4, the receiver
> will afterwards reject all packets with counter value less than 5.

I'm not really sure this is a threat you're concerned about, but
rather than stealing the car, someone could prevent you accessing
it easily.

Just monitor the transmitted packet, and send a bunch of (say 1000)
invalid commands with a steadily increasing counter and the same
transmitter id.

Then when the owner turns up with their keyfob, they have to press
their keyfob 1001 times before it works again.

-- 
David Taylor