[time-nuts] Time security musing - attacking the clock itself

Edgardo Molina xe1xus at amsat.org
Mon Dec 3 18:11:08 UTC 2012

Dear Erich,

I will allow myself to comment briefly on the RF part of your concerns.

>> * Random thought - Can I point a highly directed microwave beam at the coax
>> from the GPS antenna to the clock to cause noise inside that channel?

GPS signals are very low level as we all know and are subject to jamming either intentional or accidental as you are wondering with your microwave signal towards the transmission line. I bet that the majority of the interfering signal will be picked up by the GPS antenna and not by the transmission line. But if the transmission line has nicks, loose couplings or poor shield quality, it will definitely allow the interfering signal to come into the receiver. As a matter of fact, let me ask you this. How concentrated a microwave signal can practically be to cause the damage pointing it to a specific element of the RF chain from a distance? 1º,3º or 10º  in the H-V radiation patterns? What kind of antenna design would be practical for this radiation pattern generation? A deep parabolic dish? Corner reflector? A twenty-something elemet Yagi? At a distance, the signal dispersion will certainly not only hit the transmission line but the GPS antenna and possibly the receiver as well. Remember the microwave signal reflects from nearby objects as well and can cause a change in the wave propagation path. 

There are numerous papers and articles on GPS jamming and interference. Again, take a look at NIST archive. You will be delighted when reading about unintentional interference to GPS because of loose connectors in the RF chain.

Thank you.


Edgardo Molina
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On Dec 3, 2012, at 11:32 AM, "dlewis6767" <dlewis6767 at austin.rr.com> wrote:

> I agree, Bob.
> Like the billboard on the side of the highway says: - Does Advertising Work? JUST DID -
> The bad guys can read this list same as the good guys.
> --------------------------------------------------
> From: "Bob Camp" <lists at rtty.us>
> Sent: Monday, December 03, 2012 11:18 AM
> To: "'Discussion of precise time and frequency measurement'" <time-nuts at febo.com>
> Subject: Re: [time-nuts] Time security musing - attacking the clock itself
>> Hi
>> One very basic question might be - is a public list read by millions of
>> people the right place to dig into this?
>> The most basic thing you can detect is "time went backwards". Obviously, it
>> should never to this. Because it's easy to detect, I'd assume that the
>> attacker isn't going to do anything gross. Instead they would try to steer
>> the clock so it slowly goes out of step with the real world.
>> If that's correct, then the answer to most of the rest of the questions is
>> no. A small frequency offset is adequate to do the steer. That sort of
>> offset isn't going to mess up things like ADC's and com ports. A microsecond
>> per second slip is a 1 ppm frequency offset. There's nothing in a off the
>> shelf PC that needs to be accurate to 100 ppm, let alone 1 ppm (other than
>> the real time clock..).
>> One hundred microseconds per second is plenty of slip to get things into an
>> odd state. By the end of 24 hours, you would be off by 8.64 seconds.
>> Bob
>> -----Original Message-----
>> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
>> Behalf Of Erich Heine
>> Sent: Monday, December 03, 2012 11:30 AM
>> To: Discussion of precise time and frequency measurement
>> Subject: [time-nuts] Time security musing - attacking the clock itself
>> One of my favorite things about being in security, (and a researcher in
>> general), is that we regularly get to say "that sounds too hard, what if we
>> look $HERE instead". So while I catch up on security in the time
>> synchronization space, I've also been musing on this notion of attacking
>> the clock. By this I mean I am going to assume the protocols for
>> synchronization are secure and instead look at other things which can
>> affect measurement timestamping.
>> I also am going to assume that an attacker doesn't just want to bring down
>> any system dependent on compromised devices, but rather wants to cause
>> instabilities, inefficiencies and other long-term damage (for whatever
>> reasons - economic, political, revenge, whatever - a good attack is
>> frequently one that doesn't bring down a system, but instead makes it
>> untrustworthy and is hard to eradicate).
>> In my space (power grid) there is a lot of work being done to get good
>> synchronized measurement of the whole wide-area system. This of course
>> depends on trusting the clock. Many calculations of state, and problem
>> detection (e.g. various forms of oscillation) implicitly trust the
>> measurement is accurate within defined error bands, including time.
>> What I've learned from reading this list is that clocks are pretty
>> sensitive - a lot of factors can affect the reliability (and hence
>> trustworthiness) of the reported time.
>> So what I am trying to understand today is ways we can affect the
>> reliability of the clock, having affects on everything mentioned above.
>> Some scenarios:
>> 1) I am an attacker. I can get remote root access to a device that depends
>> on an internal clock synchronized to a trusted source. I don't want to
>> leave changes in the main firmware/os that are detectable. Once the device
>> is rebooted I want no obvious signs I was ever there. A common technique
>> for this is to put exploits into secondary controller chips in the device.
>> (System boards these days look more like networks of computers than a
>> single computer - all sorts of chips providing functionality are just
>> microcontrollers themselves with writable firmware, but limited
>> introspection capability, making them a prime target for attack). Like I
>> said, I want to attack the clock and make it unreliable.
>> * Is there a specific chip/subsystem that can be be modified via firmware
>> to mess up the clock? I presume there is because the synchronization comes
>> in off the network. What sort of modifications to the code of that firmware
>> would break it?
>> * Is the method for reading the clock a directly wired GPIO pin, or is it
>> on a shared bus like I2C or SPI? (If so, other things on the bus could be
>> compromised instead to not play nice with bus and affect readings)
>> * Is the system clock used to drive things like ADCs, if so can messing
>> with the clock affect calibration of the readings?
>> 2) I don't have access to devices or network. Is there a way to mess with
>> the time signal that is very difficult to detect. Say GPS spoofing is  no
>> longer a "safe" option. It seems there are a lot of sensitivities in the
>> timing chain. What sort of factors affect a clock signal?
>> * Random thought - Can I point a highly directed microwave beam at the coax
>> from the GPS antenna to the clock to cause noise inside that channel?
>> * What else can be used to cause external interference to timing, even in
>> well designed clocks?
>> 3) I have a long planning horizon, and access to the devices at some point
>> in the supply chain. What sort of small tweaks can I make to the circuit
>> that are easy and indistinguishable from poor quality control that would
>> add a lot of noise to a timing signal? Are these things all on a single
>> chip? Are there traces/components that can be altered/damaged/affected with
>> strange inductive effects?
>> So Time-Nuts - what are your thoughts on this musing? I am hoping you all
>> can provide some insight as to wether these are productive questions to
>> pursue, or feedback and experience on these type of problems. Mostly
>> though, I'm working towards a general refinement of my understanding, and I
>> do that best through feedback :).
>> Regards,
>> Erich
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