O Time Traveling to Defeat Timing Attacks

Although updating SSH to a current stable version might be enough to avoid that one particular type of timing attack by having SSH keep fewer key-dependent execution streams, the entire range of timing attacks can be better handled with ACPI. Here you must alter time in order to find solace.

Einstein's Theory of Relativity predicated that time and space are one. If Einstein were on heavy doses of over-the-counter cold medicine and asked how fast is fast, he would tell you in a slow, sleepy voice that fast is just relative. To defeat timing attacks you need only alter the CPU frequency and voltage scaling, which will change how the Linux system sees time, much like a drugged and drowsy Einstein. So you can alter the perception of Linux using its Performance Management feature. This doesn't alter the human time line or change the BIOS clock setting; however; it will change how Linux reacts to outside stimuli.

Under Performance Management in ACPI, you can adjust the processor frequency and voltage scaling and even script it to change at the owner's whim. However, the CPU must be able to accept software-controlled management. Not all hardware does. One version of hardware that will accept it is the Intel SpeedStep Technology, which offers two modes: one for full performance and the other for battery power. Changing back and forth between the two modes fairly often and at irregular intervals will alter how the Linux system responds to interactions. And just as using cold medicine too often may have a negative impact, changing modes often may not be healthy for the system hardware.

Frequency scaling can also be found in the newer kernels and can be modified directly precompile. Configuring the Governor for Userspace allows you to access this feature manually on demand with the cpufrequtils program available at http://www.kernel.org/ pub/linux/utils/kernel/cpufreq/cpufrequtils.html. Most new processors from Intel and AMD are supported as well as the nVidia nForce2, the older Pentium 4 clock modulation, Cyrix, and the Transmeta LongRun. Full details can be found at http://gentoo-wiki.com/ HOWTO_CPU_Throttling, which is for gentoo but applies to almost any Linux distribution.

Visual Attacks

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Everyone loves flashing lights on computers and peripherals; it makes people feel they are getting a good value for their money, as opposed to a dark gray block that might as well be a doorstop. This obsession has been around since the very early days when such status lights on mainframes were of genuine use. There is one story about how there were so many lights on one particular early IBM mainframe that if you pressed the Test Lamps button, it would blow the fuses.

In the current world, these lights are not really necessary, but they indicate the system state if only visual access is available; for instance, you can see disk drive usage, monitor the flickering of the network card for packet transmission or collision data, or note up-and downstream data transfer on a modem. On a broad information collection front, this is bad enough, but it gets more sinister.

In their 2002 paper, "Information Leakage from Optical Emanations," in ACM Transactions on Information and System Security, J. Loughry and D. Umphress demonstrate the correlation between the data being transmitted and the blinking of the LEDs showing the transmission. Of the 39 devices, made up of modems, LAN and WAN devices, storage devices, and miscellaneous items such as printers, 14 showed a strong correlation between the lights and the data, 21 had some correlation, and only 4 bore no resemblance to the data being processed.

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