Electromagnetic Radiation from VDUs: An Eavesdropping Risk? Paul Shotbolt Article in “Computers and Security” Volume 4. Number 4.by Wim van Eck (December 1985)

n Van Eck discusses briefly u the technology required to reconstruct images from the EM signals produced by Video Display units, u the ease at which this eavesdropping can be performed, u and some possible countermeasures

n All electronic equipment gives off electromagnetic (EM) signals. With the appropriate equipment, confidential data may be intercepted by analysis of these signals

n Appreciative F Van Eck does not just examine possibility, but feasibility throughout the article. He stresses the low cost of the eavesdropping equipment on several occasions (around 200 USD), and the much higher costs of the countermeasures.

n Critical F Much of the article assumes that emissions from the electron beam, containing the amplified video signal, is the only signal being attacked, as it is the ‘dominant signal’ from a CRT display. Quick dismissal of compromising the other signals emitted by the system No consideration of which signals are protected when describing countermeasures

n Critical u yet van Eck mentions shielded cabling, etc in the countermeasures section. Cabling is shielded to help prevent interference. u If emissions from the cabling can be intercepted (they can) then the video signal may not be the only EM emission causing security risks. u LCD Screens: A reader could be mislead into thinking they are not at risk.

n Critical u Much of the information is incomplete. F Van Eck omits some quite important specific technical details in the article F names & specs of parts, tuning, resynchronisation F deals with monochrome VDUs only, ignoring other monitors (eg EGA 1984). F Also, an author, John J. Williams (Consumertronics) pointed out that ‘half the information on the screen may be lost … due to the interlaced buildup’, and this was not mentioned

u But these omissions were explained: F "the publication of the work carried out at the laboratories on this topic is intended to make people aware of the problem and state ideas on the ways to solve these, rather than to provide a recipe to obtain information from compromising emanations. -W. Van Eck, in a letter to Mr. John J. Williams [Computers & Security Vol. 7, No. 4 (1988)]

n Sounds very much like n making a system more ‘secure’ by hoping the details of the system design are not known.

n Sounds very much like n...a good idea?

n Many security industry professionals take the position No.

u This is a violation of Kerchoffs Principle: (1883), paraphrased u System designers should assume that the complete design of a security system is available to all attackers, excluding cryptographic keys.

n Something to consider: n What might have happened if Van Eck had released the complete details and technical information needed to mount this attack into the public domain? n And do you agree with his decision?

End of Line

n “Just because security does not require that something be kept secret, it doesn't mean that it is automatically smart to publicise it.” Bruce Schneier, founder and CTO of Counterpane “Crypto-Gram” Newsletter May 15, 2002

n Appreciative F Note: that the cost to implement this type of attack have changed over the years, from approx $200US (1985) to $30,000US (2001), but are likely to drop dramatically again (cf Kuhn) affecting feasibility F [but Van Eck could not be expected to predict this]