INFORMATION HIDING -- AN ANNOTATED BIBLIOGRAPHY (5/10)

024130 'Laser communications for covert links'

  • JL Jaeger, RT Carlson, Laser Communications 93 pp 95 -- 106
  • The authors describe a prototype laser communications system built by MITRE and others to replace military line-of-sight RF communications. The devices operate in the infrared; this not only increases the difficulty of detection, but also provides eye safety at all distances. The design is described, and extensive field tests reported: depending on the weather, the link operates at 1,024, 128 or 16Kbps, and at the lowest of these rates, the system can cope with all conditions except for heavy fog or rain. Excellent covertness is claimed.

    034127 'Tracing Traitors'

  • A Fiat, Crypto 94 pp 257 -- 270
  • In satellite TV applications, a rogue user might leak either the key or the plaintext of an encrypted broadcast to a pirate audience; the operator will try to track such users by giving each user a personal decryption key with which he can decrypt a session key from an enabling block; thus pirate decoders can be traced. However, an attacker might take several subscriptions and try to generate an innocuous personal key from them; the author discusses various combinatorial schemes which can be used to prevent this.

    'A Cautionary Note on Image Downgrading'

  • C Kurak, J McHugh, Proceedings of the 8th Annual Computer Security Applications Conference pp 153 -- 159
  • The authors study how one image can be embedded in another; their concern is identifying the threats posed by downgrading classified satellite images. They give examples of pictures of an aircraft, an airfield, and text, embedded in each other by replacing the four least significant bits of each pixel of the cover picture by the four most significant bits of the embedded picture. The loaded pictures cannot be distinguished by eye, and the quality of the recovered hidden pictures is acceptable for intelligence purposes. They conclude that manual inspection alone is insufhcient to prevent image downgrading being used to leak information.

    'An EMACS based downgrader for the SAT'

  • J McHugh, Proceedings of the 8th NCSC; reprinted in 'Computer and Network Security' pp 228 -- 237
  • The author describes a system he developed to enable US military personnel review classified information for downgrading. It was inspired by emacs, but targeted at a Honeywell A1 machine and formally verified. It leads the officer through the text a paragraph at a time; when he has cleared it, it is reformatted. Both surplus whitespace and non-printing characters are removed.

    'A Note on the Confinement Problem'

  • B Lampson, Communications of the ACM v 16 no 10
  • This paper pointed out the existence of covert channels. These channels arise where a resourse is shared between two entities between which we wish to inhibit communication; for example, a virus attached to a 'SECRET' process might signal classified information down to another virus at 'UNCLASSIFIED' by modulating the CPU load or the position of a disk head.