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3. A.G. Kohnheim: ‘Cryptography: A Primer’, A Wiley Interscience Publication, pp. 236–240 (Jan. 1986).
4. Bert den Boer, ‘Cryptonalysis of FEAL’, Crypto’ 87-Rump Session, Aug. 1987.
5. A. Shimizu, S. Miyaguchi, ‘Fast Data Encipherment Algorihtm FEAL’ ABSTRACTS of EUROCRYPT 87 AMSTERDAM, April 1907.