Welsh, Dominic. Codes and cryptography / Dominic Welsh - Oxford [Oxfordshire] : Clarendon Press ; c1988 - ix, 257 p. ; 24 cm. Includes index. Bibliography: p. [243]-252. ISBN: 0198532873 Subjects--Topical Terms: Ciphers.Cryptography. Dewey Class. No.: 652.8 / WEL