Gardner, Martin  <br/><br/>
Codes, ciphers and secret writing 
Martin Gardner  
 - New York  Dover Publishers, Inc.  1972 
 - 96p. 
<br/><br/><label>ISBN: </label>9780486247618 
<br/><br/><label>Subjects--Topical Terms: </label><br/>Cryptography<br/>Ciphers
<br/><br/><label>Dewey Class. No.: </label>001.5436 G171c