Pritchard, J. A. T., <br/><br/>
Security in communications systems 
by J.A.T. Pritchard 
 - Manchester  NCC Publications  1979 
 - (7), 29p. ill. 30cm 
<br/><br/><label>ISBN: </label>085012199X 
<br/><br/><label>Subjects--Topical Terms: </label><br/>Data transmission systems--Security measures