     ,      ,
    .     -
 S/Key   Bellcore.  OPIE (One-time Passwords In Eve-
rything     ),    
  (U.S. Naval Research Labs),     
Bellcore.         
    .       
    .     ,
      .    -
     ,    ,    
  .         -
   ,     ,   . 
       ,    -
   .  -  ( )  -
   ,    .

         
      -. - -
      ,   -
 "-".    -   -
   ,     (),   ,    (
,    -). ,    
          
.      -  ,   
 .      , 
      .     -
        30-60 -
.  -      ,  -
    .

  

   ,     ,  -
        .     -
        ,     
 (   )    .  -
   -   .    -
   ,   ssh , kerberos.  -
      -.

      .   ,  -
   .     
   .       
 .        ssh  .

       , 
      . 
   PAP (Password Authentication Protocol   -
  ), CHAP (Challenge Handshake Authentication Protocol  
   "-")  Radius.    CHAP

 .                                                 945