// Otway Rees 
  
 A, B, S :         principal 
 M, Na, Nb :       nonce     
 Kas, Kbs, Kab :   key       
  
  
 1.   A -> B  :   M, A, B, {Na, M, A, B}Kas                    
 2.   B -> S  :   M, A, B, {Na, M, A, B}Kas , {Nb, M, A, B}Kbs 
 3.   S -> B  :   M, {Na, Kab}Kas, {Nb, Kab}Kbs                
 4.   B -> A  :   M, {Na, Kab}Kas                              
   
 // Security Protocols Open Repository 
 // http://www.lsv.ens-cachan.fr/spore 
   
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