DEFINITION MODULE DataEnc;

   (* EXPORT QUALIFIED DES, Ran4; *)

   FROM NRSystem IMPORT LongInt;
   
   TYPE Immense = RECORD (* Stores 64 bit blocks. *)
                     l, r: LongInt 
                  END;

   PROCEDURE DES(    inp, key: Immense; 
                 VAR newkey:   BOOLEAN; 
                     isw:      INTEGER; 
                 VAR out:      Immense); 
   (*
     Data Encryption Standard, Modula-2 version. Encrypts 64 bits, 
     stored as two long integers, in record inp into out using key.  
     Set newkey=true when the key is new.  Set isw=0 for encryption, 
     =1 for decryption.
   *)

   PROCEDURE Ran4(VAR idum: INTEGER): REAL; 
   (*
     Returns a uniform random deviate between 0.0 and 1.0 using DES.
     Set idum negative to initialize.  There are m possible initializations.  
     This routine is extremely slow and should be used for demonstration 
     purposes only.
   *)

   PROCEDURE Or(x: LongInt; y: LongInt): LongInt;
   (*
     Returns x OR y, where x and y represent 64 bits. This is an
     implementation dependent routine.
   *)
   
   PROCEDURE And(x: LongInt; y: LongInt): LongInt;
   (*
     Returns x AND y, where x and y represent 64 bits. This is an
     implementation dependent routine.
   *)

   PROCEDURE SHL(x: LongInt; step: INTEGER): LongInt;
   (*
     Returns x shifted left by step. x represents 64 bits. This is an
     implementation dependent routine.
   *)

   PROCEDURE SHR(x: LongInt; step: INTEGER): LongInt;
   (*
     Returns x shifted right by step. x represents 64 bits. This is an
     implementation dependent routine.
   *)

END DataEnc.