system/crypt

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(* ------------------- VERSION 2 vom 21.04.86 ------------------- *)
PACKET cryptograf DEFINES                     (* Autor: J.Liedtke *)

  crypt ,
  decrypt :
 
TEXT VAR char , in buffer, out buffer ;
INT VAR in pos , key index ;
DATASPACE VAR scratch space ;
FILE VAR in, out;
 
PROC crypt (TEXT CONST file, key) :
 
  open (file) ;
  initialize crypt (key) ;
  WHILE NOT eof REP
    read char ;
    crypt char ;
    write char
  PER ;
  close (file) .
 
crypt char :
  char := code (( character + random char + key char ) MOD 250) ;
  IF key index = LENGTH key
    THEN key index := 1
    ELSE key index INCR 1
  FI .
 
character   : code (char) .
 
random char : random (0,250).
 
key char    : code (key SUB key index) .
 
ENDPROC crypt ;
 
PROC decrypt (TEXT CONST file, key) :
 
  open (file) ;
  initialize crypt (key) ;
  WHILE NOT eof REP
    read char ;
    decrypt char ;
    write char
  PER ;
  close (file) .
 
decrypt char :
  char := code (( character - random char - key char ) MOD 250) ;
  IF key index = LENGTH key
    THEN key index := 1
    ELSE key index INCR 1
  FI .
 
character   : code (char) .
 
random char : random (0,250) .
 
key char    : code (key SUB key index) .
 
ENDPROC decrypt ;
 
PROC initialize crypt (TEXT CONST key) :
 
  INT VAR random key := 0 ;
  FOR key index FROM 1 UPTO LENGTH key REP
    random key := (random key + code (key SUB key index)) MOD 32000
  PER ;
  initialize random (random key) ;
  key index := 1
 
ENDPROC initialize crypt ;
 
PROC open (TEXT CONST source file) :
 
  in := sequential file (input, source file) ;
  getline (in, in buffer) ;
  in pos := 1 ;
  forget (scratch space) ; 
  scratch space := nilspace ; 
  out := sequential file (output, scratch space) ;
  out buffer := "" .
 
ENDPROC open ;
 
PROC close (TEXT CONST source file) :
 
  IF out buffer <> ""
    THEN putline (out, out buffer)
  FI ;
  forget (source file, quiet) ;
  copy (scratch space, source file) ;
  forget (scratch space) .
 
ENDPROC close ;
 
BOOL PROC eof :
 
  IF in pos > LENGTH in buffer
    THEN eof (in)
    ELSE FALSE
  FI
 
ENDPROC eof ;
 
PROC read char :
 
  IF in pos > 250
    THEN getline (in, in buffer) ;
         in pos := 1 ;
         read char
  ELIF in pos > LENGTH in buffer
    THEN in pos := 1 ;
         getline (in, in buffer) ;
         char := ""13""
    ELSE char := in buffer SUB in pos ;
         in pos INCR 1
  FI .
 
ENDPROC read char ;
 
PROC write char :
 
  IF char = ""13""
    THEN putline (out, out buffer) ;
         out buffer := ""
    ELSE out buffer CAT char
  FI ;
  IF LENGTH out buffer = 250
    THEN putline (out, out buffer) ;
         out buffer := ""
  FI .
 
ENDPROC write char ;
 
ENDPACKET cryptograf ;