🚀 go-pugleaf

johnyreb@ix.netcom.com(Richard Elbert Davis) wrote:

>Hey,
>I know of a college who reversed ASCII values for an encryption
>program. DOES ANYONE KNOW THE CODE TO DO THIS.

>-Jarrod

Jarrod,

"REVERSE ASCII" can be interpreted in several ways:--
(1) Using 'z' for 'a', and vice versa, etc.
(2) Taking the ASCII value, two decimal digits, and reversing the
    digits.
(3) Taking the binary byte representing the char and putting 0's
    in place of 1's and vice versa.
(4) Working from ASCII 255 to 0 and interchanging these values.

None of these is secure, may have buried control chars and all are
easily "cracked".

However, all of these use a char by char substitution. If that is
really what you want, you can do this with a CASE statement, linked
list, Arrays or Strings. In the following simple, non-secure scheme,
a string key is used as an example. Making it into 5 letter code
groups makes it no more secure, so I did not bother.

Regards,
Clif   <clifpenn@airmail.net>   }

Program SubstituteEncryption;
CONST
test1 = 'the quick brown fox jumped over the lazy dogs back';
test2 = 'FROM HERE TO ETERNITY IS A VERY LONG TIME';

VAR
Original, CodeKey, source, coded, msg:String;
Ch:Char;

Procedure StripSpaces(VAR s:String);
VAR  p:Byte ;
Begin
     Repeat
           p := POS(' ', s);
           If p > 0 then Delete(s, p, 1);
     Until p = 0;
End;

Procedure Encode(VAR c:String);
VAR i, j:Byte;
Begin
     For i := 1 to Length(c) Do
     Begin
          j := POS(c[i], Original);
          c[i] := CodeKey[j];
     End;
End;

Procedure Decode(VAR m:String);
VAR x, y:Byte;
Begin
    For x := 1 to Length(m) Do
    Begin
         y := POS(m[x], CodeKey);
         m[x] := Original[y];
    End;
End;

Begin
     Writeln;  Writeln; Writeln;

     Original := '';
     For Ch := 'A' to 'Z' Do Original := Original + Ch;
     For Ch := 'a' to 'z' Do Original := Original + Ch;
     Writeln('Original: ');  Writeln(Original);

     CodeKey := '';   (* reverse of Original *)
     For Ch := 'A' to 'Z' Do CodeKey := Ch + CodeKey ;
     For Ch := 'a' to 'z' Do CodeKey := Ch + CodeKey ;
     Writeln('CodeKey: ');  Writeln(CodeKey);

     source := test1 + test2;
     StripSpaces(source);
     Writeln('Source without spaces: ');  Writeln(source);

     coded := source;
     Encode(coded);
     Writeln('Coded: ');  Writeln(coded);

     msg := coded;
     Decode(msg);
     Writeln('Decoded: ');  Writeln(msg);
     Writeln(source);  Writeln('Above is source without spaces.');

Writeln; Write('<<< Press Enter>>>':20); Readln;
End.