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2803:How to encrypt a String

KEYWORDS: String Encryption AREA: General

Here is a program that demonstrates routines for encryption and
decryption of strings. Note: We claim no responsibily for the
security of these functions.

{ Begin code }

program Crypt;


uses WinCRT;

const
  C1 = 52845;
  C2 = 22719;

function Encrypt(const S: String; Key: Word): String;
var
  I: byte;
begin
  Result[0] := S[0];
  for I := 1 to Length(S) do begin
    Result[I] := char(byte(S[I]) xor (Key shr 8));
    Key := (byte(Result[I]) + Key) * C1 + C2;
  end;
end;

function Decrypt(const S: String; Key: Word): String;
var
  I: byte;
begin
  Result[0] := S[0];
  for I := 1 to Length(S) do begin
    Result[I] := char(byte(S[I]) xor (Key shr 8));
    Key := (byte(S[I]) + Key) * C1 + C2;
  end;
end;

var
  S: string;
begin
  Write('>');
  ReadLn(S);
  S := Encrypt(S,12345);
  WriteLn(S);
  S := Decrypt(S,12345);
  WriteLn(S);
end.

        TI

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