unit EncodStr;

interface

uses
 Classes;

type
 TEncodedStream = class (TFileStream)
 private
 FKey: Char;
 public
 constructor Create(const FileName: string; Mode: Word);
 function Read(var Buffer; Count: Longint): Longint; override;
 function Write(const Buffer; Count: Longint): Longint; override;
 property Key: Char read FKey write FKey default 'A';
 end;

implementation

constructor TEncodedStream.Create(
 const FileName: string; Mode: Word);
begin
 inherited Create (FileName, Mode);
 FKey := 'A';
end;

function TEncodedStream.Write(const Buffer;
 Count: Longint): Longint;
var
 pBuf, pEnc: PChar;
 I, EncVal: Integer;
begin
 // allocate memory for the encoded buffer
 GetMem (pEnc, Count);
 try
 // use the buffer as an array of characters
 pBuf := PChar (@Buffer);
 // for every character of the buffer
 for I := 0 to Count - 1 do
 begin
 // encode the value and store it
 EncVal := ( Ord (pBuf[I]) + Ord(Key) ) mod 256;
 pEnc [I] := Chr (EncVal);
 end;
 // write the encoded buffer to the file
 Result := inherited Write (pEnc^, Count);
 finally
 FreeMem (pEnc, Count);
 end;
end;

function TEncodedStream.Read(var Buffer; Count: Longint): Longint;
var
 pBuf, pEnc: PChar;
 I, CountRead, EncVal: Integer;
begin
 // allocate memory for the encoded buffer
 GetMem (pEnc, Count);
 try
 // read the encoded buffer from the file
 CountRead := inherited Read (pEnc^, Count);
 // use the output buffer as a string
 pBuf := PChar (@Buffer);
 // for every character actually read
 for I := 0 to CountRead - 1 do
 begin
 // decode the value and store it
 EncVal := ( Ord (pEnc[I]) - Ord(Key) ) mod 256;
 pBuf [I] := Chr (EncVal);
 end;
 finally
 FreeMem (pEnc, Count);
 end;
 // return the number of characters read
 Result := CountRead;
end;



end.

unit EncForm;

interface

uses
 Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
 StdCtrls, ExtCtrls;

type
 TFormEncode = class(TForm)
 Memo1: TMemo;
 Memo2: TMemo;
 OpenDialog1: TOpenDialog;
 SaveDialog1: TSaveDialog;
 Panel1: TPanel;
 BtnLoadPlain: TButton;
 BtnSaveEncoded: TButton;
 BtnLoadEncoded: TButton;
 Splitter1: TSplitter;
 procedure BtnSaveEncodedClick(Sender: TObject);
 procedure BtnLoadEncodedClick(Sender: TObject);
 procedure BtnLoadPlainClick(Sender: TObject);
 private
 { Private declarations }
 public
 { Public declarations }
 end;

var
 FormEncode: TFormEncode;

implementation

{$R *.DFM}

uses
 EncodStr;

procedure TFormEncode.BtnSaveEncodedClick(Sender: TObject);
var
 EncStr: TEncodedStream;
begin
 if SaveDialog1.Execute then
 begin
 EncStr := TEncodedStream.Create(
 SaveDialog1.Filename, fmCreate);
 try
 Memo1.Lines.SaveToStream (EncStr);
 finally
 EncStr.Free;
 end;
 end;
end;

procedure TFormEncode.BtnLoadEncodedClick(Sender: TObject);
var
 EncStr: TEncodedStream;
begin
 if OpenDialog1.Execute then
 begin
 EncStr := TEncodedStream.Create(
 OpenDialog1.FileName, fmOpenRead);
 try
 Memo2.Lines.LoadFromStream (EncStr);
 finally
 EncStr.Free;
 end;
 end;
end;

procedure TFormEncode.BtnLoadPlainClick(Sender: TObject);
begin
 if OpenDialog1.Execute then
 Memo1.Lines.LoadFromFile (
 OpenDialog1.FileName);
end;

end.