如何加密存档文件

下面的代码是我写的一个小的加密程序，你参考一下可以。
我操作的是无类型文件，如果你做积分榜可以用其他的方法。
unit Unit1;
interface
uses
  Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
  StdCtrls;
type
  TForm1 = class(TForm)
    Edit1: TEdit;
    Label1: TLabel;
    Button1: TButton;
    Button2: TButton;
    Button3: TButton;
    OpenDialog1: TOpenDialog;
    SaveDialog1: TSaveDialog;
    procedure Button1Click(Sender: TObject);
    procedure Button2Click(Sender: TObject);
    procedure Button3Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
    procedure bufcopy(var buf:array of byte;s:ansistring);
    procedure BufXor(var buf1,buf2,buf3:array of byte);
    procedure jiami(var buf1,buf2,buf3:array of byte);
    function comparebuf(const buf1,buf2:array of byte):boolean;
  end;
const
    fixedpassword=#133#68#183#02#08#120#76#166#212#66;
    fileheader=#0#0#0#0#0#0#0#0#0#0#76#10#30#100#200#81#255#0#100#200;
var
  Form1: TForm1;
  chgpassword,xorpassword,userpassword:array[1..20] of byte;
implementation{$R *.DFM}
//密码的最大长度是20位
{
加密的方式:
密码种类:userpassword   程序密码chgpassword  固定密码 fixedpass  异或密码 xorpassword加密的文件包括:
1.文件头 fileheader
2.用户密码长度 一个byte保存
3.程序密码 chgpassword
4.异或密码 xorpassword
5.加密文件部分
6.100字节的垃圾信息
}
procedure TForm1.Button1Click(Sender: TObject);
begin
    OpenDialog1.Execute;
end;
procedure TForm1.bufcopy(var buf:array of byte;s:ansistring);
var i,j,k,len:integer;
Begin
    len:=length(s);
    j:=low(buf);
    k:=high(buf);
    for i:=j to k do
    Begin
        if (i-j>len) or (len=0) then
        begin
            buf[i]:=0;
            continue;
        end;
        buf[i]:=byte(s[i-j+1]);
    End;
End;
procedure TForm1.BufXor(var buf1,buf2,buf3:array of byte);
var i,j,k:integer;
Begin
    j:=low(buf1);
    k:=high(buf1);
    for i:=j to k do
    Begin
        buf3[i]:=buf1[i] xor buf2[i];
    End;
End;
procedure TForm1.Button2Click(Sender: TObject);
var    i,j,retn:integer;   mysource,mydest:file;
       bufsrc,bufdst:array[1..20] of byte;
begin
    if OpenDialog1.FileName='' then
        exit;
    if not SaveDialog1.Execute then
        exit;
    Randomize;
    bufcopy(userpassword,edit1.text);        //用户密码产生
    j:=length(edit1.text);
    for i:=1 to 20 do
    begin
        chgpassword[i]:=Random(255);
        xorpassword[i]:=chgpassword[i] ;
         edit1.text;
        sleep(12);
    end;                                             //机器密码产生
    bufxor(chgpassword,userpassword,xorpassword);    //异或密码产生
    assignfile(mysource,opendialog1.filename);
    try
        assignfile(mydest,savedialog1.filename);
        try
            reset(mysource,1);
            rewrite(mydest,1);
            bufcopy(bufdst,fileheader);
            blockwrite(mydest,bufdst,20);          
            bufdst[1]:=length(edit1.text);
            blockwrite(mydest,bufdst,1);          
            blockwrite(mydest,chgpassword,sizeof(chgpassword));     
            blockwrite(mydest,xorpassword,sizeof(xorpassword));     
            repeat
                blockread(mysource,bufsrc,sizeof(bufsrc),retn);
                bufxor(bufsrc,xorpassword,bufdst);
                blockwrite(mydest,bufdst,retn);
            until retn=0;
        finally
            closefile(mydest);
        end;
    finally
        closefile(mysource);
    end;end;
function TForm1.comparebuf(const buf1,buf2:array of byte):boolean;
var i,mylow,myhigh:integer;
Begin
    mylow:=low(buf1);
    myhigh:=high(buf1);
    result:=true;
    for i:=mylow to myhigh do
    Begin
        if buf1[i]<>buf2[i] then
            result:=false
    End;
End;
procedure TForm1.Button3Click(Sender: TObject);
var i,retn:integer;   mysource,mydest:file;   bufsrc,bufdst:array[1..20] of byte;
begin
    if OpenDialog1.FileName='' then
        exit;
    if not SaveDialog1.Execute then
        exit;
    assignfile(mysource,OpenDialog1.FileName);
    try
        reset(mysource,1);
        blockread(mysource,bufsrc,sizeof(bufsrc),retn);
        bufcopy(userpassword,fileheader);
        if not comparebuf(bufsrc,userpassword) then
        Begin
            showmessage('加密文件错误!'+#13+'请确定该文件是否用本软件加密.');
            exit;
        End;
        blockread(mysource,bufsrc,1,retn);
        if length(edit1.text)<>bufsrc[1] then
        Begin
            showmessage('密码错误!'+#13+'您不能解密该文件');
            exit;
        End;
        blockread(mysource,chgpassword,20,retn);
        if retn<>20 then
        Begin
            showmessage('打开文件错误!');
            exit;
        End;
        blockread(mysource,xorpassword,20,retn);
        if retn<>20 then
        Begin
            showmessage('打开文件错误!');
            exit;
        End;
        bufxor(xorpassword,chgpassword,userpassword);
        bufcopy(bufdst,edit1.text);
        if not comparebuf(userpassword,bufdst) then
        Begin
            showmessage('密码错误!'+#13+'您不能解密该文件');
            exit;
        End;
        assignfile(mydest,savedialog1.filename);
        try
            rewrite(mydest,1);
            repeat
                blockread(mysource,bufsrc,20,retn);
                bufxor(bufsrc,xorpassword,bufdst);
                blockwrite(mydest,bufdst,retn);
            until retn=0;
        finally
            closefile(mydest);
        end;
    finally
        try
            closefile(mysource);
        except
        end;
    end;
    
end;end.