一个简单的加解密算法

  
    unit Unit1;

interface

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

type
  TForm1 = class(TForm)
    mmo: TMemo;
    mmo1: TMemo;
    mmo2: TMemo;
    key: TEdit;
    btn1: TButton;
    btn2: TButton;
    procedure btn1Click(Sender: TObject);
    procedure btn2Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
    function encryptstr(const s:string; skey:string):string;
    function decryptstr(const s:string; skey:string):string;
    function myStrtoHex(s:string):string; //原字符串转16进制字符串
    function myHextoStr(S: string): string;//16进制字符串转原字符串
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}
function TForm1.myStrtoHex(s: string): string;
var tmpstr:string;
    i:integer;
begin
    tmpstr := '';
    for i:=1 to length(s) do
    begin
        tmpstr := tmpstr + inttoHex(ord(s[i]),2);
    end;
    result := tmpstr;
end;

function TForm1.myHextoStr(S: string): string;
var hexS,tmpstr:string;
    i:integer;
    a:byte;
begin
    hexS  :=s;//应该是该字符串
    if length(hexS) mod 2=1 then
    begin
        hexS:=hexS+'0';
    end;
    tmpstr:='';
    for i:=1 to (length(hexS) div 2) do
    begin
        a:=strtoint('$'+hexS[2*i-1]+hexS[2*i]);
        tmpstr := tmpstr+chr(a);
    end;
    result :=tmpstr;
end;

function TForm1.encryptstr(const s:string; skey:string):string;
var
    i,j: integer;
    hexS,hexskey,midS,tmpstr:string;
    a,b,c:byte;
begin
    hexS   :=myStrtoHex(s);
    hexskey:=myStrtoHex(skey);
    midS   :=hexS;
    for i:=1 to (length(hexskey) div 2)   do
    begin
        if i<>1 then midS:= tmpstr;
        tmpstr:='';
        for j:=1 to (length(midS) div 2) do
        begin
            a:=strtoint('$'+midS[2*j-1]+midS[2*j]);
            b:=strtoint('$'+hexskey[2*i-1]+hexskey[2*i]);
            c:=a xor b;
            tmpstr := tmpstr+myStrtoHex(chr(c));
        end;
    end;
    result := tmpstr;
end;

function TForm1.decryptstr(const s:string; skey:string):string;
var
    i,j: integer;
    hexS,hexskey,midS,tmpstr:string;
    a,b,c:byte;
begin
    hexS  :=s;//应该是该字符串
    if length(hexS) mod 2=1 then
    begin
        showmessage('密文错误！');
        exit;
    end;
    hexskey:=myStrtoHex(skey);
    tmpstr :=hexS;
    midS   :=hexS;
    for i:=(length(hexskey) div 2) downto 1 do
    begin
        if i<>(length(hexskey) div 2) then midS:= tmpstr;
        tmpstr:='';
        for j:=1 to (length(midS) div 2) do
        begin
            a:=strtoint('$'+midS[2*j-1]+midS[2*j]);
            b:=strtoint('$'+hexskey[2*i-1]+hexskey[2*i]);
            c:=a xor b;
            tmpstr := tmpstr+myStrtoHex(chr(c));
        end;
    end;
    result := myHextoStr(tmpstr);
end;


procedure TForm1.btn1Click(Sender: TObject);
begin
  mmo1.Text:=encryptstr(mmo.Text,key.Text);
end;

procedure TForm1.btn2Click(Sender: TObject);
begin
  mmo2.Text:=decryptstr(mmo1.Text,key.Text);
end;

end.