unit1.pas

用Delphi写的一个简单的加密解密算法

unit Unit1;

interface

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

type
  TForm1 = class(TForm)
    Edit1: TEdit;
    Button1: TButton;
    Edit2: TEdit;
    Edit3: TEdit;
    Label1: TLabel;
    Label2: TLabel;
    Edit4: TEdit;
    UpDown1: TUpDown;
    UpDown2: TUpDown;
    Label3: TLabel;
    Label4: TLabel;
    Label5: TLabel;
    procedure Button1Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}
var
  start,k:Integer;//开始位置和间隔数
  i,j,i_k:integer; //数组下标
  s0:String;  //存储密文
  s1:array [0..50] of String;//存放解密明文
  len:integer;//密文长度
procedure TForm1.Button1Click(Sender: TObject);
begin
  s0:=Edit1.Text;
  len:=Length(s0);
  if s0=''then
  begin
    MessageBox(Handle,'密文为空。请重新输入!','警告',MB_OK);
    Edit1.SetFocus;Edit1.SelectAll;
    exit;
  end;
  if Pos(' ',s0)>0 then
  begin
    MessageBox(Handle,'密文中含有不正确的字符：空格。请重新输入!','警告',MB_OK);
    Edit1.SetFocus;Edit1.SelectAll;
    exit;
  end;
  j:=0;
  for i:=0 to len do
  begin
    if MidStr(s0,i,1)<>'' then j:=j+1;
  end;
  if j<len then
  begin
    MessageBox(Handle,'密文中含有不正确的字符：全角字符或中文。请重新输入!','警告',MB_OK);
    Edit1.SetFocus;Edit1.SelectAll;
    exit;
  end;
  
  start:=StrToInt(Edit2.text);
  k:=StrToInt(Edit3.Text);
  
  i:=len-start+2;
  j:=0;
  while i<=len do          //从密文后面取出明文的开始部分
  begin
    s1[j]:=MidStr(s0,i,1);
    j:=j+1;
    i:=i+1;
  end;

  if (len Mod (k+1))<>0 then
    len:=len Div (k+1)+1
  else
    len:=len Div (k+1);  
  i:=1;
  while i<=len do
  begin
    s1[j]:=MidStr(s0,i,1);//获得被加密时取出的字符
    j:=j+1;
    for i_k:=1 to k do
    begin
      s1[j]:=MidStr(s0,len+i_k+(i-1)*k,1);
      j:=j+1;
    end;
    i:=i+1;
  end;

  Edit4.Text:='';
  for i:=0 to Length(s0)-1 do
  begin
    Edit4.Text:=Edit4.Text+s1[i];
  end;
end;

end.