首先有两个自定的转换函数：  

function myStrToHex(s:string):string; //字串转16进制

var

  TmpStr:string;

  i:integer;

begin

  TmpStr:='';

  for i:=1 to Length(s)do

    TmpStr:=TmpStr+IntToHex(ord(s[i]),2);

  Result:=TmpStr;

end;    

function myHexToStr(S:string):string; //16进制转字串

var

  HexS,TmpStr:string;

  i:Integer;

  a:Byte;

begin

  HexS:=s;

  if Length(HexS) mod 2=1 then

    HexS:=HexS+'0';

  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 myStrToHex(s:string):string; //字串转16进制

var

  TmpStr:string;

  i:integer;

begin

  TmpStr:='';

  for i:=1 to Length(s)do

    TmpStr:=TmpStr+IntToHex(ord(s[i]),2);

  Result:=TmpStr;

end;  

function myHexToStr(S:string):string; //16进制转字串

var

  HexS,TmpStr:string;

  i:Integer;

  a:Byte;

begin

  HexS:=s;

  if Length(HexS) mod 2=1 then

    HexS:=HexS+'0';

  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;   

然后就是加密、解密函数了：  

{两个函数的参数相同，s为要加密、解密的字串；sKey为密匙}

function EncryptStr(const s:string;sKey:string):string; //加密

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:=''; //下面要用到TmpStr，所以要清空

    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 DecryptStr(const s:string;sKey:string):string; //解密

var

  i,j:Integer;

  HexS,HexsKey,MidS,TmpStr:string;

  a,b,c:Byte;

begin

  HexS:=s;

  if Length(HexS)mod 2=1 then //检查是否为字符串

  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:=''; //下面要用到TmpStr，所以要清空

    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;

{两个函数的参数相同，s为要加密、解密的字串；sKey为密匙}

function EncryptStr(const s:string;sKey:string):string; //加密

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:=''; //下面要用到TmpStr，所以要清空

    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 DecryptStr(const s:string;sKey:string):string; //解密

var

  i,j:Integer;

  HexS,HexsKey,MidS,TmpStr:string;

  a,b,c:Byte;

begin

  HexS:=s;

  if Length(HexS)mod 2=1 then //检查是否为字符串

  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:=''; //下面要用到TmpStr，所以要清空

    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;   

现在已经可以使用了，调用EncryptStr和DecryptStr分别加密、解密  

例：  

[delphi] view plaincopyprint?Edit1.Text:=EncryptStr('Hello','delphi');    

////////////////////////////////////////     

Edit1.Text:=DecryptStr(Edit1.Text,'delphi');

Edit1.Text:=EncryptStr('Hello','delphi');  

////////////////////////////////////////  

Edit1.Text:=DecryptStr(Edit1.Text,'delphi');