原文地址：http://blog.csdn.net/chinazhd/article/details/7578412  

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');