一個簡易的加解密字符串函數

function StrDecrypt(s: string; key: word): string;

var
  i:byte;
const
  fc1=1;
  fc2=2;
begin
  //result[0]:=s[0];
  setlength(result,length(s));
  for i:=1 to length(s)   do
  begin
    result[i]:=char(byte(s[i])xor   (key   shr  4));
    key:=(byte(result[i])+key)*fc1+fc2;
  end;
end;

function StrEncrypt(s: string; key: word): string;
var
  i:byte;
const
  fc1=1;
  fc2=2;
begin
  setlength(result,length(s));
  for i:=1 to length(s) do begin
    result[i]:=char(byte(s[i])xor(key   shr  4));
    key:=(byte(s[i])+key)*fc1+fc2;
  end;
end;