كيف يمكن تشفير النصوص بأستخدام win API

كود :
function Digest(Str1, Passward: string): string; 
const 
aMicrosoftEnhan  = 
    'Microsoft Enhanced DSS and Diffie-Hellman Cryptographic Provider'; 
var 
  hProv: HCRYPTPROV; 
  hHash: HCRYPTHASH; 
  hKey: HCRYPTKEY; 
  hHmacHash: HCRYPTHASH; 
  pbHash: PByte; 
  dwDataLen: DWORD; 
  KeyAsByte: PByte; 
  CommandAsByte: PByte; 
  HmacInfo: HMAC_INFO; 
  i: integer; 
  Key: ansistring; 
//  Decoder: TIdDecoderMIME; 
//  Uri: TidUri; 
//  Encoding: TEncoding; 
  Firma: string; 
//  Encoder: TIdEncoderMIME; 
begin 
  hProv := 0; 
  hHash := 0; 
  hKey := 0; 
  hHmacHash := 0; 
  pbHash := nil; 
  dwDataLen := 0; 
//  Decoder := TIdDecoderMIME.Create; 
//  Uri := TidUri.Create(Url); 
//  Encoding := TEncoding.Create; 
//  Encoder := TIdEncoderMIME.Create; 
  try 
//    Key := StringReplace(Base64Key, '-', '+', [rfReplaceAll]); 
//    Key := StringReplace(Key, '_', '/', [rfReplaceAll]); 
    KeyAsByte :=PByte(Str1);  //PByte(Decoder.DecodeBytes(Key)); 
    CommandAsByte :=PByte(Passward) ;//PByte(Encoding.ASCII.GetBytes(Uri.GetPathAndParams)); 
    ZeroMemory(@HmacInfo, sizeof(HmacInfo)); 
    HmacInfo.HashAlgid := CALG_MD5; 
    if not CryptAcquireContext(@hProv, nil, aMicrosoftEnhan, PROV_RSA_FULL, 
      CRYPT_VERIFYCONTEXT) then 
      raise ESysError.Create('Error in AcquireContext'); 
    if not CryptCreateHash(hProv, CALG_MD5, 0, 0, @hHash) then 
      raise ESysError.Create('Error in CryptCreateHash'); 
    if not CryptHashData(hHash, @KeyAsByte[0], sizeof(KeyAsByte), 0) then 
      raise ESysError.Create('Error in CryptHashData'); 
    if not CryptDeriveKey(hProv, CALG_RC2, hHash, CRYPT_EXPORTABLE, @hKey) then 
      raise ESysError.Create('Error in CryptDeriveKey'); 
    if not CryptCreateHash(hProv, CALG_HMAC, hKey, 0, @hHmacHash) then 
      raise ESysError.Create('Error in CryptCreateHash'); 
    if not CryptSetHashParam(hHmacHash, HP_HMAC_INFO, @HmacInfo, 0) then 
      raise ESysError.Create('Error in CryptSetHashParam'); 
    if not CryptHashData(hHmacHash, @CommandAsByte[0], 
      sizeof(CommandAsByte), 0) then 
      raise ESysError.Create('Error in CryptHashData 0x%08x'); 
    if not CryptGetHashParam(hHmacHash, HP_HASHVAL, nil, @dwDataLen, 0) then 
      raise ESysError.Create('Error in CryptGetHashParam'); 
    GetMem(pbHash, dwDataLen); 
    if not CryptGetHashParam(hHmacHash, HP_HASHVAL, pbHash, @dwDataLen, 0) then 
      raise ESysError.Create('Error in CryptGetHashParam'); 
    Firma := ''; 
    for i := 0 to dwDataLen - 1 do 
      Firma := Firma + Format('%.2x', [pbHash[i]]); 
//    Firma := Encoder.EncodeString(Firma); 
//    Firma := StringReplace(Firma, '+', '-', [rfReplaceAll]); 
//    Firma := StringReplace(Firma, '/', '_', [rfReplaceAll]); 
    result := Firma; 
  finally 
    if hHmacHash <> 0 then 
      CryptDestroyHash(hHmacHash); 
    if hKey <> 0 then 
      CryptDestroyKey(hKey); 
    if hHash <> 0 then 
      CryptDestroyHash(hHash); 
    if hProv <> 0 then 
      CryptReleaseContext(hProv, 0); 
    if pbHash <> nil then 
      FreeMem(pbHash); 
    (* Decoder.Free; 
    Uri.Free; 
    Encoding.Free; 
    Encoder.Free; *) 
  end; 
end; 
  procedure TForm1.Button1Click(Sender: TObject); 
begin 
  Memo1.Text := 'Key=' + Digest(Edit1.Text, Edit2.Text); 
end;