Artigos Delphi Function para Criptografar em Md5
Obs : para que essa function possa funcioanar precisa ter :

 unit Wcrypt2.pas.
http://stuff.irsoft.de/CryptoAPI2.zip
nesse link acima tem Wicrypt2.pas para download



function TForm1.md5(const Input: String): String;
var
  hCryptProvider: HCRYPTPROV;
  hHash: HCRYPTHASH;
  bHash: array[0..$7f] of Byte;
  dwHashLen: DWORD;
  pbContent: PByte;
  i: Integer;
begin
  dwHashLen := 16;
  pbContent := Pointer(PChar(Input));
  Result := '';

  if CryptAcquireContext(@hCryptProvider, nil, nil, PROV_RSA_FULL, CRYPT_VERIFYCONTEXT or CRYPT_MACHINE_KEYSET) then
  begin
    if CryptCreateHash(hCryptProvider, CALG_MD5, 0, 0, @hHash) then
    begin
      if CryptHashData(hHash, pbContent, Length(Input), 0) then
      begin
        if CryptGetHashParam(hHash, HP_HASHVAL, @bHash[0], @dwHashLen, 0) then
        begin
          for i := 0 to dwHashLen - 1 do
          begin
            Result := Result + Format('%.2x', [bHash[i]]);
          end;
        end;
      end;
      CryptDestroyHash(hHash);
    end;
    CryptReleaseContext(hCryptProvider, 0);
  end;
  Result := AnsiLowerCase(Result);

end;