According to Microsoft sources, BitLocker does not contain an intentionally built-in backdoor; without which there is no way for law enforcement to have a guaranteed passage to the data on the user's drives that is provided by Microsoft. In 2006 the UK Home Office expressed concern over the lack of a backdoor and tried entering into talks with Microsoft to get one introduced, although Microsoft developer Niels Ferguson and other Microsoft spokesmen state that they will not grant the wish to have one added. Microsoft engineers have said that FBI agents also put pressure on them in numerous meetings in order to add a backdoor, although no formal, written request was ever made; Microsoft engineers eventually suggested to the FBI that agents should look for the hard copy of the key that the BitLocker program suggests its users to make. Although the AES encryption algorithm used in BitLocker is in the public domain, its implementation in BitLocker, as well as other components of the software, are proprietary; however, the code is available for scrutiny by Microsoft partners and enterprises, subject to a non-disclosure agreement.