Authentication involves verifying the validity of at least one form of identification. It is often connected with allowing access to confidential data or systems. Centralized authority-based trust relationships back most secure digital communication through known public certificate authorities; decentralized peer-based trust, also known as a web of trust, is used for personal services such as email or files (e.g. Pretty Good Privacy-PGP) and trust is established by known individuals signing each other’s cryptographic key at Key signing parties. In a computer science, a user can be given access to secure systems based on user credentials that imply authenticity. A network administrator can give a user a password, or provide the user with a key card or other access device to allow system access. In this case, authenticity is implied but not guaranteed.