In virtualized environments a method of determining authorization to a resource cannot use a hardware specific identifier, such as a MAC address. As a result upgrading a virtual host may cause licenses associated with that host to be invalid, even though the upgraded virtual host should be authorized. Authentication methods and systems are disclosed such that a key may be shared with a second host along with a license file and, provided at least the second host has a key associated with its system identifier and a key associated with a license file, access to a licensed resource may be authorized.