US Patent 10116645 Controlling use of encryption keys

A computing device includes a processor and a persistent memory for storing information about a first public key associated with a first asymmetric key pair for authenticating the source of a digital certificate. The computing device also includes a second memory for storing one or more current key version indicators. Each of the current key version indicators is associated with a corresponding secondary public key, and the one or more current key version indicators are used by the processor to determine the trust of the corresponding secondary public key.