A computer configured to execute an operating system that is stored on a replaceable storage medium configured to store the operating system and an encrypted certificate, the computer comprising:
- at least one replaceable storage medium connector configured to receive the replaceable storage medium;
- and
- a boot control apparatus comprising an encryption and decryption unit configured to:
- read the encrypted certificate from the replaceable storage medium;
- decrypt the encrypted certificate to obtain a decrypted certificate;
- authenticate the replaceable storage medium by identifying a code phrase in the decrypted certificate;
- after authenticating the replaceable storage medium, checking user supplied information in order to validate a user's authorization to use the operating system;
- and
- allow execution of the operating system on the computer in response to successfully authenticating the replaceable storage medium and validating the user's authorization.