Secure access to accessory device resources

An accessory device receives authentication information from a host computing device connected thereto and determines whether the authentication information is valid. If the authentication information is valid, the accessory device applies a first access policy that specifies whether the accessory device can provide the host computing device with access to none, some, or all of various computing resources of the accessory device. If the authentication information is not valid, the accessory device applies a second access policy that is different than the first access policy. The accessory device can also be provisioned with access policies by a host computing device if the host computing device successfully authenticates with the accessory device. In either case, authenticating the host computing device may include verifying a digital signature of a certificate provided by the host computing device using a public key of a certificate authority that has been provisioned to the accessory device.