METHOD AND APPARATUS FOR MAINTAINING EPHEMERAL KEYS IN LIMITED SPACE

One embodiment of the present invention provides a system that maintains keys using limited storage space on a computing device, such as a smart card. During operation, the system receives a request at the computing device to perform an operation involving a key. While processing the request, the system obtains an encrypted key from remote storage located outside of the computing device, wherein the encrypted key was created by encrypting the key along with an expiration time for the key. Next, the system decrypts the encrypted key to restore the key and the expiration time, wherein the encrypted key is decrypted using a computing-device key, which is maintained locally on the computing device. Finally, if the expiration time has not passed, the system uses the key to perform the requested operation. Note that by storing the encrypted key in remote storage, the computing device is able to use the key without consuming local storage space to store the key.