Patent ID: 7031469
Filing Date: 2006-04-18
Classification: H04L

Abstract:
1. In a public key encryption system, a method for selecting a current secret key to be used to encrypt a message, the method comprising: determining whether a new secret key is required, wherein determining whether a new secret key is required further comprises: determining whether a previous message has been sent to a recipient; if a previous message has not been sent to the recipient, determining that a new secret key is required, and if a previous message has been sent to the recipient: retrieving counter data from a local data store; and comparing the counter data to a reuse criterion, wherein the reuse criterion comprises a maximum number of bytes of message data and the counter data comprises a cumulative number of bytes of message data previously sent using an associated reusable secret key; if the counter data satisfies the reuse criterion, determining that a new secret key is not required; and if the counter data fails to satisfy the reuse criterion, determining that a new secret key is required; if a new secret key is required; generating the new secret key; generating a new encrypted secret key by encrypting the new secret key using a public key associated with the recipient of the message; storing in the local data store the new secret key as a reusable secret key, the new encrypted secret key as a corresponding reusable encrypted secret key, and counter data associated with the reusable secret key; and selecting as the current secret key the new secret key; and if a new secret key is not required: retrieving from the local data store a reusable secret key and the corresponding reusable encrypted secret key; updating the counter data associated with the reusable secret key in the local data store; selecting as the current secret key the reusable secret key; encrypting the message using the current secret key; and sending the encrypted message and the encrypted secret key.