Patent ID: 8499157
Filing Date: 2013-07-30
Classification: H04L,H04W

Abstract:
1. A method by which a first device manages a first key required for execution of a security operation with a second device, comprising: calculating and storing a key seed during a period in which the first key is stored in a memory of the first device, the key seed being calculated by a first cryptographic operation using the first key and a second key shared with a third device; subsequently erasing at least a portion of the first and second keys to prevent execution of the security operation by the first device; and during a subsequent period in which the first device is in communication with the third device: receiving a key hint from the third device, the key hint being generated by a second cryptographic operation at the third device using the second key and a message known to the first device; regenerating the second key using the key hint and the known message; and regenerating the first key by performing a third cryptographic operation using the key seed and the regenerated second key; wherein the third device is a portable device that is in communication with the first device when located with the first device and is not in communication with the first device when located away from the first device; wherein the subsequent period in which the first device is in communication with the third device is a period in which the third device is co-located with the first device following an immediately preceding period in which the third device is not co-located with the first device and not in communication with the first device; and the erasing is performed during the immediately preceding period.