Leak-resistant cryptography method an apparatus

摘要

The present invention provides a method and apparatus for securing cryptographic devices against attacks involving external monitoring and analysis. A typical leak-resistant cryptographic operation modifies or updates secret key material in a manner designed to render useless any information about the secrets that may have previously leaked from the system. In a symmetric authentication system used in performing secure transactions, a token, e.g. smartcard, is initialised with an initial key value and an initial transaction counter value, and an updated key value is computed (120) by cryptographically transforming the stored key value and transaction counter value, the transforming obscuring at least partial information about the stored key value. The stored key value is then replaced by the updated key value, and the transaction counter value incremented. The updated key value is used to compute an authenticator which is sent with the transaction counter value to a server to verify the transaction.