Consider the problem of securely downloading n application blocks B(1), B(2), ..., B(n) from an application provider to a smart card (SC) with the possibility of updating a block B(i) at a later time. In this paper we describe a scheme called Ordered Authentication Trees (OTA), which solves the problem of downloading and updating application blocks with the following properties: (1) a single signature based on an authentication tree is computed for the blocks, (2) only O(log n) additional memory is required by SC beyond the memory for the blocks themselves, (3) block B(i) can be verified as correct upon receipt at the SC, and (4) blocks can be updated in O(log n) time. All previously known solutions require O(n) memory and/or delay requirements for the download/update of n code blocks. The OTA scheme also generalizes to other portable devices that share common characteristics with smart cards.
Keywords:
Portable device, smart card, authentication tree, digital signature.
By: Luke O'Connor and Günter Karjoth
Published in: RZ3215 in 2000
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