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cryptography and copy protection

Cryptography and copy protection

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Unformatted text preview: D Naccache Cryptography and Copy Protection Cryptography (are algorithms sufficient?) Typical s/w protection problem two bytes chess software 2 chess player Rennes presentation Typical s/w protection problem two bytes chess software 3 chess player Rennes presentation Typical s/w protection problem two bytes chess software 4 chess player Rennes presentation Typical s/w protection problem two bytes chess software 5 chess player Rennes presentation Typical s/w protection problem two bytes chess software 6 chess player Rennes presentation A solution s Code the chess algorithm inside a smart card. x The user exchanges the moves with the card through the PC. s Install the display, hall of fame and user interface parts on the PC. x These are useless for playing chess without the card 7 Rennes presentation Typical use of card for s/w protection user I/F hall of fame etc. {xu,yu} chess player chess software 8 Rennes presentation Typical use of card for s/w protection user I/F hall of fame etc. chess player {xu,yu} chess software 9 Rennes presentation Typical use of card for s/w protection user I/F hall of fame etc. chess player {xc,yc} chess software 10 Rennes presentation Typical use of card for s/w protection user I/F hall of fame etc. {xc,yc} chess player chess software 11 Rennes presentation What if the code is much bigger? s Execute it by chunks! x For instance, if the function to protect consists in computing the 3D distance between a destroyer and a target in the course of a naval simulation, then encrypted assembly code of the function sqrt[(x-x’)2+(y-y’)2] will be downloaded into the card; x the card will then decrypt the received string and install the code in RAM. x Finally, the card will get from the PC an input (say {x=3, y=12} and {x’=11, y’=6}), execute the function on this input and output the result (in our specific example “10 Km”). x When a new function will have to be executed (say compute the time it would take to get to the target, sailing at 12 Km/hour) the RAM will be reset, the code t =x/v (encrypted) will be sent into the card and the process would repeat itself (eventually resulting in the output “50 minutes”). x etc 12 Rennes presentation Typical...
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