A security unit to prevent unauthorized retrieval of data includes an encrypting unit for encrypting data in accordance with commands received by the security unit, and a common register for storing both intermediate results and final results of the data encryption. A switching element operatively coupled to the register selectively outputs the contents of the register. The switching element is controlled to prevent external access to the intermediate results of the encryption. The security unit is particularly useful as part of a memory unit that is attachable to a recording/reproduction device such as a digital audio recorder/player.

 
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< Receiving device for securely storing a content item, and playback device

< Information transmission system, and information sending apparatus and information receiving apparatus used therein

> System for dynamically encrypting information for secure internet commerce and providing embedded fulfillment software

> Method and apparatus for securely associating an optically readable memory with a user machine

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