| 摘要 |
Generation of n control words for encryption of a content item. A device (200) obtains a first key K start and a second key K end ; generates (S42) the n control words using the formula: CW i = h 1 i (K start ) Š• h2 n-i (K End ) , i= 0 ... n -1, wherein CW i denotes control word i, h 1 and h 2 denote one-way functions, and Š• denotes a combination operation; and outputs the n generated control words. At least one one-way function is preferably a hash function and the combination operation is preferably XOR. In an embodiment, a license is generated (S43) for the content item encrypted using the generated control words, the license comprising the first key K start , the second key K end and the integer n; and the license is transmitted (S44) to a receiver. A method and a device (200) are provided. An advantage is that it is possible to send to a receiver a third key and a fourth key that lie between the first and the second key and that the receiver is unable to generate key words lying 'outside' the third and fourth key. |
