Patent ID: 6880081

Claim:
A method for black box analysis of a device capable of accessing protected content, the method comprising: providing a device to be analyzed; providing a plurality of group keys comprising n+m group keys, each of n and m being greater than or equal to 1; inputting to the device a data item comprising encrypted protected content and n encrypted versions of a content key for accessing the protected content, each of the n encrypted versions being encrypted in accordance with a different one of the n group keys; receiving, from the device, decrypted content representing a decryption of the protected content; determining whether the received content is one of the following: erroneous; and null, and producing a result; and identifying a set of group keys comprising at least one group key which is known to the device based, at least in part, on the result, wherein the data item also comprises m encrypted versions of at least one invalid content key encrypted in accordance with the m group keys.