Abstract: The present invention concerns a method for deriving from an arbitrary local image descriptor a descriptor that is invariant under arbitrary mirror symmetries. For a point of interest, pi, for which the descriptor is to be determined a direction, ODi is determined. The local patch from which the descriptor is to be extracted is mirrored along ODi if a “smaller than” relation does not hold a feature extracted from the left half of the local image patch, in regard of ODi, compared to the right half of the local image patch. Thereby, the local patch is brought into a normalized intrinsic orientation. Thereafter, the descriptor is extracted. Examples include a mirror symmetry invariant version of Lowe's SIFT.

Abstract: A method of encryption, using an encryption key K with key length k, of at least one message M comprising uniformly distributed symbols, k bits are encrypted of messages at least k bits long, while shorter messages are lengthened, e.g. by padding or concatenation, to obtain a lengthened message at least k bits long before encryption. The encryption efficiency is thus optimized while the encryption security is retained. The encryption method is particularly suitable for JPEG2000 encoded packets comprising a message M. Also provided are an encryption apparatus, a decryption method and a decryption apparatus.

Abstract: The present invention concerns a method for deriving from an arbitrary local image descriptor a descriptor that is invariant under arbitrary mirror symmetries. For a point of interest, pi, for which the descriptor is to be determined a direction, ODi is determined. The local patch from which the descriptor is to be extracted is mirrored along ODi if a “smaller than” relation does not hold a feature extracted from the left half of the local image patch, in regard of ODi, compared to the right half of the local image patch. Thereby, the local patch is brought into a normalized intrinsic orientation. Thereafter, the descriptor is extracted. Examples include a mirror symmetry invariant version of Lowe's SIFT.

Abstract: A method of generating a segment key KSmt from a given basic key KmT and a given modification key K?MT in a key space with M*T keys. The basic key KMT is split into two parts LmT, RmT onto which a one-way function is applied M?m and T?t times, respectively, and the results are combined again to form a target basic key. A one-way function is applied to the modification key K?MT a number of times that corresponds to a distance value z between the given basic key and the segment key; in one preferred embodiment z=(M?m)+(T?t). This result is XOR-ed with the target basic key to obtain the segment key KSmtAlso provided is a device.

Abstract: A layered audiovisual packet data stream, such as one obtained by a JPEG2000 encoder, is received together with information (metadata) about the contribution of each packet to the reduction of image distortion. The distortion-to-rate ratio for each packet is calculated and the packets are ordered in descending ratio. The non-encrypted packet having the highest ratio is encrypted until the target distortion is obtained. Also provided is an apparatus. In a variant, the data in the packets are substituted by dummy data instead of encrypted.

Abstract: The invention concerns a method for computing a fingerprint of a video sequence. The method comprises the steps of—Computation of a visual digest for each frame of the video, —Computation of the distance between the visual digest of each frame of the video in order to detect shots, —Detection, for each detected shot of the video, of a frame, called stable frame, having the smallest content variation of the shot, —Calculation of a local fingerprint for said stable frame.

Abstract: A method of generating a segment key KSmt from a given basic key KmT and a given modification key K?MT in a key space with M*T keys. The basic key KMT is split into two parts LmT, RmT onto which a one-way function is applied M?m and T?t times, respectively, and the results are combined again to form a target basic key. A one-way function is applied to the modification key K?MT a number of times that corresponds to a distance value z between the given basic key and the segment key; in one preferred embodiment z=(M?m)+(T?t). This result is XOR-ed with the target basic key to obtain the segment key KSmtAlso provided is a device.

Abstract: A method of encryption, using an encryption key K with key length k, of at least one message M comprising uniformly distributed symbols, k bits are encrypted of messages at least k bits long, while shorter messages are lengthened, e.g. by padding or concatenation, to obtain a lengthened message at least k bits long before encryption. The encryption efficiency is thus optimized while the encryption security is retained. The encryption method is particularly suitable for JPEG2000 encoded packets comprising a message M. Also provided are an encryption apparatus, a decryption method and a decryption apparatus.

Abstract: The invention concerns a method for computing a fingerprint of a video sequence. The method comprises the steps of—Computation of a visual digest for each frame of the video, —Computation of the distance between the visual digest of each frame of the video in order to detect shots, —Detection, for each detected shot of the video, of a frame, called stable frame, having the smallest content variation of the shot, —Calculation of a local fingerprint for said stable frame.