Abstract: The useful signal of a sampled video line is, at least partially, spliced to two adjacent segments (AB, BC), each of which has at least two states. The splicing point (B) between the two segments is synchronously defined in a pseudo-random manner at transmission and reception. Upon transmission, at each line and in a pseudo-random manner, one of two possible scrambling schemes is selected. The first scheme involves local reversing of the second segment, and the second scheme involves a reversing of the second segment followed by a permutation with the first segment. Upon reception, the processing is the inverse of the processing which occurred at transmission and is applied in order to reintroduce intelligibility to the video signal. That is the locally reversed segments are received and reversed, following the permutation used at transmission. The process applies to a MAC signal.

Abstract: An encryption key, required to encrypt and decrypt data according to a predefined algorithm is usually retained in a volatile memory device. Detection of loss of the key or corruption of the key is frequently possible only be means of the encryption circuit itself testing the key. Automated and repetitive testing of encryption keys by means of a processor or a control circuit periodically requesting the encryption circuit to test an encryption key minimizes data loss and system down time due to corrupted or lost keys.

Abstract: A method of measuring optical properties of a transparency uses a video camera for focusing and then refocusing an image of a point source of light transmitted through a test region when the transparency is first absent and then later present at the test region. The distance the camera needs to be moved together with the focal length of a focusing lens used in carrying out the method provide sufficient quantitative data to calculate the spherical optical power of the transparency. Also, the camera generates video images of the point source both before and after the transparency is present in the test region. These images are displayed on a screen containing a grid pattern which facilitates measurement of the displacement of the image from the center of the grid or from the optical axis due to the presence of prismatic deviation in the transparency. Given the earlier data and supplemented by the latter displacement quantity, the prismatic deviation of the transpareny can also be calculated.