Cryptography – Communication system using cryptography – Position dependent or authenticating
Reexamination Certificate
1997-06-16
2001-11-13
Hayes, Gail (Department: 2131)
Cryptography
Communication system using cryptography
Position dependent or authenticating
C380S270000
Reexamination Certificate
active
06317500
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to control of decryption of an encrypted message, based upon the location where such decryption is performed.
BACKGROUND OF THE INVENTION
Satellite (re)transmission of a restricted distribution television program relies upon transmission of an encrypted version of the program. The encrypted program is decrypted at the television receiver by a decryption chip or module that is provided for legitimate subscribers. Unfortunately, these decryption chips are often cloned without authorization, and the satellite television broadcasting industry estimates that as much as $8 billion in potential revenues is lost annually because of these clones. Various signal encryption schemes have been proposed by workers in this field.
Hermann, in U.S. Pat. No. 4,102,521, discloses a system for coding guidance signals that are produced at a central station and transmitted to a self-propelled vehicle, such as a missile or guidable satellite, that is to be guided or whose control surfaces are to be adjusted from time to time. The length of the coded signal is kept low, and transmission of the coded signal is immediately preceded by transmission of a noise signal with uniform power density per unit frequency interval, to frustrate attempts to jam or interfere with transmission and receipt of the coded signal. The coded signal, when received by the vehicle, is decoded and applied to guide or control the vehicle. The concern here is interference with receipt by the intended recipient (the vehicle) of the transmitted message, not receipt and comprehension of the guidance signal by some other entity. Coding and anti-interference measures, but not encryption and decryption, are employed.
Teeter et al disclose use of pseudo-noise modulations and specific address encoding to permit multiple conversations or signal transmissions between a central station and a plurality of vehicles, or between the vehicles, in U.S. Pat. No. 4,117,271. A receiver for such (broadcast) signals is provided with a filter that accepts only signals with the proper address coding and disposes of all other messages. The encoded address also identifies the source of the message. The inventors note that this technique is useful only over modest ranges and that the most suitable frequency range is tens of kilohertz up to tens of megahertz.
U.S. Pat. No. 4,205,343, issued to Barrett, discloses transmission of an enciphered television signal during a field blanking interval that can be received, recognized and deciphered by a viewer with an authorized signal decoder and deciphering key. A subset of television viewers, those with the decoder and particular key, can be addressed for particular messages or programs.
Stern et al, in U.S. Pat. No. 4,222,067, disclose a tamper-resistant subscription television signal descrambling system in which a security carrier signal causes a television receiver to receive a selected program or an adjacent channel program, depending on whether the subscriber is or is not authorized to receive the selected program. If the viewer attempts to tamper with the descrambling system, to retune the receiver to receive a program on an unauthorized channel, the security carrier signal interferes with and blocks reception of comprehensible signals on the unauthorized channel.
Provision of a television signal filter, arranged for maximum attenuation for channels that a receiver is not authorized to receive, is disclosed by Waldo in U.S. Pat. No. 4,286,288. Authorized channel signals have little or no attenuation. Any attempt to disable the filter results in blockage of signals on all channels.
Encryption using destination addresses using a TDMA satellite communications system is disclosed in U.S. Pat. No. 4,418,415, issued to Fennel et al. A common encryption/decryption key is held by all authorized users of a network. This key is EXclusively ORed with the specified destination address, and the output (digital) signal is passed through an encryption engine, on the satellite and at the intended ground-based receiver, using the same key or another key. The encryption engine output signal is then combined with the channel data to be transmitted in another EXclusive OR circuit and transmitted to the network users. Each of the receivers receives the message and reverses the encryption process, using its own destination address as part of the decryption key. However, only the (single) intended receiver produces a cleartext message that is comprehensible.
Hanas et al, in U.S. Pat. No. 4,709,266, disclose use of a satellite scrambling network to provide messages that are scrambled or encrypted differently for different geographical regions. This is useful for distributing scrambled video, voice and data subscriber messages. A master uplink message (ground-to-satellite) is used to control the scrambling or encryption commands that determine the scrambling applied to each geographical area and/or to groups of individual subscribers.
A cable television subscriber system with two-way telephone communication is disclosed in U.S. Pat. No. 4,710,955, issued to Kauffman. When a receiver transmits a request to view a particular television program, the headend determines if sufficient credits are available to pay for viewing the requested program. The requested program signals are descrambled only if sufficient credits are available.
A cable television security arrangement disclosed in U.S. Pat. No. 4,712,239, issued to Frezza et al, attaches a bootable checksum to the requested program signals transmitted to a requesting receiver. The receiver compares the received checksum with a checksum stored at the receiver. The signal descrambler is enabled only if the two checksums agree.
U.S. Pat. No. 4,739,510, issued to Jeffers et al, discloses insertion of digitized audio and control signals in the horizontal blanking intervals of a television signal. The control signals appear as frames or packets, with a header containing a group address, synchronization and program-related information. A second portion of the header, containing control information addressed only to one or more specified receiver units, allows control of certain receiver functions at the transmission end of the system. The system uses several tiers of message authorization levels and a common audio or video key that is encrypted differently for use by each receiving authorized receiver. An authorized receiver receives only the information intended for that receiver, and unauthorized receivers receive only a scrambled message.
A cable television system with signal descrambling circuits located remote from the subscriber's premises is disclosed by Dumbauld et al in U.S. Pat. No. 4,823,386. When a receiver requests viewing of a particular channel, the requested channel is compared with a list of channels authorized for viewing by that receiver. Signal descrambling occurs only if the requested channel is on the authorized list.
Horne, in U.S. Pat. No. 4,887,296, discloses a three-key cryptographic system for a direct broadcast satellite system, to be used in video broadcasting to a plurality of ground-based receivers, each having a unique address number. A signature key, which is an encryption using the address number for that receiver, is stored in the receiver at the time of manufacturing. At the transmitter, a common key is encrypted, using the unique signature key for a receiver that is targeted for a portion of the message to be transmitted. The data stream contains message portions intended for all receivers and message portions intended for, and decryptable only by, individual receivers. A target receiver decrypts its messages, using the common key and signature key used by the transmitter to encrypt the receiver's portions of the message.
Use of frequency hopping for transmission of cleartext cable television signals is disclosed in U.S. Pat. Nos. 4,912,760 and 5,014,309, issued to West et al. An assembly of off-premises voltage-controlled oscillators provides jamming of the transmitted signal for a requesting rec
Hayes Gail
Schipper John F.
Seal James
Trimble Navigation Limited
LandOfFree
Method and apparatus for location-sensitive decryption of an... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for location-sensitive decryption of an..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for location-sensitive decryption of an... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2575799