Abstract: Frames of data are encrypted by combining each of the frames with a mask that varies from frame to frame. The mask is obtained by using a frame counter as the seed for a pseudo random number generator, generating n pseudo random numbers, where n is the number of bytes to be encrypted in each frame, and concatenating the most significant bytes of each of the n pseudo random numbers to form the mask. The encrypted frames are transmitted, received and decrypted by combining them with the mask, which is independently generated at the receiver. The frame counter is aperiodically reset to a new initial value that is a substantially random number with respect to a previous initial value.

Abstract: A method and apparatus for compressing and expanding discrete signals is disclosed which comprises two compression methods which interact synergistically. Illustratively, a minimum-redundancy Huffman code, which partially represents a compressed signal, is used in conjunction with a uniquely decodable code which comprises two components. The first component represents its own length, the length of the second component and partially represents the compressed signal and the second component partially represents the compressed signal.

Abstract: A secure cellular telephony arrangement where the mobile unit maintains a secret that is assigned to it by the service provider, and which is known to the provider (home cellular geographic service are--CGSA) but not to any other base station. A shared secret datum is generated by the home CGSA with the aid of the secret and some other data. That data is transmitted to the mobile unit to enable it to also generate the shared secret datum. A mobile unit wishing to communicate with a base station creates an authentication string with the aid of the shared secret datum and sends it and the unit's identity to the base station. A base station which does not have the shared secret datum is unable to immediately authenticate the mobile unit. It therefore contacts the home CGSA, receives the shared secret datum and the other data, and proceeds to authenticate the mobile unit's authentication string.

Abstract: A protocol for authenticating a mobile customer unit to a service provider where signaling messages are encrypted and where voice communications can be encrypted. A service provider assigns to each mobile customer unit a unique "secret", along with other information such as a telephone number. At the pleasure of the service provider, a directive is sent to the mobile customer unit to create a shared secret datum based on the secret. The shared secret datum is created with the aid of a bit string that is sent for thatpurpose by the provider. A portion of the created shared secret datum is used for encrypting speech and the same or other portion of the created shared secret datum is used as an input to a process for creating a second encryption key. That key is employed in the mobile customer unit to encode those of the control signals generated by the mobile customer until that affect the nature of the call in progress.

Abstract: A relatively secure, self-inverting, symmetric key cryptosystem designed for efficient implementation on an 8-bit microcomputer. The cryptosystem is especially well suited use in cellular telephony. The method of encryption is comprised of three stages: 1) an autokeyed encryption, 2) the use of a one-time pad encryption where the key is derived from a portion of the message as encrypted by the first stage, and 3) a second autokeyed decryption that is the inverse of the first.

Abstract: A protocol for authenticating a cellular telephone to a service provider for the purpose of preventing the piracy of cellular services. A service provider assigns a unique "secret", along with other information such as a telephone number, to each cellular telephone when the telephone service is established with the service provider. Each base station of a service provider continuously broadcasts a periodically changing random number to all of the cellular telephones within the base station's jurisdiction. When a cellular telephone first enters the jurisdiction of a base station, it registers itself with the base station by concatenating a secret password and the most recently broadcast random number, along with other information, and passing the concatenated information to a hash function. The cellular telephone then sends the output of the hash function, along with other identifying information to the service provider.