US 5412730

Here is a concise summary of US Patent 5,412,730.

Title: Encrypted data transmission system employing means for randomly altering the encryption keys

Assignee: The original assignee was Telequip Corp. The current assignee is TQP DEVELOPMENT LLC.

Inventors: Michael F. Jones

Filing Date: April 23, 1992

Issue Date: May 2, 1995

Abstract: The patent describes a modem designed for transmitting encrypted data over standard voice-grade telephone lines. The system uses a combination of a microprocessor, a serial communications controller, and a modulator/demodulator. To secure the data, pseudo-random number generators are used at both the sending and receiving ends to create identical sequences of encryption keys. An initial "seed" value is provided to both stations to synchronize the key generation. The encryption keys are changed based on predetermined characteristics of the data being transmitted, ensuring that only the intended transmitter and receiver can know the common encryption key after the transmission has started.

Plain-Language Overview of Independent Claims:

Claim 1: This claim outlines a method for securely transmitting a sequence of data blocks over a communication link. The core idea is to provide both the transmitter and receiver with a secret starting value, or "seed." This seed is used by both ends to independently generate the same sequence of random encryption keys. A new key is generated at the transmitter based on specific characteristics of the data being sent. The data is then encrypted with these keys before being sent. The receiver, using the same seed and monitoring the same data characteristics, generates the identical sequence of keys to decrypt the incoming data. This process happens in a synchronized manner, allowing for secure communication.

Claim 6: This claim describes the receiving end of the secure communication system. It details a method for a receiver to decrypt data that has been encrypted using a sequence of changing keys. The receiver is initially provided with the same secret "seed" value as the transmitter. It then generates a sequence of pseudo-random decryption keys based on this seed. As it receives the encrypted data, it monitors for a predetermined characteristic within that data. When this characteristic is detected, the receiver switches to the next key in its generated sequence to continue decrypting the data.

Claim 8: This claim focuses on a modem specifically designed to carry out the secure data transmission method. The modem includes a standard modulator/demodulator for sending and receiving signals over a communication channel. Crucially, it contains a programmable processor. This processor is responsible for generating a sequence of pseudo-random encryption keys starting from a pre-shared "seed" value. It then encrypts the outgoing data using these keys, with the timing of the key changes being dependent on the data itself.

Claim 9: This claim describes a secure communication network that utilizes the method of changing encryption keys. The network has a central control station and multiple remote terminals. The central station securely provides each terminal with the necessary encryption keys to communicate with other authorized terminals. This allows the central control to manage which terminals can securely communicate with each other, and it can update these permissions as needed.

A search of the CAFC (Court of Appeals for the Federal Circuit) dockets for 2026 for cases involving patent 5,412,730 yielded no results. However, it's important to note that this patent has been the subject of extensive litigation in the past.