Prior art — US Patent 5412730

Analysis of Prior Art Cited in US Patent 5,412,730

The following is a technical analysis of the prior art references cited by the examiner during the prosecution of US Patent 5,412,730. This analysis focuses on the potential relevance of each reference to the patent's claims under 35 U.S.C. § 102 (Anticipation).

A core concept of US 5,412,730 is the use of synchronized pseudo-random number generators at both the transmitting and receiving stations, initialized by a common "seed," with the sequence of keys being advanced based on a predetermined characteristic of the data being transmitted (e.g., a data block count). This avoids transmitting the keys themselves or separate synchronization signals.

U.S. Patent 4,205,201

Full Citation: US Patent 4,205,201, "Digital cipher system"
Publication Date: May 27, 1980
Brief Description: This patent describes a digital cipher system where a pseudo-random binary sequence is generated and combined with a plain text signal. The state of the pseudo-random generator can be advanced by a number of steps determined by a portion of the preceding plain text message. This ensures that the encrypting sequence is dependent on the message itself.
Potential Anticipation Analysis: This reference is highly relevant. It teaches the use of a pseudo-random generator for encryption where the key sequence is altered based on the data being transmitted ("a portion of the...plain text message"). This appears to directly teach the core mechanism of advancing the key sequence based on a "predetermined characteristic of the data," as recited in Claim 1 and Claim 6. The key point of differentiation for '730 would be whether the "seed value" concept in the claims is distinct from the initialization method in '201 and whether the monitoring mechanism is identical.

U.S. Patent 4,316,055

Full Citation: US Patent 4,316,055, "Stream cipher cryptographic system"
Publication Date: February 16, 1982
Brief Description: This patent details a cryptographic system where a key stream, generated by a non-linear combination of shift register outputs, is used to encrypt data. The system includes a method for self-synchronization after a transmission error by using the cipher text itself to reload the registers at the receiver.
Potential Anticipation Analysis: The '055 patent's focus is on self-synchronization using the cipher text. While it involves synchronized key stream generation, the mechanism for maintaining synchronization appears different from that in '730. The '730 patent advances its key based on monitoring the clear text data count before encryption (or after decryption), a process independent of the cipher text content. Therefore, '055 likely does not anticipate the key advancement method based on a predetermined data characteristic as claimed in Claim 1 and Claim 6.

U.S. Patent 4,423,287

Full Citation: US Patent 4,423,287, "Key notation and management system"
Publication Date: December 27, 1983
Brief Description: This patent describes a system for managing cryptographic keys in a network. It focuses on a "key notarizing" scheme where keys are encrypted under a master key and include data identifying the intended users and context, preventing misuse or replay of old keys. It manages the lifecycle and distribution of keys in a secure manner.
Potential Anticipation Analysis: This reference addresses key management and distribution within a network, which relates to the environment described in Claim 9 of patent '730. '287 teaches a method for a central authority to manage which parties can communicate securely. However, it does not appear to describe the specific method of dynamically and randomly altering keys based on the data stream itself. Its primary contribution is to the secure management of static keys for sessions, not the continuous, data-dependent key alteration central to Claim 1.

U.S. Patent 4,817,141

Full Citation: US Patent 4,817,141, "Communication system with cryptosynchronization"
Publication Date: March 28, 1989
Brief Description: This patent describes a secure communication system that uses a block chaining method. Each block of cipher text is used as a feedback input to the key stream generator for encrypting the next block of plain text. This makes the key stream dependent on all previous message content, and provides self-synchronization.
Potential Anticipation Analysis: Similar to '055, this patent uses cipher text feedback for synchronization. This differs from the method claimed in '730, which relies on monitoring the quantity or another characteristic of the data stream, independent of its encrypted value. The '730 patent explicitly notes that "no additional synchronization information needs to be added to the data stream" (Col. 3, lines 5-7), which contrasts with the inherent synchronization-via-data-content taught by '141. Thus, it is unlikely to anticipate Claim 1 or Claim 6.

U.S. Patent 4,850,017

Full Citation: US Patent 4,850,017, "Encrypted data communication system with master and remote stations"
Publication Date: July 18, 1989
Brief Description: This reference discloses a system where a master station and multiple remote stations share a common, periodically changing encryption key. The key change is triggered after a specific number of data transmissions have occurred. Both the master and remote stations contain counters that are incremented with each transmission to maintain synchronization for the key changes.
Potential Anticipation Analysis: This patent is also highly relevant prior art. It teaches synchronized key changes at both a transmitter and receiver, triggered by counting a characteristic of the transmission ("a specific number of data transmissions"). This directly maps to the method described in the specification of '730 and recited in Claim 1 ("monitoring said sequence of data blocks for a predetermined characteristic thereof" and "generating a next one of said pseudo-random numbers in response thereto"). The use of counters at both ends is a clear embodiment of the claimed monitoring and advancing steps. The novelty of '730 may depend on the specifics of using a "pseudo-random number seed value" to generate a sequence of keys versus the method of generating new keys in '017.

U.S. Patent 4,941,175

Full Citation: US Patent 4,941,175, "Method and apparatus for effecting secure communications"
Publication Date: July 10, 1990
Brief Description: This patent describes a secure communication system where a key is changed on a message-by-message basis. A new key is generated for each new message, and this new key is itself encrypted using a "master key" and transmitted to the receiver along with the message.
Potential Anticipation Analysis: This method is fundamentally different from that in patent '730. The '175 patent explicitly transmits the next session key (albeit in an encrypted form), which '730 is designed to avoid. The abstract of '730 states its system works "without these keys being transmitted in any form over the transmission facility." Therefore, '175 does not anticipate Claim 1, Claim 6, or Claim 8.

U.S. Patent 5,052,040

Full Citation: US Patent 5,052,040, "Cryptographic communication system and method with chaining and final-block-dependent key"
Publication Date: September 24, 1991
Brief Description: This patent describes a system using a block chaining algorithm where the encryption of each block depends on the previous block. To enhance security, it generates a unique "message key" for each message, which is derived from a master key and a "message sequence number." This message sequence number is incremented for each message, ensuring a unique key for each transmission and preventing replay attacks.
Potential Anticipation Analysis: This patent discloses synchronized key generation based on a counter (the "message sequence number"). This is conceptually similar to the '730 patent's method of advancing a key sequence based on counting data blocks. Both systems use a shared secret (master key) and a synchronized counter to generate keys. This reference could be seen as anticipating the core process of Claim 1 and Claim 6. The distinction would lie in whether the "pseudo-random number seed value" and the resulting sequence in '730 is patentably distinct from the use of a master key and an incrementing message number in '040.