# US 5,351,295 A · Secure method of neighbor discovery over a multiaccess medium

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- Number: US 5,351,295 A
- Document ID: US5351295A
- Status: Granted
- Kind: A
- Application number: 08/086,596
- Filed: 1993-07-01
- Granted: 1994-09-27
- Earliest claimed: 1993-07-01
- Assignees: Digital Equipment Corporation
- Inventors: Radia J. Perlman; Charles W. Kaufman
- Web page: https://patentgrep.com/patent/US5351295A

## CPC

- H04L 9/3226: {using a predetermined code, e.g. password, passphrase or PIN (network architectures or network communication protocols for supporting authentication of entities using passwords in a packet data network H04L63/083)}
- H04L 9/3297: {involving time stamps, e.g. generation of time stamps}
- H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M)

## Abstract

A secure arrangement in which stations in a communications network are informed of the addresses of their neighbors by means of identifying messages transmitted by the stations. To prevent the insertion of illegitimate stations into the network, the system makes use of passwords included in the station-identifying messages. In networks where eavesdropping is possible, the passwords are encrypted versions of the identities of the stations transmitting the messages and in systems where stations can also be impersonated, the encrypted passwords also include time stamps.

## Claims

### Claim 1

An apparatus for communicating to a station in a communication network addresses of other stations within said communication network which said station is capable of communicating with directly, said other stations being referred to as neighbors of said station, said apparatus comprising:
means for implementing a message protocol for exchanging identifying messages between said station and said neighbors of said station to identify said neighbors to said station;
means for including a password with each of said identifying messages; and
means for restricting communications between said station and said neighbors of said station to those of said neighbors of said station identified to said station through identifying messages containing said password.

### Claim 2 (depends on 1)

The apparatus of claim 1 in which each station within said communication network includes:
means for storing a common secret number; and
means for forming said password by using the secret number to encrypt an identification of the station.

### Claim 3 (depends on 2)

The apparatus of claim 2 in which the identification of the station is an address of the station as contained in a frame header.

### Claim 4 (depends on 3)

The apparatus of claim 3 wherein said means for forming the password includes:
means responsive to the secret number for encrypting a combination of a time stamp and the identification of the station.

### Claim 5 (depends on 4)

The apparatus of claim 4 in which each station receiving one of said identifying messages includes:
means for decrypting the password;
means for making a first comparison of the encrypted time stamp with a time of receipt of the identifying message and making a second comparison of a transmitting station identification in the password with a received unencrypted identification of the transmitting station; and
means for responding to the identifying message only if both comparisons are positive.

### Claim 6 (depends on 2)

The apparatus of claim 2 in which each station receiving one of said identifying messages includes:
means for comparing the identification of a transmitting station as encrypted in the password included with each identifying message to a non-encrypted identification of the transmitting station; and
means for responding to the identifying message only if the identification of the transmitting station as encrypted corresponds with the non-encrypted identification of the transmitting station.