WO2000008879A1

WO2000008879A1 - Method for authenticating a source of communication in a communication system

Info

Publication number: WO2000008879A1
Application number: PCT/US1999/012454
Authority: WO
Inventors: Daniel Peter Brown; Valentin Oprescu-Surcobe
Original assignee: Motorola Inc.
Priority date: 1998-08-06
Filing date: 1999-06-04
Publication date: 2000-02-17

Abstract

In a communication system that includes a base station and a mobile station, a method of authenticating a source of communication includes authenticating a source of a first communication between the mobile station and base station, generating a token field of data based on at least a result of the authenticating step, and adding the token field of data to a data field to produce a burst of data for a second communication between the mobile station and base station. The token field of data authenticates the source of the second communication.

Description

Method for Authenticating a Source of Communication in a Communication system

Field of the Invention The present invention generally relates to communication systems, and

more particularly to a method of authenticating a source of communication in a

communication system.

Background of the Invention In most communication systems, such as cellular communication systems

(e.g. communication systems: TIA/ELA/IS-41, -95, -136, and GSM), base stations authenticate the sources of communications by interacting with the sources through exchanges of several data. If the data supplied by the source matches an expected data in the base station, the sources of the communication are authenticated, and as a result, allowed to function in the communication system. Base stations are vulnerable to access by unauthorized mobile stations. Therefore,

in current cellular communication systems, the mobile stations are authenticated by the base station before the mobile stations are allowed to function in the communication system. However, in most instances, the mobile stations do not authenticate the base stations which are also sources of communication in the system.

The mobile stations are also vulnerable to unauthorized probing by a base station. The base station may probe the mobile station to acquire sensitive information, such as the mobile station location. Since the mobile station does not perform an authentication of a source of communication, practically, it may respond to any base station that originates a communication with the mobile station. As such, one may fraudulently set up a base station in a communication

system to probe the mobile stations in that communication system. Therefore, there is a need for the mobile station to authenticate the source of a communication before it responds to the communication source.

The process of authentication is lengthy and time consuming in most

instances. In most communication systems, the mobile station user and the base station network share a secret number. Through a one-way mixing function, the secret number is used to calculate an authentication response to a random challenge number. The one way mixing function does not permit synthesis of the secret number from the authentication response, and as such, the user secret number remains secret. The authentication response is transmitted so the source

of the communication can prove its identity without the need to transmit the secret number over the air interface. The authentication response in the recipient of the

communication is compared with a locally produced authentication response to authenticate the source of the communication. In few of the North American systems, the process is sometimes mutual, whereby the network authenticates the user and the user authenticates the network.

A traditional means of performing mutual authentication requires the mobile station and the base station network to transmit challenge numbers to each other, to calculate responses, to transmit the responses, and to confirm the matching of the received responses with the internally-calculated responses. Nevertheless, these techniques impose a burden, specially, on packet communications where transmissions are typically short and bursty. Furthermore, a source of communication (the mobile station or the base station) may not need to be in an active state in certain types of short communications.

The source of communication may not be in an active state at all times. It may go into a "dormant" state or inactive state from time to time to conserve resources. When the mobile station is required to use the conventional means to authenticate the source of every communication, it has to wake-up from the inactive state and switch to an active state every time a source of communication attempts to communicate to the mobile station. Therefore, if the mobile station is required to authenticate the source of every communication, it may spend a

considerable amount of time and battery power to authenticate the sources of the

communications . Therefore, there is a need for an efficient method of authenticating a source of a communication in a communication system.

Detailed Description of the Preferred Embodimentfs^") According to an aspect of the invention, in a communication system that includes a base station and a mobile station, a method of authenticating a source

of communication includes authenticating a source of a first communication between the mobile station and base station, generating a token field of data based on at least a result of the authenticating step, and adding the token field of data to a data field to produce a burst of data for a second communication between the mobile station and base station. The data field may be a control data field, a message data field, or a signaling data field. The second communication may be a communication subsequent to the first communication. The token field of data authenticates the source of the second communication. According to the invention, there is no transmission of mobile and base station "challenges" beyond the authentication of the first communication. The first communication may be a component of an initial call set-up exchange. The authentication of the second source of communication may thus be performed with minimal overhead in over-the-air communication. Accordingly, the invention permits an efficient method of authenticating a source of communication.

The first communication may occur after said mobile station has switched from an inactive state to said active state. Such a switch normally occurs when the mobile station makes an initial communication with a base station. The mobile station may have a plurality of quasi-active states corresponding to a plurality of activity levels. Such activity levels are normally defined by the system specification. One example of a quasi-active state is when the mobile station is in a state which allows its location to be acquired by the base station. The second communication is after the mobile station has switched from at least one of the plurality of quasi-active states to the active state. The token fields of data may be generated in conjunction with the authenticating step. In any case, the source of the second communication may be the mobile station or the base station. As such, the invention provides an efficient method of mutual

authentication during any state of the mobile station.

At the receiving end of the second communication, the token field of data is locally generated to produce an identical token field of data using the same parameters used to generate the token field of data, followed by comparing the identical token field of data with the token field of data received via the second communication to authenticate a source of the second communication. The

recipient of the second communication may the mobile station or the base station.

Token fields of data are short information fields that are derived from the

authentication step. Such authentication may be performed upon the initial access of the mobile station with the network. Token fields of data are generated by further execution of the authentication algorithm, with additional inputs that may include time, direction of transmission and possibly sequence number. A message check sum or CRC may also be added. The invention accordingly permits efficient use of air interface bandwidth and time. Adding the token fields of data to a subset of data packets is an efficient means of providing authentication with a minimum of overhead information. The token fields of data are relatively short fields of data compared to data packets. Such authentication may be mutual between the mobile station and the base station. The invention allows the mobile station and the base station a means of authenticating each other without substantial overhead. Each packet of data that is transmitted may be added with a token field of data for authentication purpose. In a typical application, a one way mixing function such as CAVE (CAVE is an authentication algorithm commonly used by those skilled in the art) is initialized with a set of parameters including a random challenge number, a user secret number and other information. The parameters are mixed according to the CAVE algorithm to produce an authentication response that is used for user-to- network authentication of a session. Upon establishing the initial session, two

copies of the state of CAVE are retained. These two copies are used at the mobile station of the user and at the base station of the network to generate token fields of data. Each side may have a "network-to-subscriber" version and a "subscriber-to-

network" version. A token is generated upon the transmission of a packet from

the network to the subscriber. The token is calculated by running the network-to- subscriber copy of CAVE for an additional 8 rounds, with a modification to the initial state of CAVE. This modification consists of an exclusive-oring of the "authentication- data" input stages with a 24-bit number consisting of a single bit direction indicator, a seven-bit packet number, and a 16-bit cyclic redundancy check (CRC) that is the result of running the packet through an appropriate polynomial generator. The resulting token is added to the data packet. The packet may or may not be encrypted, depending on regulatory and service provider policies. The token is similarly calculated at the subscriber terminal. If it matches the token that was sent from the network, the transmission is considered to be authentic. Tokens that are sent from the subscriber terminal to the network are generated in the same manner, except that the direction bit is inverted relative to the network-to-subscriber direction bit. When a transmitter or receiver in either the mobile station or the base station wakes up from any state to an active state to transmit or receive data, the first few packets of data that are communicated most preferably include token fields of data. Such packets include the packets that are communicated to initiate the wake-up process. The wake-up process may be from an inactive state which is normally a sleep or dormant state.

The advantage of the invention includes a means for authenticating the

network or the base station as a source of communication. As such, a base station

can not fraudulently access a mobile station. Moreover, the invention provides

the authentication through an efficient means.

According to various aspect of the invention, the generating step may include generating a plurality of token fields of data based on at least the result of said authenticating step, and one of the plurality of token fields of data is used in the adding step. The plurality of token fields of data corresponds to a plurality of the second communications where each token field of data is not reused. In the recipient of the second communication, the plurality of token fields of data are locally generated to produce an identical plurality of token fields of data, followed by comparing the identical plurality of token fields of data with the token field of data received via the second communication to authenticate a source of the second communication. The second communication is authenticated when the received token field of data matches at least one of the locally generated identical plurality of token fields of data. -o-

Moreover, the plurality of token fields of data may be corresponding to the plurality of second communications in a pre-defined order. In a recipient of the second communication, the plurality of token fields of data are locally generated to produce an identical plurality of token fields of data. The recipient receives at

least a first and second of the plurality of second communications, and compares the identical plurality of token fields of data with the token field of data received via the first of plurality of second communications to authenticate a source of the first of plurality of second communications. It is followed by comparing the

token field of data received via the second received second communication with the pre-defined order to authenticate a source of the second of plurality of second communications. In case one or more of the tokens are missing due to loss of communications, the pre-defined order is adjusted in the recipient of the plurality of second communications to coincide with an order of token fields of data received via the plurality of second communications. Synchronization of data which may include the token field of data or data field may be used as a means for facilitating the adjustment process.

Transmission of some data packets may not need authentications. A qualifier may be generated along with the data packets. The qualifier may be based on the content of the data packet or order of the data packets. The qualifier

indicates if any token field of data is added to the data field in the burst of data.

While the invention has been particularly shown and described with reference to a particular embodiment, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention. The corresponding structures, materials, acts and equivalents of all means or step plus function elements in the claims below are intended to include any structure, material, or acts for performing the functions in combination with other claimed elements as specifically claimed.

Claims

What is claimed is:

1. In a communication system that includes a base station, and at least a mobile station, a method comprising the steps of: authenticating a source of a first communication between said mobile station and base station; generating a token field of data based on at least a result of said authenticating step; adding said token field of data to a data field to produce a burst of data for a second communication between said mobile station and said base station, wherein said token field of data authenticates a source of said second communication.

2. The method as recited in claim 1 wherein said second communication is subsequent to said first communication.

3. The method as recited in claim 1 wherein said second communication occurs after said mobile station switches from a quasi-active state to an active state.

4. The method as recited in claim 1 wherein said first communication occurs after said mobile station or the base station switches from an inactive state to said active state.

5. The method as recited in claim 1 wherein said generating step is in conjunction with said authenticating step.

6. The method as recited in claim 1 wherein said source of said second communication is said mobile station.

7. The method as recited in claim 1 wherein said source of second communication is said base station.

8. The method as recited in claim 1 further comprising the steps of: generating in a recipient of said second communication said token field of data to produce an identical token field of data; comparing said identical token field of data in said recipient of said second communication with said token field of data received via said second communication to authenticate a source of said second communication.

9. The method as recited in claim 8 wherein said recipient of said second communication is said mobile station.

10. The method as recited in claim 8 wherein said recipient of said second communication is said base station.