Electrical computers and digital processing systems: support – Multiple computer communication using cryptography – Protection at a particular protocol layer
Reexamination Certificate
1999-05-21
2004-08-03
Sheikh, Ayaz (Department: 2131)
Electrical computers and digital processing systems: support
Multiple computer communication using cryptography
Protection at a particular protocol layer
C713S151000, C713S178000, C713S182000, C713S152000, C380S029000, C380S029000, C370S313000, C707S793000, C707S793000
Reexamination Certificate
active
06772331
ABSTRACT:
The present invention relates generally to security management for wireless devices and more particularly to creating a secure, short-range network for securely transmitting information among wireless devices and creating a secure communications mechanism for paired devices.
BACKGROUND
The proliferation of wireless devices in computer networks has created a significant problem in the synchronization and secure interconnection of devices. Most wireless devices today are digital, using radio waves to communicate. A typical professional utilizing wireless devices today has a pager which receives digital messages, a digital cellular phone and a notebook computer with a wireless modem to retrieve and send e-mail. To connect to the office or other networks requires special hardware (such as adapter cards having transmission mechanisms) designed to connect to a wide-area or local-area network, which will then allow wire line access to the resources that the professional worker is accustomed to accessing.
A standard has been proposed for the merger of mobile communications with mobile computing. This standard, referred to herein as ‘Bluetooth’, proposes the incorporation of a small, inexpensive radio into every mobile device. Since this radio is designed to a standard, the mobile device and radio combination can then be optimized to reduce interference. The optimization is feasible since there is a common wireless protocol implemented in a single radio frequency band, rather than the multitude of optional devices using diverse technologies in various radio frequency bands available for wireless access today. The small, low-powered radio is intended for distribution in a module or chip that will communicate with other ‘Bluetooth’ enabled products. The Bluetooth standard is defining the communications between two selected devices and/or multiple selected devices. Further information regarding the Bluetooth standard is available at their website at http://www.bluetooth.com.
The standard currently defines the use of an available, unlicensed 2.4 GHz radio band that can support both voice and data exchange. While numerous commonly agreed-upon radio frequencies would work, this particular portion of the radio spectrum appears to be available worldwide for low-power unlicensed use. With a 0-dBm transmitter, this low-powered radio will be effective to establish networks of devices within about a 10 meter radius, with rapid degradation as the distance increases. With a 20-dBm transmitter the effective radio range will be about 100 meters. The low-powered radio module is intended to be built into mobile computers, mobile phones, 3-in-1 phones, printers, fax machines, modems, network interfaces (such as LAN or WAN connections), digital cameras, pagers, headphones, etc. Speeds of up to 721 Kbps for asymmetrical asynchronous data transmission, or up to three isochronous 64 Kbps voice channels, or a combination of voice and data channels totaling less than 1 Mbps symbol rate per picocell, are currently supported by the specification, and it is expected that the communication speeds will increase as the technology advances. Because Bluetooth uses frequency-hopping, several uncoordinated picocells can coexist within radio proximity of each other.
While this specification describes a major leap in the ability of devices to interact, there is still a significant problem with the establishment of secure channels for the devices. The specification allows the hand held or wireless devices to connect into what we will term a “piconet” or “picocell”. The picocell is just a physically proximate (or small) network. This piconet replaces cables for interconnecting physically proximate devices (within the above-described radio range). An ‘access point’ (or wireless device) with a Bluetooth radio can attach a picocell to an enterprise LAN or WAN. Deploying these new devices in an enterprise uncovers several unique security and management issues.
Prior art in this area, such as the above specification, defines methods for authentication and encryption at the baseband (physical) layer of the device, but these methods have heretofore-unrecognized limitations, which will be analyzed below. All of the prior-art methods that will be described have the goal of securely providing a secret cryptographic key to both devices that is then used with suitable cryptographic means to perform authentication and encryption. These methods differ as to the manner in which the key is obtained. They also differ as to their policies regarding the reuse of keys or their precursor PIN codes.
A first typical method that the prior art allows for is for two devices to receive, through some unspecified external means, a secret key known only to them. This method might be appropriate for two devices that are manufactured to be permanently paired with each other. They can store this key in association with the partner device's identifier and reuse the key every time they wish to communicate. If no method is provided for changing the key, the two devices are permanently paired with one another and can never be paired with other devices that received a different permanent key at the time of manufacture. One drawback of such a policy of key reuse is that the security association between the two devices is permanent. Another drawback is that if a third party was somehow able to learn the key, it would be able to impersonate another device or eavesdrop on the two devices at will thereafter. In all these scenarios, the third party could even impersonate or eavesdrop unobserved, since radio frequency communications in the intended RF spectrum can penetrate sight-barriers such as buildings and walls.
A second method often described, slightly more secure than the first, might be appropriate for two devices that are to be exclusively paired with one another on a long-term basis, such as a personal computer and its wireless mouse, or a cellular telephone and its wireless telephone headset. This method requires both devices to be provided with the same string called a “PIN”. The PIN may be provided by the manufacturer, or entered at each device by a user. The prior art defines how the PIN is combined with certain known, fixed data and certain ephemeral data to generate a secret key that is subsequently used for authentication and encryption. The precise details of how that occurs are not important here. Both devices wishing to create a long-term “pairing” relationship store the key associated with the paired device. The PIN that was used to generate the key is no longer needed, and can either be kept or discarded. This stored key is then reused anytime the paired devices wish to communicate securely. If a device changes ownership, it is possible to delete the prior key, enter a PIN for a new pairing relationship, and create and store a new key. One drawback of this method is that if a third party somehow learns the PIN, such as by eavesdropping on a verbal exchange or keypad entry, it can learn the key by eavesdropping on the pairing flows. Once it knows the key, it can impersonate another device or eavesdrop on encrypted communications.
A third variation provided by the prior art might be appropriate for two devices that wish to trust each other only for the duration of a single transaction or data exchange. In this method, the user enters a PIN on both devices just prior to the transaction. The PIN is used, as above, to generate a key. The key is used for authentication and encryption for the transaction, but both the PIN and the key are deleted after the transaction. If the two devices wish to do another transaction sometime in the future, both must be configured with a PIN again, a process that is burdensome to the user.
In a less-secure variation of this third method, a device stores the PIN in association with an identifier for the partner device, but deletes the key after use. Thus it reuses the same PIN whenever communicating with the same partner, but generates a fresh key before each communications session. The third method improves upon t
Hind John Raithel
Peters Marcia Lambert
Arani Taghi
Herndon Jerry W.
Ray-Yarletts Jeanine S.
Sheikh Ayaz
Synnestvedt & Lechner LLP
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