Cryptography – Communication system using cryptography – Wireless communication
Reexamination Certificate
2001-08-20
2004-12-07
Sheikh, Ayaz (Department: 2131)
Cryptography
Communication system using cryptography
Wireless communication
C380S270000, C380S273000, C370S324000, C455S410000, C455S411000
Reexamination Certificate
active
06829358
ABSTRACT:
BACKGROUND OF INVENTION
1. Field of the Invention
The present invention relates to a wireless communications protocol. In particular, the present invention discloses the handling of a channel reset condition while processing a ciphering configuration change in a wireless communications protocol.
2. Description of the Prior Art
Please refer to FIG.
1
.
FIG. 1
is a simplified block diagram of a prior art wireless communications system. The wireless communications system includes a first station
10
in wireless communications with a second station
20
. As an example, the first station
10
may be a base station, while the second station
20
is a mobile unit, such as a cellular telephone. The first station
10
communicates with the second station
20
over a plurality of channels
12
. The second station
20
thus has corresponding channels
22
, one for each of the channels
12
. Each channel
12
has a receiving buffer
12
r
for holding protocol data units (PDUs)
11
r
received from the corresponding channel
22
of the second station
20
. Each channel
12
also has a transmitting buffer
12
t
for holding PDUs
11
t
that are awaiting transmission to the corresponding channel
22
of the second station
20
. A PDU
11
t
is transmitted by the first station
10
along a channel
12
and received by the second station
20
to generate a corresponding PDU
21
r
in the receiving buffer
22
r
of the corresponding channel
22
. Similarly, a PDU
21
t
is transmitted by the second station
20
along a channel
22
and received by the first station
10
to generate a corresponding PDU
11
r
in the receiving buffer
12
r
of the corresponding channel
12
.
For the sake of consistency, the data structures of pair entity (PDUs)
11
t
,
21
r
, and
21
t
,
11
r
along corresponding channels
12
and
22
are identical. That is, a transmitted (PDUs)
11
t
generates an identical corresponding received PDU
21
r
, and a transmitted PDU
21
t
generates an identical corresponding PDU
11
r
. Although the data structure of each pair entity PDU
11
t
,
21
r
, and
21
t
,
11
r
along corresponding channels
12
and
22
is identical, different channels
12
,
22
may use different PDU data structures according to the type of connection agreed upon along the channels
12
,
22
. In general, though, every PDU
11
r
,
11
t
,
21
r
and
21
t
will have a sequence number
5
r
,
5
t
,
6
r
,
6
t
. The sequence number
5
r
,
5
t
,
6
r
,
6
t
is an m-bit number that is incremented for each PDU
11
r
,
11
t
,
21
r
,
21
t
. The magnitude of the sequence number
5
r
,
5
t
,
6
r
,
6
t
indicates the sequential ordering of the PDU
11
r
,
11
t
,
21
r
,
21
t
in its buffer
12
r
,
12
t
,
22
r
,
22
t
. For example, a received PDU
11
r
with a sequence number
5
r
of 108 is sequentially before a received PDU
11
r
with a sequence number
5
r
of 109, and sequentially after a PDU
11
r
with a sequence number
5
r
of 107. The sequence number
5
t
,
6
t
is often explicitly carried by the PDU
11
t
,
21
t
, but may also be implicitly assigned by the station
10
,
20
. For example, in an acknowledged mode setup for corresponding channels
12
and
22
, each transmitted PDU
11
t
, successful reception of which generates an identical corresponding PDU
21
r
, is acknowledged as received by the second station
20
. A 12-bit sequence number
5
t
is explicitly carried by each PDU
11
t
in acknowledged mode transmissions. The second station
20
scans the sequence numbers
6
r
embedded within the received PDUs
21
r
to determine the sequential ordering of the PDUs
21
r
, and to determine if any PDUs
21
r
are missing. The second station
20
can then send a message to the first station
10
that indicates which PDUs
21
r
were received by using the sequence numbers
6
r
of each received PDU
21
r
, or may request that a PDU
11
t
be re-transmitted by specifying the sequence number
5
t
of the PDU
11
t
to be re-transmitted. Alternatively, in an unacknowledged transmission mode, 7-bit sequence numbers
5
t
,
6
t
are explicitly carried by the transmitted (PDUs)
11
t
,
21
t
, but received PDUs
11
r
,
21
r
are not acknowledged as successfully received. In certain special cases, such as a transparent transmission mode, sequence numbers are not even assigned to (PDUs)
11
t
,
11
r
,
21
t
,
21
r
. This transparent transmission mode, however, is not of direct relevance to the present invention. The present invention concerns itself with only acknowledged and unacknowledged transmission modes, both of which use explicitly embedded sequence numbers
5
t
,
6
t
in the transmitted PDUs
11
t
,
21
t.
The PDUs
11
t
and
21
t
are generally not transmitted “out in the open”. A ciphering engine
14
on the first station
10
, and a corresponding ciphering engine
24
on the second station
20
, together ensure secure and private exchanges of data exclusively between the first station
10
and the second station
20
. A primary function of the ciphering engine
14
,
24
is the obfuscation (i.e., ciphering, or encryption) of data held within a transmitted PDU
11
t
,
21
t
so that the corresponding PDU
11
r
,
21
r
presents a meaningless collection of random numbers to an eavesdropper. For transmitting a PDU
11
t
, the ciphering engine
14
uses, amongst other inputs, a ciphering key
14
k
to perform ciphering functions upon a PDU
11
t
. To properly decipher a corresponding PDU
21
r
, the corresponding ciphering engine
24
must use an identical ciphering key
24
k
. The ciphering keys
14
k
,
24
k
remain constant across all PDUs
11
t
,
21
t
(and thus corresponding PDUs
21
r
,
11
r
) and channels
12
,
22
, until explicitly changed by both the first station
10
and the second station
20
. Changing of the ciphering keys
14
k
,
24
k
is effected by a security mode reconfiguration process that involves handshaking between the first station
10
and the second station
20
to ensure proper synchronization of the ciphering engines
14
,
24
. The base station, i.e., the first station
10
, typically initiates the security mode reconfiguration process. Security mode reconfiguration is used to both activate and deactivate ciphering of transmitted PDUs
11
t
,
21
t
, and to change the ciphering key
14
k
,
24
k.
It is noted that, for the sake of security, the ciphering keys
14
k
and
24
k
should be changed after a predetermined security interval
14
x
. The security interval
14
x
may depend upon an actual elapsed time-of-use of the ciphering key
14
k
,
24
k
, or upon a usage count of the ciphering key
14
k
,
24
k
. Regardless, periodic changing of the ciphering key
14
k
,
24
k
makes unauthorized deciphering of received PDUs
11
r
,
21
r
more difficult. When an established channel
12
,
22
exceeds the security interval
14
x
, the first station
10
(i.e., the base station) may initiate a security mode reconfiguration process to change the ciphering keys
14
k
and
24
k
to new ciphering keys
14
n
and
24
n
. Both of the ciphering keys
14
n
and
24
n
are identical, and should not be the same as the previous ciphering keys
14
k
and
24
k
. Changing over to the new ciphering keys
14
n
,
24
n
must be carefully synchronized across all channels
12
,
22
to ensure that transmitted (PDUs)
11
t
,
21
t
are properly deciphered into received PDUs
21
r
,
11
r
. For example, if a (PDUs)
11
t
is enciphered using the ciphering key
14
k
, and the ciphering engine
24
attempts to decipher the corresponding received PDU
21
r
using the new ciphering key
24
n
, the received PDU
21
r
will be deciphered into meaningless data due to the lack of synchronization of the ciphering keys
14
k
and
24
n
as applied to the PDUs
11
t
and
21
r.
Security mode reconfiguration is a somewhat complicated process that involves several steps. One of the initial steps is the transmitting by the first station
10
of a ciphering reconfiguration message, a so-called security mode command, along a special signaling channel
12
s
to the second statio
AsusTek Computer Inc.
Hsu Winston
Sheikh Ayaz
Vaughan Michael
LandOfFree
Processing channel resets while performing a ciphering... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Processing channel resets while performing a ciphering..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Processing channel resets while performing a ciphering... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3273014