Method and apparatus to maintain encryption synchronization in a multi-modulation TDM system

• US 20030188148A1
• Filed: 03/29/2002
• Published: 10/02/2003
• Est. Priority Date: 03/29/2002
• Status: Active Grant

• Current Assignee: Motorola Solutions, Inc.
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Logalbo, Robert D., Stogner, Darrell, Conrad, Alan
• Granted Patent: US 7,095,856 B2
• Time in Patent Office: Days
• US Class Current: 713/150
• CPC Class Codes: H04K 1/00 Secret communication
• CPC Class Codes: H04L 2209/80 Wireless network architectures or network communication protocols for wireless network security H04W12/00
• CPC Class Codes: H04L 9/0668 producing a non-linear pseudorandom sequence
• CPC Class Codes: H04L 9/12 Transmitting and receiving encryption devices synchronised or initially set up in a particular manner

Abstract

Encryption synchronization (e-sync) is maintained between a transmitter (104) and one or more receivers (102) in a multi-modulation TDM system (100) where information is communicated in slots (402) comprising a slot header (404) and one or more data blocks (406), and wherein the data blocks are eligible to be encoded at different modulation rates thereby creating a likelihood of different numbers of blocks in different slots. The receiver and transmitter employ respective encryption elements (200, 300) comprising e-sync shifter elements (202, 302) and encryption algorithm blocks (204, 304). The e-sync shifter element provides an e-sync signal defining an encryption state vector to the encryption algorithm block and is operable to advance the encryption state vector (in the case of the receiver) according to a number of received bits plus a variable number of bits. The variable number depends on the number of bits within a block, the maximum number of blocks that could be within a slot and the actual number of blocks within the slot.

Claims

1. A method for a receiving device to maintain encryption synchronization in a multi-modulation TDM system whereby information is communicated in slots comprising a slot header and one or more data blocks, the data blocks each including a number of bits (NB) and being eligible to be encoded at different respective modulation rates thereby creating a likelihood of different numbers of blocks in different slots, the method comprising:

attempting, by the receiving device, to determine a number of blocks (B) in at least a first received slot;

if the receiving device can not determine the number of blocks (B) in the first slot,

determining a maximum number of blocks (B_MAX) that could be within the slot; and

advancing an encryption state of the receiving device a number of bits (N_B×

B_MAX).

2. The method of claim 1, wherein the step of attempting to determine the number of blocks (B) in at least a first slot comprises attempting to decode the slot header of the first slot, wherein the slot header defines at least the number of blocks (B) in the first slot.

3. The method of claim 1, wherein the step of determining a maximum number of blocks (B_MAX) that could be within the slot comprises:

determining a maximum modulation rate that is eligible to be used within the slot; and

determining a number of blocks that would occur in the slot corresponding to the maximum modulation rate.

4. The method of claim 1, wherein the step of advancing the encryption state of the receiving device the number of bits (N_B×

B_MAX) comprises;

decoding, by the receiving device, N_B×

B_MAX bits; and

advancing a shift register in an encryption device associated with the receiving device, a number of bits corresponding to the N_B×

B_MAX bits.

5. The method of claim 1, further comprising, if the receiving device determines the number of blocks (B) in the first slot, steps of:

advancing the encryption state of the receiving device B×

N_B bits, thereby corresponding to the number of bits in the first slot; and

advancing the encryption state N_B×

(B_MAX−

B) bits defining a shift of zero or more bits in addition to the number of bits in the first slot.

6. The method of claim 5, wherein the step of advancing the encryption state N_B×

(B_MAX−

B) bits is accomplished after the step of advancing the encryption state of the receiving device B×

N_B bits.

7. The method of claim 5, wherein the step of advancing the encryption state N_B×

(B_MAX−

B) bits is accomplished prior to the step of advancing the encryption state of the receiving device B×

N_B bits.

8. The method of claim 5, wherein the step of advancing the encryption state of the receiving device B×

N_B bits comprises;

for each consecutive block, generating N_B bits, and advancing a shift register corresponding to the N_B bits.

9. The method of claim 8, further comprising:

for each consecutive block, attempting to determine a targeted recipient of the block; and

if the receiving device can not determine the targeted recipient of a block, discarding the block and the N_B bits generated for the block.

10. The method of claim 9, further comprising:

if the receiving device determines itself not to be the targeted recipient of a block, discarding the block and the NB bits generated for the block.

11. The method of claim 9, further comprising:

if the receiving device determines itself to be the targeted recipient of a block, apply the N_B bits to the block to process the block.

12. An encryption element comprising:

an e-sync shifter element; and

an encryption algorithm block,

the e-sync shifter element being operable to provide an e-sync signal defining an encryption state vector to the encryption algorithm block, the e-sync shifter element being operable to advance the encryption state vector according to a number of received bits plus a variable number of zero or more bits.

13. The encryption element of claim 12, being employed in a multi-modulation TDM system whereby information is communicated in slots comprising a slot header and one or more data blocks, the data blocks each including a number of bits (N_B) and being eligible to be encoded at different respective modulation rates thereby creating a likelihood of different numbers of blocks in different slots,

the variable number comprising N_B×

(B_MAX−

B) bits, wherein B_MAX defines a maximum number of blocks that could be within a slot and B defines the actual number of blocks within the slot.