Symmetric key encryption system with synchronously updating expanded key

• US 20070053516A1
• Filed: 08/19/2005
• Published: 03/08/2007
• Est. Priority Date: 08/19/2005
• Status: Active Grant

• Current Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Original Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Inventors: Katoozi, Mehdi, Jelatis, George
• Granted Patent: US 8,041,032 B2
• Time in Patent Office: Days
• US Class Current: 380/259
• CPC Class Codes: H04L 2209/08 Randomization, e.g. dummy operations or using noise
• CPC Class Codes: H04L 2209/20 Manipulating the length of blocks of bits, e.g. padding or block truncation
• CPC Class Codes: H04L 9/0631 Substitution permutation network [SPN], i.e. cipher composed of a number of stages or rounds each involving linear and nonlinear transformations, e.g. AES algorithms

Abstract

A method, apparatus, and system of encryption, including embedding reconfiguration information within a ciphertext block destined for a decryptor. The decryptor identifies the reconfiguration information, extracts such information, and uses it to alter a pre-cipher, which is used for decryption. The encryptor alters its pre-cipher synchronously with the decryptor.

Claims

1. A method comprising:

receiving a cipher key;

expanding the cipher key into a plurality of round keys;

creating a pre-cipher, based at least in part upon the cipher key and the plurality of round keys;

receiving a plurality of ciphertext blocks;

using the pre-cipher to decrypt the plurality of ciphertext blocks, yielding a plurality of plaintext blocks;

extracting a pre-cipher reconfiguration parameter from at least one of the plaintext blocks; and

altering the pre-cipher based upon the parameter.

2. The method of claim 1, wherein the act of receiving the cipher key comprises:

transmitting a public key to an external system prior to receiving the cipher key;

receiving a message containing the cipher key, the message having been encrypted by the public key; and

decrypting the message with a private key, to obtain the cipher key.

3. The method of claim 1, wherein the round keys are generated by an AES key expansion algorithm.

4. The method of claim 3, wherein the pre-cipher is generated by an AES cipher algorithm.

5. The method of claim 1, wherein the act of altering the pre-cipher comprises shifting the pre-cipher a quantity of bits determined by the parameter.

6. The method of claim 1, wherein the act of altering the pre-cipher comprises shuffling the pre-cipher based upon the parameter.

7. The method of claim 1, wherein the act of altering the pre-cipher comprises generating a pseudo-random number based upon the parameter, and using the pseudo-random number to determine a shift operation to be performed on the pre-cipher.

8. The method of claim 1, wherein the act of altering the pre-cipher comprises generating a pseudo-random number based upon the parameter, and using the pseudo-random number to determine a shuffle operation to be performed on the pre-cipher.

9. A method comprising:

transmitting a cipher key;

encrypting a plurality of plaintext blocks based upon a pre-cipher generated from the cipher key, yielding a plurality of ciphertext blocks;

transmitting the plurality of ciphertext blocks; and

subsequent to occurrence of a condition, transmitting a pre-cipher reconfiguration parameter.

10. The method of claim 9, wherein the condition comprises having transmitted more than a threshold quantity of ciphertext blocks.

11. The method of claim 9, wherein the condition comprises elapsing of a timer.

12. The method of claim 9, wherein the act of transmitting the parameter comprises inserting the parameter into a plaintext block, encrypting the plaintext block, and transmitting the plaintext block.

13. The method of claim 9, wherein the act of transmitting the parameter comprises inserting a plurality of parameters into a plurality of plaintext blocks, encrypting the plaintext blocks, and transmitting the plaintext blocks.

14. The method of claim 9, further comprising altering the pre-cipher based upon the parameter.

15. The method of claim 14, further comprising encrypting subsequent plaintext blocks using the altered pre-cipher.

16. An implantable device comprising:

a sense/stimulator channel; and

an input/output (I/O) interface; and

a controller coupled to the sense/stimulator channel and-to the I/O interface, the controller being configured to receive physiological or behavioral data from the sensor, and being further configured to receive a cipher key via the I/O interface, expand the cipher key into a plurality of round keys, create a pre-cipher, based at least in part upon the cipher key and the plurality of round keys, receive a plurality of ciphertext blocks via the I/O interface, use the pre-cipher to decrypt the plurality of ciphertext blocks, yielding a plurality of plaintext blocks, extract a pre-cipher reconfiguration parameter from at least one of the plaintext blocks, and alter the pre-cipher based upon the parameter.

17. The device of claim 16, wherein the controller is further configured to generate the round keys based upon an AES key expansion algorithm.

18. The device of claim 17, wherein the controller is further configured to generate the pre-cipher based upon an AES cipher algorithm.

19. The device of claim 16, wherein the controller is further configured to alter the pre-cipher by shifting the pre-cipher a quantity of bytes determined by the parameter.

20. The device of claim 16, wherein the controller is further configured to alter the pre-cipher by shuffling the pre-cipher based upon the parameter.

21. The device of claim 16, wherein the controller is further configured to alter the pre-cipher by generating a pseudo-random number based upon the parameter, and by using the pseudo-random number to determine a shift operation to be performed on the pre-cipher.

22. The device of claim 16, wherein the controller is further configured to alter the pre-cipher by generating a pseudo-random number based upon the parameter, and by using the pseudo-random number to determine a shuffle operation to be performed on the pre-cipher.

23. An implantable device comprising:

a sense/stimulator channel; and

an input/output (I/O) interface; and

a means for altering a pre-cipher based upon a parameter embedded in at least one ciphertext block received from the I/O interface.