FPGA configuration bitstream encryption using modified key

• US 8,750,503 B1
• Filed: 01/25/2013
• Issued: 06/10/2014
• Est. Priority Date: 01/25/2005
• Status: Active Grant

• Current Assignee: Altera Corporation (Intel Corporation)
• Original Assignee: Altera Corporation (Intel Corporation)
• Inventors: Streicher, Keone, Jefferson, David, Joyce, Juju, Langhammer, Martin
• Primary Examiner(s): POWERS, WILLIAM S
• Application Number:
  US13/750,360
• Time in Patent Office: 501 Days
• Field of Search: 380/44
• US Class Current: 380/44
• CPC Class Codes: H04L 2209/24 Key scheduling, i.e. generating round keys or sub-keys for block encryption
• 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
• CPC Class Codes: H04L 9/065 Encryption by serially and continuously modifying data stream elements, e.g. stream cipher systems, RC4, SEAL or A5/3
• CPC Class Codes: H04L 9/0822 using key encryption key
• CPC Class Codes: H04L 9/0861 Generation of secret information including derivation or calculation of cryptographic keys or passwords

Abstract

Circuits, methods, and apparatus that prevent detection and erasure of a configuration bitstream or other data for an FPGA or other device. An exemplary embodiment of the present invention masks a user key in order to prevent its detection. In a specific embodiment, the user key is masked by software that performs a function on it a first number of times. The result is used to encrypt a configuration bitstream. The user key is also provided to an FPGA or other device, where the function is performed a second number of times and the result stored. When the device is configured, the result is retrieved, the function is performed on it the first number of times less the second number of times and then it is used to decrypt the configuration bitstream. A further embodiment uses a one-time programmable fuse (OTP) array to prevent erasure or modification.

Claims

1. A method of decrypting data on an integrated circuit, the method comprising:

retrieving a count value from a memory of the integrated circuit;

processing a data encryption key based on the count value to produce a modified data encryption key;

modifying contents of the memory containing the count value after producing the modified data encryption key; and

decrypting data based on the modified data encryption key.

2. The method of claim 1, further comprising obtaining a data encryption function and wherein processing the data encryption key based on the count value comprises applying the data encryption function to the data encryption key for a number of times equal to the count value.

3. The method of claim 2, wherein:

the data encryption function comprises a first sub-function and a second sub-function; and

the count value comprises a first sub-count value and a second sub-count value corresponding to the first sub-function and second sub-function, respectively.

4. The method of claim 2, wherein the data encryption function is based on the Advanced Encryption Standard (AES).

5. The method of claim 1, wherein the data encryption key is obtained from a device external to the integrated circuit.

6. The method of claim 1, wherein the retrieving, processing, and modifying steps each occur prior to configuration of the integrated circuit for operational use.

7. The method of claim 1, further comprising:

receiving encrypted configuration data; and

decrypting the encrypted configuration data using the modified data encryption key.

8. The method of claim 1, wherein the integrated circuit is a field programmable gate array (FPGA).

9. The method of claim 1, wherein the count value is not recoverable from the modified data encryption key.

10. The method of claim 1, wherein the count value is an integer value greater than one.

11. An integrated circuit comprising:

read circuitry configured to retrieve a count value from a memory of the integrated circuit; and

encryption circuitry configured to;

process a data encryption key based on the count value to produce a modified data encryption key;

modify contents of the memory containing the count value after producing the modified data encryption key; and

decrypt data based on the modified data encryption key.

12. The integrated circuit of claim 11, further comprising interface circuitry configured to obtain a data encryption function and wherein the encryption circuitry is further configured to process the data encryption key based on the count value by applying the data encryption function to the data encryption key for a number of times equal to the count value.

13. The integrated circuit of claim 11, further comprising interface circuitry configured to obtain the data encryption key from a device external to the integrated circuit.

14. The integrated circuit of claim 11, wherein the encryption circuitry is further configured to perform the processing and modifying steps prior to a configuration of the integrated circuit for operational use.

15. The integrated circuit of claim 11, wherein the integrated circuit is a field programmable gate array (FPGA).

16. A method of decrypting data on an integrated circuit, the method comprising:

receiving encrypted configuration data;

retrieving a count value from a memory of the integrated circuit;

generating a modified data encryption key based on the count value;

modifying contents of the memory containing the count value after producing the modified data encryption key; and

decrypting the encrypted configuration data using the modified data encryption key.

17. The method of claim 16, wherein generating the modified data encryption key based on the count value comprises:

obtaining a data encryption function and an unmodified data encryption key from a device external to the integrated circuit, and

applying the data encryption function to the unmodified data encryption key for a number of times equal to the count value to produce the modified data encryption key.

18. The method of claim 17, wherein the modifying step occurs prior to configuration of the integrated circuit for operational use.

19. The method of claim 16, wherein the count value is not recoverable from the modified data encryption key.

20. The method of claim 16, wherein said modifying contents of the memory containing the count value comprises deleting the count value from the memory.