Code authentication upon bootup for cable modems

• US 20060156007A1
• Filed: 01/07/2005
• Published: 07/13/2006
• Est. Priority Date: 01/07/2005
• Status: Active Grant

• Current Assignee: Google Technology Holdings LLC (Alphabet Inc.)
• Original Assignee: General Instrument Corporation (CommScope Holding Company, Inc.)
• Inventors: Stephens-Doll, Robert M.
• Granted Patent: US 7,454,616 B2
• Time in Patent Office: Days
• US Class Current: 713/176
• CPC Class Codes: H04L 9/3239 involving non-keyed hash functions, e.g. modification detection codes [MDCs], MD5, SHA or RIPEMD
• CPC Class Codes: H04L 9/3249 using RSA or related signature schemes, e.g. Rabin scheme

Abstract

An exemplary embodiment of a method (10) for authenticating software in a cable modem makes use of a secure key and certificate stored in flash memory. In this exemplary embodiment, the code employs a key to validate (16) a signature that is generated for each new build of the code. During build of the code, the code is digitally signed (12) using e.g., a Motorola RSA private key. The message digest and the signature are then stored at the end of code file itself (13). Each time the modem (52) reboots, the code can validate (16) that the image in flash has not been modified. This validation function (16) can be accomplished e.g., by calling an RSA Signature Verification function to confirm that the signature in the header equals the message digest signed by the manufacturer'"'"'s private key or the manufacturer'"'"'s CVC.

Claims

1. A method (10) for operating a cable modem comprising:

inserting (13) a RSA-SHA-1 based signature and related authenticated attributes at an end of the code file; and

validating (16) the code file during each reboot operation of the cable modem to confirm that the signature in a header equals the authenticated attributes signed by a private key that created the RSA-SHA-1 based signature.

2. The method (10) according to claim 1, further comprising:

signing (12) the code file using a private key to create an RSA-SHA-1 based signature.

3. The method (10) according to claim 1, further comprising:

modifying (14) an image code length in a code header to account for any extra bytes at the end of the code file.

4. The method (10) according to claim 3, further comprising:

recalculating (15) a message digest in the code header to account for the extra bytes stored at the end of the code file.

5. The method (10) according to claim 1, wherein said validating (16) is accomplished by calling an RSA Signature Verification function to confirm that the signature in the header equals the authenticated attributes signed by the private key.

6. A method (40) for authenticating software in a cable modem comprising:

storing (42) an RSA SHA-1 based signature, one or more authenticated attributes, and a Subject Public Key from the manufacturer'"'"'s CVC in flash memory during download of new code to the cable modem; and

during a reboot process, validating (43) that the image in flash has not been modified.

7. A method (10) for authenticating code in an electronic device comprising:

generating (11) the code;

signing (12) the code using a signing key;

validating (16) the code during a reboot process of the electronic device by verifying that a signature in a header equals signed authenticated attributes.

8. The method (10) according to claim 7, further comprising:

inserting (13) the signature and authenticated attributes at an end of the signed code along with a current copy of said header.

9. The method (10) according to claim 8, further comprising:

modifying (14) a code length in a new header to account for extra bytes stored at the end of the code; and

recalculating (15) a message digest to account for the modified code length.

10. An apparatus (52) including self-authenticating code comprising:

a memory (51) storing the code; and

a processor (55a) coupled to the memory (51) and inserting an RSA-SHA-1 based signature and related authenticated attributes at an end of the code file, and validating the code file during each reboot operation of the cable modem to confirm that the signature in a header equals the authenticated attributes signed by a private key that created the RSA-SHA-1 based signature.

11. The apparatus (52) according to claim 10, wherein said code is digitally signed using a private key to create an RSA-SHA-1 based signature.

12. The apparatus (52) according to claim 10, wherein said processor (55a) modifies an image code length in a code header to account for any extra bytes at the end of the code file.

13. The apparatus (52) according to claim 12, wherein said processor (55a) recalculates a message digest in the code header to account for the extra bytes stored at the end of the code file.

14. The apparatus (52) according to claim 10, wherein said processor validates the code by calling an RSA Signature Verification function to confirm that the signature in the header equals the authenticated attributes signed by the private key.

15. An apparatus (50) for communicating new code to a plurality of electronic devices (52a-n) via a network (53) comprising:

a server (54) stored a current version of code to be downloaded to the plurality of electronic devices (52a-n);

a memory (51a-n) disposed in each of the plurality of electronic devices (52a-n) to store code having an RSA-SHA-1 based signature and related authenticated attributes stored at an end of the code file; and

a processor (55a-n) disposed in each of the plurality of electronic devices (52a-n) communicating with the server (54), said processor (55a-n) being coupled to the memory (51a-n) and validating the code file during each reboot operation to confirm that the signature in a header equals the authenticated attributes signed by a private key that created the RSA-SHA-1 based signature.

16. The apparatus (50) according to claim 15, wherein said code is digitally signed using a private key to create an RSA-SHA-1 based signature.

17. The apparatus (50) according to claim 15, wherein said processor (55a) modifies an image code length in a code header to account for any extra bytes at the end of the code file.

18. The apparatus (50) according to claim 17, wherein said processor (55a) recalculates a message digest in the code header to account for the extra bytes stored at the end of the code file.

19. The apparatus (50) according to claim 15, wherein said processor (55a) validates the code by calling an RSA Signature Verification function to confirm that the signature in the header equals the authenticated attributes signed by the private key.

20. A method (20) for authenticating code in a device comprising:

calculating (21) an on-the-fly SHA-1 message digest over a stored Code Header and the Code Image;

comparing (22) a new message digest with a message digest that was stored;

if the new message digest is not the same as the stored message digest, declaring (24) the image to be invalid and sending (25) a syslog message to a system operator informing the system operator of a tampered image and shutting down the device; and

if the new message digest is the same as the stored message digest, then;

calling (27) an RSA Signature Verification function to confirm that a signature equals signed Authenticated Attributes;

if the signature is valid, executing (29) the code normally; and

if the signature is not valid, sending (25) sends a syslog message to the system operator informing the system operator of a tampered image and shutting the device down.