System for preventing electronic memory tampering

• US 6,026,293 A
• Filed: 09/05/1996
• Issued: 02/15/2000
• Est. Priority Date: 09/05/1996
• Status: Expired due to Term

• Current Assignee: Ericsson, Inc. (Telefonaktiebolaget LM Ericsson)
• Original Assignee: Ericsson, Inc. (Telefonaktiebolaget LM Ericsson)
• Inventors: Osborn, William R.
• Primary Examiner(s): Dolinar, Andrew M.
• Application Number:
  US08/706,574
• Time in Patent Office: 1,258 Days
• Field of Search: 455/410, 455/411, 455/418, 455/419, 711/163, 711/164, 395/186, 380/4, 380/25, 380/30
• US Class Current: 455/411
• CPC Class Codes: G06F 21/565 by checking file integrity
• CPC Class Codes: H04L 2209/80 Wireless network architectures or network communication protocols for wireless network security H04W12/00
• CPC Class Codes: H04L 63/0823 using certificates cryptographic mechanisms or cryptographic arrangements for entity authentication involving certificates H04L9/3263
• CPC Class Codes: H04L 63/123 received data contents, e.g. message integrity
• CPC Class Codes: H04L 9/0643 Hash functions, e.g. MD5, SHA, HMAC or f9 MAC
• 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 9/3247 involving digital signatures
• CPC Class Codes: H04L 9/3271 using challenge-response
• CPC Class Codes: H04W 12/06 Authentication
• CPC Class Codes: H04W 12/10 Integrity
• CPC Class Codes: H04W 12/126 Anti-theft arrangements, e.g. protection against subscriber identity module [SIM] cloning
• CPC Class Codes: H04W 12/71 Hardware identity
• CPC Class Codes: H04W 88/02 Terminal devices

Abstract

Methods and apparatus for preventing tampering with memory in an electronic device, such as a cellular telephone, are disclosed. An electronic device having a memory and a processing means contains logic that is used to perform a one-way hash calculation on the device'"'"'s memory contents whereby an audit hash value, or signature, of such contents is derived. The audit hash value is compared to a an authenticated valid hash value derived from authentic memory contents. A difference between the audit and valid hash values can be indicative of memory tampering. In accordance with another aspect of the invention, electronic device memory contents can be updated by a data transfer device that is authenticated before being permitted access to the memory contents. Data transfer device authentication involves the use of a public/private key encryption scheme. When the data transfer device interfaces with a electronic device and requests memory access, a process to authenticate the data transfer device is initiated.

Claims

1. A cellular telephone comprising:

a microprocessor; and

a memory;

wherein the microprocessor performs a hash calculation on contents of the memory to derive an audit hash value, which audit hash value is compared to a valid hash value previously derived from perlormance of the hash calculation on authentic memory contents, said hash calculation and comparison being secure from tampering.

2. The cellular telephone claimed in claim 1, wherein the audit hash value is periodically derived and compared to the valid hash value.

3. The cellular telephone claimed in claim 2, wherein the periodic derivation of the hash value is performed pursuant to expiration of a hardware-based timer.

4. The cellular telephone claimed in claim 1, wherein said memory includes a flash memory and an EEPROM.

5. The cellular telephone claimed in claim 4, wherein the audit hash value derived based on selected contents of the flash memory and the EEPROM.

6. The cellular telephone claimed in claim 5, wherein the selected contents include an electronic serial number.

7. The cellular telephone claimed in claim 5, wherein the selected contents include microprocessor program code.

8. The cellular telephone claimed in claim 1, further comprising:

a protected random access memory;

wherein the hash calculation is performed in conjunction with the protected random access memory.

9. The cellular telephone claimed in claim 8, further comprising security logic, wherein the security logic supervises access to the protected random access memory.

10. The cellular telephone claimed in claim 1, wherein the valid hash value is authenticated using a public key stored within the memory.

11. The cellular telephone claimed in claim 1, wherein the valid hash value is given a digital signature using a private key.

12. The cellular telephone claimed in claim 10, wherein a public/private key system is used that is selected from the group of algorithms consisting of:

ELGAMAL, RSA, DSA, Fiege-Fiat-Shamir, and Fiat-Shamir.

13. The cellular telephone claimed in claim 1, wherein the hash calculation performed is selected from the group of hash functions consisting of:

Snerfu, H-Hash, MD2, MD4, MD5, Secure Hash Algorithm (SHA), and HAVAL.

14. In a cellular telephone, a method for detecting memory tampering, the method comprising the steps of:

storing a signed valid hash value produced by performing a hash calculation on selected contents of a memory which memory selected contents are known to be authentic;

producing an audit hash value by performing the hash calculation on the selected contents of the memory; and

comparing the audit hash value to the valid hash value, whereby a difference between the audit and the valid hash values indicates alteration of the selected memory contents, wherein the steps of storing, producing, and comparing are secure from tampering.

15. The method claimed in claim 14, wherein the step of producing the audit hash value is performed in conjunction with a protected random access memory.

16. The method claimed in claim 14, further including the step of:

signing the valid hash value with a digital signature based on a private key.

17. The method claimed in claim 14, wherein the steps of producing the audit hash value and of comparing The audit and valid hash values are performed periodically.

18. The method claimed in claim 14, wherein the step of producing the audit hash value is performed pursuant to the expiration of a hardware-based timer.

19. The method claimed in claim 14, wherein the step of producing the audit hash value involves calculating audit hash value segments.

20. The method claimed in claim 19, wherein calculation of an audit hash value segment can be delayed as necessary while other processes occurring within the cellular telephone are completed.

21. The method claimed in claim 14, wherein the valid hash value is given a digital signature, and wherein the step of comparing the audit hash value to the valid hash value includes the step of authenticating the valid hash value against the signature.

22. In a cellular telephone, an apparatus comprising:

a microprocessor;

a flash memory whose contents include operating instructions for the cellular telephone; and

an electronically erasable programmable read-only memory (EEPROM) whose contents include a valid hash value derived by performing a one-way hash calculation over selected portions of authentic flash and EEPROM memory contents;

wherein the microprocessor periodically generates an audit hash value by performing the hash calculation over the selected portions, which audit hash value is compared to the authenticated valid hash value to assess whether at least one of the flash and the EEPROM memories have been altered.

23. The apparatus claimed in claim 22, wherein the one-way hash calculation is selected from the group consisting of:

Snerfu, H-Hash, MD2, MD4, MD5, Secure Hash Algorithm (SHA), and HAVAL.

24. The apparatus claimed in claim 22, wherein the valid hash value receives a digital signature by a private key prior to being stored, and is authenticated by a public key for the purpose of comparison with the audit hash value.

25. The apparatus claimed in claim 24, wherein a public/private key system used is selected from the group of algorithms consisting of:

ELGAMAL, RSA, DSA, Fiege-Fiat-Shamir, and Fiat-Shamir.

26. The apparatus claimed in claim 24, wherein the valid hash value receives a digital signature by the private key using processing means external to the cellular telephone.

27. A system for preventing unauthorized access to a cellular telephone memory programming capability, the system comprising:

a cellular telephone, including

a memory for storing data, and

a microprocessor having a means for authentication; and

a data transfer device including signature means for supplying a signed message to the cellular mobile telephone;

wherein the cellular telephone microprocessor assesses the authenticity of the data transfer device based upon an analysis of a signed message supplied by the data transfer device via a first port and a second port of a general purpose computer, wherein the data transfer device is attachable to the first port, and the second port is used to interface with the cellular telephone.

28. A method for assessing the authenticity of a cellular telephone programming device, the method comprising the steps of:

sending a challenge message in response to a programming request via a first port and a second port of a general purpose computer, wherein the cellular telephone programming device is attachable to the first port, and the second port is used to interface with the cellular telephone;

signing the challenge message in the cellular telephone programming device;

sending the signed challenge message to the cellular telephone;

authenticating the challenge message within the cellular telephone; and

rejecting the cellular telephone programming device if the challenge message is not received by the authentication step.

29. In a system comprising a data transfer device for programming a cellular telephone, a method for preventing unauthorized access to memory in the cellular telephone, said method comprising the steps of:

sending a programming request from the data transfer device to the cellular telephone via a first port and a second port of a general purpose computer, wherein the data transfer device is attachable to the first port, and the second port is used to interface with the cellular telephone;

sending a challenge message from the cellular telephone to the data transfer device in response to the programming request;

signing a challengeresponse message within the data transfer device;

sending the signed challenge response message to the cellular telephone;

authenticating the challenge response message within the cellular telephone; and

entering a programming miode if authentication of the signal challenge response message confirms authenticity of the data transfer device.

30. A system for programming a cellular telephone, the system comprising:

a programmer;

a general purpose computer having a first and a second port;

wherein the programmer is attachable to the first port, and the second port is used to interface with a cellular telephone to be programmed, wherein in response to a request to program the cellular telephone received from the programmer, the cellular telephone returns a challenge which challenge is signed by the programmer and returned to the cellular telephone for authentication, whereby recovery of the challenge through authentication of the signed challenge is indicative of programmer authenticity and causes the cellular telephone to enter into a programming mode.

31. The system of claim 30, wherein the cellular telephone comprises:

a microprocessor,

wherein in response to the request to program the cellular telephone received from the programmer, the microprocessor in the cellular telephone issues the challenge to the programmer.

32. In a cellular telephone, a system for preventing fraudulent memory access, comprising:

security logic;

a read only memory containing instruction code;

protected random access memory;

wherein the security logic prevents accesses to the protected random access memory by elements other than the read only memory; and

a hardware-based timer, wherein the security logic prevents accesses to the hardware-based timer by elements other than the read only memory.

33. The system claimed in claim 32, wherein accesses to the protected random access memory pursuant to instruction code in the read only memory can only take place when the system is in a supervisory mode.

34. An electronic device comprising:

a microprocessor; and

a memory;

wherein the microprocessor performs a hash calculation on contents of the memory to derive an audit hash value, which audit hash value is compared to a valid hash value previously derived from performance of the hash calculation on authentic memory contents, said hash calculation and comparison being secure from tampering.

35. The electronic device claimed in claim 34, wherein the audit hash value is periodically derived and compared to the valid hash value.

36. The electronic device claimed in claim 35, wherein the selected contents include microprocessor programming code.

37. The electronic device claimed in claim 34, wherein the memory includes a flash memory and an EEPROM.

38. The electronic device claimed in claim 37, wherein the audit hash value derived based on selected contents of the flash memory and the EEPROM.

39. The electronic device claimed in claim 34, wherein the valid hash value is authenticated using a public key stored within the memory.

40. The electronic device claimed in claim 34, wherein the valid hash value is given a digital signature using a private key.

41. The electronic device claimed in claim 40, wherein a public/private key system used is selected from the group of public key algorithms consisting of:

ELGAMAL, RSA, DSA, Fiege-Fiat-Shamir, and Fiat-Shamir.

42. The electronic device claimed in claim 34, wherein the hash calculation performed is selected from the group of hash functions consisting of:

Snerfu, H-Hash, MD2, MD4, MD5, Secure Hash Algorithm (SHA), and HAVAL.

43. In an electronic device, a method for detecting memory tampering, the method comprising the steps of:

storing a signed valid hash value produced by performing a hash calculation on selected contents of a memory which memory selected contents are known to be authentic;

producing an audit hash value by performing the hash calculation on the selected contents of the memory; and

comparing the audit hash value to the valid hash value, whereby a difference between the audit and the valid hash values indicates alteration of the selected memory contents, wherein the steps of storing, producing, and comparing are secure from tampering.

44. The method claimed in claim 43, further including the step of:

signing the valid hash value with a digital signature based on a private key.

45. The method claimed in claim 43, wherein the steps of producing the audit hash value and of comparing the audit and valid hash values are performed periodically.

46. The method claimed in claim 43, wherein the step of producing the audit hash value involves calculating audit hash value segments.

47. The method claimed in claim 46, wherein calculation of an audit hash value segment can be delayed as necessary while other processes occurring within the electronic device are completed.

48. The method claimed in claim 43, wherein the valid hash value is given a digital signature, and wherein the step of comparing the audit hash value to the valid hash value includes the step of authenticating the valid hash value against the signature.

49. A system for preventing memory access, said system comprising:

security logic

a read only memory containing instruction code;

protected random access memory;

wherein the security logic prevents accesses to the protected random access memory by elements other than the read only memory; and

a hardware-based timer, wherein the security logic prevents accesses to the hardware-based timer by elements other than the read only memory.

50. The system claimed in claim 49, wherein accesses to the protected random access memory pursuant to instruction code in the read only memory can only take place when the system is in a supervisory mode.