Method for cryptographic authentication

• US 8,195,955 B2
• Filed: 05/16/2007
• Issued: 06/05/2012
• Est. Priority Date: 05/30/2006
• Status: Active Grant

• Current Assignee: NXP B.V. (NXP Semiconductors NV)
• Original Assignee: NXP B.V. (NXP Semiconductors NV)
• Inventors: Nowottnick, Juergen, Boeh, Frank
• Primary Examiner(s): Srivastava, Vivek
• Assistant Examiner(s): Salehi, Helai
• Application Number:
  US12/302,610
• Publication Number:
  US 20090158055A1
• Time in Patent Office: 1,847 Days
• Field of Search: 713/189, 726 1- 36
• US Class Current: 713/189
• CPC Class Codes: G06F 21/34 involving the use of external additional devices, e.g. dongles or smart cards
• CPC Class Codes: G06F 2221/2103 Challenge-response

Abstract

The invention relates to a method for cryptographic authentication in access security systems. The aim of the invention is to provide a software solution. To this end, the method for secured storage of counter states in a non-volatile memory (EEPROM) (10) involves an incrementing (11) process, and the current counter state is updated in only one EEPROM segment following each incrementing process (11), a subsequent access to the EEPROM (10) only being enabled in the event of a successful incrementing (11) of an EEPROM-based counter.

Claims

1. A method for cryptographic authentication in an access security system, the method comprising:

incrementing consecutive counts in segments of an Electrically Erasable Programmable Read-Only Memory (EEPROM) by;

retrieving an invalid count in one of three EEPROM segments;

detecting a maximum valid count from two remaining valid counts if an invalid count exists;

overwriting the invalid count with the maximum valid count;

when no invalid count exists, detecting a smallest valid count from three valid counts, wherein detecting the smallest valid count follows the retrieving step;

detecting a largest valid count from the three valid counts; and

overwriting the smallest valid count with the largest valid count, wherein the cryptographic authentication occurs after each successful execution of the incrementing step; and

after each incrementation, updating a current count in not more than one EEPROM segment to produce an updated counter value; and

using each updated counter value as a changing initialization value in subsequent cryptographic authentications.

2. The method as claimed in claim 1, wherein the access security system is a transponder.

3. The method as claimed in claim 1, further comprising:

determining the invalid count via a calculation of differences from the two remaining valid counts, where the invalid count has the largest difference from the two remaining valid counts.

4. The method as claimed in claim 1, further comprising:

forming, with the EEPROM-based count, a changing initialization value for a suitable cryptoalgorithm which serves to authenticate communication with the transponder.

5. The method as claimed in claim 1, further comprising:

producing the consecutive counts in the event of each incrementation by an up-counter or a down-counter.

6. The method of claim 1, further comprising:

storing each new count in only one EEPROM segment.

7. The method of claim 1, further comprising:

recording each authentication sequence with ensuing EEPROM access only once.

8. The method as claimed in claim 1, further comprising:

using a known counting rate to detect the invalid count.

9. The method of claim 1, further comprising:

calculating two cryptographic signatures based upon both a changing value from a base station and a changing value from the access security system.

10. The method as claimed in claim 3, further comprising:

defining threshold values for the differences from which a count is detected to be invalid.

11. The method of claim 5, wherein the up-counter is a stepsize up-counter.