Method for authenticating access to a secured chip by test device

Abstract

A method for authenticating access to a secured chip SC by a test device TD, the test device storing at least one common key CK and one test key TK, the secured chip SC storing the same common key CK and a reference digest F(TK) resulting from a cryptographic function on the test key TK, the method comprising the steps of:—receiving, by the test device TD, a challenge R produced by the secured chip SC,—combining, by the test device TD, the received challenge R with the test key TK by applying a bidirectional mathematical operation (op), encrypting the result (TK op R) with the common key CK, obtaining a cryptogram CK(TK op R),—sending the cryptogram CK(TK op R) to the secured chip SC—decrypting, by the secured chip SC, the cryptogram CK(TK op R) with the common key CK, obtaining an image key TK′ representing the test key TK by applying, with the challenge R, the reverse operation (op-1) of the mathematical operation (op) previously used by the test device TD,—calculating an expected digest F(TK′) of the image key TK′ with a cryptographic one-way function,—verifying validity by comparing the expected digest F(TK′) with the reference digest F(TK),—if the result of the comparison between the digest F(TK′) of the image key TK′ and the reference digest F(TK) is positive, accessing, by the test device TD, the secure chip SC in a test mode.

Dependencies are inferred from the claim text.