Cryptographic device with stored key data and method for using stored key data to perform an authentication exchange or self test
View Patent ↗In preferred embodiments, a cryptographic device in which two key sets are stored: a normal key set (typically unique to the device) and a test key set (typically used by each of a relatively large number of devices). The device uses the normal key set in a normal operating mode and uses the test key set in at least one test mode which can be a built-in self test mode. Alternatively, the device stores test data (e.g., an intermediate result of an authentication exchange) in addition to or instead of the test key set. In other embodiments, the invention is a cryptographic device including a cache memory which caches a portion of a key set for performing an authentication exchange and/or at least one authentication value generated during an authentication exchange. Other embodiments of the invention are systems including devices that embody the invention and methods that can be performed by systems or devices that embody the invention.
1. A method for performing a self test of a cryptographic device, wherein a first key set and test data are stored in the device, the test data include authentication test data indicative of at least one result of at least one predetermined operation on a test key set, the authentication test data consist of fewer bits than the test key set, and the device is operable in a normal mode to perform at least one of encryption and decryption on input data using the first key set, said method including the steps of:
(a) upon initiation of the self test, selecting the test data rather than the first key set;
(b) performing an abbreviated authentication procedure using the authentication test data, wherein the abbreviated authentication procedure is an abbreviated version of a full authentication procedure that can be performed on the test key set, and the abbreviated authentication procedure on the authentication test data produces a result identical to a result of the full authentication procedure on the test key set; and
(c) comparing at least one result of the authentication procedure to at least one expected result determined by the test data, and setting a flag indicative of the result of the comparison.
2. The method of claim 1 , wherein step (b) also includes the step of performing one of encryption and decryption on a block of the test data.
3. The method of claim 1 , wherein the predetermined operation is an HDCP authentication exchange, and the authentication test data are indicative of an HDCP shared value, Km.
4. The method of claim 1 , wherein a subset of the test key set is also stored in the device, and wherein step (a) includes the step of selecting the subset of the test key set, and wherein step (b) includes the step of performing the abbreviated authentication procedure using at least some of the test data and the subset of the test key set.
5. The method of claim 4 , wherein the predetermined operation is an HDCP authentication exchange, the authentication test data are indicative of an HDCP shared value, Km, and the subset of the test key set includes a key selection vector.
6. A method for performing a self test of a cryptographic device, wherein a first key set and test data are stored in the device, the test data include authentication test data indicative of at least one result of at least one predetermined operation on a test key set, the authentication test data consist of fewer bits than the test key set, and the device is operable in a normal mode to perform at least one of encryption and decryption on input data using the first key set, said method including the steps of:
(a) upon initiation of the self test, selecting the test data rather than the first key set;
(b) performing an abbreviated authentication procedure using the authentication test data, and performing one of encryption and decryption on a block of data, wherein the abbreviated authentication procedure is an abbreviated version of a full authentication procedure that can be performed on the test key set, and the abbreviated authentication procedure on the authentication test data produces a result identical to a result of the full authentication procedure on the test key set; and
(c) comparing at least one result of an operation performed in step (b) to at least one expected result indicated by the test data, and setting a flag indicative of the result of the comparison.
7. The method of claim 6 , wherein step (c) includes the step of comparing at least one result of the abbreviated authentication procedure to at least one expected authorization procedure result determined by the test data.
8. The method of claim 6 , wherein the predetermined operation is an HDCP authentication exchange, and the authentication test data are indicative of an HDCP shared value, Km.