Protecting secret information in a programmed electronic device

A method for protecting secret information in a programmed electronic device, the programmed electronic device comprising a non-trusted memory containing software, a data memory containing the secret information, and an access restriction logic unit that is adapted to allow or block read access to the secret information, the secret information being stored unalterably in the data memory, the secret information being adapted to be used for verifying the integrity of the software, the method comprising:

• when starting up the programmed electronic device, the access restriction logic unit allowing read access to the secret information;
• accessing the secret information for use in verifying the integrity of the software;
• the access restriction logic unit blocking further read access to the secret information while the device remains powered on, wherein the access restriction logic unit is a hardware component coupled between a processor unit and the data memory;
• and
• verifying the integrity of the software using the secret information, including:
• computing a hash value of the software using a secret key related to the secret information;
• and
• comparing the computed hash value with a predetermined signature associated with the software,
• wherein the software is executed in the programmed electronic device only if the integrity of the software has been verified successfully.

A semiconductor device, comprising:

• a data memory storing secret information;
• a program memory storing startup code;
• a processor unit adapted for executing the startup code, the startup code being adapted to cause the processor unit to access the secret information in the data memory for use in verifying the integrity of software to be executed by the processor unit;
• and
• an access restriction logic unit that allows the processor unit to access the secret information after starting up the semiconductor device and blocks access to the secret information after the processor unit has accessed the secret information,
• wherein the access restriction logic unit is adapted to block access to the secret information when a predetermined amount of time has passed after said starting up the programmed electronic device and while the device remains powered on, wherein the access restriction logic unit is a hardware component coupled between the processor unit and the data memory.

A programmed electronic device, comprising:

• a data memory unalterably storing secret information;
• a program memory storing startup code;
• a non-trusted memory storing software;
• a processor unit adapted for executing the startup code, the startup code being adapted to cause the processor unit to access the secret information in the data memory for use in verifying the integrity of the software stored in the non-trusted memory;
• and
• an access restriction logic unit that allows the processor unit to read the secret information after starting up the programmed electronic device and blocks read access to the secret information while the device remains powered on and after the processor unit has accessed the secret information, wherein the access restriction logic unit is a hardware component coupled between the processor unit and the data memory;
• wherein the startup code is further adapted to cause the processor unit to verify the integrity of the software using the secret information,
• wherein the startup code is further adapted to cause the processor unit to compute a hash value of the software using a secret key related to the secret information,
• wherein the startup code is further adapted to cause the processor unit to compare the computed hash value with a predetermined signature associated with the software and
• wherein the software is executed in the programmed electronic device only if the integrity of the software has been verified successfully.