Associating a processing chip and a non-volatile memory chip
Techniques in electronic systems, such as in systems including a processing chip and one or more external memory chips, provide improvements in one or more of system security, performance, cost, and efficiency. The processing chip includes autonomous hardware that enables the processing chip, without a use of any CPUs, to form an association between itself and a particular flash chip. Prior to an initial operational use of the processing chip, the autonomous hardware is able to generate a key unique to the processing chip using a physically unclonable function, and then to form the association by encrypting a stream of data using the key and writing the encrypted result to the flash chip. For example, the stream of data comprises a bootloader and an operating system, and the processing chip is able to begin the initial operational use by securely booting using data copied from the flash chip.
1. A method, comprising:
prior to an initial operational use of a particular one of two or more processing chips, creating, in the particular processing chip via autonomous hardware comprising a physically unclonable function, a key, wherein the key is only accessible by the autonomous hardware and at least a portion of the key is never exposed outside of the particular processing chip;
prior to the initial operational use, associating, by the autonomous hardware, a particular flash chip with the particular processing chip, by performing operations comprising:
encrypting, using the key, a stream of data; and
writing the encrypted stream of data to the particular flash chip, wherein none of the two or more processing chips except the particular processing chip are able to decrypt the encrypted stream of data in the particular flash chip; and
wherein the stream of data comprises executable code used to securely boot the particular processing chip for the initial operational use; and
after the encrypted stream of data is written to the particular flash chip, changing a state of a read-only memory in the particular processing chip to change a function of the autonomous hardware and to prevent the key from being used in a subsequent encryption operation.
2. The method of claim 1 , wherein the particular flash chip is one of multiple flash chips.
3. The method of claim 2 , wherein only the particular processing chip is able to be securely booted with the particular flash chip.
4. The method of claim 2 , wherein only the particular flash chip is able to be used to securely boot the particular processing chip.
5. The method of claim 1 , wherein the key is used to encrypt the stream of data in a section of the particular flash chips and a second key is used to encrypt a second stream of data in a second section of the particular flash chip, and the second section is different from the section.
6. The method of claim 5 , further comprising:
securely booting the particular processing chip by performing operations comprising:
while holding one or more central processing units (CPUs) of the particular processing chip that are to be securely booted in a respective reset state, copying the encrypted stream of data from the particular flash chip to another memory chip coupled to the particular processing chip; and subsequent to the copying, releasing the reset state on at least one of the CPUs and allowing the at least one CPU to complete an initial instruction fetch referencing the executable code stored in the other memory chip by the copying.
7. The method of claim 1 , further comprising, subsequent to the associating, changing state in an on-chip read only memory (ROM) of the particular processing chip to disable use of the key for encryption, wherein the particular processing chip is able, using the key, to decrypt only the data stored in the particular flash chip.
8. The method of claim 1 , wherein the associating further comprises reading an external memory coupled to the particular processing chip to obtain the stream of data.
9. The method of claim 8 , wherein, the stream of data read from the external memory is stored unencrypted in the external memory; and
wherein the method further comprises, subsequent to the associating, changing state in an on-chip read only memory (ROM) of the particular processing chip so that further writes to the particular flash chip to update contents of the particular flash chip require that update data to be written to the particular flash chip from the external memory is stored encrypted in the external memory.
10. The method of claim 1 , wherein the creating is at a chip-level manufacturing time of the particular processing chip.
11. The method of claim 1 , wherein the associating further comprises computing an integrity check on the stream of data.
12. The method of claim 1 , wherein the key comprises a symmetric key.
13. The method of claim 1 , wherein the key comprises a public/private key pair;
wherein the private portion of the key is inaccessible other than to the autonomous hardware; and
wherein the method further comprises, prior to the initial operational use, providing the public portion of the key to an entity.
14. A system, comprising:
a particular one of two or more processing chips; and
a particular flash chip, wherein, prior to an initial operational use of the particular processing chip, a key is created in the particular processing chip via autonomous hardware comprising a physically unclonable function;
wherein the key is only accessible by the autonomous hardware and at least a portion of the key is never exposed outside of the particular processing chip;
wherein, prior to the initial operational use, the particular flash chip is associated, by the autonomous hardware, with the particular processing chip, by performing operations comprising:
encrypting, using the key, a stream of data; and
writing the encrypted stream of data to the particular flash chip, wherein none of the two or more processing chips except the particular processing chip are able to decrypt the encrypted stream of data in the particular flash chip; and
wherein the stream of data comprises executable code used to securely boot the particular processing chip for the initial operational use; and
after the encrypted stream of data is written to the particular flash chip, changing a state of a read-only memory in the particular processing chip to change a function of the autonomous hardware and to prevent the key from being used in a subsequent encryption operation.
15. The system of claim 14 , wherein the particular flash chip is included in one of multiple flash chips.
16. The system of claim 15 , wherein only the particular processing chip is able to be securely booted with the particular flash chip.
17. The system of claim 15 , wherein only the particular flash chip is able to be used to securely boot the particular processing chip.
18. The system of claim 14 , wherein the key is used to encrypt the stream of data in a section of the particular flash chips and a second key is used to encrypt a second stream of data in a second section of the particular flash chip, and the second section is different from the section.
19. The system of claim 18 , wherein the system comprises another memory chip coupled to the particular processing chip; and
wherein the system is configured to securely boot the particular processing chip by performing operations comprising:
while holding one or more central processing units (CPUs) of the particular processing chip that are to be securely booted in a respective reset state, copying the encrypted stream of data from the particular flash chip to the other memory chip; and
subsequent to the copying, releasing the reset state on at least one of the CPUs and allowing the at least one CPU to complete an initial instruction fetch referencing the executable code stored in the other memory chip by the copying.
20. The system of claim 14 , wherein the system is configured to, subsequent to the associating, change state in an on-chip read only memory (ROM) of the particular processing chip to disable use of the key for encryption, wherein the particular processing chip is able, using the key, to decrypt only the data stored in the particular flash chip.