# US 11,451,378 B2 · Device and method for encryption

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- Number: US 11,451,378 B2
- Document ID: US11451378B2
- Status: Granted
- Kind: B2
- Application number: 17/024,501
- Filed: 2020-09-17
- Published: 2021-04-01
- Granted: 2022-09-20
- Earliest claimed: 2019-09-30
- Assignees: STMicroelectronics S.r.l.
- Applicants: STMicroelectronics SA
- Inventors: Benjamin Baratte; Laurent Halajko
- Web page: https://patentgrep.com/patent/US11451378B2

## CPC

- H04L 9/0825: {using asymmetric-key encryption or public key infrastructure [PKI], e.g. key signature or public key certificates}
- H04L 9/0822: {using key encryption key}
- H04L 9/0841: {involving Diffie-Hellman or related key agreement protocols}
- H04L 9/088: {Usage controlling of secret information, e.g. techniques for restricting cryptographic keys to pre-authorized uses, different access levels, validity of crypto-period, different key- or password length, or different strong and weak cryptographic algorithms (network architectures or network communication protocols for using time-dependent keys in a packet data network H04L63/068)}
- H04L 9/0894: {Escrow, recovery or storing of secret information, e.g. secret key escrow or cryptographic key storage}
- H04L 9/14: using a plurality of keys or algorithms
- H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M)

## Abstract

An embodiment encryption method, implemented by an electronic circuit including a first non-volatile memory, comprises the creation of one or more first pairs of asymmetrical keys, the first pair or each of the first pairs comprising first private and public keys, and, for the or at least one of the first pairs, storing the first public key in the first memory, receiving a second public key during a communication session, and forming a first symmetrical key from the first private key and the second public key, the first public key staying stored in the first memory after the communication session.

## Claims

### Claim 1

An encryption method implemented by an electronic circuit including a first non-volatile memory, the method comprising:
creating a first pair of asymmetrical keys including a first private key and a first public key;
storing the first public key in the first non-volatile memory;
receiving a second public key during a communication session;
forming a first symmetrical key from the first private key and the second public key during the communication session;
erasing the first private key after forming the first symmetrical key and before the communication session ends; and
ending the communication session, the first public key remaining stored in the first non-volatile memory after the communication session ends.

### Claim 2 (depends on 1)

The method according to claim 1, further comprising forming at least one second symmetrical key from the first private key and the second public key.

### Claim 3 (depends on 2)

The method according to claim 2, further comprising forming the first and second symmetrical keys from a seed formed from the first private key and the second public key.

### Claim 4 (depends on 3)

The method according to claim 3, further comprising storing, in the first non-volatile memory, the seed and the first symmetrical key.

### Claim 5 (depends on 4)

The method according to claim 4, further comprising encrypting the stored seed and first symmetrical keys with an internal key internal to the electronic circuit.

### Claim 6 (depends on 2)

The method according to claim 2, further comprising storing the first symmetrical key in another memory that is volatile and/or configured to be erased in response to an attack being detected.

### Claim 7 (depends on 1)

The method according to claim 1, further comprising storing data, encrypted by the first symmetrical key, in a second nonvolatile memory.

### Claim 8 (depends on 1)

The method according to claim 1, further comprising encrypting communications internal to the electronic circuit with an additional symmetrical key.

### Claim 9 (depends on 8)

The method according to claim 8, further comprising:
encrypting the additional symmetrical key with the first private key; and
storing the encrypted additional symmetrical key in the first non-volatile memory.

### Claim 10 (depends on 8)

The method according to claim 8, wherein the first non-volatile memory is readable only by a holder of the additional symmetrical key and/or an administrator.

### Claim 11 (depends on 10)

The method according to claim 10, wherein the first non-volatile memory is readable by the administrator using a third private key.

### Claim 12 (depends on 1)

The method according to claim 1, further comprising storing, by the electronic circuit, the first public key in signed form.

### Claim 13 (depends on 1)

The method according to claim 1, wherein the second public key is from a second pair of asymmetrical keys comprising a second private key, and the first symmetrical key is deduce-able from the second private key and the first public key.

### Claim 14 (depends on 13)

The method according to claim 13, further comprising obtaining the first and second pairs of asymmetrical keys using a Diffie-Hellman algorithm.

### Claim 15 (depends on 13)

The method according to claim 13, further comprising:
reading, by an administrator having a third private key, the first public key of the first pair of asymmetrical keys;
sending the first public key of the first pair of asymmetrical keys to a holder of the second private key; and
deducing the first symmetrical key from the first public key and the second private key.

### Claim 16

An electronic circuit comprising:
a first non-volatile memory; and
a data processing circuit coupled to the first non-volatile memory, the data processing circuit configured to:
create a first pair of asymmetrical keys including a first private key and a first public key;
store the first public key in the first non-volatile memory;
receive a second public key during a communication session;
form a first symmetrical key from the first private key and the second public key during the communication session;
erase the first private key after forming the first symmetrical key and before the communication session ends; and
end the communication session, wherein the first public key remains stored in the first non-volatile memory after the communication session ends.

### Claim 17 (depends on 16)

The electronic circuit according to claim 16, wherein the data processing circuit is configured to form at least one second symmetrical key from the first private key and the second public key.

### Claim 18 (depends on 17)

The electronic circuit according to claim 17, wherein the data processing circuit is further configured to form the first and second symmetrical keys from a seed formed from the first private key and the second public key.

### Claim 19 (depends on 16)

The electronic circuit according to claim 16, wherein the data processing circuit is configured to encrypt communications internal to the electronic circuit with an additional symmetrical key.

### Claim 20 (depends on 16)

The electronic circuit according to claim 16, further comprising another memory that is volatile and/or configured to be erased in response to an attack being detected;
wherein the data processing circuit is further configured to store the first symmetrical key in the another memory.

### Claim 21 (depends on 16)

The electronic circuit according to claim 16, further comprising a second nonvolatile memory;
wherein the data processing circuit is further configured to store data, encrypted by the first symmetrical key, in the second nonvolatile memory.

### Claim 22

A system comprising:
an electronic circuit comprising:
a first non-volatile memory; and
a data processing circuit coupled to the first non-volatile memory, the data processing circuit configured to:
create a first pair of asymmetrical keys including a first private key and a first public key;
store the first public key in the first non-volatile memory;
receive a second public key during a communication session;
form a first symmetrical key from the first private key and the second public key, wherein the first public key remains stored in the first non-volatile memory after the communication session, wherein the second public key is from a second pair of asymmetrical keys comprising a second private key, and wherein the first symmetrical key is deduce-able from the second private key and the first public key;
reading, by an administrator having a third private key, the first public key of the first pair of asymmetrical keys;
sending the first public key of the first pair of asymmetrical keys to a holder of the second private key; and
deducing the first symmetrical key from the first public key and the second private key.