# US 12,010,243 B2 · Methods and devices for providing message authentication code suitable for short messages

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- Number: US 12,010,243 B2
- Document ID: US12010243B2
- Status: Granted
- Kind: B2
- Application number: 17/293,200
- Filed: 2019-11-13
- Published: 2022-01-06
- Granted: 2024-06-11
- Earliest claimed: 2018-11-13
- Assignees: Koninklijke Philips N.V.
- Applicants: Koninklijke Philips N.V.
- Inventors: Johannes Arnoldus Cornelis Bernsen
- Web page: https://patentgrep.com/patent/US12010243B2

## CPC

- H04L 9/3242: {involving keyed hash functions, e.g. message authentication codes [MACs], CBC-MAC or HMAC}
- G06F 21/44: Program or device authentication
- G06F 21/445: {by mutual authentication, e.g. between devices or programs}
- H04L 9/32: including means for verifying the identity or authority of a user of the system {or for message authentication, e.g. authorization, entity authentication, data integrity or data verification, non-repudiation, key authentication or verification of credentials}
- H04L 9/3215: {using a plurality of channels (network architectures or network communication protocols using different networks H04L63/18)}
- H04L 9/50: {using hash chains, e.g. blockchains or hash trees}
- H04L 2209/805: Lightweight hardware, e.g. radio-frequency identification [RFID] or sensor
- H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M)
- G06F: ELECTRIC DIGITAL DATA PROCESSING (computer systems based on specific computational models G06N)

## Abstract

This application relates to devices and methods of authenticating messages exchanged over a network between a transmitter and a receiver. The transmitter generates a truncated MAC code by selecting predetermined bits from a message authentication code (MAC) computed over a concatenation of a part of the message with a part of a previously transmitted message. The transmitter appends the truncated MAC code to the message for transmission. The receiver receives a previously transmitted message, the currently transmitted message, and the truncated MAC code, and generates an expected truncated MAC code by selecting predetermined bits from a message authentication code (MAC) computed over a concatenation of the part of the message with the previously transmitted message. The receiver authenticates the message and the previously transmitted message if the truncated MAC code as received is identical to the expected truncated MAC code.

## Claims

### Claim 1

A method of authenticating messages exchanged over a network between a transmitter and a receiver, the method comprising:
transmitting a message at a transmitter side;
generating a truncated message authentication code (MAC) by selecting or generating predetermined bits from a MAC computed over a concatenation of a predetermined part of the message with at least one predetermined part of a previously transmitted message;
wherein a bitlength of truncated MAC is smaller than a bitlength of the message authentication code;
appending the truncated MAC to the message for transmission;
authenticating a message at a receiver side;
receiving a previously transmitted message, the message and the truncated MAC code;
generating an expected truncated MAC by selecting or generating predetermined bits from a MAC computed over a concatenation of a predetermined part of the message with at least one predetermined part of a previously transmitted message, and
authenticating the message and the previously transmitted message if the truncated MAC as received is identical to the expected truncated MAC, and
not authenticating the message and the previously transmitted message if the truncated MAC as received is not identical to the expected truncated MAC, overriding an authentication of the previously transmitted message.

### Claim 2 (depends on 1)

The method of claim 1, wherein for a first transmitted message, the MAC is computed over a predetermined part of the first message without concatenation with at least one predetermined part of a previously transmitted message.

### Claim 3 (depends on 2)

The method of claim 2, wherein the MAC is computed either
over a concatenation of a predetermined part of the message with a sequence of second predetermined number of parts of previously transmitted messages; or
over a concatenation of a predetermined part of the message with a sequence of predetermined parts of each preceding messages starting from the first transmitted message,
depending on whichever sequence is shorter.

### Claim 4 (depends on 3)

A transmitter for transmitting short messages and corresponding message authentication codes over a network, the transmitter comprising:
an antenna and a transceiver for transmitting a message;
a processor coupled to the antenna and the transceiver for controlling transmission and generation of a message authentication code (MAC);
wherein the processor is configured to perform the methods according to claim 3.

### Claim 5 (depends on 2)

The method of claim 2, wherein the message is provided with at least one of:
a first identifier identifying that the MAC is computed over a predetermined part of the first message without concatenation with at least one predetermined part of a previously transmitted message;
a second identifier identifying that the MAC is computed over a concatenation of a predetermined part of the message with at least one predetermined part of a previously transmitted message.

### Claim 6 (depends on 5)

The method of claim 5, wherein at least one of the first identifier or second identifier has a bitlength of 1 bit.

### Claim 7 (depends on 6)

The method of claim 6, wherein at least one of the first identifier or second identifier is provided in either a packet header or concatenated with the truncated MAC.

### Claim 8 (depends on 1)

The method of claim 1, wherein the message is provided with at least one of:
a third identifier identifying that the MAC is truncated;
a fourth identifier identifying that the MAC is truncated to n bits.

### Claim 9 (depends on 1)

The method of claim 1, wherein the message is provided with at least one of
a third identifier identifying that the MAC is truncated;
a fourth identifier identifying that the MAC is not truncated.

### Claim 10

A method of transmitting messages and authentication codes over a network by a transmitter, the method comprising:
generating a truncated message authentication code (MAC) by selecting or generating predetermined bits from a MAC computed over a concatenation of a predetermined part of the message with at least one predetermined part of a previously transmitted message;
wherein a bitlength of the truncated MAC is smaller than a bitlength of the MAC; and
appending the truncated MAC to the message for transmission.

### Claim 11

A method of authenticating messages received by a receiver over a network, the messages comprising a truncated message authentication code (MAC) computed by selecting or generating predetermined bits from a MAC computed over a concatenation of a predetermined part of the message with at least one predetermined part of a previously transmitted message, wherein a bitlength of truncated MAC is smaller than a bitlength of the MAC, the method comprising:
receiving a previously transmitted message, the message, and the truncated MAC,
generating an expected truncated MAC by selecting or generating predetermined bits from a MAC computed over a concatenation of a predetermined part of the message with at least one predetermined part of a previously transmitted message;
authenticating the message and the previously transmitted message if the truncated MAC as received is identical to the expected truncated MAC; and
not authenticating the message and the previously transmitted message if the truncated MAC as received is not identical to the expected truncated MAC, overriding an authentication of the previously transmitted message.

### Claim 12 (depends on 11)

The method of claim 11, wherein for a received first message which is a first transmitted message wherein the (MAC) is computed over a predetermined part of the first message without concatenation with at least one predetermined part of a previously transmitted message,
the method comprising:
generating an expected truncated MAC by selecting or generating predetermined bits from a MAC computed over the first message without concatenation with at least one predetermined part of a previously transmitted message.

### Claim 13 (depends on 11)

The method of claim 11, wherein the message is provided with either:
a first identifier identifying that the message authentication code (MAC) is computed over a predetermined part of the first message without concatenation with at least one predetermined part of a previously transmitted message; or
a second identifier identifying that the MAC is computed a concatenation of a predetermined part of the message with at least one predetermined part of a previously transmitted message;
the method comprising:
using either the first identifier or the second identifier in determining previously transmitted messages to be used in generating an expected truncated MAC.

### Claim 14 (depends on 11)

A receiver for receiving short messages and corresponding message authentication codes (MAC) over a network, the receiver comprising:
an antenna and a transceiver for receiving a message comprising a MAC;
a processor coupled to the antenna and the transceiver for controlling receiving and generation of a MAC;
wherein the processor is configured to perform the methods according to claim 11.