aes_cmac.h File Reference

AES-128-CMAC (RFC 4493 / NIST SP800-38B) one-shot MAC. More...

#include <stddef.h>
#include <stdint.h>

Go to the source code of this file.

Macros
#define	PC_AES_CMAC_LEN   16
	AES-128-CMAC output length (one AES block).

Functions
void	pc_aes_cmac (const uint8_t key[16], const uint8_t *msg, size_t msg_len, uint8_t mac[PC_AES_CMAC_LEN])
	Compute the AES-128-CMAC of msg under key (RFC 4493).

Detailed Description

AES-128-CMAC (RFC 4493 / NIST SP800-38B) one-shot MAC.

The CMAC construction over the AES-128 block cipher: derive two subkeys K1/K2 from AES-128(key, 0^128), CBC-MAC the message, and XOR the final block with K1 (message a whole number of blocks) or the 10*-padded last block with K2. SMB 3.x uses it as the message-signing MAC when the negotiated signing algorithm is AES-CMAC (MS-SMB2 §3.1.4.1, dialects 3.0 / 3.0.2 / 3.1.1); it is a general primitive, not SMB-specific.

On ESP32/Arduino the AES-128 block runs on the mbedTLS context (hardware AES accelerator); on the native host build it uses the shared table-free software AES (crypto/cipher/aes_block.h). Pure, zero heap. Verified against the RFC 4493 §4 worked examples.

Author

Douglas Quigg (dstroy0)

Date

2026

Definition in file aes_cmac.h.

Macro Definition Documentation

PC_AES_CMAC_LEN

#define PC_AES_CMAC_LEN   16

AES-128-CMAC output length (one AES block).

Definition at line 29 of file aes_cmac.h.

Function Documentation

pc_aes_cmac()

void pc_aes_cmac	(	const uint8_t	key[16],
		const uint8_t *	msg,
		size_t	msg_len,
		uint8_t	mac[PC_AES_CMAC_LEN]
	)

Compute the AES-128-CMAC of msg under key (RFC 4493).

Parameters

key	the 16-byte AES-128 key.
msg	the message (may be null iff msg_len is 0).
msg_len	message length in bytes (0 is valid - the empty-message CMAC).
mac	receives the 16-byte tag.

Definition at line 110 of file aes_cmac.cpp.