aes_block.h File Reference

Compact table-free software AES key schedule + single-block encrypt (FIPS 197) - one source of truth. More...

#include "crypto/cipher/aes_sbox.h"
#include <stdint.h>
#include <string.h>

Go to the source code of this file.

Functions
uint8_t	pc_aes_xtime (uint8_t a)
	GF(2^8) multiply-by-2 (xtime) for the AES MixColumns step.
uint32_t	pc_aes_sub_word (uint32_t w)
	AES SubWord (FIPS 197 sec 5.2): apply the S-box to each of the four bytes of a 32-bit word.
uint32_t	pc_aes_rot_word (uint32_t w)
	AES RotWord (FIPS 197 sec 5.2): cyclically rotate a 32-bit word one byte left.
void	pc_aes_key_expand (const uint8_t *key, int nk, uint32_t *rk)
	AES key expansion (FIPS 197 sec 5.2). nk key words (4=AES-128, 8=AES-256); rk receives 4*(nk + 7) round-key words (44 for AES-128, 60 for AES-256).
void	pc_aes_encrypt_block (const uint32_t *rk, int nr, const uint8_t in[16], uint8_t out[16])
	AES single-block encrypt (FIPS 197 sec 5.1), nr rounds (10=AES-128, 14=AES-256). State is column-major: s[col*4 + row]. rk is the schedule from pc_aes_key_expand.

Detailed Description

Compact table-free software AES key schedule + single-block encrypt (FIPS 197) - one source of truth.

The SSH AES-256-GCM, SSH AES-256-CTR, and QUIC/TLS AES-128 modules each carried a byte-for-byte copy of the same software AES (key expansion + the SubBytes/ShiftRows/MixColumns/AddRoundKey block cipher). They differ ONLY in the key size: parameterize on nk (key words: 4 for AES-128, 8 for AES-256) and nr (rounds: 10 or 14) and one implementation serves all three.

Only the S-box (PC_AES_SBOX from aes_sbox.h) and the GF(2^8) xtime are used - no large T-tables - so this is the same "constant-time by structure" shape the copies had (a table-indexed S-box; no secret- dependent branching introduced here). Header-only and pure (S-box + <string.h>), so it is compiled into only the NATIVE software path of each module; the #ifdef ARDUINO mbedTLS/HW branches are untouched.

Author

Douglas Quigg (dstroy0)

Date

2026

Definition in file aes_block.h.

Function Documentation

pc_aes_xtime()

uint8_t pc_aes_xtime ( uint8_t  a )

inline

GF(2^8) multiply-by-2 (xtime) for the AES MixColumns step.

Definition at line 30 of file aes_block.h.

Referenced by pc_aes_encrypt_block().

pc_aes_sub_word()

uint32_t pc_aes_sub_word ( uint32_t  w )

inline

AES SubWord (FIPS 197 sec 5.2): apply the S-box to each of the four bytes of a 32-bit word.

Definition at line 36 of file aes_block.h.

Referenced by pc_aes_key_expand().

pc_aes_rot_word()

uint32_t pc_aes_rot_word ( uint32_t  w )

inline

AES RotWord (FIPS 197 sec 5.2): cyclically rotate a 32-bit word one byte left.

Definition at line 43 of file aes_block.h.

Referenced by pc_aes_key_expand().

pc_aes_key_expand()

void pc_aes_key_expand ( const uint8_t *  key, int  nk, uint32_t *  rk  )

inline

AES key expansion (FIPS 197 sec 5.2). nk key words (4=AES-128, 8=AES-256); rk receives 4*(nk + 7) round-key words (44 for AES-128, 60 for AES-256).

Definition at line 52 of file aes_block.h.

References pc_aes_rot_word(), and pc_aes_sub_word().

Referenced by pc_aes256ctr_get_length().

pc_aes_encrypt_block()

void pc_aes_encrypt_block ( const uint32_t *  rk, int  nr, const uint8_t  in[16], uint8_t  out[16]  )

inline

AES single-block encrypt (FIPS 197 sec 5.1), nr rounds (10=AES-128, 14=AES-256). State is column-major: s[col*4 + row]. rk is the schedule from pc_aes_key_expand.

Definition at line 82 of file aes_block.h.

References pc_aes_xtime().

Referenced by pc_aes256ctr_get_length().