ssh_aes256ctr.cpp File Reference

AES-256-CTR implementation. More...

#include "network_drivers/presentation/ssh/crypto/ssh_aes256ctr.h"
#include <string.h>

Go to the source code of this file.

Functions
void	ssh_aes256ctr_init (SshAesCtrCtx *ctx, const uint8_t key[32], const uint8_t iv[16])
	Initialize an AES-256-CTR context.
void	ssh_aes256ctr_crypt (SshAesCtrCtx *ctx, const uint8_t *in, uint8_t *out, size_t len)
	Encrypt or decrypt len bytes in-place (or src→dst).
void	ssh_aes256ctr_wipe (SshAesCtrCtx *ctx)
	Zero the key schedule and all context fields.

Detailed Description

AES-256-CTR implementation.

Arduino path: delegates block encryption to mbedtls_aes_crypt_ecb(), which the ESP32 mbedtls port routes to the hardware AES accelerator.

Native path: compact software AES-256 using only the 256-byte forward S-box and GF(2^8) multiply-by-2/3 for MixColumns. No large lookup tables.

Definition in file ssh_aes256ctr.cpp.

Function Documentation

ssh_aes256ctr_init()

void ssh_aes256ctr_init	(	SshAesCtrCtx *	ctx,
		const uint8_t	key[32],
		const uint8_t	iv[16]
	)

Initialize an AES-256-CTR context.

Expands the key schedule (hardware on Arduino, software on native) and stores the initial counter/IV.

Parameters

ctx	Uninitialized context.
key	32-byte AES-256 key (derived from KEX via RFC 4253 §7.2).
iv	16-byte initial counter block (derived from KEX).

Definition at line 24 of file ssh_aes256ctr.cpp.

References SshAesCtrCtx::_mbed, SshAesCtrCtx::counter, SshAesCtrCtx::keystream, and SshAesCtrCtx::pos.

Referenced by ssh_dh_derive_keys_sid().

ssh_aes256ctr_crypt()

void ssh_aes256ctr_crypt	(	SshAesCtrCtx *	ctx,
		const uint8_t *	in,
		uint8_t *	out,
		size_t	len
	)

Encrypt or decrypt len bytes in-place (or src→dst).

AES-CTR is symmetric: XOR with keystream is its own inverse. Calling this function for encryption and decryption is identical.

The counter advances by ceil(len/16) blocks. If in == out the operation is in-place (the only mode used by ssh_packet.cpp).

Parameters

ctx	Initialized AES-256-CTR context.
in	Input bytes.
out	Output bytes (may equal in for in-place).
len	Number of bytes to process.

Definition at line 33 of file ssh_aes256ctr.cpp.

References SshAesCtrCtx::_mbed, SshAesCtrCtx::counter, SshAesCtrCtx::keystream, and SshAesCtrCtx::pos.

Referenced by ssh_pkt_recv(), and ssh_pkt_send().

ssh_aes256ctr_wipe()

void ssh_aes256ctr_wipe

(

SshAesCtrCtx *

ctx

)

Zero the key schedule and all context fields.

Call on disconnect. Uses a volatile wipe so the compiler cannot elide it. On Arduino also calls mbedtls_aes_free() to release any internal resources.

Parameters

ctx	Context to wipe.

Definition at line 46 of file ssh_aes256ctr.cpp.

References SshAesCtrCtx::_mbed.