Module symmetric 

Symmetric crypto engines: AES, hash and ChaCha.

The three engines share one DMA, so only one of them runs at a time. They are owned together through the CRYPTO_SYMMETRIC peripheral and the Symmetric driver.

The state of every operation lives in a context object outside the driver. Any number of operations of any kind can be in progress at once, and their calls can be interleaved.

AES

Mode	Authenticated	nRF52840, nRF91	nRF5340	nRF54L
ECB	No	✓	✓	✓
CBC	No	✓	✓	✓
CTR	No	✓	✓	✓
CMAC	MAC only	✓	✓	✓
CCM	Yes	✓	✓	✓
GCM	Yes	✗	✓	✓

128-bit keys are supported on all chips. 192-bit and 256-bit keys are supported on nRF5340 and nRF54L.

To run a cipher operation:

1. Start it with Symmetric::aes_start. This returns an AesContext.
2. Feed additional authenticated data with Symmetric::aes_blocking_aad (authenticated modes only).
3. Feed the payload with Symmetric::aes_blocking_payload.
4. Finish with Symmetric::aes_blocking_finish. For MAC and AEAD modes this returns the authentication tag.

Hash and HMAC

Algorithm	nRF52840, nRF91, nRF5340	nRF54L
SHA-1	✓	✓
SHA-224	✓	✓
SHA-256	✓	✓
SHA-384	✗	✓
SHA-512	✗	✓
SHA-512/224	✗	✓
SHA-512/256	✗	✓

HMAC is available for every supported algorithm.

To compute a digest:

1. Start with Symmetric::hash_start or Symmetric::hmac_start.
2. Feed data with Symmetric::hash_blocking_update.
3. Finish with Symmetric::hash_blocking_finish.

ChaCha and ChaCha-Poly1305

Both follow RFC 8439: a 256-bit key, a 96-bit nonce and a 32-bit block counter. The ChaChaVariant selects the number of rounds: ChaCha20 everywhere, and also the reduced-round ChaCha12 and ChaCha8 on the CryptoCell.

• The plain keystream is started with Symmetric::chacha_start and applied with Symmetric::chacha_blocking_apply_keystream.
• The AEAD is started with Symmetric::chachapoly_start and then driven like an AES AEAD, with the chachapoly_blocking_* methods.

The CryptoCell has no Poly1305 engine. There, the authenticator runs in software.

Input data may be anywhere in memory, including flash.

Structs

AesCbc

AES in CBC (cipher block chaining) mode.

AesCcm

AES in CCM (counter with CBC-MAC) authenticated mode, as in NIST SP 800-38C.

AesCmac

AES-CMAC message authentication code, as in NIST SP 800-38B.

AesContext

State of an AES operation in progress. Created by Symmetric::aes_start.

AesCtr

AES in CTR (counter) mode, as in NIST SP 800-38A.

AesEcb

AES in ECB (electronic codebook) mode.

ChaChaContext

State of a ChaCha keystream in progress. Created by Symmetric::chacha_start.

ChaChaPolyContext

State of an in-progress ChaCha-Poly1305 operation, created by Symmetric::chachapoly_start.

HashContext

State of a hash computation in progress. Created by Symmetric::hash_start.

HmacContext

State of an HMAC computation in progress. Created by Symmetric::hmac_start.

Sha1

SHA-1.

Sha224

SHA-224.

Sha256

SHA-256.

Symmetric

Driver for the symmetric crypto engines: AES, hash and ChaCha.

Enums

ChaChaVariant

Number of rounds of the ChaCha block function.

Direction

Cipher direction.

Error

Symmetric crypto error.

Constants

AES_BLOCK_LEN

AES block length in bytes.

CHACHA_BLOCK_LEN

ChaCha20 block length in bytes.

CHACHA_KEY_LEN

ChaCha20 key length in bytes.

CHACHA_NONCE_LEN

ChaCha20 nonce length in bytes.

Traits

AuthenticatedCipher

AES cipher mode that accepts additional authenticated data. Implemented by AesCcm and AesGcm.

Buffer

Fixed-size byte buffer. Implemented for [u8; N].

Cipher

AES cipher mode. Implemented by AesEcb, AesCbc, AesCtr, AesCmac, AesCcm and AesGcm.

DigestContext

A hash or HMAC context. Implemented by HashContext and HmacContext.

HashAlgorithm

Hash algorithm. Implemented by Sha1, Sha224, Sha256 and, on CRACEN, the SHA-512 family.