Legacy configurations and supported features

This section covers the configurations available when using Legacy crypto support.

Configuring backends

The legacy configuration does not allow multiple backends being enabled at the same time.

The choice of implementation is controlled by setting CONFIG_CC3XX_BACKEND for devices with the CryptoCell hardware peripheral, or CONFIG_OBERON_BACKEND.

cc3xx backend

Setting the Kconfig option CONFIG_CC3XX_BACKEND enables legacy crypto support for hardware accelerated cryptography using nrf_cc3xx_mbedcrypto library.

Oberon backend

Setting the Kconfig option CONFIG_CC3XX_OBERON enables legacy crypto support using nrf_oberon crypto library.

Original Mbed TLS backend

The Original Mbed TLS backend is no longer available as a configuration option, and is only used if any of the enabled backends does not support a specific cryptographic algorithm or feature.

AES configuration

The AES core is enabled with the Kconfig option CONFIG_MBEDTLS_AES_C.

This enables AES ECB cipher mode and allows the following ciphers and modes to be configured:

  • CTR

  • OFB

  • CFB

  • CBC

  • XTS

  • CMAC

  • CCM/CCM*

  • GCM

Feature support

Cipher mode

Backend

Key size

ECB

cc310

128-bit key

cc312

128-bit key

192-bit key

256-bit key

nrf_oberon

128-bit key

192-bit key

256-bit key

Note

The Oberon backend uses some functionality from the original Mbed TLS for AES operations.

AES cipher configuration

To configure AES cipher modes, set the following Kconfig options:

Cipher mode

Configurations

Note

CTR

CONFIG_MBEDTLS_CIPHER_MODE_CTR

CBC

CONFIG_MBEDTLS_CIPHER_MODE_CBC

CFB

CONFIG_MBEDTLS_CIPHER_MODE_CFB

nrf_oberon only

OFB

CONFIG_MBEDTLS_CIPHER_MODE_OFB

nrf_oberon only

XTS

CONFIG_MBEDTLS_CIPHER_MODE_XTS

nrf_oberon only

Note

AES cipher modes are dependent on enabling AES core support according to AES configuration.

Feature support

Cipher mode

Backend

Key size

Note

CTR

cc310

128-bit key

cc312

128-bit key

192-bit key

256-bit key

nrf_oberon

128-bit key

192-bit key

256-bit key

CBC

cc310

128-bit key

cc312

128-bit key

192-bit key

256-bit key

nrf_oberon

128-bit key

192-bit key

256-bit key

CFB

cc310

N/A

Backend not supported

cc312

N/A

Backend not supported

nrf_oberon

128-bit key

192-bit key

256-bit key

OFB

cc310

N/A

Backend not supported

cc312

N/A

Backend not supported

nrf_oberon

128-bit key

192-bit key

256-bit key

XTS

cc310

N/A

Backend not supported

cc312

N/A

Backend not supported

nrf_oberon

128-bit key

192-bit key

256-bit key

CMAC configuration

To configure Cipher-based Message Authentication Code (CMAC) support, set the CONFIG_MBEDTLS_CMAC_C Kconfig option.

Feature support

Algorithm

Backend

Key size

CMAC

cc310

128-bit key

cc312

128-bit key

192-bit key

256-bit key

nrf_oberon

128-bit key

192-bit key

256-bit key

AEAD configurations

To configure Authenticated Encryption with Associated Data (AEAD), set the following Kconfig options:

AEAD cipher

Configurations

Note

AES CCM/CCM*

CONFIG_MBEDTLS_CCM_C

AES GCM

CONFIG_MBEDTLS_GCM_C

nrf_oberon or cc312

ChaCha20

CONFIG_MBEDTLS_CHACHA20_C

Poly1305

CONFIG_MBEDTLS_POLY1305_C

ChaCha-Poly

CONFIG_MBEDTLS_CHACHAPOLY_C

Requires Poly1305 and ChaCha20

Note

  • AEAD AES cipher modes are dependent on enabling AES core support according to AES configuration.

  • When Arm CryptoCell cc310 backend is used, AES GCM is provided by the original Mbed TLS implementation.

  • The ChaCha-Poly implemented by the Arm CryptoCell cc3xx backend does not support incremental operations.

  • The ChaCha-Poly implemented by the cc3xx backend does not support incremental operations.

Feature support

AEAD cipher

Backend

Key size

Note

AES CCM/CCM*

cc310

128-bit key

cc312

128-bit key

192-bit key

256-bit key

nrf_oberon

128-bit key

192-bit key

256-bit key

AES GCM

cc312

128-bit key

192-bit key

256-bit key

nrf_oberon

128-bit key

192-bit key

256-bit key

ChaCha20

cc3xx

256-bit key

nrf_oberon

256-bit key

Poly1305

cc3xx

256-bit key

nrf_oberon

256-bit key

ChaCha-Poly

cc3xx

256-bit key

The ChaCha-Poly implementation in cc3xx backend does not support incremental operations.

nrf_oberon

256-bit key

DHM configurations

To configure Diffie-Hellman-Merkle (DHM) support, set the CONFIG_MBEDTLS_DHM_C Kconfig option.

Feature support

Algorithm

Backend

Key size

Note

DHM

cc3xx

Limited to 2048 bits

nrf_oberon

N/A

Backend not supported

Note

The Oberon backend uses functionality from the original Mbed TLS for DHM operations.

ECC configurations

Elliptic Curve Cryptography (ECC) configuration provides support for Elliptic Curve over GF(p).

To configure ECC core support, set the CONFIG_MBEDTLS_ECP_C Kconfig option.

Enabling CONFIG_MBEDTLS_ECP_C will activate configuration options that depend on ECC, such as ECDH, ECDSA, ECJPAKE, and a selection of ECC curves to support in the system.

Feature support

Algorithm

Backend

Curve group

Curve type

ECP

cc3xx

NIST

secp192r1

secp224r1

secp256r1

secp384r1

secp521r1

Koblitz

secp192k1

secp224k1

secp256k1

Curve25519

Curve25519

nrf_oberon

NIST

secp256r1

secp224r1

Curve25519

Curve25519

ECDH configurations

To configure Elliptic Curve Diffie-Hellman (ECDH) support, set the CONFIG_MBEDTLS_ECDH_C Kconfig option.

Algorithm

Configurations

ECDH

CONFIG_MBEDTLS_ECDH_C

Note

Feature support

Algorithm

Backend

Curve group

Curve type

ECDH

cc3xx

NIST

secp192r1

secp224r1

secp256r1

secp384r1

secp521r1

Koblitz

secp192k1

secp224k1

secp256k1

Curve25519

Curve25519

nrf_oberon

NIST

secp256r1

secp224r1

Curve25519

Curve25519

ECDSA configurations

To configure Elliptic Curve Digital Signature Algorithm (ECDSA) support, set the CONFIG_MBEDTLS_ECDSA_C Kconfig option.

Algorithm

Configurations

ECDSA

CONFIG_MBEDTLS_ECDSA_C

Note

Feature support

Algorithm

Backend

Curve group

Curve type

ECDSA

cc3xx

NIST

secp192r1

secp224r1

secp256r1

secp384r1

secp521r1

Koblitz

secp192k1

secp224k1

secp256k1

Curve25519

Curve25519

nrf_oberon

NIST

secp256r1

secp224r1

Curve25519

Curve25519

ECJPAKE configurations

To configure Elliptic Curve, Password Authenticated Key Exchange by Juggling (ECJPAKE) support, set the CONFIG_MBEDTLS_ECJPAKE_C Kconfig option.

Algorithm

Configurations

ECJPAKE

CONFIG_MBEDTLS_ECJPAKE_C

Note

ECJPAKE support depends upon ECC Configurations being enabled.

Feature support

Algorithm

Backend

Curve group

Curve type

ECJPAKE

cc3xx

NIST

secp256r1

nrf_oberon

NIST

secp256r1

ECC curves configurations

It is possible to configure the curves that should be supported in the system depending on the backend selected.

The following curves can be enabled:

Curve

Configurations

Note

NIST secp192r1

CONFIG_MBEDTLS_ECP_DP_SECP192R1_ENABLED

NIST secp224r1

CONFIG_MBEDTLS_ECP_DP_SECP224R1_ENABLED

NIST secp256r1

CONFIG_MBEDTLS_ECP_DP_SECP256R1_ENABLED

NIST secp384r1

CONFIG_MBEDTLS_ECP_DP_SECP384R1_ENABLED

NIST secp521r1

CONFIG_MBEDTLS_ECP_DP_SECP521R1_ENABLED

Koblitz secp192k1

CONFIG_MBEDTLS_ECP_DP_SECP192K1_ENABLED

Koblitz secp224k1

CONFIG_MBEDTLS_ECP_DP_SECP224K1_ENABLED

Koblitz secp256k1

CONFIG_MBEDTLS_ECP_DP_SECP256K1_ENABLED

Curve25519

CONFIG_MBEDTLS_ECP_DP_CURVE25519_ENABLED

Note

  • The nrf_oberon crypto library only supports ECC curve secp224r1 and secp256r1.

  • Choosing the nrf_oberon backend does not allow enabling the rest of the ECC curve types.

RSA configurations

To configure Rivest-Shamir-Adleman (RSA) support, set the CONFIG_MBEDTLS_RSA_C Kconfig option.

Feature support

Algorithm

Backend

Key size

Note

RSA

cc3xx

Limited to 2048 bits

nrf_oberon

N/A

Backend not supported

Note

The Oberon backend uses functionality from the original Mbed TLS for RSA operations.

Secure Hash configurations

To configure the Secure Hash algorithms, set the following Kconfig options:

Algorithm

Support

Backend selection

SHA-1

CONFIG_MBEDTLS_SHA1_C

SHA-224

CONFIG_MBEDTLS_SHA224_C

SHA-256

CONFIG_MBEDTLS_SHA256_C

SHA-384

CONFIG_MBEDTLS_SHA384_C

SHA-512

CONFIG_MBEDTLS_SHA512_C

Feature support

Algorithm

Supported backends

Note

SHA-1

cc3xx

nrf_oberon

SHA-224

cc3xx

SHA-224 must be enabled when enabling SHA-256

nrf_oberon

SHA-256

cc3xx

nrf_oberon

SHA-384

cc3xx

nrf_oberon

SHA-512

cc3xx

nrf_oberon