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 ciphers and modes CTR, OFB, CFB, CBC, XTS, CMAC, CCM/CCM*, and GCM to be configured.

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 Original Mbed TLS for AES operations.

AES cipher configuration

AES cipher modes can be configured by setting Kconfig variables in the following table:

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

Cipher-based Message Authentication Code (CMAC) support can be configured by setting the CONFIG_MBEDTLS_CMAC_C Kconfig variable.

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

Authenticated Encryption with Associated Data (AEAD) can be configured by setting Kconfig variables in the following table:

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 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

Diffie-Hellman-Merkle (DHM) support can be configured by setting the CONFIG_MBEDTLS_DHM_C Kconfig variable.

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 Original Mbed TLS for DHM operations.

ECC configurations

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

ECC core support can be configured by setting the CONFIG_MBEDTLS_ECP_C Kconfig variable.

Enabling CONFIG_MBEDTLS_ECP_C will activate configuration options that depend upon 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

Elliptic Curve Diffie-Hellman (ECDH) support can be configured by setting the CONFIG_MBEDTLS_ECDH_C Kconfig variable.

Algorithm	Configurations
ECDH	CONFIG_MBEDTLS_ECDH_C

Note

• ECDH support depends upon ECC Configurations being enabled.

• The nrf_cc3xx_mbedcrypto library does not integrate on ECP layer. Only the top-level APIs for ECDH are replaced.

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

Elliptic Curve Digital Signature Algorithm (ECDSA) support can be configured be configured by setting the CONFIG_MBEDTLS_ECDSA_C Kconfig variable.

Algorithm	Configurations
ECDSA	CONFIG_MBEDTLS_ECDSA_C

Note

• ECDSA support depends upon ECC Configurations being enabled.

• The nrf_cc3xx_mbedcrypto library does not integrate on ECP layer. Only the top-level APIs for ECDSA are replaced.

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

Elliptic Curve, Password Authenticated Key Exchange by Juggling (ECJPAKE) support can be configured by setting the CONFIG_MBEDTLS_ECJPAKE_C Kconfig variable.

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 table shows the curves that 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

Rivest-Shamir-Adleman (RSA) support can be configured by setting the CONFIG_MBEDTLS_RSA_C Kconfig variable.

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 Original Mbed TLS for RSA operations.

Secure Hash configurations

The Secure Hash algorithms can be configured by setting Kconfig variables in the following table:

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