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
ChaCha20	nrf_oberon	256-bit key
Poly1305	cc3xx	256-bit key
Poly1305	nrf_oberon	256-bit key
ChaCha-Poly	cc3xx	256-bit key	The ChaCha-Poly implementation in cc3xx backend does not support incremental operations.
ChaCha-Poly	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
DHM	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
		NIST	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

ECDH support depends on 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
		NIST	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

ECDSA support depends on 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
		NIST	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
ECJPAKE	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
RSA	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
SHA-1	nrf_oberon
SHA-224	cc3xx	SHA-224 must be enabled when enabling SHA-256
SHA-224	nrf_oberon	SHA-224 must be enabled when enabling SHA-256
SHA-256	cc3xx
SHA-256	nrf_oberon
SHA-384	cc3xx
SHA-384	nrf_oberon
SHA-512	cc3xx
SHA-512	nrf_oberon