9.2. Key types
9.2.1. Key type encoding
psa_key_type_t
(type)
Encoding of a key type.
typedef uint16_t psa_key_type_t;
This is a structured bitfield that identifies the category and type of key. The range of key type values is divided as follows:
PSA_KEY_TYPE_NONE
== 0
Reserved as an invalid key type.
0
x0001
 0
x7fff
Specificationdefined key types. Key types defined by this standard always have bit 15 clear. Unallocated key type values in this range are reserved for future use.
0
x8000
 0
xffff
Implementationdefined key types. Implementations that define additional key types must use an encoding with bit 15 set. The related support macros will be easier to write if these key encodings also respect the bitwise structure used by standard encodings.
PSA_KEY_TYPE_NONE
(macro)
An invalid key type value.
#define PSA_KEY_TYPE_NONE ((psa_key_type_t)0x0000)
Zero is not the encoding of any key type.
9.2.2. Key categories
PSA_KEY_TYPE_IS_UNSTRUCTURED
(macro)
Whether a key type is an unstructured array of bytes.
#define PSA_KEY_TYPE_IS_UNSTRUCTURED(type) /* specificationdefined value */
Parameters

type
A key type (value of type
psa_key_type_t
).
Description
This encompasses both symmetric keys and nonkey data.
See Symmetric keys for a list of symmetric key types.
PSA_KEY_TYPE_IS_ASYMMETRIC
(macro)
Whether a key type is asymmetric: either a key pair or a public key.
#define PSA_KEY_TYPE_IS_ASYMMETRIC(type) /* specificationdefined value */
Parameters

type
A key type (value of type
psa_key_type_t
).
Description
See RSA keys for a list of asymmetric key types.
PSA_KEY_TYPE_IS_PUBLIC_KEY
(macro)
Whether a key type is the public part of a key pair.
#define PSA_KEY_TYPE_IS_PUBLIC_KEY(type) /* specificationdefined value */
Parameters

type
A key type (value of type
psa_key_type_t
).
PSA_KEY_TYPE_IS_KEY_PAIR
(macro)
Whether a key type is a key pair containing a private part and a public part.
#define PSA_KEY_TYPE_IS_KEY_PAIR(type) /* specificationdefined value */
Parameters

type
A key type (value of type
psa_key_type_t
).
9.2.3. Symmetric keys
PSA_KEY_TYPE_RAW_DATA
(macro)
Raw data.
#define PSA_KEY_TYPE_RAW_DATA ((psa_key_type_t)0x1001)
A “key” of this type cannot be used for any cryptographic operation. Applications can use this type to store arbitrary data in the keystore.
The bit size of a raw key must be a nonzero multiple of 8. The maximum size of a raw key is IMPLEMENTATION DEFINED.
PSA_KEY_TYPE_HMAC
(macro)
HMAC key.
#define PSA_KEY_TYPE_HMAC ((psa_key_type_t)0x1100)
The key policy determines which underlying hash algorithm the key can be used for.
The bit size of an HMAC key must be a nonzero multiple of 8. An HMAC key is typically the same size as the output of the underlying hash algorithm. An HMAC key that is longer than the block size of the underlying hash algorithm will be hashed before use.
When an HMAC key is created that is longer than the block size, it is implementation defined whether the implementation stores the original HMAC key, or the hash of the HMAC key. If the hash of the key is stored, the key size reported by psa_get_key_attributes()
will be the size of the hashed key.
Note
PSA_HASH_LENGTH
(
alg
)
provides the output size of hash algorithm alg
, in bytes.
PSA_HASH_BLOCK_LENGTH
(
alg
)
provides the block size of hash algorithm alg
, in bytes.
PSA_KEY_TYPE_DERIVE
(macro)
A secret for key derivation.
#define PSA_KEY_TYPE_DERIVE ((psa_key_type_t)0x1200)
The key policy determines which key derivation algorithm the key can be used for.
The bit size of a secret for key derivation must be a nonzero multiple of 8. The maximum size of a secret for key derivation is IMPLEMENTATION DEFINED.
PSA_KEY_TYPE_AES
(macro)
Key for a cipher, AEAD or MAC algorithm based on the AES block cipher.
#define PSA_KEY_TYPE_AES ((psa_key_type_t)0x2400)
The size of the key is related to the AES algorithm variant. For algorithms except the XTS block cipher mode, the following key sizes are used:
AES128 uses a 16byte key :
key_bits = 128
AES192 uses a 24byte key :
key_bits = 192
AES256 uses a 32byte key :
key_bits = 256
For the XTS block cipher mode (PSA_ALG_XTS
), the following key sizes are used:
AES128XTS uses two 16byte keys :
key_bits = 256
AES192XTS uses two 24byte keys :
key_bits = 384
AES256XTS uses two 32byte keys :
key_bits = 512
The AES block cipher is defined in FIPS Publication 197: Advanced Encryption Standard (AES) [FIPS197].
PSA_KEY_TYPE_DES
(macro)
Key for a cipher or MAC algorithm based on DES or 3DES (TripleDES).
#define PSA_KEY_TYPE_DES ((psa_key_type_t)0x2301)
The size of the key determines which DES algorithm is used:
Single DES uses an 8byte key :
key_bits = 64
2key 3DES uses a 16byte key :
key_bits = 128
3key 3DES uses a 24byte key :
key_bits = 192
Warning
Single DES and 2key 3DES are weak and strongly deprecated and are only recommended for decrypting legacy data.
3key 3DES is weak and deprecated and is only recommended for use in legacy protocols.
The DES and 3DES block ciphers are defined in NIST Special Publication 80067: Recommendation for the Triple Data Encryption Algorithm (TDEA) Block Cipher [SP80067].
PSA_KEY_TYPE_CAMELLIA
(macro)
Key for a cipher, AEAD or MAC algorithm based on the Camellia block cipher.
#define PSA_KEY_TYPE_CAMELLIA ((psa_key_type_t)0x2403)
The size of the key is related to the Camellia algorithm variant. For algorithms except the XTS block cipher mode, the following key sizes are used:
Camellia128 uses a 16byte key :
key_bits = 128
Camellia192 uses a 24byte key :
key_bits = 192
Camellia256 uses a 32byte key :
key_bits = 256
For the XTS block cipher mode (PSA_ALG_XTS
), the following key sizes are used:
Camellia128XTS uses two 16byte keys :
key_bits = 256
Camellia192XTS uses two 24byte keys :
key_bits = 384
Camellia256XTS uses two 32byte keys :
key_bits = 512
The Camellia block cipher is defined in Specification of Camellia — a 128bit Block Cipher [NTTCAM] and also described in A Description of the Camellia Encryption Algorithm [RFC3713].
PSA_KEY_TYPE_SM4
(macro)
Key for a cipher, AEAD or MAC algorithm based on the SM4 block cipher.
#define PSA_KEY_TYPE_SM4 ((psa_key_type_t)0x2405)
For algorithms except the XTS block cipher mode, the SM4 key size is 128 bits (16 bytes).
For the XTS block cipher mode (PSA_ALG_XTS
), the SM4 key size is 256 bits (two 16byte keys).
The SM4 block cipher is defined in GB/T 329072016: Information security technology — SM4 block cipher algorithm [PRCSM4] and also described in The SM4 Blockcipher Algorithm And Its Modes Of Operations [IETFSM4].
PSA_KEY_TYPE_ARC4
(macro)
Key for the ARC4 stream cipher.
#define PSA_KEY_TYPE_ARC4 ((psa_key_type_t)0x2002)
Warning
The ARC4 cipher is weak and deprecated and is only recommended for use in legacy protocols.
The ARC4 cipher supports key sizes between 40 and 2048 bits, that are multiples of 8. (5 to 256 bytes)
Use algorithm PSA_ALG_STREAM_CIPHER
to use this key with the ARC4 cipher.
PSA_KEY_TYPE_CHACHA20
(macro)
Key for the ChaCha20 stream cipher or the ChaCha20Poly1305 AEAD algorithm.
#define PSA_KEY_TYPE_CHACHA20 ((psa_key_type_t)0x2004)
The ChaCha20 key size is 256 bits (32 bytes).
Use algorithm
PSA_ALG_STREAM_CIPHER
to use this key with the ChaCha20 cipher for unauthenticated encryption. SeePSA_ALG_STREAM_CIPHER
for details of this algorithm.Use algorithm
PSA_ALG_CHACHA20_POLY1305
to use this key with the ChaCha20 cipher and Poly1305 authenticator for AEAD. SeePSA_ALG_CHACHA20_POLY1305
for details of this algorithm.
9.2.4. RSA keys
PSA_KEY_TYPE_RSA_PUBLIC_KEY
(macro)
RSA public key.
#define PSA_KEY_TYPE_RSA_PUBLIC_KEY ((psa_key_type_t)0x4001)
PSA_KEY_TYPE_RSA_KEY_PAIR
(macro)
RSA key pair: both the private and public key.
#define PSA_KEY_TYPE_RSA_KEY_PAIR ((psa_key_type_t)0x7001)
PSA_KEY_TYPE_IS_RSA
(macro)
Whether a key type is an RSA key. This includes both key pairs and public keys.
#define PSA_KEY_TYPE_IS_RSA(type) /* specificationdefined value */
Parameters

type
A key type (value of type
psa_key_type_t
).
9.2.5. Elliptic Curve keys
psa_ecc_family_t
(type)
The type of PSA elliptic curve family identifiers.
typedef uint8_t psa_ecc_family_t;
The curve identifier is required to create an ECC key using the PSA_KEY_TYPE_ECC_KEY_PAIR()
or PSA_KEY_TYPE_ECC_PUBLIC_KEY()
macros.
The specific ECC curve within a family is identified by the key_bits
attribute of the key.
The range of Elliptic curve family identifier values is divided as follows:
0
x00
 0
x7f
ECC family identifiers defined by this standard. Unallocated values in this range are reserved for future use.
0
x80
 0
xff
Implementations that define additional families must use an encoding in this range.
PSA_KEY_TYPE_ECC_KEY_PAIR
(macro)
Elliptic curve key pair: both the private and public key.
#define PSA_KEY_TYPE_ECC_KEY_PAIR(curve) /* specificationdefined value */
Parameters

curve
A value of type
psa_ecc_family_t
that identifies the ECC curve family to be used.
PSA_KEY_TYPE_ECC_PUBLIC_KEY
(macro)
Elliptic curve public key.
#define PSA_KEY_TYPE_ECC_PUBLIC_KEY(curve) /* specificationdefined value */
Parameters

curve
A value of type
psa_ecc_family_t
that identifies the ECC curve family to be used.
PSA_ECC_FAMILY_SECP_K1
(macro)
SEC Koblitz curves over prime fields.
#define PSA_ECC_FAMILY_SECP_K1 ((psa_ecc_family_t) 0x17)
This family comprises the following curves:
secp192k1 :
key_bits = 192
secp224k1 :
key_bits = 225
secp256k1 :
key_bits = 256
They are defined in SEC 2: Recommended Elliptic Curve Domain Parameters [SEC2].
PSA_ECC_FAMILY_SECP_R1
(macro)
SEC random curves over prime fields.
#define PSA_ECC_FAMILY_SECP_R1 ((psa_ecc_family_t) 0x12)
This family comprises the following curves:
secp192r1 :
key_bits = 192
secp224r1 :
key_bits = 224
secp256r1 :
key_bits = 256
secp384r1 :
key_bits = 384
secp521r1 :
key_bits = 521
They are defined in [SEC2].
PSA_ECC_FAMILY_SECP_R2
(macro)
Warning
This family of curves is weak and deprecated.
#define PSA_ECC_FAMILY_SECP_R2 ((psa_ecc_family_t) 0x1b)
This family comprises the following curves:
secp160r2 :
key_bits = 160
(Deprecated)
It is defined in the superseded SEC 2: Recommended Elliptic Curve Domain Parameters, Version 1.0 [SEC2v1].
PSA_ECC_FAMILY_SECT_K1
(macro)
SEC Koblitz curves over binary fields.
#define PSA_ECC_FAMILY_SECT_K1 ((psa_ecc_family_t) 0x27)
This family comprises the following curves:
sect163k1 :
key_bits = 163
(Deprecated)sect233k1 :
key_bits = 233
sect239k1 :
key_bits = 239
sect283k1 :
key_bits = 283
sect409k1 :
key_bits = 409
sect571k1 :
key_bits = 571
They are defined in [SEC2].
Warning
The 163bit curve sect163k1 is weak and deprecated and is only recommended for use in legacy protocols.
PSA_ECC_FAMILY_SECT_R1
(macro)
SEC random curves over binary fields.
#define PSA_ECC_FAMILY_SECT_R1 ((psa_ecc_family_t) 0x22)
This family comprises the following curves:
sect163r1 :
key_bits = 163
(Deprecated)sect233r1 :
key_bits = 233
sect283r1 :
key_bits = 283
sect409r1 :
key_bits = 409
sect571r1 :
key_bits = 571
They are defined in [SEC2].
Warning
The 163bit curve sect163r1 is weak and deprecated and is only recommended for use in legacy protocols.
PSA_ECC_FAMILY_SECT_R2
(macro)
SEC additional random curves over binary fields.
#define PSA_ECC_FAMILY_SECT_R2 ((psa_ecc_family_t) 0x2b)
This family comprises the following curves:
sect163r2 :
key_bits = 163
(Deprecated)
It is defined in [SEC2].
Warning
The 163bit curve sect163r2 is weak and deprecated and is only recommended for use in legacy protocols.
PSA_ECC_FAMILY_BRAINPOOL_P_R1
(macro)
Brainpool P random curves.
#define PSA_ECC_FAMILY_BRAINPOOL_P_R1 ((psa_ecc_family_t) 0x30)
This family comprises the following curves:
brainpoolP160r1 :
key_bits = 160
(Deprecated)brainpoolP192r1 :
key_bits = 192
brainpoolP224r1 :
key_bits = 224
brainpoolP256r1 :
key_bits = 256
brainpoolP320r1 :
key_bits = 320
brainpoolP384r1 :
key_bits = 384
brainpoolP512r1 :
key_bits = 512
They are defined in Elliptic Curve Cryptography (ECC) Brainpool Standard Curves and Curve Generation [RFC5639].
Warning
The 160bit curve brainpoolP160r1 is weak and deprecated and is only recommended for use in legacy protocols.
PSA_ECC_FAMILY_FRP
(macro)
Curve used primarily in France and elsewhere in Europe.
#define PSA_ECC_FAMILY_FRP ((psa_ecc_family_t) 0x33)
This family comprises one 256bit curve:
FRP256v1 :
key_bits = 256
This is defined by Publication d'un paramétrage de courbe elliptique visant des applications de passeport électronique et de l'administration électronique française [FRP].
PSA_ECC_FAMILY_MONTGOMERY
(macro)
Montgomery curves.
#define PSA_ECC_FAMILY_MONTGOMERY ((psa_ecc_family_t) 0x41)
This family comprises the following Montgomery curves:
Curve25519 :
key_bits = 255
Curve448 :
key_bits = 448
Keys in this family can only be used with the PSA_ALG_ECDH
key agreement algorithm.
Curve25519 is defined in Curve25519: new DiffieHellman speed records [Curve25519]. Curve448 is defined in Ed448Goldilocks, a new elliptic curve [Curve448].
PSA_KEY_TYPE_IS_ECC
(macro)
Whether a key type is an elliptic curve key, either a key pair or a public key.
#define PSA_KEY_TYPE_IS_ECC(type) /* specificationdefined value */
Parameters

type
A key type (value of type
psa_key_type_t
).
PSA_KEY_TYPE_IS_ECC_KEY_PAIR
(macro)
Whether a key type is an elliptic curve key pair.
#define PSA_KEY_TYPE_IS_ECC_KEY_PAIR(type) /* specificationdefined value */
Parameters

type
A key type (value of type
psa_key_type_t
).
PSA_KEY_TYPE_IS_ECC_PUBLIC_KEY
(macro)
Whether a key type is an elliptic curve public key.
#define PSA_KEY_TYPE_IS_ECC_PUBLIC_KEY(type) /* specificationdefined value */
Parameters

type
A key type (value of type
psa_key_type_t
).
PSA_KEY_TYPE_ECC_GET_FAMILY
(macro)
Extract the curve family from an elliptic curve key type.
#define PSA_KEY_TYPE_ECC_GET_FAMILY(type) /* specificationdefined value */
Parameters

type
An elliptic curve key type (value of type
psa_key_type_t
such thatPSA_KEY_TYPE_IS_ECC
(
type
)
is true).
Returns: psa_ecc_family_t
The elliptic curve family id, if type
is a supported elliptic curve key. Unspecified if type
is not a supported elliptic curve key.
9.2.6. Diffie Hellman keys
psa_dh_family_t
(type)
The type of PSA finitefield DiffieHellman group family identifiers.
typedef uint8_t psa_dh_family_t;
The group family identifier is required to create a finitefield DiffieHellman key using the PSA_KEY_TYPE_DH_KEY_PAIR()
or PSA_KEY_TYPE_DH_PUBLIC_KEY()
macros.
The specific DiffieHellman group within a family is identified by the key_bits
attribute of the key.
The range of DiffieHellman group family identifier values is divided as follows:
0
x00
 0
x7f
DH group family identifiers defined by this standard. Unallocated values in this range are reserved for future use.
0
x80
 0
xff
Implementations that define additional families must use an encoding in this range.
PSA_KEY_TYPE_DH_KEY_PAIR
(macro)
Finitefield DiffieHellman key pair: both the private key and public key.
#define PSA_KEY_TYPE_DH_KEY_PAIR(group) /* specificationdefined value */
Parameters

group
A value of type
psa_dh_family_t
that identifies the DiffieHellman group family to be used.
PSA_KEY_TYPE_DH_PUBLIC_KEY
(macro)
Finitefield DiffieHellman public key.
#define PSA_KEY_TYPE_DH_PUBLIC_KEY(group) /* specificationdefined value */
Parameters

group
A value of type
psa_dh_family_t
that identifies the DiffieHellman group family to be used.
PSA_DH_FAMILY_RFC7919
(macro)
Finitefield DiffieHellman groups defined for TLS in RFC 7919.
#define PSA_DH_FAMILY_RFC7919 ((psa_dh_family_t) 0x03)
This family includes groups with the following key sizes (in bits): 2048, 3072, 4096, 6144, 8192. An implementation can support all of these sizes or only a subset.
Keys is this group can only be used with the PSA_ALG_FFDH
key agreement algorithm.
These groups are defined by Negotiated Finite Field DiffieHellman Ephemeral Parameters for Transport Layer Security (TLS) [RFC7919] Appendix A.
PSA_KEY_TYPE_KEY_PAIR_OF_PUBLIC_KEY
(macro)
The key pair type corresponding to a public key type.
#define PSA_KEY_TYPE_KEY_PAIR_OF_PUBLIC_KEY(type) \ /* specificationdefined value */
Parameters

type
A public key type or key pair type.
Returns
The corresponding key pair type. If type
is not a public key or a key pair, the return value is undefined.
Description
If type
is a key pair type, it will be left unchanged.
PSA_KEY_TYPE_PUBLIC_KEY_OF_KEY_PAIR
(macro)
The public key type corresponding to a key pair type.
#define PSA_KEY_TYPE_PUBLIC_KEY_OF_KEY_PAIR(type) \ /* specificationdefined value */
Parameters

type
A public key type or key pair type.
Returns
The corresponding public key type. If type
is not a public key or a key pair, the return value is undefined.
Description
If type
is a public key type, it will be left unchanged.
PSA_KEY_TYPE_IS_DH
(macro)
Whether a key type is a DiffieHellman key, either a key pair or a public key.
#define PSA_KEY_TYPE_IS_DH(type) /* specificationdefined value */
Parameters

type
A key type (value of type
psa_key_type_t
).
PSA_KEY_TYPE_IS_DH_KEY_PAIR
(macro)
Whether a key type is a DiffieHellman key pair.
#define PSA_KEY_TYPE_IS_DH_KEY_PAIR(type) /* specificationdefined value */
Parameters

type
A key type (value of type
psa_key_type_t
).
PSA_KEY_TYPE_IS_DH_PUBLIC_KEY
(macro)
Whether a key type is a DiffieHellman public key.
#define PSA_KEY_TYPE_IS_DH_PUBLIC_KEY(type) /* specificationdefined value */
Parameters

type
A key type (value of type
psa_key_type_t
).
PSA_KEY_TYPE_DH_GET_FAMILY
(macro)
Extract the group family from a DiffieHellman key type.
#define PSA_KEY_TYPE_DH_GET_FAMILY(type) /* specificationdefined value */
Parameters

type
A DiffieHellman key type (value of type
psa_key_type_t
such thatPSA_KEY_TYPE_IS_DH
(
type
)
is true).
Returns: psa_dh_family_t
The DiffieHellman group family id, if type
is a supported DiffieHellman key. Unspecified if type
is not a supported DiffieHellman key.
9.2.7. Attribute accessors
psa_set_key_type
(function)
Declare the type of a key.
void psa_set_key_type(psa_key_attributes_t * attributes, psa_key_type_t type);
Parameters

attributes
The attribute object to write to.

type
The key type to write. If this is
PSA_KEY_TYPE_NONE
, the key type inattributes
becomes unspecified.
Returns: void
Description
This function overwrites any key type previously set in attributes
.
Implementation note
This is a simple accessor function that is not required to validate its inputs. The following approaches can be used to provide an efficient implementation:
This function can be declared as
static
orinline
, instead of using the default external linkage.This function can be provided as a functionlike macro. In this form, the macro must evaluate each of its arguments exactly once, as if it was a function call.
psa_get_key_type
(function)
Retrieve the key type from key attributes.
psa_key_type_t psa_get_key_type(const psa_key_attributes_t * attributes);
Parameters

attributes
The key attribute object to query.
Returns: psa_key_type_t
The key type stored in the attribute object.
Description
Implementation note
This is a simple accessor function that is not required to validate its inputs. The following approaches can be used to provide an efficient implementation:
This function can be declared as
static
orinline
, instead of using the default external linkage.This function can be provided as a functionlike macro. In this form, the macro must evaluate each of its arguments exactly once, as if it was a function call.
psa_get_key_bits
(function)
Retrieve the key size from key attributes.
size_t psa_get_key_bits(const psa_key_attributes_t * attributes);
Parameters

attributes
The key attribute object to query.
Returns: size_t
The key size stored in the attribute object, in bits.
Description
Implementation note
This is a simple accessor function that is not required to validate its inputs. The following approaches can be used to provide an efficient implementation:
This function can be declared as
static
orinline
, instead of using the default external linkage.This function can be provided as a functionlike macro. In this form, the macro must evaluate each of its arguments exactly once, as if it was a function call.
psa_set_key_bits
(function)
Declare the size of a key.
void psa_set_key_bits(psa_key_attributes_t * attributes, size_t bits);
Parameters

attributes
The attribute object to write to.

bits
The key size in bits. If this is
0
, the key size inattributes
becomes unspecified. Keys of size0
are not supported.
Returns: void
Description
This function overwrites any key size previously set in attributes
.
Implementation note
This is a simple accessor function that is not required to validate its inputs. The following approaches can be used to provide an efficient implementation:
This function can be declared as
static
orinline
, instead of using the default external linkage.This function can be provided as a functionlike macro. In this form, the macro must evaluate each of its arguments exactly once, as if it was a function call.