Group attributes

group attributes

Defines

PSA_KEY_ATTRIBUTES_INIT

This macro returns a suitable initializer for a key attribute structure of type psa_key_attributes_t.

PSA_DH_FAMILY_CUSTOM

Custom Diffie-Hellman group.

For keys of type PSA_KEY_TYPE_DH_PUBLIC_KEY(PSA_DH_FAMILY_CUSTOM) or PSA_KEY_TYPE_DH_KEY_PAIR(PSA_DH_FAMILY_CUSTOM), the group data comes from domain parameters set by psa_set_key_domain_parameters().

PSA_KEY_DOMAIN_PARAMETERS_SIZE(key_type, key_bits)

Safe output buffer size for psa_get_key_domain_parameters().

This macro returns a compile-time constant if its arguments are compile-time constants.

Note

This is an experimental extension to the interface. It may change in future versions of the library.

Warning

This function may call its arguments multiple times or zero times, so you should not pass arguments that contain side effects.

Parameters

• key_type – A supported key type.

• key_bits – The size of the key in bits.

Returns

If the parameters are valid and supported, return a buffer size in bytes that guarantees that psa_get_key_domain_parameters() will not fail with PSA_ERROR_BUFFER_TOO_SMALL. If the parameters are a valid combination that is not supported by the implementation, this macro shall return either a sensible size or 0. If the parameters are not valid, the return value is unspecified.

PSA_DH_KEY_DOMAIN_PARAMETERS_SIZE(key_bits)

PSA_DSA_KEY_DOMAIN_PARAMETERS_SIZE(key_bits)

Typedefs

typedef struct psa_key_attributes_s psa_key_attributes_t

The type of a structure containing key attributes.

This is an opaque structure that can represent the metadata of a key object. Metadata that can be stored in attributes includes:

• The location of the key in storage, indicated by its key identifier and its lifetime.

• The key’s policy, comprising usage flags and a specification of the permitted algorithm(s).

• Information about the key itself: the key type and its size.

• Additional implementation-defined attributes.

The actual key material is not considered an attribute of a key. Key attributes do not contain information that is generally considered highly confidential.

An attribute structure works like a simple data structure where each function psa_set_key_xxx sets a field and the corresponding function psa_get_key_xxx retrieves the value of the corresponding field. However, a future version of the library may report values that are equivalent to the original one, but have a different encoding. Invalid values may be mapped to different, also invalid values.

An attribute structure may contain references to auxiliary resources, for example pointers to allocated memory or indirect references to pre-calculated values. In order to free such resources, the application must call psa_reset_key_attributes(). As an exception, calling psa_reset_key_attributes() on an attribute structure is optional if the structure has only been modified by the following functions since it was initialized or last reset with psa_reset_key_attributes():

• psa_set_key_id()

• psa_set_key_lifetime()

• psa_set_key_type()

• psa_set_key_bits()

• psa_set_key_usage_flags()

• psa_set_key_algorithm()

Before calling any function on a key attribute structure, the application must initialize it by any of the following means:

• Set the structure to all-bits-zero, for example:

  psa_key_attributes_t attributes;
  memset(&attributes, 0, sizeof(attributes));
  

• Initialize the structure to logical zero values, for example:

  psa_key_attributes_t attributes = {0};
  

• Initialize the structure to the initializer PSA_KEY_ATTRIBUTES_INIT, for example:

  psa_key_attributes_t attributes = PSA_KEY_ATTRIBUTES_INIT;
  

• Assign the result of the function psa_key_attributes_init() to the structure, for example:

  psa_key_attributes_t attributes;
  attributes = psa_key_attributes_init();
  

A freshly initialized attribute structure contains the following values:

• lifetime: PSA_KEY_LIFETIME_VOLATILE.

• key identifier: 0 (which is not a valid key identifier).

• type: 0 (meaning that the type is unspecified).

• key size: 0 (meaning that the size is unspecified).

• usage flags: 0 (which allows no usage except exporting a public key).

• algorithm: 0 (which allows no cryptographic usage, but allows exporting).

A typical sequence to create a key is as follows:

1. Create and initialize an attribute structure.

2. If the key is persistent, call psa_set_key_id(). Also call psa_set_key_lifetime() to place the key in a non-default location.

3. Set the key policy with psa_set_key_usage_flags() and psa_set_key_algorithm().

4. Set the key type with psa_set_key_type(). Skip this step if copying an existing key with psa_copy_key().

5. When generating a random key with psa_generate_key() or deriving a key with psa_key_derivation_output_key(), set the desired key size with psa_set_key_bits().

6. Call a key creation function: psa_import_key(), psa_generate_key(), psa_key_derivation_output_key() or psa_copy_key(). This function reads the attribute structure, creates a key with these attributes, and outputs a key identifier to the newly created key.

7. The attribute structure is now no longer necessary. You may call psa_reset_key_attributes(), although this is optional with the workflow presented here because the attributes currently defined in this specification do not require any additional resources beyond the structure itself.

A typical sequence to query a key’s attributes is as follows:

1. Call psa_get_key_attributes().

2. Call psa_get_key_xxx functions to retrieve the attribute(s) that you are interested in.

3. Call psa_reset_key_attributes() to free any resources that may be used by the attribute structure.

Once a key has been created, it is impossible to change its attributes.

typedef uint64_t psa_key_slot_number_t

Functions

static psa_key_attributes_t psa_key_attributes_init(void)

Return an initial value for a key attributes structure.

static void psa_set_key_id(psa_key_attributes_t *attributes, mbedtls_svc_key_id_t key)

Declare a key as persistent and set its key identifier.

If the attribute structure currently declares the key as volatile (which is the default content of an attribute structure), this function sets the lifetime attribute to PSA_KEY_LIFETIME_PERSISTENT.

This function does not access storage, it merely stores the given value in the structure. The persistent key will be written to storage when the attribute structure is passed to a key creation function such as psa_import_key(), psa_generate_key(), psa_key_derivation_output_key() or psa_copy_key().

This function may be declared as static (i.e. without external linkage). This function may be provided as a function-like macro, but in this case it must evaluate each of its arguments exactly once.

Parameters

• attributes – [out] The attribute structure to write to.

• key – The persistent identifier for the key.

static void mbedtls_set_key_owner_id(psa_key_attributes_t *attributes, mbedtls_key_owner_id_t owner)

Set the owner identifier of a key.

When key identifiers encode key owner identifiers, psa_set_key_id() does not allow to define in key attributes the owner of volatile keys as psa_set_key_id() enforces the key to be persistent.

This function allows to set in key attributes the owner identifier of a key. It is intended to be used for volatile keys. For persistent keys, it is recommended to use the PSA Cryptography API psa_set_key_id() to define the owner of a key.

Parameters

• attributes – [out] The attribute structure to write to.

• owner – The key owner identifier.

static void psa_set_key_lifetime(psa_key_attributes_t *attributes, psa_key_lifetime_t lifetime)

Set the location of a persistent key.

To make a key persistent, you must give it a persistent key identifier with psa_set_key_id(). By default, a key that has a persistent identifier is stored in the default storage area identifier by PSA_KEY_LIFETIME_PERSISTENT. Call this function to choose a storage area, or to explicitly declare the key as volatile.

This function does not access storage, it merely stores the given value in the structure. The persistent key will be written to storage when the attribute structure is passed to a key creation function such as psa_import_key(), psa_generate_key(), psa_key_derivation_output_key() or psa_copy_key().

This function may be declared as static (i.e. without external linkage). This function may be provided as a function-like macro, but in this case it must evaluate each of its arguments exactly once.

Parameters

• attributes – [out] The attribute structure to write to.

• lifetime – The lifetime for the key. If this is PSA_KEY_LIFETIME_VOLATILE, the key will be volatile, and the key identifier attribute is reset to 0.

static mbedtls_svc_key_id_t psa_get_key_id(const psa_key_attributes_t *attributes)

Retrieve the key identifier from key attributes.

This function may be declared as static (i.e. without external linkage). This function may be provided as a function-like macro, but in this case it must evaluate its argument exactly once.

Parameters

attributes – [in] The key attribute structure to query.

Returns

The persistent identifier stored in the attribute structure. This value is unspecified if the attribute structure declares the key as volatile.

static psa_key_lifetime_t psa_get_key_lifetime(const psa_key_attributes_t *attributes)

Retrieve the lifetime from key attributes.

This function may be declared as static (i.e. without external linkage). This function may be provided as a function-like macro, but in this case it must evaluate its argument exactly once.

Parameters

attributes – [in] The key attribute structure to query.

Returns

The lifetime value stored in the attribute structure.

static void psa_set_key_usage_flags(psa_key_attributes_t *attributes, psa_key_usage_t usage_flags)

Declare usage flags for a key.

Usage flags are part of a key’s usage policy. They encode what kind of operations are permitted on the key. For more details, refer to the documentation of the type psa_key_usage_t.

This function overwrites any usage flags previously set in attributes.

This function may be declared as static (i.e. without external linkage). This function may be provided as a function-like macro, but in this case it must evaluate each of its arguments exactly once.

Parameters

• attributes – [out] The attribute structure to write to.

• usage_flags – The usage flags to write.

static psa_key_usage_t psa_get_key_usage_flags(const psa_key_attributes_t *attributes)

Retrieve the usage flags from key attributes.

This function may be declared as static (i.e. without external linkage). This function may be provided as a function-like macro, but in this case it must evaluate its argument exactly once.

Parameters

attributes – [in] The key attribute structure to query.

Returns

The usage flags stored in the attribute structure.

static void psa_set_key_algorithm(psa_key_attributes_t *attributes, psa_algorithm_t alg)

Declare the permitted algorithm policy for a key.

The permitted algorithm policy of a key encodes which algorithm or algorithms are permitted to be used with this key. The following algorithm policies are supported:

• 0 does not allow any cryptographic operation with the key. The key may be used for non-cryptographic actions such as exporting (if permitted by the usage flags).

• An algorithm value permits this particular algorithm.

• An algorithm wildcard built from PSA_ALG_ANY_HASH allows the specified signature scheme with any hash algorithm.

• An algorithm built from PSA_ALG_AT_LEAST_THIS_LENGTH_MAC allows any MAC algorithm from the same base class (e.g. CMAC) which generates/verifies a MAC length greater than or equal to the length encoded in the wildcard algorithm.

• An algorithm built from PSA_ALG_AEAD_WITH_AT_LEAST_THIS_LENGTH_TAG allows any AEAD algorithm from the same base class (e.g. CCM) which generates/verifies a tag length greater than or equal to the length encoded in the wildcard algorithm.

This function overwrites any algorithm policy previously set in attributes.

This function may be declared as static (i.e. without external linkage). This function may be provided as a function-like macro, but in this case it must evaluate each of its arguments exactly once.

Parameters

• attributes – [out] The attribute structure to write to.

• alg – The permitted algorithm policy to write.

static psa_algorithm_t psa_get_key_algorithm(const psa_key_attributes_t *attributes)

Retrieve the algorithm policy from key attributes.

This function may be declared as static (i.e. without external linkage). This function may be provided as a function-like macro, but in this case it must evaluate its argument exactly once.

Parameters

attributes – [in] The key attribute structure to query.

Returns

The algorithm stored in the attribute structure.

static void psa_set_key_type(psa_key_attributes_t *attributes, psa_key_type_t type)

Declare the type of a key.

This function overwrites any key type previously set in attributes.

This function may be declared as static (i.e. without external linkage). This function may be provided as a function-like macro, but in this case it must evaluate each of its arguments exactly once.

Parameters

• attributes – [out] The attribute structure to write to.

• type – The key type to write. If this is 0, the key type in attributes becomes unspecified.

static void psa_set_key_bits(psa_key_attributes_t *attributes, size_t bits)

Declare the size of a key.

This function overwrites any key size previously set in attributes.

This function may be declared as static (i.e. without external linkage). This function may be provided as a function-like macro, but in this case it must evaluate each of its arguments exactly once.

Parameters

• attributes – [out] The attribute structure to write to.

• bits – The key size in bits. If this is 0, the key size in attributes becomes unspecified. Keys of size 0 are not supported.

static psa_key_type_t psa_get_key_type(const psa_key_attributes_t *attributes)

Retrieve the key type from key attributes.

This function may be declared as static (i.e. without external linkage). This function may be provided as a function-like macro, but in this case it must evaluate its argument exactly once.

Parameters

attributes – [in] The key attribute structure to query.

Returns

The key type stored in the attribute structure.

static size_t psa_get_key_bits(const psa_key_attributes_t *attributes)

Retrieve the key size from key attributes.

This function may be declared as static (i.e. without external linkage). This function may be provided as a function-like macro, but in this case it must evaluate its argument exactly once.

Parameters

attributes – [in] The key attribute structure to query.

Returns

The key size stored in the attribute structure, in bits.

psa_status_t psa_get_key_attributes(mbedtls_svc_key_id_t key, psa_key_attributes_t *attributes)

Retrieve the attributes of a key.

This function first resets the attribute structure as with psa_reset_key_attributes(). It then copies the attributes of the given key into the given attribute structure.

Note

This function may allocate memory or other resources. Once you have called this function on an attribute structure, you must call psa_reset_key_attributes() to free these resources.

Parameters

• key – [in] Identifier of the key to query.

• attributes – [inout] On success, the attributes of the key. On failure, equivalent to a freshly-initialized structure.

Return values

• PSA_SUCCESS –

• PSA_ERROR_INVALID_HANDLE –

• PSA_ERROR_INSUFFICIENT_MEMORY –

• PSA_ERROR_COMMUNICATION_FAILURE –

• PSA_ERROR_CORRUPTION_DETECTED –

• PSA_ERROR_STORAGE_FAILURE –

• PSA_ERROR_DATA_CORRUPT –

• PSA_ERROR_DATA_INVALID –

• PSA_ERROR_BAD_STATE – The library has not been previously initialized by psa_crypto_init(). It is implementation-dependent whether a failure to initialize results in this error code.

void psa_reset_key_attributes(psa_key_attributes_t *attributes)

Reset a key attribute structure to a freshly initialized state.

You must initialize the attribute structure as described in the documentation of the type psa_key_attributes_t before calling this function. Once the structure has been initialized, you may call this function at any time.

This function frees any auxiliary resources that the structure may contain.

Parameters

attributes – [inout] The attribute structure to reset.

static inline void psa_set_key_enrollment_algorithm(psa_key_attributes_t *attributes, psa_algorithm_t alg2)

Declare the enrollment algorithm for a key.

An operation on a key may indifferently use the algorithm set with psa_set_key_algorithm() or with this function.

Warning

Setting an enrollment algorithm is not recommended, because using the same key with different algorithms can allow some attacks based on arithmetic relations between different computations made with the same key, or can escalate harmless side channels into exploitable ones. Use this function only if it is necessary to support a protocol for which it has been verified that the usage of the key with multiple algorithms is safe.

Parameters

• attributes – [out] The attribute structure to write to.

• alg2 – A second algorithm that the key may be used for, in addition to the algorithm set with psa_set_key_algorithm().

static inline psa_algorithm_t psa_get_key_enrollment_algorithm(const psa_key_attributes_t *attributes)

Retrieve the enrollment algorithm policy from key attributes.

Parameters

attributes – [in] The key attribute structure to query.

Returns

The enrollment algorithm stored in the attribute structure.

psa_status_t psa_get_key_slot_number(const psa_key_attributes_t *attributes, psa_key_slot_number_t *slot_number)

Retrieve the slot number where a key is stored.

A slot number is only defined for keys that are stored in a secure element.

This information is only useful if the secure element is not entirely managed through the PSA Cryptography API. It is up to the secure element driver to decide how PSA slot numbers map to any other interface that the secure element may have.

Parameters

• attributes – [in] The key attribute structure to query.

• slot_number – [out] On success, the slot number containing the key.

Return values

• PSA_SUCCESS – The key is located in a secure element, and *slot_number indicates the slot number that contains it.

• PSA_ERROR_NOT_PERMITTED – The caller is not permitted to query the slot number. Mbed TLS currently does not return this error.

• PSA_ERROR_INVALID_ARGUMENT – The key is not located in a secure element.

static inline void psa_set_key_slot_number(psa_key_attributes_t *attributes, psa_key_slot_number_t slot_number)

Choose the slot number where a key is stored.

This function declares a slot number in the specified attribute structure.

A slot number is only meaningful for keys that are stored in a secure element. It is up to the secure element driver to decide how PSA slot numbers map to any other interface that the secure element may have.

Note

Setting a slot number in key attributes for a key creation can cause the following errors when creating the key:

• PSA_ERROR_NOT_SUPPORTED if the selected secure element does not support choosing a specific slot number.

• PSA_ERROR_NOT_PERMITTED if the caller is not permitted to choose slot numbers in general or to choose this specific slot.

• PSA_ERROR_INVALID_ARGUMENT if the chosen slot number is not valid in general or not valid for this specific key.

• PSA_ERROR_ALREADY_EXISTS if there is already a key in the selected slot.

Parameters

• attributes – [out] The attribute structure to write to.

• slot_number – The slot number to set.

static inline void psa_clear_key_slot_number(psa_key_attributes_t *attributes)

Remove the slot number attribute from a key attribute structure.

This function undoes the action of psa_set_key_slot_number().

Parameters

attributes – [out] The attribute structure to write to.

psa_status_t mbedtls_psa_register_se_key(const psa_key_attributes_t *attributes)

Register a key that is already present in a secure element.

The key must be located in a secure element designated by the lifetime field in attributes, in the slot set with psa_set_key_slot_number() in the attribute structure. This function makes the key available through the key identifier specified in attributes.

Parameters

attributes – [in] The attributes of the existing key.

Return values

• PSA_SUCCESS – The key was successfully registered. Note that depending on the design of the driver, this may or may not guarantee that a key actually exists in the designated slot and is compatible with the specified attributes.

• PSA_ERROR_ALREADY_EXISTS – There is already a key with the identifier specified in attributes.

• PSA_ERROR_NOT_SUPPORTED – The secure element driver for the specified lifetime does not support registering a key.

• PSA_ERROR_INVALID_ARGUMENT – The identifier in attributes is invalid, namely the identifier is not in the user range, or attributes specifies a lifetime which is not located in a secure element, or no slot number is specified in attributes, or the specified slot number is not valid.

• PSA_ERROR_NOT_PERMITTED – The caller is not authorized to register the specified key slot.

• PSA_ERROR_INSUFFICIENT_MEMORY –

• PSA_ERROR_INSUFFICIENT_STORAGE –

• PSA_ERROR_COMMUNICATION_FAILURE –

• PSA_ERROR_DATA_INVALID –

• PSA_ERROR_DATA_CORRUPT –

• PSA_ERROR_CORRUPTION_DETECTED –

• PSA_ERROR_BAD_STATE – The library has not been previously initialized by psa_crypto_init(). It is implementation-dependent whether a failure to initialize results in this error code.

psa_status_t psa_set_key_domain_parameters(psa_key_attributes_t *attributes, psa_key_type_t type, const uint8_t *data, size_t data_length)

Set domain parameters for a key.

Some key types require additional domain parameters in addition to the key type identifier and the key size. Use this function instead of psa_set_key_type() when you need to specify domain parameters.

The format for the required domain parameters varies based on the key type.

• For RSA keys (PSA_KEY_TYPE_RSA_PUBLIC_KEY or PSA_KEY_TYPE_RSA_KEY_PAIR), the domain parameter data consists of the public exponent, represented as a big-endian integer with no leading zeros. This information is used when generating an RSA key pair. When importing a key, the public exponent is read from the imported key data and the exponent recorded in the attribute structure is ignored. As an exception, the public exponent 65537 is represented by an empty byte string.

• For DSA keys (PSA_KEY_TYPE_DSA_PUBLIC_KEY or PSA_KEY_TYPE_DSA_KEY_PAIR), the Dss-Params format as defined by RFC 3279 2.3.2.

  Dss-Params ::= SEQUENCE  {
     p       INTEGER,
     q       INTEGER,
     g       INTEGER
  }
  

• For Diffie-Hellman key exchange keys (PSA_KEY_TYPE_DH_PUBLIC_KEY(PSA_DH_FAMILY_CUSTOM) or PSA_KEY_TYPE_DH_KEY_PAIR(PSA_DH_FAMILY_CUSTOM)), the DomainParameters format as defined by RFC 3279 2.3.3.

  DomainParameters ::= SEQUENCE {
     p               INTEGER,                    -- odd prime, p=jq +1
     g               INTEGER,                    -- generator, g
     q               INTEGER,                    -- factor of p-1
     j               INTEGER OPTIONAL,           -- subgroup factor
     validationParams ValidationParams OPTIONAL
  }
  ValidationParams ::= SEQUENCE {
     seed            BIT STRING,
     pgenCounter     INTEGER
  }
  

Note

This function may allocate memory or other resources. Once you have called this function on an attribute structure, you must call psa_reset_key_attributes() to free these resources.

Note

This is an experimental extension to the interface. It may change in future versions of the library.

Parameters

• attributes – [inout] Attribute structure where the specified domain parameters will be stored. If this function fails, the content of attributes is not modified.

• type – Key type (a PSA_KEY_TYPE_XXX value).

• data – [in] Buffer containing the key domain parameters. The content of this buffer is interpreted according to type as described above.

• data_length – Size of the data buffer in bytes.

Return values

• PSA_SUCCESS –

• PSA_ERROR_INVALID_ARGUMENT –

• PSA_ERROR_NOT_SUPPORTED –

• PSA_ERROR_INSUFFICIENT_MEMORY –

psa_status_t psa_get_key_domain_parameters(const psa_key_attributes_t *attributes, uint8_t *data, size_t data_size, size_t *data_length)

Get domain parameters for a key.

Get the domain parameters for a key with this function, if any. The format of the domain parameters written to data is specified in the documentation for psa_set_key_domain_parameters().

Note

This is an experimental extension to the interface. It may change in future versions of the library.

Parameters

• attributes – [in] The key attribute structure to query.

• data – [out] On success, the key domain parameters.

• data_size – Size of the data buffer in bytes. The buffer is guaranteed to be large enough if its size in bytes is at least the value given by PSA_KEY_DOMAIN_PARAMETERS_SIZE().

• data_length – [out] On success, the number of bytes that make up the key domain parameters data.

Return values

• PSA_SUCCESS –

• PSA_ERROR_BUFFER_TOO_SMALL –