Key attributes

Macros
#define	PSA_KEY_ATTRIBUTES_INIT   {PSA_CORE_KEY_ATTRIBUTES_INIT, NULL, 0}
	This macro returns a suitable initializer for a key attribute structure of type psa_key_attributes_t. More...
#define	PSA_DH_FAMILY_CUSTOM   ((psa_dh_family_t) 0x7e)
	Custom Diffie-Hellman group. More...
#define	PSA_KEY_DOMAIN_PARAMETERS_SIZE(key_type, key_bits)
	Safe output buffer size for psa_get_key_domain_parameters(). More...

Typedefs
typedef struct psa_key_attributes_s	psa_key_attributes_t
	The type of a structure containing key attributes. More...

Functions
psa_status_t	psa_get_key_attributes (mbedtls_svc_key_id_t key, psa_key_attributes_t *attributes)
	Retrieve the attributes of a key. More...
void	psa_reset_key_attributes (psa_key_attributes_t *attributes)
	Reset a key attribute structure to a freshly initialized state. More...
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. More...
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. More...

Detailed Description

Macro Definition Documentation

PSA_KEY_ATTRIBUTES_INIT

#define PSA_KEY_ATTRIBUTES_INIT   {PSA_CORE_KEY_ATTRIBUTES_INIT, NULL, 0}

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

Definition at line 365 of file crypto_struct.h.

PSA_DH_FAMILY_CUSTOM

#define PSA_DH_FAMILY_CUSTOM   ((psa_dh_family_t) 0x7e)

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().

Definition at line 422 of file crypto_extra.h.

PSA_KEY_DOMAIN_PARAMETERS_SIZE

#define PSA_KEY_DOMAIN_PARAMETERS_SIZE	(		key_type,
			key_bits
	)

Value:

    (PSA_KEY_TYPE_IS_RSA(key_type) ? sizeof(int) :                      \
     PSA_KEY_TYPE_IS_DH(key_type) ? PSA_DH_KEY_DOMAIN_PARAMETERS_SIZE(key_bits) : \
     PSA_KEY_TYPE_IS_DSA(key_type) ? PSA_DSA_KEY_DOMAIN_PARAMETERS_SIZE(key_bits) : \
     0)

Safe output buffer size for psa_get_key_domain_parameters().

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

Warning

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

Note

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

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.

Definition at line 550 of file crypto_extra.h.

Typedef Documentation

psa_key_attributes_t

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.
• Implementations may define additional 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 can be 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, implementations may report values that are equivalent to the original one, but have a different encoding. For example, an implementation may use a more compact representation for types where many bit-patterns are invalid or not supported, and store all values that it does not support as a special marker value. In such an implementation, after setting an invalid value, the corresponding get function returns an invalid value which may not be the one that was originally stored.

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.

Definition at line 374 of file crypto_types.h.

Function Documentation

psa_get_key_attributes()

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

[in]	key	Identifier of the key to query.
[in,out]	attributes	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_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_reset_key_attributes()

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

[in,out]

attributes

The attribute structure to reset.

psa_set_key_domain_parameters()

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-Parms format as defined by RFC 3279 §2.3.2.

  Dss-Parms ::= 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
     validationParms ValidationParms OPTIONAL
  }
  ValidationParms ::= 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.

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

Parameters

[in,out]	attributes	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).
[in]	data	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_get_key_domain_parameters()

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

[in]	attributes	The key attribute structure to query.
[out]	data	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().
[out]	data_length	On success, the number of bytes that make up the key domain parameters data.

Return values

PSA_SUCCESS
PSA_ERROR_BUFFER_TOO_SMALL