Type Alias esp_idf_sys::psa_key_attributes_t

pub type psa_key_attributes_t = psa_key_attributes_s;

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: \code psa_key_attributes_t attributes; memset(&attributes, 0, sizeof(attributes)); \endcode
• Initialize the structure to logical zero values, for example: \code psa_key_attributes_t attributes = {0}; \endcode
• Initialize the structure to the initializer #PSA_KEY_ATTRIBUTES_INIT, for example: \code psa_key_attributes_t attributes = PSA_KEY_ATTRIBUTES_INIT; \endcode
• Assign the result of the function psa_key_attributes_init() to the structure, for example: \code psa_key_attributes_t attributes; attributes = psa_key_attributes_init(); \endcode

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: \c 0 (meaning that the type is unspecified).
• key size: \c 0 (meaning that the size is unspecified).
• usage flags: \c 0 (which allows no usage except exporting a public key).
• algorithm: \c 0 (which allows no cryptographic usage, but allows exporting).

A typical sequence to create a key is as follows: -# Create and initialize an attribute structure. -# 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. -# Set the key policy with psa_set_key_usage_flags() and psa_set_key_algorithm(). -# Set the key type with psa_set_key_type(). Skip this step if copying an existing key with psa_copy_key(). -# 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(). -# 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. -# 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: -# Call psa_get_key_attributes(). -# Call psa_get_key_xxx functions to retrieve the attribute(s) that you are interested in. -# 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.

Aliased Type

struct psa_key_attributes_t {
    pub private_type: u16,
    pub private_bits: u16,
    pub private_lifetime: u32,
    pub private_policy: psa_key_policy_s,
    pub private_id: u32,
}

Fields

private_type: u16

private_bits: u16

private_lifetime: u32

private_policy: psa_key_policy_s

private_id: u32