Message authentication codes#

psa_mac_compute#

psa_status_t psa_mac_compute (mbedtls_svc_key_id_t key, psa_algorithm_t alg, const uint8_t * input, size_t input_length, uint8_t * mac, size_t mac_size, size_t * mac_length)

Calculate the MAC (message authentication code) of a message.

Note

• To verify the MAC of a message against an expected value, use psa_mac_verify() instead. Beware that comparing integrity or authenticity data such as MAC values with a function such as memcmp is risky because the time taken by the comparison may leak information about the MAC value which could allow an attacker to guess a valid MAC and thereby bypass security controls.

psa_mac_verify#

psa_status_t psa_mac_verify (mbedtls_svc_key_id_t key, psa_algorithm_t alg, const uint8_t * input, size_t input_length, const uint8_t * mac, size_t mac_length)

Calculate the MAC of a message and compare it with a reference value.

psa_mac_operation_init#

static psa_mac_operation_t psa_mac_operation_init (void )

Return an initial value for a MAC operation object.

psa_mac_sign_setup#

psa_status_t psa_mac_sign_setup (psa_mac_operation_t * operation, mbedtls_svc_key_id_t key, psa_algorithm_t alg)

Set up a multipart MAC calculation operation.

This function sets up the calculation of the MAC (message authentication code) of a byte string. To verify the MAC of a message against an expected value, use psa_mac_verify_setup() instead.

The sequence of operations to calculate a MAC is as follows:

1. Allocate an operation object which will be passed to all the functions listed here.

2. Initialize the operation object with one of the methods described in the documentation for #psa_mac_operation_t, e.g. #PSA_MAC_OPERATION_INIT.

3. Call psa_mac_sign_setup() to specify the algorithm and key.

4. Call psa_mac_update() zero, one or more times, passing a fragment of the message each time. The MAC that is calculated is the MAC of the concatenation of these messages in order.

5. At the end of the message, call psa_mac_sign_finish() to finish calculating the MAC value and retrieve it.

If an error occurs at any step after a call to psa_mac_sign_setup(), the operation will need to be reset by a call to psa_mac_abort(). The application may call psa_mac_abort() at any time after the operation has been initialized.

After a successful call to psa_mac_sign_setup(), the application must eventually terminate the operation through one of the following methods:

• A successful call to psa_mac_sign_finish().

• A call to psa_mac_abort().

psa_mac_verify_setup#

psa_status_t psa_mac_verify_setup (psa_mac_operation_t * operation, mbedtls_svc_key_id_t key, psa_algorithm_t alg)

Set up a multipart MAC verification operation.

This function sets up the verification of the MAC (message authentication code) of a byte string against an expected value.

The sequence of operations to verify a MAC is as follows:

1. Allocate an operation object which will be passed to all the functions listed here.

2. Initialize the operation object with one of the methods described in the documentation for #psa_mac_operation_t, e.g. #PSA_MAC_OPERATION_INIT.

3. Call psa_mac_verify_setup() to specify the algorithm and key.

4. Call psa_mac_update() zero, one or more times, passing a fragment of the message each time. The MAC that is calculated is the MAC of the concatenation of these messages in order.

5. At the end of the message, call psa_mac_verify_finish() to finish calculating the actual MAC of the message and verify it against the expected value.

If an error occurs at any step after a call to psa_mac_verify_setup(), the operation will need to be reset by a call to psa_mac_abort(). The application may call psa_mac_abort() at any time after the operation has been initialized.

After a successful call to psa_mac_verify_setup(), the application must eventually terminate the operation through one of the following methods:

• A successful call to psa_mac_verify_finish().

• A call to psa_mac_abort().

psa_mac_update#

psa_status_t psa_mac_update (psa_mac_operation_t * operation, const uint8_t * input, size_t input_length)

Add a message fragment to a multipart MAC operation.

The application must call psa_mac_sign_setup() or psa_mac_verify_setup() before calling this function.

If this function returns an error status, the operation enters an error state and must be aborted by calling psa_mac_abort().

psa_mac_sign_finish#

psa_status_t psa_mac_sign_finish (psa_mac_operation_t * operation, uint8_t * mac, size_t mac_size, size_t * mac_length)

Finish the calculation of the MAC of a message.

The application must call psa_mac_sign_setup() before calling this function. This function calculates the MAC of the message formed by concatenating the inputs passed to preceding calls to psa_mac_update().

When this function returns successfully, the operation becomes inactive. If this function returns an error status, the operation enters an error state and must be aborted by calling psa_mac_abort().

Warnings

• Applications should not call this function if they expect a specific value for the MAC. Call psa_mac_verify_finish() instead. Beware that comparing integrity or authenticity data such as MAC values with a function such as memcmp is risky because the time taken by the comparison may leak information about the MAC value which could allow an attacker to guess a valid MAC and thereby bypass security controls.

psa_mac_verify_finish#

psa_status_t psa_mac_verify_finish (psa_mac_operation_t * operation, const uint8_t * mac, size_t mac_length)

Finish the calculation of the MAC of a message and compare it with an expected value.

The application must call psa_mac_verify_setup() before calling this function. This function calculates the MAC of the message formed by concatenating the inputs passed to preceding calls to psa_mac_update(). It then compares the calculated MAC with the expected MAC passed as a parameter to this function.

When this function returns successfully, the operation becomes inactive. If this function returns an error status, the operation enters an error state and must be aborted by calling psa_mac_abort().

Note

• Implementations shall make the best effort to ensure that the comparison between the actual MAC and the expected MAC is performed in constant time.

psa_mac_abort#

psa_status_t psa_mac_abort (psa_mac_operation_t * operation)

Abort a MAC operation.

Aborting an operation frees all associated resources except for the operation structure itself. Once aborted, the operation object can be reused for another operation by calling psa_mac_sign_setup() or psa_mac_verify_setup() again.

You may call this function any time after the operation object has been initialized by one of the methods described in #psa_mac_operation_t.

In particular, calling psa_mac_abort() after the operation has been terminated by a call to psa_mac_abort(), psa_mac_sign_finish() or psa_mac_verify_finish() is safe and has no effect.