Authenticated encryption with associated data (AEAD)#

psa_aead_encrypt#

psa_status_t psa_aead_encrypt (mbedtls_svc_key_id_t key, psa_algorithm_t alg, const uint8_t * nonce, size_t nonce_length, const uint8_t * additional_data, size_t additional_data_length, const uint8_t * plaintext, size_t plaintext_length, uint8_t * ciphertext, size_t ciphertext_size, size_t * ciphertext_length)

Process an authenticated encryption operation.

psa_aead_decrypt#

psa_status_t psa_aead_decrypt (mbedtls_svc_key_id_t key, psa_algorithm_t alg, const uint8_t * nonce, size_t nonce_length, const uint8_t * additional_data, size_t additional_data_length, const uint8_t * ciphertext, size_t ciphertext_length, uint8_t * plaintext, size_t plaintext_size, size_t * plaintext_length)

Process an authenticated decryption operation.

psa_aead_operation_init#

static psa_aead_operation_t psa_aead_operation_init (void )

Return an initial value for an AEAD operation object.

psa_aead_encrypt_setup#

psa_status_t psa_aead_encrypt_setup (psa_aead_operation_t * operation, mbedtls_svc_key_id_t key, psa_algorithm_t alg)

Set the key for a multipart authenticated encryption operation.

The sequence of operations to encrypt a message with authentication 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_aead_operation_t, e.g. #PSA_AEAD_OPERATION_INIT.

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

4. If needed, call psa_aead_set_lengths() to specify the length of the inputs to the subsequent calls to psa_aead_update_ad() and psa_aead_update(). See the documentation of psa_aead_set_lengths() for details.

5. Call either psa_aead_generate_nonce() or psa_aead_set_nonce() to generate or set the nonce. You should use psa_aead_generate_nonce() unless the protocol you are implementing requires a specific nonce value.

6. Call psa_aead_update_ad() zero, one or more times, passing a fragment of the non-encrypted additional authenticated data each time.

7. Call psa_aead_update() zero, one or more times, passing a fragment of the message to encrypt each time.

8. Call psa_aead_finish().

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

After a successful call to psa_aead_encrypt_setup(), the application must eventually terminate the operation. The following events terminate an operation:

• A successful call to psa_aead_finish().

• A call to psa_aead_abort().

psa_aead_decrypt_setup#

psa_status_t psa_aead_decrypt_setup (psa_aead_operation_t * operation, mbedtls_svc_key_id_t key, psa_algorithm_t alg)

Set the key for a multipart authenticated decryption operation.

The sequence of operations to decrypt a message with authentication 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_aead_operation_t, e.g. #PSA_AEAD_OPERATION_INIT.

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

4. If needed, call psa_aead_set_lengths() to specify the length of the inputs to the subsequent calls to psa_aead_update_ad() and psa_aead_update(). See the documentation of psa_aead_set_lengths() for details.

5. Call psa_aead_set_nonce() with the nonce for the decryption.

6. Call psa_aead_update_ad() zero, one or more times, passing a fragment of the non-encrypted additional authenticated data each time.

7. Call psa_aead_update() zero, one or more times, passing a fragment of the ciphertext to decrypt each time.

8. Call psa_aead_verify().

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

After a successful call to psa_aead_decrypt_setup(), the application must eventually terminate the operation. The following events terminate an operation:

• A successful call to psa_aead_verify().

• A call to psa_aead_abort().

psa_aead_generate_nonce#

psa_status_t psa_aead_generate_nonce (psa_aead_operation_t * operation, uint8_t * nonce, size_t nonce_size, size_t * nonce_length)

Generate a random nonce for an authenticated encryption operation.

This function generates a random nonce for the authenticated encryption operation with an appropriate size for the chosen algorithm, key type and key size.

The application must call psa_aead_encrypt_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_aead_abort().

psa_aead_set_nonce#

psa_status_t psa_aead_set_nonce (psa_aead_operation_t * operation, const uint8_t * nonce, size_t nonce_length)

Set the nonce for an authenticated encryption or decryption operation.

This function sets the nonce for the authenticated encryption or decryption operation.

The application must call psa_aead_encrypt_setup() or psa_aead_decrypt_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_aead_abort().

Note

• When encrypting, applications should use psa_aead_generate_nonce() instead of this function, unless implementing a protocol that requires a non-random IV.

psa_aead_set_lengths#

psa_status_t psa_aead_set_lengths (psa_aead_operation_t * operation, size_t ad_length, size_t plaintext_length)

Declare the lengths of the message and additional data for AEAD.

The application must call this function before calling psa_aead_update_ad() or psa_aead_update() if the algorithm for the operation requires it. If the algorithm does not require it, calling this function is optional, but if this function is called then the implementation must enforce the lengths.

You may call this function before or after setting the nonce with psa_aead_set_nonce() or psa_aead_generate_nonce().

• For PSA_ALG_CCM, calling this function is required.

• For the other AEAD algorithms defined in this specification, calling this function is not required.

• For vendor-defined algorithm, refer to the vendor documentation.

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

psa_aead_update_ad#

psa_status_t psa_aead_update_ad (psa_aead_operation_t * operation, const uint8_t * input, size_t input_length)

Pass additional data to an active AEAD operation.

Additional data is authenticated, but not encrypted.

You may call this function multiple times to pass successive fragments of the additional data. You may not call this function after passing data to encrypt or decrypt with psa_aead_update().

Before calling this function, you must:

1. Call either psa_aead_encrypt_setup() or psa_aead_decrypt_setup().

2. Set the nonce with psa_aead_generate_nonce() or psa_aead_set_nonce().

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

Warnings

• When decrypting, until psa_aead_verify() has returned PSA_SUCCESS, there is no guarantee that the input is valid. Therefore, until you have called psa_aead_verify() and it has returned PSA_SUCCESS, treat the input as untrusted and prepare to undo any action that depends on the input if psa_aead_verify() returns an error status.

psa_aead_update#

psa_status_t psa_aead_update (psa_aead_operation_t * operation, const uint8_t * input, size_t input_length, uint8_t * output, size_t output_size, size_t * output_length)

Encrypt or decrypt a message fragment in an active AEAD operation.

Before calling this function, you must:

1. Call either psa_aead_encrypt_setup() or psa_aead_decrypt_setup(). The choice of setup function determines whether this function encrypts or decrypts its input.

2. Set the nonce with psa_aead_generate_nonce() or psa_aead_set_nonce().

3. Call psa_aead_update_ad() to pass all the additional data.

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

Warnings

• When decrypting, until psa_aead_verify() has returned PSA_SUCCESS, there is no guarantee that the input is valid. Therefore, until you have called psa_aead_verify() and it has returned PSA_SUCCESS:

  • Do not use the output in any way other than storing it in a confidential location. If you take any action that depends on the tentative decrypted data, this action will need to be undone if the input turns out not to be valid. Furthermore, if an adversary can observe that this action took place (for example through timing), they may be able to use this fact as an oracle to decrypt any message encrypted with the same key.

  • In particular, do not copy the output anywhere but to a memory or storage space that you have exclusive access to.

This function does not require the input to be aligned to any particular block boundary. If the implementation can only process a whole block at a time, it must consume all the input provided, but it may delay the end of the corresponding output until a subsequent call to psa_aead_update(), psa_aead_finish() or psa_aead_verify() provides sufficient input. The amount of data that can be delayed in this way is bounded by #PSA_AEAD_UPDATE_OUTPUT_SIZE.

psa_aead_finish#

psa_status_t psa_aead_finish (psa_aead_operation_t * operation, uint8_t * ciphertext, size_t ciphertext_size, size_t * ciphertext_length, uint8_t * tag, size_t tag_size, size_t * tag_length)

Finish encrypting a message in an AEAD operation.

The operation must have been set up with psa_aead_encrypt_setup().

This function finishes the authentication of the additional data formed by concatenating the inputs passed to preceding calls to psa_aead_update_ad() with the plaintext formed by concatenating the inputs passed to preceding calls to psa_aead_update().

This function has two output buffers:

• ciphertext contains trailing ciphertext that was buffered from preceding calls to psa_aead_update().

• tag contains the authentication tag.

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_aead_abort().

psa_aead_verify#

psa_status_t psa_aead_verify (psa_aead_operation_t * operation, uint8_t * plaintext, size_t plaintext_size, size_t * plaintext_length, const uint8_t * tag, size_t tag_length)

Finish authenticating and decrypting a message in an AEAD operation.

The operation must have been set up with psa_aead_decrypt_setup().

This function finishes the authenticated decryption of the message components:

• The additional data consisting of the concatenation of the inputs passed to preceding calls to psa_aead_update_ad().

• The ciphertext consisting of the concatenation of the inputs passed to preceding calls to psa_aead_update().

• The tag passed to this function call.

If the authentication tag is correct, this function outputs any remaining plaintext and reports success. If the authentication tag is not correct, this function returns PSA_ERROR_INVALID_SIGNATURE.

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_aead_abort().

Note

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

psa_aead_abort#

psa_status_t psa_aead_abort (psa_aead_operation_t * operation)

Abort an AEAD 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_aead_encrypt_setup() or psa_aead_decrypt_setup() again.

You may call this function any time after the operation object has been initialized as described in #psa_aead_operation_t.

In particular, calling psa_aead_abort() after the operation has been terminated by a call to psa_aead_abort(), psa_aead_finish() or psa_aead_verify() is safe and has no effect.