Symmetric ciphers#

psa_cipher_encrypt#

psa_status_t psa_cipher_encrypt (mbedtls_svc_key_id_t key, psa_algorithm_t alg, const uint8_t *input, size_t input_length, uint8_t *output, size_t output_size, size_t *output_length)

Encrypt a message using a symmetric cipher.

This function encrypts a message with a random IV (initialization vector). Use the multipart operation interface with a #psa_cipher_operation_t object to provide other forms of IV.

psa_cipher_decrypt#

psa_status_t psa_cipher_decrypt (mbedtls_svc_key_id_t key, psa_algorithm_t alg, const uint8_t *input, size_t input_length, uint8_t *output, size_t output_size, size_t *output_length)

Decrypt a message using a symmetric cipher.

This function decrypts a message encrypted with a symmetric cipher.

psa_cipher_operation_init#

static psa_cipher_operation_t psa_cipher_operation_init (void)

Return an initial value for a cipher operation object.

psa_cipher_encrypt_setup#

psa_status_t psa_cipher_encrypt_setup (psa_cipher_operation_t *operation, mbedtls_svc_key_id_t key, psa_algorithm_t alg)

Set the key for a multipart symmetric encryption operation.

The sequence of operations to encrypt a message with a symmetric cipher 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_cipher_operation_t, e.g. #PSA_CIPHER_OPERATION_INIT.

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

4. Call either psa_cipher_generate_iv() or psa_cipher_set_iv() to generate or set the IV (initialization vector). You should use psa_cipher_generate_iv() unless the protocol you are implementing requires a specific IV value.

5. Call psa_cipher_update() zero, one or more times, passing a fragment of the message each time.

6. Call psa_cipher_finish().

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

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

• A successful call to psa_cipher_finish().

• A call to psa_cipher_abort().

psa_cipher_decrypt_setup#

psa_status_t psa_cipher_decrypt_setup (psa_cipher_operation_t *operation, mbedtls_svc_key_id_t key, psa_algorithm_t alg)

Set the key for a multipart symmetric decryption operation.

The sequence of operations to decrypt a message with a symmetric cipher 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_cipher_operation_t, e.g. #PSA_CIPHER_OPERATION_INIT.

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

4. Call psa_cipher_set_iv() with the IV (initialization vector) for the decryption. If the IV is prepended to the ciphertext, you can call psa_cipher_update() on a buffer containing the IV followed by the beginning of the message.

5. Call psa_cipher_update() zero, one or more times, passing a fragment of the message each time.

6. Call psa_cipher_finish().

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

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

• A successful call to psa_cipher_finish().

• A call to psa_cipher_abort().

psa_cipher_generate_iv#

psa_status_t psa_cipher_generate_iv (psa_cipher_operation_t *operation, uint8_t *iv, size_t iv_size, size_t *iv_length)

Generate an IV for a symmetric encryption operation.

This function generates a random IV (initialization vector), nonce or initial counter value for the encryption operation as appropriate for the chosen algorithm, key type and key size.

The application must call psa_cipher_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_cipher_abort().

psa_cipher_set_iv#

psa_status_t psa_cipher_set_iv (psa_cipher_operation_t *operation, const uint8_t *iv, size_t iv_length)

Set the IV for a symmetric encryption or decryption operation.

This function sets the IV (initialization vector), nonce or initial counter value for the encryption or decryption operation.

The application must call psa_cipher_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_cipher_abort().

Note

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

psa_cipher_update#

psa_status_t psa_cipher_update (psa_cipher_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 cipher operation.

Before calling this function, you must:

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

2. If the algorithm requires an IV, call psa_cipher_generate_iv() (recommended when encrypting) or psa_cipher_set_iv().

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

psa_cipher_finish#

psa_status_t psa_cipher_finish (psa_cipher_operation_t *operation, uint8_t *output, size_t output_size, size_t *output_length)

Finish encrypting or decrypting a message in a cipher operation.

The application must call psa_cipher_encrypt_setup() or psa_cipher_decrypt_setup() before calling this function. The choice of setup function determines whether this function encrypts or decrypts its input.

This function finishes the encryption or decryption of the message formed by concatenating the inputs passed to preceding calls to psa_cipher_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_cipher_abort().

psa_cipher_abort#

psa_status_t psa_cipher_abort (psa_cipher_operation_t *operation)

Abort a cipher 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_cipher_encrypt_setup() or psa_cipher_decrypt_setup() again.

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

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