Symmetric Key Cipher Request Handle

crypto_skcipher_reqsize — obtain size of the request data structure
skcipher_request_set_tfm — update cipher handle reference in request
skcipher_request_alloc — allocate request data structure
skcipher_request_free — zeroize and free request data structure
skcipher_request_set_callback — set asynchronous callback function
skcipher_request_set_crypt — set data buffers

The skcipher_request data structure contains all pointers to data required for the symmetric key cipher operation. This includes the cipher handle (which can be used by multiple skcipher_request instances), pointer to plaintext and ciphertext, asynchronous callback function, etc. It acts as a handle to the skcipher_request_* API calls in a similar way as skcipher handle to the crypto_skcipher_* API calls.