Re: [PATCH v3 1/2] mac80211: fils_aead: Use crypto api CMAC shash rather than bare cipher

On Wed, 2017-02-08 at 07:45 +0000, Ard Biesheuvel wrote:

On 8 February 2017 at 07:00, Johannes Berg <johannes@sipsolutions.net

quoted

wrote:
This looks strange to me:

quoted

+static int aes_s2v(struct crypto_shash *tfm,
                 size_t num_elem, const u8 *addr[], size_t len[],
u8 *v)
 {
-     u8 d[AES_BLOCK_SIZE], tmp[AES_BLOCK_SIZE];
+     u8 d[AES_BLOCK_SIZE], tmp[AES_BLOCK_SIZE] = {};
+     SHASH_DESC_ON_STACK(desc, tfm);

desc declared

quoted

+     crypto_shash_digest(desc, tmp, AES_BLOCK_SIZE, d);

used here

Each digest() call combines a init()/update()/final() sequence

quoted

quoted

+     crypto_shash_init(desc);

but initialized now?

... for the 6th time, or so. The final vector may require two
update()s, so we cannot use digest() here. But we can use finup() for
the last one, which combines update() and final().

Hence,

init()/finup()

or

init()/update()/finup()

depending on the length of the last vector.

Great, thanks for the explanation :)

johannes