On Sun, Jun 16, 2019 at 12:01:38PM -0700, Eric Biggers wrote:
> Hi Ard,
>
> On Fri, Jun 14, 2019 at 11:29:22AM +0200, Ard Biesheuvel wrote:
> > -static void ccmp_init_blocks(struct crypto_cipher *tfm,
> > - struct ieee80211_hdr *hdr,
> > - u8 * pn, size_t dlen, u8 * b0, u8 * auth, u8 * s0)
> > +static void ccmp_init_blocks(struct ieee80211_hdr *hdr,
> > + u8 * pn, size_t dlen, u8 * b0, u8 * aad)
> > {
> > u8 *pos, qc = 0;
> > size_t aad_len;
> > int a4_included, qc_included;
> > - u8 aad[2 * AES_BLOCK_LEN];
> >
> > a4_included = ieee80211_has_a4(hdr->frame_control);
> > qc_included = ieee80211_is_data_qos(hdr->frame_control);
> > @@ -131,17 +123,19 @@ static void ccmp_init_blocks(struct crypto_cipher *tfm,
> > aad_len += 2;
> > }
> >
> > - /* CCM Initial Block:
> > - * Flag (Include authentication header, M=3 (8-octet MIC),
> > - * L=1 (2-octet Dlen))
> > - * Nonce: 0x00 | A2 | PN
> > - * Dlen */
> > - b0[0] = 0x59;
> > + /* In CCM, the initial vectors (IV) used for CTR mode encryption and CBC
> > + * mode authentication are not allowed to collide, yet both are derived
> > + * from this vector b0. We only set L := 1 here to indicate that the
> > + * data size can be represented in (L+1) bytes. The CCM layer will take
> > + * care of storing the data length in the top (L+1) bytes and setting
> > + * and clearing the other bits as is required to derive the two IVs.
> > + */
> > + b0[0] = 0x1;
> > +
> > + /* Nonce: QC | A2 | PN */
> > b0[1] = qc;
> > memcpy(b0 + 2, hdr->addr2, ETH_ALEN);
> > memcpy(b0 + 8, pn, CCMP_PN_LEN);
> > - b0[14] = (dlen >> 8) & 0xff;
> > - b0[15] = dlen & 0xff;
> >
> > /* AAD:
> > * FC with bits 4..6 and 11..13 masked to zero; 14 is always one
> > @@ -166,16 +160,6 @@ static void ccmp_init_blocks(struct crypto_cipher *tfm,
> > aad[a4_included ? 30 : 24] = qc;
> > /* rest of QC masked */
> > }
> > -
> > - /* Start with the first block and AAD */
> > - lib80211_ccmp_aes_encrypt(tfm, b0, auth);
> > - xor_block(auth, aad, AES_BLOCK_LEN);
> > - lib80211_ccmp_aes_encrypt(tfm, auth, auth);
> > - xor_block(auth, &aad[AES_BLOCK_LEN], AES_BLOCK_LEN);
> > - lib80211_ccmp_aes_encrypt(tfm, auth, auth);
> > - b0[0] &= 0x07;
> > - b0[14] = b0[15] = 0;
> > - lib80211_ccmp_aes_encrypt(tfm, b0, s0);
> > }
>
> How about shifting the contents of aad over by 2 bytes and returning the AAD
> length from this function instead? It's confusing to still manually format the
> AAD length for CCM mode, when actually it's ignored now.
>
> Also I suggest fixing up the naming:
>
> ccmp_init_blocks() => ccmp_init_iv_and_aad()
> b0 => iv
>
Okay, couple more things. The 'dlen' parameter is no longer used so should be
removed. Also consider constifying 'hdr' and 'pn' to make it clear what's input
vs. output.
Also, xor_block() is no longer used so should be removed.
- Eric
