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Improve readability of expansion size

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Signed-off-by: Jerry Yu <jerry.h.yu@arm.com>
This commit is contained in:
Jerry Yu 2023-02-23 11:07:57 +08:00
parent fac5a54f8a
commit 947bf969e0
1 changed files with 8 additions and 6 deletions
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14
library/aesce.c
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@ -185,15 +185,17 @@ static void aesce_setkey_enc(unsigned char *rk,
const unsigned char *key,
const size_t key_bit_length)
{
const uint32_t key_len_in_words = key_bit_length / 32;
const size_t round_key_len_in_words = 4;
static uint8_t const rcon[] = { 0x01, 0x02, 0x04, 0x08, 0x10,
0x20, 0x40, 0x80, 0x1b, 0x36 };
/* Require max(key_len_in_words, round_key_len_len_in_words) + 7 */
const size_t round_keys_needed = key_len_in_words + 7;
/* See https://nvlpubs.nist.gov/nistpubs/FIPS/NIST.FIPS.197.pdf
* - Section 5, Nr = Nk + 6
* - Section 5.2, the key expansion size is Nb*(Nr+1)
*/
const uint32_t key_len_in_words = key_bit_length / 32; /* Nk */
const size_t round_key_len_in_words = 4; /* Nb */
const size_t round_keys_needed = key_len_in_words + 6; /* Nr */
const size_t key_expansion_size_in_words =
round_keys_needed * round_key_len_in_words;
round_key_len_in_words * (round_keys_needed + 1); /* Nb*(Nr+1) */
const uint32_t *rko_end = (uint32_t *) rk + key_expansion_size_in_words;
memcpy(rk, key, key_len_in_words * 4);