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Removes division/modulo reduces memset

This commit is contained in:
Shawn Nock 2017-08-02 16:20:06 -04:00
parent ec5d64c3a6
commit 3a5f4eb319
3 changed files with 15 additions and 14 deletions
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4
Makefile
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@ -13,7 +13,7 @@ SDK_PATH = $(HOME)/devel/nrf-sdk/10.0/
TEMPLATE_PATH = ./template/ TEMPLATE_PATH = ./template/
HOST_CC = gcc # Used when running tests on host HOST_CC = gcc # Used when running tests on host
CFLAGS = -Os -Wall -Werror -flto -g CFLAGS = -Os -Wall -Werror -g
LDFLAGS = -Os -flto -g LDFLAGS = -Os -g
include $(TEMPLATE_PATH)Makefile include $(TEMPLATE_PATH)Makefile

13
cmac.c
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@ -59,16 +59,17 @@ static void cmac_truncate(uint8_t *dest, uint8_t *tag, uint_fast8_t tag_len) {
void cmac_aes128(uint8_t *dest, uint8_t *msg, size_t msg_len, void cmac_aes128(uint8_t *dest, uint8_t *msg, size_t msg_len,
uint_fast8_t tag_len) { uint_fast8_t tag_len) {
/* Simulate ceiling integer division by adding a block if remainder */ /* Simulate ceiling integer division by adding a block if remainder */
size_t num_blocks = msg_len / 16 + (msg_len % 16 ? 1 : 0); size_t num_blocks = msg_len >> 4 + (msg_len & 15 ? 1 : 0);
bool last_block_complete = !(msg_len % 16 ? 1 : 0); bool last_block_complete = !(msg_len & 15 ? 1 : 0);
if (msg_len == 0) { if (msg_len == 0) {
num_blocks = 1; num_blocks = 1;
last_block_complete = false; last_block_complete = false;
} }
uint8_t alt_msg[num_blocks * 16], size_t padded_len = num_blocks << 4;
*last_block = &alt_msg[(num_blocks - 1) * 16]; uint8_t alt_msg[padded_len],
memset(alt_msg, 0, num_blocks * 16); *last_block = &alt_msg[padded_len - 16];
memset(alt_msg+msg_len, 0, padded_len - msg_len);
memcpy(alt_msg, msg, msg_len); memcpy(alt_msg, msg, msg_len);
if (!last_block_complete) { if (!last_block_complete) {
@ -83,7 +84,7 @@ void cmac_aes128(uint8_t *dest, uint8_t *msg, size_t msg_len,
uint8_t *x = (uint8_t *)zeros, y[16] = {0}; uint8_t *x = (uint8_t *)zeros, y[16] = {0};
for (uint32_t i = 0; i < num_blocks; i++) { for (uint32_t i = 0; i < num_blocks; i++) {
uint8_t *block = &alt_msg[i * 16]; uint8_t *block = &alt_msg[i << 4];
block_xor(y, x, block); block_xor(y, x, block);
x = aes128_ecb(y); x = aes128_ecb(y);
} }

12
ctr.c
View File

@ -14,23 +14,23 @@ void aes128_ctr_init(uint8_t *key, uint8_t *counter) {
} }
} }
void aes128_ctr_evolve_counter(void) { static void aes128_ctr_evolve_counter(void) {
block_incr(g_counter); block_incr(g_counter);
return; return;
} }
void aes128_ctr(uint8_t *dest, uint8_t *msg, uint32_t msg_len) { void aes128_ctr(uint8_t *dest, uint8_t *msg, uint32_t msg_len) {
uint8_t *buffer; uint8_t *buffer;
uint32_t num_blocks = msg_len / 16; uint32_t num_blocks = msg_len >> 4;
for (uint32_t i = 0; i < num_blocks; i++) { for (uint32_t i = 0; i < num_blocks; i++) {
buffer = aes128_ecb(g_counter); buffer = aes128_ecb(g_counter);
aes128_ctr_evolve_counter(); aes128_ctr_evolve_counter();
block_xor(dest + (i * 16), msg + (i * 16), buffer); block_xor(dest + (i << 4), msg + (i << 4), buffer);
} }
if (msg_len % 16) { if (msg_len & 15) {
buffer = aes128_ecb(g_counter); buffer = aes128_ecb(g_counter);
for (uint8_t i = 0; i < msg_len % 16; i++) { for (uint8_t i = 0; i < (msg_len & 15); i++) {
dest[num_blocks * 16 + i] = msg[num_blocks * 16 + i] ^ buffer[i]; dest[(num_blocks << 4) + i] = msg[(num_blocks << 4) + i] ^ buffer[i];
} }
} }
} }