nrf51-cryptolib/ctr.c

#include <string.h>

#include "aes.h"
#include "block.h"

static uint8_t g_counter[16];

void aes128_ctr_init(uint8_t *key, uint8_t *counter) {
  if (counter != NULL) {
    memcpy(g_counter, counter, 16);
  }
  aes128_init(key);
}

void aes128_ctr_evolve_counter(void) {
  block_incr(g_counter);
  return;
}

void aes128_ctr(uint8_t *dest, uint8_t *msg, uint32_t msg_len) {
  uint8_t buffer[16];
  uint32_t num_blocks = msg_len / 16;
  for (uint32_t i = 0; i < num_blocks; i++) {
    aes128_ecb(buffer, g_counter);
    aes128_ctr_evolve_counter();
    block_xor(dest+(i*16), msg+(i*16), buffer);
  }
  if (msg_len % 16) {
    aes128_ecb(buffer, g_counter);
    for (uint8_t i = 0; i < msg_len % 16; i++) {
      dest[num_blocks*16+i] = msg[num_blocks*16+i] ^ buffer[i];
    }
  }
}