29 lines
742 B
C
29 lines
742 B
C
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#include <string.h>
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#include "aes.h"
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#include "block.h"
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static uint8_t g_counter[16];
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void aes128_ctr_init(uint8_t *key, uint8_t *counter) {
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memcpy(g_counter, counter, 16);
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/* Decrementing the counter so that initial value will match without
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special logic during encryption */
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block_decr(g_counter);
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aes128_init(key);
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}
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uint8_t *aes128_ctr_evolve_counter(void) {
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block_incr(g_counter);
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return g_counter;
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}
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void aes128_ctr(uint8_t *dest, uint8_t *msg, uint32_t msg_len) {
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uint32_t num_blocks = msg_len / 16 + (msg_len % 16 ? 1 : 0);
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for (uint32_t i = 0; i < num_blocks; i++) {
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uint8_t keystream[16];
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aes128_ecb(keystream, aes128_ctr_evolve_counter());
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block_xor(dest+(i*16), keystream, msg+(i*16));
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}
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}
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