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268 lines
7.4 KiB
268 lines
7.4 KiB
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// Values used in the guard key integrity check.
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#define GUARD_KEY_MODULUS 6311
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#define GUARD_KEY_REMAINDER 15
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#define LOW_MASK 0x55555555
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// The length of the guard key in words.
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#define GUARD_KEY_WORDS 1
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// The length of the PIN entry log or the PIN success log in words.
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#define PIN_LOG_WORDS 16
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// The length of a word in bytes.
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#define WORD_SIZE (sizeof(uint32_t))
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static secbool check_guard_key(const uint32_t guard_key) {
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if (guard_key % GUARD_KEY_MODULUS != GUARD_KEY_REMAINDER) {
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return secfalse;
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}
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// Check that each byte of (guard_key & 0xAAAAAAAA) has exactly two bits set.
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uint32_t count = (guard_key & 0x22222222) + ((guard_key >> 2) & 0x22222222);
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count = count + (count >> 4);
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if ((count & 0x0e0e0e0e) != 0x04040404) {
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return secfalse;
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}
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// Check that the guard_key does not contain a run of 5 (or more) zeros or
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// ones.
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uint32_t zero_runs = ~guard_key;
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zero_runs = zero_runs & (zero_runs >> 2);
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zero_runs = zero_runs & (zero_runs >> 1);
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zero_runs = zero_runs & (zero_runs >> 1);
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uint32_t one_runs = guard_key;
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one_runs = one_runs & (one_runs >> 2);
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one_runs = one_runs & (one_runs >> 1);
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one_runs = one_runs & (one_runs >> 1);
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if ((one_runs != 0) || (zero_runs != 0)) {
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return secfalse;
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}
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return sectrue;
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}
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static uint32_t generate_guard_key(void) {
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uint32_t guard_key = 0;
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do {
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guard_key = random_uniform((UINT32_MAX / GUARD_KEY_MODULUS) + 1) *
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GUARD_KEY_MODULUS +
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GUARD_KEY_REMAINDER;
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} while (sectrue != check_guard_key(guard_key));
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return guard_key;
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}
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static secbool expand_guard_key(const uint32_t guard_key, uint32_t *guard_mask,
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uint32_t *guard) {
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if (sectrue != check_guard_key(guard_key)) {
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handle_fault("guard key check");
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return secfalse;
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}
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*guard_mask = ((guard_key & LOW_MASK) << 1) | ((~guard_key) & LOW_MASK);
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*guard = (((guard_key & LOW_MASK) << 1) & guard_key) |
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(((~guard_key) & LOW_MASK) & (guard_key >> 1));
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return sectrue;
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}
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static secbool pin_logs_init(uint32_t fails) {
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if (fails >= PIN_MAX_TRIES) {
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return secfalse;
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}
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// The format of the PIN_LOGS_KEY entry is:
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// guard_key (1 word), pin_success_log (PIN_LOG_WORDS), pin_entry_log
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// (PIN_LOG_WORDS)
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uint32_t logs[GUARD_KEY_WORDS + 2 * PIN_LOG_WORDS] = {0};
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logs[0] = generate_guard_key();
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uint32_t guard_mask = 0;
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uint32_t guard = 0;
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wait_random();
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if (sectrue != expand_guard_key(logs[0], &guard_mask, &guard)) {
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return secfalse;
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}
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uint32_t unused = guard | ~guard_mask;
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for (size_t i = 0; i < 2 * PIN_LOG_WORDS; ++i) {
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logs[GUARD_KEY_WORDS + i] = unused;
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}
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// Set the first word of the PIN entry log to indicate the requested number of
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// fails.
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logs[GUARD_KEY_WORDS + PIN_LOG_WORDS] =
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((((uint32_t)0xFFFFFFFF) >> (2 * fails)) & ~guard_mask) | guard;
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return norcow_set(PIN_LOGS_KEY, logs, sizeof(logs));
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}
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static secbool pin_fails_reset(void) {
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const void *logs = NULL;
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uint16_t len = 0;
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if (sectrue != norcow_get(PIN_LOGS_KEY, &logs, &len) ||
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len != WORD_SIZE * (GUARD_KEY_WORDS + 2 * PIN_LOG_WORDS)) {
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return secfalse;
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}
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uint32_t new_logs[GUARD_KEY_WORDS + 2 * PIN_LOG_WORDS];
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secbool edited = secfalse;
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memcpy(new_logs, logs, len);
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uint32_t guard_mask = 0;
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uint32_t guard = 0;
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wait_random();
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if (sectrue !=
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expand_guard_key(*(const uint32_t *)logs, &guard_mask, &guard)) {
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return secfalse;
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}
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uint32_t unused = guard | ~guard_mask;
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const uint32_t *success_log = ((const uint32_t *)logs) + GUARD_KEY_WORDS;
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const uint32_t *entry_log = success_log + PIN_LOG_WORDS;
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for (size_t i = 0; i < PIN_LOG_WORDS; ++i) {
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if (entry_log[i] == unused) {
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if (edited == sectrue) {
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return norcow_set(PIN_LOGS_KEY, new_logs, sizeof(new_logs));
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}
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return sectrue;
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}
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if (success_log[i] != guard) {
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if (new_logs[(i + GUARD_KEY_WORDS)] != entry_log[i]) {
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edited = sectrue;
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new_logs[(i + GUARD_KEY_WORDS)] = entry_log[i];
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}
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}
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}
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return pin_logs_init(0);
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}
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secbool pin_fails_increase(void) {
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const void *logs = NULL;
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uint16_t len = 0;
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wait_random();
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if (sectrue != norcow_get(PIN_LOGS_KEY, &logs, &len) ||
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len != WORD_SIZE * (GUARD_KEY_WORDS + 2 * PIN_LOG_WORDS)) {
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handle_fault("no PIN logs");
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return secfalse;
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}
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uint32_t new_logs[GUARD_KEY_WORDS + 2 * PIN_LOG_WORDS];
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memcpy(new_logs, logs, len);
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uint32_t guard_mask = 0;
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uint32_t guard = 0;
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wait_random();
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if (sectrue !=
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expand_guard_key(*(const uint32_t *)logs, &guard_mask, &guard)) {
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handle_fault("guard key expansion");
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return secfalse;
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}
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const uint32_t *entry_log =
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((const uint32_t *)logs) + GUARD_KEY_WORDS + PIN_LOG_WORDS;
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for (size_t i = 0; i < PIN_LOG_WORDS; ++i) {
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wait_random();
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if ((entry_log[i] & guard_mask) != guard) {
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handle_fault("guard bits check");
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return secfalse;
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}
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if (entry_log[i] != guard) {
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wait_random();
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uint32_t word = entry_log[i] & ~guard_mask;
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word = ((word >> 1) | word) & LOW_MASK;
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word = (word >> 2) | (word >> 1);
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wait_random();
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new_logs[(i + GUARD_KEY_WORDS + PIN_LOG_WORDS)] =
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(word & ~guard_mask) | guard;
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if (sectrue != norcow_set(PIN_LOGS_KEY, new_logs, sizeof(new_logs))) {
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handle_fault("PIN logs update");
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return secfalse;
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}
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return sectrue;
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}
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}
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handle_fault("PIN log exhausted");
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return secfalse;
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}
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static secbool pin_get_fails(uint32_t *ctr) {
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*ctr = PIN_MAX_TRIES;
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const void *logs = NULL;
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uint16_t len = 0;
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wait_random();
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if (sectrue != norcow_get(PIN_LOGS_KEY, &logs, &len) ||
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len != WORD_SIZE * (GUARD_KEY_WORDS + 2 * PIN_LOG_WORDS)) {
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handle_fault("no PIN logs");
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return secfalse;
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}
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uint32_t guard_mask = 0;
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uint32_t guard = 0;
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wait_random();
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if (sectrue !=
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expand_guard_key(*(const uint32_t *)logs, &guard_mask, &guard)) {
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handle_fault("guard key expansion");
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return secfalse;
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}
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const uint32_t unused = guard | ~guard_mask;
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const uint32_t *success_log = ((const uint32_t *)logs) + GUARD_KEY_WORDS;
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const uint32_t *entry_log = success_log + PIN_LOG_WORDS;
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volatile int current = -1;
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volatile size_t i = 0;
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for (i = 0; i < PIN_LOG_WORDS; ++i) {
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if ((entry_log[i] & guard_mask) != guard ||
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(success_log[i] & guard_mask) != guard ||
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(entry_log[i] & success_log[i]) != entry_log[i]) {
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handle_fault("PIN logs format check");
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return secfalse;
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}
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if (current == -1) {
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if (entry_log[i] != guard) {
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current = i;
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}
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} else {
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if (entry_log[i] != unused) {
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handle_fault("PIN entry log format check");
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return secfalse;
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}
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}
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}
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if (current < 0 || current >= PIN_LOG_WORDS || i != PIN_LOG_WORDS) {
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handle_fault("PIN log exhausted");
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return secfalse;
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}
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// Strip the guard bits from the current entry word and duplicate each data
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// bit.
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wait_random();
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uint32_t word = entry_log[current] & ~guard_mask;
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word = ((word >> 1) | word) & LOW_MASK;
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word = word | (word << 1);
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// Verify that the entry word has form 0*1*.
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if ((word & (word + 1)) != 0) {
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handle_fault("PIN entry log format check");
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return secfalse;
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}
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if (current == 0) {
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++current;
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}
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// Count the number of set bits in the two current words of the success log.
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wait_random();
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*ctr = hamming_weight(success_log[current - 1] ^ entry_log[current - 1]) +
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hamming_weight(success_log[current] ^ entry_log[current]);
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return sectrue;
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}
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