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config: Check mnemonic by comparing hashes instead of the actual mnemonics, to mitigate side-channel attacks.

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This commit is contained in:
Andrew Kozlik 2019-02-18 18:12:04 +01:00 committed by Pavol Rusnak
parent 827df268a6
commit c58c265d9c
2 changed files with 16 additions and 13 deletions
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27
firmware/config.c
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@ -684,22 +684,25 @@ bool config_getMnemonic(char *dest, uint16_t dest_size)
bool config_containsMnemonic(const char *mnemonic)
{
uint16_t len = 0;
uint8_t stored_mnemonic[MAX_MNEMONIC_LEN + 1];
if (sectrue != storage_get(KEY_MNEMONIC, stored_mnemonic, MAX_MNEMONIC_LEN, &len)) {
uint8_t stored_mnemonic[MAX_MNEMONIC_LEN];
if (sectrue != storage_get(KEY_MNEMONIC, stored_mnemonic, sizeof(stored_mnemonic), &len)) {
return false;
}
stored_mnemonic[len] = '\0';
/* The execution time of the following code only depends on the
* (public) input. This avoids timing attacks.
*/
char diff = 0;
uint32_t i = 0;
for (; mnemonic[i]; i++) {
diff |= (stored_mnemonic[i] - mnemonic[i]);
}
diff |= stored_mnemonic[i];
// Compare the digests to mitigate side-channel attacks.
uint8_t digest_stored[SHA256_DIGEST_LENGTH];
sha256_Raw(stored_mnemonic, len, digest_stored);
memzero(stored_mnemonic, sizeof(stored_mnemonic));
uint8_t digest_input[SHA256_DIGEST_LENGTH];
sha256_Raw((const uint8_t*)mnemonic, strnlen(mnemonic, MAX_MNEMONIC_LEN), digest_input);
uint8_t diff = 0;
for (size_t i = 0; i < sizeof(digest_input); i++) {
diff |= (digest_stored[i] - digest_input[i]);
}
memzero(digest_stored, sizeof(digest_stored));
memzero(digest_input, sizeof(digest_input));
return diff == 0;
}

2
firmware/fsm_msg_common.h
View File

@ -339,7 +339,7 @@ void fsm_msgApplyFlags(const ApplyFlags *msg)
void fsm_msgRecoveryDevice(const RecoveryDevice *msg)
{
CHECK_PIN
CHECK_PIN_UNCACHED
const bool dry_run = msg->has_dry_run ? msg->dry_run : false;
if (!dry_run) {