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feat(storage): Rework PIN processing and upgrade storage.

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This commit is contained in:
Andrew Kozlik 2024-06-13 14:27:51 +02:00 committed by Andrew Kozlik
parent 7b636df35f
commit 183e53d3c2
5 changed files with 126 additions and 78 deletions
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1
core/.changelog.d/+pin.changed Normal file
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@ -0,0 +1 @@
Reworked PIN processing.

2
core/embed/extmod/modtrezorconfig/norcow_config.h
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@ -30,6 +30,6 @@
/*
* Current storage version.
*/
#define NORCOW_VERSION ((uint32_t)0x00000004)
#define NORCOW_VERSION ((uint32_t)0x00000005)
#endif

1
legacy/firmware/.changelog.d/+pin.changed Normal file
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@ -0,0 +1 @@
Reworked PIN processing.

2
legacy/norcow_config.h
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@ -38,6 +38,6 @@ extern const flash_area_t STORAGE_AREAS[NORCOW_SECTOR_COUNT];
/*
* Current storage version.
*/
#define NORCOW_VERSION ((uint32_t)0x00000004)
#define NORCOW_VERSION ((uint32_t)0x00000005)
#endif

198
storage/storage.c
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@ -469,10 +469,11 @@ static secbool ui_progress(uint32_t elapsed_ms) {
}
#if !USE_OPTIGA
static void derive_kek(const uint8_t *pin, size_t pin_len,
const uint8_t *storage_salt, const uint8_t *ext_salt,
uint8_t kek[SHA256_DIGEST_LENGTH],
uint8_t keiv[SHA256_DIGEST_LENGTH]) {
static void derive_kek_v4(const uint8_t *pin, size_t pin_len,
const uint8_t *storage_salt, const uint8_t *ext_salt,
uint8_t kek[SHA256_DIGEST_LENGTH],
uint8_t keiv[SHA256_DIGEST_LENGTH]) {
// Legacy PIN verification method used in storage versions 1, 2, 3 and 4.
uint8_t salt[HARDWARE_SALT_SIZE + STORAGE_SALT_SIZE + EXTERNAL_SALT_SIZE] = {
0};
size_t salt_len = 0;
@ -518,11 +519,10 @@ static void derive_kek(const uint8_t *pin, size_t pin_len,
}
#endif
#if USE_OPTIGA
static void stretch_pin_optiga(const uint8_t *pin, size_t pin_len,
const uint8_t storage_salt[STORAGE_SALT_SIZE],
const uint8_t *ext_salt,
uint8_t stretched_pin[OPTIGA_PIN_SECRET_SIZE]) {
static void stretch_pin(const uint8_t *pin, size_t pin_len,
const uint8_t storage_salt[STORAGE_SALT_SIZE],
const uint8_t *ext_salt,
uint8_t stretched_pin[SHA256_DIGEST_LENGTH]) {
// Combining the PIN with the storage salt aims to ensure that if the
// MCU-Optiga communication is compromised, then a user with a low-entropy PIN
// remains protected against an attacker who is not able to read the contents
@ -566,10 +566,10 @@ static void stretch_pin_optiga(const uint8_t *pin, size_t pin_len,
#endif
memzero(&ctx, sizeof(ctx));
}
#endif
#if USE_OPTIGA
static void derive_kek_optiga(
static void derive_kek_optiga_v4(
// Legacy PIN verification method used in storage versions 3 and 4.
const uint8_t optiga_secret[OPTIGA_PIN_SECRET_SIZE],
uint8_t kek[SHA256_DIGEST_LENGTH], uint8_t keiv[SHA256_DIGEST_LENGTH]) {
PBKDF2_HMAC_SHA256_CTX ctx = {0};
@ -587,39 +587,30 @@ static void derive_kek_optiga(
}
#endif
static secbool __wur derive_kek_set(const uint8_t *pin, size_t pin_len,
const uint8_t *storage_salt,
const uint8_t *ext_salt,
uint8_t kek[SHA256_DIGEST_LENGTH],
uint8_t keiv[SHA256_DIGEST_LENGTH]) {
static secbool __wur derive_kek_set(
const uint8_t *pin, size_t pin_len, const uint8_t *storage_salt,
const uint8_t *ext_salt, uint8_t stretched_pin[SHA256_DIGEST_LENGTH]) {
stretch_pin(pin, pin_len, storage_salt, ext_salt, stretched_pin);
#if USE_OPTIGA
uint8_t optiga_secret[OPTIGA_PIN_SECRET_SIZE] = {0};
uint8_t stretched_pin[OPTIGA_PIN_SECRET_SIZE] = {0};
stretch_pin_optiga(pin, pin_len, storage_salt, ext_salt, stretched_pin);
int ret = optiga_pin_set(ui_progress, stretched_pin, optiga_secret);
memzero(stretched_pin, sizeof(stretched_pin));
if (ret != OPTIGA_SUCCESS) {
memzero(optiga_secret, sizeof(optiga_secret));
if (optiga_pin_set(ui_progress, stretched_pin) != OPTIGA_SUCCESS) {
memzero(stretched_pin, SHA256_DIGEST_LENGTH);
return secfalse;
}
derive_kek_optiga(optiga_secret, kek, keiv);
memzero(optiga_secret, sizeof(optiga_secret));
#else
derive_kek(pin, pin_len, storage_salt, ext_salt, kek, keiv);
#endif
return sectrue;
}
static secbool __wur derive_kek_unlock(const uint8_t *pin, size_t pin_len,
const uint8_t *storage_salt,
const uint8_t *ext_salt,
uint8_t kek[SHA256_DIGEST_LENGTH],
uint8_t keiv[SHA256_DIGEST_LENGTH]) {
static secbool __wur derive_kek_unlock_v4(const uint8_t *pin, size_t pin_len,
const uint8_t *storage_salt,
const uint8_t *ext_salt,
uint8_t kek[SHA256_DIGEST_LENGTH],
uint8_t keiv[SHA256_DIGEST_LENGTH]) {
// Legacy PIN verification method used in storage versions 1, 2, 3 and 4.
#if USE_OPTIGA
uint8_t optiga_secret[OPTIGA_PIN_SECRET_SIZE] = {0};
uint8_t stretched_pin[OPTIGA_PIN_SECRET_SIZE] = {0};
stretch_pin_optiga(pin, pin_len, storage_salt, ext_salt, stretched_pin);
int ret = optiga_pin_verify(ui_progress, stretched_pin, optiga_secret);
stretch_pin(pin, pin_len, storage_salt, ext_salt, stretched_pin);
int ret = optiga_pin_verify_v4(ui_progress, stretched_pin, optiga_secret);
memzero(stretched_pin, sizeof(stretched_pin));
if (ret != OPTIGA_SUCCESS) {
memzero(optiga_secret, sizeof(optiga_secret));
@ -632,10 +623,32 @@ static secbool __wur derive_kek_unlock(const uint8_t *pin, size_t pin_len,
"optiga_pin_verify failed");
return secfalse;
}
derive_kek_optiga(optiga_secret, kek, keiv);
derive_kek_optiga_v4(optiga_secret, kek, keiv);
memzero(optiga_secret, sizeof(optiga_secret));
#else
derive_kek(pin, pin_len, storage_salt, ext_salt, kek, keiv);
derive_kek_v4(pin, pin_len, storage_salt, ext_salt, kek, keiv);
#endif
return sectrue;
}
static secbool __wur derive_kek_unlock(
const uint8_t *pin, size_t pin_len, const uint8_t *storage_salt,
const uint8_t *ext_salt, uint8_t stretched_pin[SHA256_DIGEST_LENGTH]) {
stretch_pin(pin, pin_len, storage_salt, ext_salt, stretched_pin);
#if USE_OPTIGA
int ret = optiga_pin_verify(ui_progress, stretched_pin);
if (ret != OPTIGA_SUCCESS) {
memzero(stretched_pin, SHA256_DIGEST_LENGTH);
if (ret == OPTIGA_ERR_COUNTER_EXCEEDED) {
// Unreachable code. Wipe should have already been triggered in unlock().
storage_wipe();
show_pin_too_many_screen();
}
ensure(ret == OPTIGA_ERR_AUTH_FAIL ? sectrue : secfalse,
"optiga_pin_verify failed");
return secfalse;
}
#endif
return sectrue;
}
@ -649,15 +662,14 @@ static secbool set_pin(const uint8_t *pin, size_t pin_len,
uint8_t *pvc = buffer + STORAGE_SALT_SIZE + KEYS_SIZE;
uint8_t kek[SHA256_DIGEST_LENGTH] = {0};
uint8_t keiv[SHA256_DIGEST_LENGTH] = {0};
uint8_t keiv[12] = {0};
chacha20poly1305_ctx ctx = {0};
random_buffer(rand_salt, STORAGE_SALT_SIZE);
ui_progress(0);
ensure(derive_kek_set(pin, pin_len, rand_salt, ext_salt, kek, keiv),
ensure(derive_kek_set(pin, pin_len, rand_salt, ext_salt, kek),
"derive_kek_set failed");
rfc7539_init(&ctx, kek, keiv);
memzero(kek, sizeof(kek));
memzero(keiv, sizeof(keiv));
chacha20poly1305_encrypt(&ctx, cached_keys, ekeys, KEYS_SIZE);
rfc7539_finish(&ctx, 0, KEYS_SIZE, pvc);
memzero(&ctx, sizeof(ctx));
@ -827,7 +839,9 @@ secbool check_storage_version(void) {
return sectrue;
}
static secbool decrypt_dek(const uint8_t *kek, const uint8_t *keiv) {
static secbool __wur decrypt_dek(const uint8_t *pin, size_t pin_len,
const uint8_t *ext_salt) {
// Read the storage salt, EDEK, ESAK and PIN verification code entry.
const void *buffer = NULL;
uint16_t len = 0;
if (sectrue != initialized ||
@ -837,12 +851,28 @@ static secbool decrypt_dek(const uint8_t *kek, const uint8_t *keiv) {
return secfalse;
}
const uint8_t *storage_salt = (const uint8_t *)buffer;
const uint8_t *ekeys = (const uint8_t *)buffer + STORAGE_SALT_SIZE;
const uint32_t *pvc = (const uint32_t *)buffer +
(STORAGE_SALT_SIZE + KEYS_SIZE) / sizeof(uint32_t);
_Static_assert(((STORAGE_SALT_SIZE + KEYS_SIZE) & 3) == 0, "PVC unaligned");
_Static_assert((PVC_SIZE & 3) == 0, "PVC size unaligned");
// Derive the key encryption key and IV.
uint8_t kek[SHA256_DIGEST_LENGTH] = {0};
uint8_t keiv[SHA256_DIGEST_LENGTH] = {0};
if (get_lock_version() >= 5) {
if (sectrue !=
derive_kek_unlock(pin, pin_len, storage_salt, ext_salt, kek)) {
return secfalse;
}
} else {
if (sectrue !=
derive_kek_unlock_v4(pin, pin_len, storage_salt, ext_salt, kek, keiv)) {
return secfalse;
};
}
uint8_t keys[KEYS_SIZE] = {0};
uint8_t tag[POLY1305_TAG_SIZE] __attribute__((aligned(sizeof(uint32_t))));
chacha20poly1305_ctx ctx = {0};
@ -850,6 +880,8 @@ static secbool decrypt_dek(const uint8_t *kek, const uint8_t *keiv) {
// Decrypt the data encryption key and the storage authentication key and
// check the PIN verification code.
rfc7539_init(&ctx, kek, keiv);
memzero(kek, sizeof(kek));
memzero(keiv, sizeof(keiv));
chacha20poly1305_decrypt(&ctx, ekeys, keys, KEYS_SIZE);
rfc7539_finish(&ctx, 0, KEYS_SIZE, tag);
memzero(&ctx, sizeof(ctx));
@ -877,18 +909,22 @@ static secbool unlock(const uint8_t *pin, size_t pin_len,
const uint8_t *unlock_pin = pin;
size_t unlock_pin_len = pin_len;
// In case of an upgrade from version 1 or 2, encode the PIN to the old format
// and bump the total time of UI progress to account for the set_pin() call in
// storage_upgrade_unlocked().
// In case of an upgrade from version 1 or 2, encode the PIN to the old
// format.
uint32_t legacy_pin = 0;
if (get_lock_version() <= 2) {
ui_total += PIN_DERIVE_MS;
ui_rem += PIN_DERIVE_MS;
legacy_pin = pin_to_int(pin, pin_len);
unlock_pin = (const uint8_t *)&legacy_pin;
unlock_pin_len = sizeof(legacy_pin);
}
// In case of an upgrade from version 4 or earlier bump the total time of UI
// progress to account for the set_pin() call in storage_upgrade_unlocked().
if (get_lock_version() <= 4) {
ui_total += PIN_DERIVE_MS;
ui_rem += PIN_DERIVE_MS;
}
// Now we can check for wipe code.
ensure_not_wipe_code(unlock_pin, unlock_pin_len);
@ -934,25 +970,8 @@ static secbool unlock(const uint8_t *pin, size_t pin_len,
return secfalse;
}
// Read the random salt from EDEK_PVC_KEY and use it to derive the KEK and
// KEIV from the PIN.
const void *rand_salt = NULL;
uint16_t len = 0;
if (sectrue != initialized ||
sectrue != norcow_get(EDEK_PVC_KEY, &rand_salt, &len) ||
len != STORAGE_SALT_SIZE + KEYS_SIZE + PVC_SIZE) {
memzero(&legacy_pin, sizeof(legacy_pin));
handle_fault("no EDEK");
return secfalse;
}
uint8_t kek[SHA256_DIGEST_LENGTH] = {0};
uint8_t keiv[SHA256_DIGEST_LENGTH] = {0};
// Check whether the entered PIN is correct.
if (sectrue != derive_kek_unlock(unlock_pin, unlock_pin_len,
(const uint8_t *)rand_salt, ext_salt, kek,
keiv) ||
sectrue != decrypt_dek(kek, keiv)) {
if (sectrue != decrypt_dek(unlock_pin, unlock_pin_len, ext_salt)) {
memzero(&legacy_pin, sizeof(legacy_pin));
// Wipe storage if too many failures
wait_random();
@ -973,8 +992,6 @@ static secbool unlock(const uint8_t *pin, size_t pin_len,
return secfalse;
}
memzero(&legacy_pin, sizeof(legacy_pin));
memzero(kek, sizeof(kek));
memzero(keiv, sizeof(keiv));
// Check for storage upgrades that need to be performed after unlocking and
// check that the authenticated version number matches the unauthenticated
@ -1437,6 +1454,24 @@ static uint32_t pin_to_int(const uint8_t *pin, size_t pin_len) {
return val;
}
// Legacy conversion of PIN from the uint32 scheme that was used prior to
// storage version 3.
static size_t int_to_pin(uint32_t val, uint8_t pin[V0_MAX_PIN_LEN]) {
size_t i = V0_MAX_PIN_LEN;
while (val > 9) {
i -= 1;
pin[i] = (val % 10) + '0';
val /= 10;
}
if (val != 1) {
return 0;
}
memmove(pin, &pin[i], V0_MAX_PIN_LEN - i);
return V0_MAX_PIN_LEN - i;
}
// Legacy conversion of wipe code from the uint32 scheme that was used prior to
// storage version 3.
static char *int_to_wipe_code(uint32_t val) {
@ -1471,6 +1506,7 @@ static secbool storage_upgrade(void) {
// Storage version 2: adds 9 digit wipe code
// Storage version 3: adds variable length PIN and wipe code
// Storage version 4: changes data structure of encrypted data
// Storage version 5: unifies KEK derivation for non-Optiga and Optiga
const uint16_t V0_PIN_KEY = 0x0000;
const uint16_t V0_PIN_FAIL_KEY = 0x0001;
@ -1486,7 +1522,7 @@ static secbool storage_upgrade(void) {
auth_init();
// Set the new storage version number.
uint32_t version = 1;
uint32_t version = NORCOW_VERSION;
if (sectrue !=
storage_set_encrypted(VERSION_KEY, &version, sizeof(version))) {
return secfalse;
@ -1496,13 +1532,14 @@ static secbool storage_upgrade(void) {
ui_total = PIN_DERIVE_MS;
ui_rem = ui_total;
ui_message = PROCESSING_MSG;
uint8_t pin[V0_MAX_PIN_LEN] = {0};
size_t pin_len = 0;
secbool found = norcow_get(V0_PIN_KEY, &val, &len);
if (sectrue == found && *(const uint32_t *)val != V0_PIN_EMPTY) {
set_pin((const uint8_t *)val, len, NULL);
} else {
set_pin((const uint8_t *)&V0_PIN_EMPTY, sizeof(V0_PIN_EMPTY), NULL);
ret = norcow_set(PIN_NOT_SET_KEY, &TRUE_BYTE, sizeof(TRUE_BYTE));
pin_len = int_to_pin(*(const uint32_t *)val, pin);
}
set_pin(pin, pin_len, NULL);
memzero(pin, sizeof(pin));
// Convert PIN failure counter.
uint32_t fails = 0;
@ -1582,12 +1619,22 @@ static secbool storage_upgrade(void) {
version = 2;
}
// Version 0 upgrades directly to the latest.
if (norcow_active_version == 0) {
version = NORCOW_VERSION;
}
if (sectrue != norcow_set(UNAUTH_VERSION_KEY, &version, sizeof(version))) {
return secfalse;
}
}
norcow_set(STORAGE_UPGRADED_KEY, &TRUE_WORD, sizeof(TRUE_WORD));
if (norcow_active_version == 0) {
// Version 0 upgrades directly to the latest.
norcow_set(STORAGE_UPGRADED_KEY, &FALSE_WORD, sizeof(FALSE_WORD));
} else {
norcow_set(STORAGE_UPGRADED_KEY, &TRUE_WORD, sizeof(TRUE_WORD));
}
norcow_active_version = NORCOW_VERSION;
return norcow_upgrade_finish();
@ -1605,9 +1652,10 @@ static secbool storage_upgrade_unlocked(const uint8_t *pin, size_t pin_len,
}
secbool ret = sectrue;
if (version <= 2) {
// Upgrade EDEK_PVC_KEY from the old uint32 PIN scheme to the new
// variable-length PIN scheme.
if (version <= 4) {
// Upgrade EDEK_PVC_KEY from the uint32 PIN scheme (versions 1 and 2) or
// from the version 3 and 4 variable-length PIN scheme to the unified PIN
// scheme.
if (sectrue != set_pin(pin, pin_len, ext_salt)) {
return secfalse;
}
@ -1634,7 +1682,5 @@ static secbool storage_upgrade_unlocked(const uint8_t *pin, size_t pin_len,
memzero(wipe_code, wipe_code_len);
}
// nothing to do for upgrading to version 4
return ret;
}