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trezor-firmware/storage/storage.c

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/*
* This file is part of the TREZOR project, https://trezor.io/
*
* Copyright (c) SatoshiLabs
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#include <string.h>
#include "common.h"
#include "norcow.h"
#include "storage.h"
#include "pbkdf2.h"
#include "sha2.h"
#include "hmac.h"
#include "rand.h"
#include "memzero.h"
#include "chacha20poly1305/rfc7539.h"
#define LOW_MASK 0x55555555
// The APP namespace which is reserved for storage related values.
#define APP_STORAGE 0x00
// Norcow storage key of the PIN entry log and PIN success log.
#define PIN_LOGS_KEY ((APP_STORAGE << 8) | 0x01)
// Norcow storage key of the combined salt, EDEK, ESAK and PIN verification code entry.
#define EDEK_PVC_KEY ((APP_STORAGE << 8) | 0x02)
// Norcow storage key of the PIN set flag.
#define PIN_NOT_SET_KEY ((APP_STORAGE << 8) | 0x03)
// Norcow storage key of the storage version.
#define VERSION_KEY ((APP_STORAGE << 8) | 0x04)
// Norcow storage key of the storage authentication tag.
#define STORAGE_TAG_KEY ((APP_STORAGE << 8) | 0x05)
// The PIN value corresponding to an empty PIN.
#define PIN_EMPTY 1
// Maximum number of failed unlock attempts.
// NOTE: The PIN counter logic relies on this constant being less than or equal to 16.
#define PIN_MAX_TRIES 16
// The total number of iterations to use in PBKDF2.
#define PIN_ITER_COUNT 20000
// The number of seconds required to derive the KEK and KEIV.
#define DERIVE_SECS 1
// If the top bit of APP is set, then the value is not encrypted.
#define FLAG_PUBLIC 0x80
// If the top two bits of APP are set, then the value is not encrypted and it
// can be written even when the storage is locked.
#define FLAGS_WRITE 0xC0
// The length of the guard key in words.
#define GUARD_KEY_WORDS 1
// The length of the PIN entry log or the PIN success log in words.
#define PIN_LOG_WORDS 16
// The length of a word in bytes.
#define WORD_SIZE (sizeof(uint32_t))
// The length of the hashed hardware salt in bytes.
#define HARDWARE_SALT_SIZE SHA256_DIGEST_LENGTH
// The length of the random salt in bytes.
#define RANDOM_SALT_SIZE 4
// The length of the data encryption key in bytes.
#define DEK_SIZE 32
// The length of the storage authentication key in bytes.
#define SAK_SIZE 16
// The combined length of the data encryption key and the storage authentication key in bytes.
#define KEYS_SIZE (DEK_SIZE + SAK_SIZE)
// The length of the PIN verification code in bytes.
#define PVC_SIZE 8
// The length of the storage authentication tag in bytes.
#define STORAGE_TAG_SIZE 16
// The length of the Poly1305 authentication tag in bytes.
#define POLY1305_TAG_SIZE 16
// The length of the ChaCha20 IV (aka nonce) in bytes as per RFC 7539.
#define CHACHA20_IV_SIZE 12
// The length of the ChaCha20 block in bytes.
#define CHACHA20_BLOCK_SIZE 64
// The length of the counter tail in words.
#define COUNTER_TAIL_WORDS 2
// Values used in the guard key integrity check.
#define GUARD_KEY_MODULUS 6311
#define GUARD_KEY_REMAINDER 15
const char* const VERIFYING_PIN_MSG = "Verifying PIN";
const char* const PROCESSING_MSG = "Processing";
const char* const STARTING_MSG = "Starting up";
static secbool initialized = secfalse;
static secbool unlocked = secfalse;
static PIN_UI_WAIT_CALLBACK ui_callback = NULL;
static uint32_t ui_total = 0;
static uint32_t ui_rem = 0;
static const char *ui_message = NULL;
static uint8_t cached_keys[KEYS_SIZE] = {0};
static uint8_t *const cached_dek = cached_keys;
static uint8_t *const cached_sak = cached_keys + DEK_SIZE;
static uint8_t authentication_sum[SHA256_DIGEST_LENGTH] = {0};
static uint8_t hardware_salt[HARDWARE_SALT_SIZE] = {0};
static uint32_t norcow_active_version = 0;
static const uint8_t TRUE_BYTE = 0x01;
static const uint8_t FALSE_BYTE = 0x00;
static void __handle_fault(const char *msg, const char *file, int line, const char *func);
#define handle_fault(msg) (__handle_fault(msg, __FILE__, __LINE__, __func__))
static secbool storage_upgrade(void);
static secbool storage_set_encrypted(const uint16_t key, const void *val, const uint16_t len);
static secbool storage_get_encrypted(const uint16_t key, void *val_dest, const uint16_t max_len, uint16_t *len);
static secbool secequal(const void* ptr1, const void* ptr2, size_t n) {
const uint8_t* p1 = ptr1;
const uint8_t* p2 = ptr2;
uint8_t diff = 0;
size_t i;
for (i = 0; i < n; ++i) {
diff |= *p1 ^ *p2;
++p1;
++p2;
}
// Check loop completion in case of a fault injection attack.
if (i != n) {
handle_fault("loop completion check");
}
return diff ? secfalse : sectrue;
}
static secbool secequal32(const uint32_t* ptr1, const uint32_t* ptr2, size_t n) {
uint32_t diff = 0;
size_t i;
for (i = 0; i < n; ++i) {
uint32_t mask = random32();
diff |= (*ptr1 + mask - *ptr2) ^ mask;
++ptr1;
++ptr2;
}
// Check loop completion in case of a fault injection attack.
if (i != n) {
handle_fault("loop completion check");
}
return diff ? secfalse : sectrue;
}
static secbool is_protected(uint16_t key) {
const uint8_t app = key >> 8;
return ((app & FLAG_PUBLIC) == 0 && app != APP_STORAGE) ? sectrue : secfalse;
}
/*
* Initialize the storage authentication tag for freshly wiped storage.
*/
static secbool auth_init(void) {
uint8_t tag[SHA256_DIGEST_LENGTH];
memzero(authentication_sum, sizeof(authentication_sum));
hmac_sha256(cached_sak, SAK_SIZE, authentication_sum, sizeof(authentication_sum), tag);
return norcow_set(STORAGE_TAG_KEY, tag, STORAGE_TAG_SIZE);
}
/*
* Update the storage authentication tag with the given key.
*/
static secbool auth_update(uint16_t key) {
if (sectrue != is_protected(key)) {
return sectrue;
}
uint8_t tag[SHA256_DIGEST_LENGTH];
hmac_sha256(cached_sak, SAK_SIZE, (uint8_t*)&key, sizeof(key), tag);
for (uint32_t i = 0; i < SHA256_DIGEST_LENGTH; i++) {
authentication_sum[i] ^= tag[i];
}
hmac_sha256(cached_sak, SAK_SIZE, authentication_sum, sizeof(authentication_sum), tag);
return norcow_set(STORAGE_TAG_KEY, tag, STORAGE_TAG_SIZE);
}
/*
* A secure version of norcow_set(), which updates the storage authentication tag.
*/
static secbool auth_set(uint16_t key, const void *val, uint16_t len) {
secbool found;
secbool ret = norcow_set_ex(key, val, len, &found);
if (sectrue == ret && secfalse == found) {
ret = auth_update(key);
if (sectrue != ret) {
norcow_delete(key);
}
}
return ret;
}
/*
* A secure version of norcow_get(), which checks the storage authentication tag.
*/
static secbool auth_get(uint16_t key, const void **val, uint16_t *len)
{
*val = NULL;
*len = 0;
uint32_t sum[SHA256_DIGEST_LENGTH/sizeof(uint32_t)] = {0};
// Prepare inner and outer digest.
uint32_t odig[SHA256_DIGEST_LENGTH / sizeof(uint32_t)];
uint32_t idig[SHA256_DIGEST_LENGTH / sizeof(uint32_t)];
hmac_sha256_prepare(cached_sak, SAK_SIZE, odig, idig);
// Prepare SHA-256 message padding.
uint32_t g[SHA256_BLOCK_LENGTH / sizeof(uint32_t)] = {0};
uint32_t h[SHA256_BLOCK_LENGTH / sizeof(uint32_t)] = {0};
g[15] = (SHA256_BLOCK_LENGTH + 2) * 8;
h[15] = (SHA256_BLOCK_LENGTH + SHA256_DIGEST_LENGTH) * 8;
h[8] = 0x80000000;
uint32_t offset = 0;
uint16_t k = 0;
uint16_t l = 0;
uint16_t tag_len = 0;
uint16_t entry_count = 0; // Mitigation against fault injection.
uint16_t other_count = 0; // Mitigation against fault injection.
const void *v = NULL;
const void *tag_val = NULL;
while (sectrue == norcow_get_next(&offset, &k, &v, &l)) {
++entry_count;
if (k == key) {
*val = v;
*len = l;
} else {
++other_count;
}
if (sectrue != is_protected(k)) {
if (k == STORAGE_TAG_KEY) {
tag_val = v;
tag_len = l;
}
continue;
}
g[0] = (((uint32_t)k & 0xff) << 24) | (((uint32_t)k & 0xff00) << 8) | 0x8000; // Add SHA message padding.
sha256_Transform(idig, g, h);
sha256_Transform(odig, h, h);
for (uint32_t i = 0; i < SHA256_DIGEST_LENGTH/sizeof(uint32_t); i++) {
sum[i] ^= h[i];
}
}
memcpy(h, sum, sizeof(sum));
sha256_Transform(idig, h, h);
sha256_Transform(odig, h, h);
memzero(odig, sizeof(odig));
memzero(idig, sizeof(idig));
// Cache the authentication sum.
for (size_t i = 0; i < SHA256_DIGEST_LENGTH/sizeof(uint32_t); i++) {
#if BYTE_ORDER == LITTLE_ENDIAN
REVERSE32(sum[i], ((uint32_t*)authentication_sum)[i]);
#else
((uint32_t*)authentication_sum)[i] = sum[i];
#endif
}
// Check loop completion in case of a fault injection attack.
if (secfalse != norcow_get_next(&offset, &k, &v, &l)) {
handle_fault("loop completion check");
}
// Check storage authentication tag.
#if BYTE_ORDER == LITTLE_ENDIAN
for (size_t i = 0; i < SHA256_DIGEST_LENGTH/sizeof(uint32_t); i++) {
REVERSE32(h[i], h[i]);
}
#endif
if (tag_val == NULL || tag_len != STORAGE_TAG_SIZE || sectrue != secequal(h, tag_val, STORAGE_TAG_SIZE)) {
handle_fault("storage tag check");
}
if (*val == NULL) {
// Check for fault injection.
if (other_count != entry_count) {
handle_fault("sanity check");
}
return secfalse;
}
return sectrue;
}
/*
* Generates a delay of random length. Use this to protect sensitive code against fault injection.
*/
static void wait_random(void)
{
#ifndef TREZOR_STORAGE_TEST
int wait = random32() & 0xff;
volatile int i = 0;
volatile int j = wait;
while (i < wait) {
if (i + j != wait) {
handle_fault("sanity check");
}
++i;
--j;
}
// Double-check loop completion.
if (i != wait) {
handle_fault("loop completion check");
}
#endif
}
static void derive_kek(uint32_t pin, const uint8_t *random_salt, uint8_t kek[SHA256_DIGEST_LENGTH], uint8_t keiv[SHA256_DIGEST_LENGTH])
{
#if BYTE_ORDER == BIG_ENDIAN
REVERSE32(pin, pin);
#endif
uint8_t salt[HARDWARE_SALT_SIZE + RANDOM_SALT_SIZE];
memcpy(salt, hardware_salt, HARDWARE_SALT_SIZE);
memcpy(salt + HARDWARE_SALT_SIZE, random_salt, RANDOM_SALT_SIZE);
uint32_t progress = (ui_total - ui_rem) * 1000 / ui_total;
if (ui_callback && ui_message) {
ui_callback(ui_rem, progress, ui_message);
}
PBKDF2_HMAC_SHA256_CTX ctx;
pbkdf2_hmac_sha256_Init(&ctx, (const uint8_t*) &pin, sizeof(pin), salt, sizeof(salt), 1);
for (int i = 1; i <= 5; i++) {
pbkdf2_hmac_sha256_Update(&ctx, PIN_ITER_COUNT / 10);
if (ui_callback && ui_message) {
progress = ((ui_total - ui_rem) * 1000 + i * DERIVE_SECS * 100) / ui_total;
ui_callback(ui_rem - i * DERIVE_SECS / 10, progress, ui_message);
}
}
pbkdf2_hmac_sha256_Final(&ctx, kek);
pbkdf2_hmac_sha256_Init(&ctx, (const uint8_t*) &pin, sizeof(pin), salt, sizeof(salt), 2);
for (int i = 6; i <= 10; i++) {
pbkdf2_hmac_sha256_Update(&ctx, PIN_ITER_COUNT / 10);
if (ui_callback && ui_message) {
progress = ((ui_total - ui_rem) * 1000 + i * DERIVE_SECS * 100) / ui_total;
ui_callback(ui_rem - i * DERIVE_SECS / 10, progress, ui_message);
}
}
pbkdf2_hmac_sha256_Final(&ctx, keiv);
ui_rem -= DERIVE_SECS;
memzero(&ctx, sizeof(PBKDF2_HMAC_SHA256_CTX));
memzero(&pin, sizeof(pin));
memzero(&salt, sizeof(salt));
}
static secbool set_pin(uint32_t pin)
{
uint8_t buffer[RANDOM_SALT_SIZE + KEYS_SIZE + POLY1305_TAG_SIZE];
uint8_t *salt = buffer;
uint8_t *ekeys = buffer + RANDOM_SALT_SIZE;
uint8_t *pvc = buffer + RANDOM_SALT_SIZE + KEYS_SIZE;
uint8_t kek[SHA256_DIGEST_LENGTH];
uint8_t keiv[SHA256_DIGEST_LENGTH];
chacha20poly1305_ctx ctx;
random_buffer(salt, RANDOM_SALT_SIZE);
derive_kek(pin, salt, kek, keiv);
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));
secbool ret = norcow_set(EDEK_PVC_KEY, buffer, RANDOM_SALT_SIZE + KEYS_SIZE + PVC_SIZE);
memzero(buffer, sizeof(buffer));
if (ret == sectrue)
{
if (pin == PIN_EMPTY) {
ret = norcow_set(PIN_NOT_SET_KEY, &TRUE_BYTE, sizeof(TRUE_BYTE));
} else {
ret = norcow_set(PIN_NOT_SET_KEY, &FALSE_BYTE, sizeof(FALSE_BYTE));
}
}
memzero(&pin, sizeof(pin));
return ret;
}
static secbool check_guard_key(const uint32_t guard_key)
{
if (guard_key % GUARD_KEY_MODULUS != GUARD_KEY_REMAINDER) {
return secfalse;
}
// Check that each byte of (guard_key & 0xAAAAAAAA) has exactly two bits set.
uint32_t count = (guard_key & 0x22222222) + ((guard_key >> 2) & 0x22222222);
count = count + (count >> 4);
if ((count & 0x0e0e0e0e) != 0x04040404) {
return secfalse;
}
// Check that the guard_key does not contain a run of 5 (or more) zeros or ones.
uint32_t zero_runs = ~guard_key;
zero_runs = zero_runs & (zero_runs >> 2);
zero_runs = zero_runs & (zero_runs >> 1);
zero_runs = zero_runs & (zero_runs >> 1);
uint32_t one_runs = guard_key;
one_runs = one_runs & (one_runs >> 2);
one_runs = one_runs & (one_runs >> 1);
one_runs = one_runs & (one_runs >> 1);
if ((one_runs != 0) || (zero_runs != 0)) {
return secfalse;
}
return sectrue;
}
static uint32_t generate_guard_key(void)
{
uint32_t guard_key = 0;
do {
guard_key = random_uniform((UINT32_MAX/GUARD_KEY_MODULUS) + 1) * GUARD_KEY_MODULUS + GUARD_KEY_REMAINDER;
} while (sectrue != check_guard_key(guard_key));
return guard_key;
}
static secbool expand_guard_key(const uint32_t guard_key, uint32_t *guard_mask, uint32_t *guard)
{
if (sectrue != check_guard_key(guard_key)) {
handle_fault("guard key check");
return secfalse;
}
*guard_mask = ((guard_key & LOW_MASK) << 1) | ((~guard_key) & LOW_MASK);
*guard = (((guard_key & LOW_MASK) << 1) & guard_key) | (((~guard_key) & LOW_MASK) & (guard_key >> 1));
return sectrue;
}
static secbool pin_logs_init(uint32_t fails)
{
if (fails >= PIN_MAX_TRIES) {
return secfalse;
}
// The format of the PIN_LOGS_KEY entry is:
// guard_key (1 word), pin_success_log (PIN_LOG_WORDS), pin_entry_log (PIN_LOG_WORDS)
uint32_t logs[GUARD_KEY_WORDS + 2*PIN_LOG_WORDS];
logs[0] = generate_guard_key();
uint32_t guard_mask;
uint32_t guard;
wait_random();
if (sectrue != expand_guard_key(logs[0], &guard_mask, &guard)) {
return secfalse;
}
uint32_t unused = guard | ~guard_mask;
for (size_t i = 0; i < 2*PIN_LOG_WORDS; ++i) {
logs[GUARD_KEY_WORDS + i] = unused;
}
// Set the first word of the PIN entry log to indicate the requested number of fails.
logs[GUARD_KEY_WORDS + PIN_LOG_WORDS] = ((((uint32_t)0xFFFFFFFF) >> (2*fails)) & ~guard_mask) | guard;
return norcow_set(PIN_LOGS_KEY, logs, sizeof(logs));
}
/*
* Initializes the values of VERSION_KEY, EDEK_PVC_KEY, PIN_NOT_SET_KEY and PIN_LOGS_KEY using an empty PIN.
* This function should be called to initialize freshly wiped storage.
*/
static void init_wiped_storage(void)
{
if (sectrue != initialized) {
// We cannot initialize the storage contents if the hardware_salt is not set.
return;
}
random_buffer(cached_keys, sizeof(cached_keys));
uint32_t version = NORCOW_VERSION;
ensure(auth_init(), "set_storage_auth_tag failed");
ensure(storage_set_encrypted(VERSION_KEY, &version, sizeof(version)), "set_storage_version failed");
ensure(pin_logs_init(0), "init_pin_logs failed");
ui_total = DERIVE_SECS;
ui_rem = ui_total;
ui_message = PROCESSING_MSG;
ensure(set_pin(PIN_EMPTY), "init_pin failed");
if (unlocked != sectrue) {
memzero(cached_keys, sizeof(cached_keys));
}
}
void storage_init(PIN_UI_WAIT_CALLBACK callback, const uint8_t *salt, const uint16_t salt_len)
{
initialized = secfalse;
unlocked = secfalse;
norcow_init(&norcow_active_version);
initialized = sectrue;
ui_callback = callback;
sha256_Raw(salt, salt_len, hardware_salt);
if (norcow_active_version < NORCOW_VERSION) {
if (sectrue != storage_upgrade()) {
storage_wipe();
ensure(secfalse, "storage_upgrade failed");
}
}
// If there is no EDEK, then generate a random DEK and SAK and store them.
const void *val;
uint16_t len;
if (secfalse == norcow_get(EDEK_PVC_KEY, &val, &len)) {
init_wiped_storage();
}
memzero(cached_keys, sizeof(cached_keys));
}
static secbool pin_fails_reset(void)
{
const void *logs = NULL;
uint16_t len = 0;
if (sectrue != norcow_get(PIN_LOGS_KEY, &logs, &len) || len != WORD_SIZE*(GUARD_KEY_WORDS + 2*PIN_LOG_WORDS)) {
return secfalse;
}
uint32_t guard_mask;
uint32_t guard;
wait_random();
if (sectrue != expand_guard_key(*(const uint32_t*)logs, &guard_mask, &guard)) {
return secfalse;
}
uint32_t unused = guard | ~guard_mask;
const uint32_t *success_log = ((const uint32_t*)logs) + GUARD_KEY_WORDS;
const uint32_t *entry_log = success_log + PIN_LOG_WORDS;
for (size_t i = 0; i < PIN_LOG_WORDS; ++i) {
if (entry_log[i] == unused) {
return sectrue;
}
if (success_log[i] != guard) {
if (sectrue != norcow_update_word(PIN_LOGS_KEY, sizeof(uint32_t)*(i + GUARD_KEY_WORDS), entry_log[i])) {
return secfalse;
}
}
}
return pin_logs_init(0);
}
secbool storage_pin_fails_increase(void)
{
if (sectrue != initialized) {
return secfalse;
}
const void *logs = NULL;
uint16_t len = 0;
wait_random();
if (sectrue != norcow_get(PIN_LOGS_KEY, &logs, &len) || len != WORD_SIZE*(GUARD_KEY_WORDS + 2*PIN_LOG_WORDS)) {
handle_fault("no PIN logs");
return secfalse;
}
uint32_t guard_mask;
uint32_t guard;
wait_random();
if (sectrue != expand_guard_key(*(const uint32_t*)logs, &guard_mask, &guard)) {
handle_fault("guard key expansion");
return secfalse;
}
const uint32_t *entry_log = ((const uint32_t*)logs) + GUARD_KEY_WORDS + PIN_LOG_WORDS;
for (size_t i = 0; i < PIN_LOG_WORDS; ++i) {
wait_random();
if ((entry_log[i] & guard_mask) != guard) {
handle_fault("guard bits check");
return secfalse;
}
if (entry_log[i] != guard) {
wait_random();
uint32_t word = entry_log[i] & ~guard_mask;
word = ((word >> 1) | word) & LOW_MASK;
word = (word >> 2) | (word >> 1);
wait_random();
if (sectrue != norcow_update_word(PIN_LOGS_KEY, sizeof(uint32_t)*(i + GUARD_KEY_WORDS + PIN_LOG_WORDS), (word & ~guard_mask) | guard)) {
handle_fault("PIN logs update");
return secfalse;
}
return sectrue;
}
}
handle_fault("PIN log exhausted");
return secfalse;
}
static uint32_t hamming_weight(uint32_t value)
{
value = value - ((value >> 1) & 0x55555555);
value = (value & 0x33333333) + ((value >> 2) & 0x33333333);
value = (value + (value >> 4)) & 0x0F0F0F0F;
value = value + (value >> 8);
value = value + (value >> 16);
return value & 0x3F;
}
static secbool pin_get_fails(uint32_t *ctr)
{
*ctr = PIN_MAX_TRIES;
const void *logs = NULL;
uint16_t len = 0;
wait_random();
if (sectrue != norcow_get(PIN_LOGS_KEY, &logs, &len) || len != WORD_SIZE*(GUARD_KEY_WORDS + 2*PIN_LOG_WORDS)) {
handle_fault("no PIN logs");
return secfalse;
}
uint32_t guard_mask;
uint32_t guard;
wait_random();
if (sectrue != expand_guard_key(*(const uint32_t*)logs, &guard_mask, &guard)) {
handle_fault("guard key expansion");
return secfalse;
}
const uint32_t unused = guard | ~guard_mask;
const uint32_t *success_log = ((const uint32_t*)logs) + GUARD_KEY_WORDS;
const uint32_t *entry_log = success_log + PIN_LOG_WORDS;
volatile int current = -1;
volatile size_t i;
for (i = 0; i < PIN_LOG_WORDS; ++i) {
if ((entry_log[i] & guard_mask) != guard || (success_log[i] & guard_mask) != guard || (entry_log[i] & success_log[i]) != entry_log[i]) {
handle_fault("PIN logs format check");
return secfalse;
}
if (current == -1) {
if (entry_log[i] != guard) {
current = i;
}
} else {
if (entry_log[i] != unused) {
handle_fault("PIN entry log format check");
return secfalse;
}
}
}
if (current < 0 || current >= PIN_LOG_WORDS || i != PIN_LOG_WORDS) {
handle_fault("PIN log exhausted");
return secfalse;
}
// Strip the guard bits from the current entry word and duplicate each data bit.
wait_random();
uint32_t word = entry_log[current] & ~guard_mask;
word = ((word >> 1) | word ) & LOW_MASK;
word = word | (word << 1);
// Verify that the entry word has form 0*1*.
if ((word & (word + 1)) != 0) {
handle_fault("PIN entry log format check");
return secfalse;
}
if (current == 0) {
++current;
}
// Count the number of set bits in the two current words of the success log.
wait_random();
*ctr = hamming_weight(success_log[current-1] ^ entry_log[current-1]) + hamming_weight(success_log[current] ^ entry_log[current]);
return sectrue;
}
secbool storage_is_unlocked(void)
{
if (sectrue != initialized) {
return secfalse;
}
return unlocked;
}
void storage_lock(void)
{
unlocked = secfalse;
memzero(cached_keys, sizeof(cached_keys));
memzero(authentication_sum, sizeof(authentication_sum));
}
static secbool decrypt_dek(const uint8_t *kek, const uint8_t *keiv)
{
const void *buffer = NULL;
uint16_t len = 0;
if (sectrue != initialized || sectrue != norcow_get(EDEK_PVC_KEY, &buffer, &len) || len != RANDOM_SALT_SIZE + KEYS_SIZE + PVC_SIZE) {
handle_fault("no EDEK");
return secfalse;
}
const uint8_t *ekeys = (const uint8_t*) buffer + RANDOM_SALT_SIZE;
const uint32_t *pvc = (const uint32_t*) buffer + (RANDOM_SALT_SIZE + KEYS_SIZE)/sizeof(uint32_t);
_Static_assert(((RANDOM_SALT_SIZE + KEYS_SIZE) & 3) == 0, "PVC unaligned");
_Static_assert((PVC_SIZE & 3) == 0, "PVC size unaligned");
uint8_t keys[KEYS_SIZE];
uint8_t tag[POLY1305_TAG_SIZE] __attribute__((aligned(sizeof(uint32_t))));
chacha20poly1305_ctx ctx;
// Decrypt the data encryption key and the storage authentication key and check the PIN verification code.
rfc7539_init(&ctx, kek, keiv);
chacha20poly1305_decrypt(&ctx, ekeys, keys, KEYS_SIZE);
rfc7539_finish(&ctx, 0, KEYS_SIZE, tag);
memzero(&ctx, sizeof(ctx));
wait_random();
if (secequal32((const uint32_t*) tag, pvc, PVC_SIZE/sizeof(uint32_t)) != sectrue) {
memzero(keys, sizeof(keys));
memzero(tag, sizeof(tag));
return secfalse;
}
memcpy(cached_keys, keys, sizeof(keys));
memzero(keys, sizeof(keys));
memzero(tag, sizeof(tag));
// Check that the authenticated version number matches the norcow version.
// NOTE: storage_get_encrypted() calls auth_get(), which initializes the authentication_sum.
uint32_t version;
if (sectrue != storage_get_encrypted(VERSION_KEY, &version, sizeof(version), &len) || len != sizeof(version) || version != norcow_active_version) {
handle_fault("storage version check");
return secfalse;
}
return sectrue;
}
static secbool unlock(uint32_t pin)
{
if (sectrue != initialized) {
return secfalse;
}
// Get the pin failure counter
uint32_t ctr;
if (sectrue != pin_get_fails(&ctr)) {
memzero(&pin, sizeof(pin));
return secfalse;
}
// Wipe storage if too many failures
wait_random();
if (ctr >= PIN_MAX_TRIES) {
storage_wipe();
error_shutdown("Too many wrong PIN", "attempts. Storage has", "been wiped.", NULL);
return secfalse;
}
// Sleep for 2^ctr - 1 seconds before checking the PIN.
uint32_t wait = (1 << ctr) - 1;
ui_total += wait;
uint32_t progress = 0;
for (ui_rem = ui_total; ui_rem > ui_total - wait; ui_rem--) {
for (int i = 0; i < 10; i++) {
if (ui_callback && ui_message) {
if (ui_total > 1000000) { // precise enough
progress = (ui_total - ui_rem) / (ui_total / 1000);
} else {
progress = ((ui_total - ui_rem) * 10 + i) * 100 / ui_total;
}
if (sectrue == ui_callback(ui_rem, progress, ui_message)) {
return secfalse;
}
}
hal_delay(100);
}
}
// Read the random salt from EDEK_PVC_KEY and use it to derive the KEK and KEIV from the PIN.
const void *salt = NULL;
uint16_t len = 0;
if (sectrue != initialized || sectrue != norcow_get(EDEK_PVC_KEY, &salt, &len) || len != RANDOM_SALT_SIZE + KEYS_SIZE + PVC_SIZE) {
memzero(&pin, sizeof(pin));
handle_fault("no EDEK");
return secfalse;
}
uint8_t kek[SHA256_DIGEST_LENGTH];
uint8_t keiv[SHA256_DIGEST_LENGTH];
derive_kek(pin, (const uint8_t*) salt, kek, keiv);
memzero(&pin, sizeof(pin));
// First, we increase PIN fail counter in storage, even before checking the
// PIN. If the PIN is correct, we reset the counter afterwards. If not, we
// check if this is the last allowed attempt.
if (sectrue != storage_pin_fails_increase()) {
return secfalse;
}
// Check that the PIN fail counter was incremented.
uint32_t ctr_ck;
if (sectrue != pin_get_fails(&ctr_ck) || ctr + 1 != ctr_ck) {
handle_fault("PIN counter increment");
return secfalse;
}
// Check that the PIN was correct.
if (sectrue != decrypt_dek(kek, keiv)) {
// Wipe storage if too many failures
wait_random();
if (ctr + 1 >= PIN_MAX_TRIES) {
storage_wipe();
error_shutdown("Too many wrong PIN", "attempts. Storage has", "been wiped.", NULL);
}
return secfalse;
}
memzero(kek, sizeof(kek));
memzero(keiv, sizeof(keiv));
unlocked = sectrue;
// Finally set the counter to 0 to indicate success.
return pin_fails_reset();
}
secbool storage_unlock(uint32_t pin)
{
ui_total = DERIVE_SECS;
ui_rem = ui_total;
if (pin == PIN_EMPTY) {
if (ui_message == NULL) {
ui_message = STARTING_MSG;
} else {
ui_message = PROCESSING_MSG;
}
} else {
ui_message = VERIFYING_PIN_MSG;
}
return unlock(pin);
}
/*
* Finds the encrypted data stored under key and writes its length to len.
* If val_dest is not NULL and max_len >= len, then the data is decrypted
* to val_dest using cached_dek as the decryption key.
*/
static secbool storage_get_encrypted(const uint16_t key, void *val_dest, const uint16_t max_len, uint16_t *len)
{
const void *val_stored = NULL;
if (sectrue != auth_get(key, &val_stored, len)) {
return secfalse;
}
if (*len < CHACHA20_IV_SIZE + POLY1305_TAG_SIZE) {
handle_fault("ciphertext length check");
return secfalse;
}
*len -= CHACHA20_IV_SIZE + POLY1305_TAG_SIZE;
if (val_dest == NULL) {
return sectrue;
}
if (*len > max_len) {
return secfalse;
}
const uint8_t *iv = (const uint8_t*) val_stored;
const uint8_t *tag_stored = (const uint8_t*) val_stored + CHACHA20_IV_SIZE;
const uint8_t *ciphertext = (const uint8_t*) val_stored + CHACHA20_IV_SIZE + POLY1305_TAG_SIZE;
uint8_t tag_computed[POLY1305_TAG_SIZE];
chacha20poly1305_ctx ctx;
rfc7539_init(&ctx, cached_dek, iv);
rfc7539_auth(&ctx, (const uint8_t*)&key, sizeof(key));
chacha20poly1305_decrypt(&ctx, ciphertext, (uint8_t*) val_dest, *len);
rfc7539_finish(&ctx, sizeof(key), *len, tag_computed);
memzero(&ctx, sizeof(ctx));
// Verify authentication tag.
if (secequal(tag_computed, tag_stored, POLY1305_TAG_SIZE) != sectrue) {
memzero(val_dest, max_len);
memzero(tag_computed, sizeof(tag_computed));
handle_fault("authentication tag check");
return secfalse;
}
memzero(tag_computed, sizeof(tag_computed));
return sectrue;
}
/*
* Finds the data stored under key and writes its length to len. If val_dest is
* not NULL and max_len >= len, then the data is copied to val_dest.
*/
secbool storage_get(const uint16_t key, void *val_dest, const uint16_t max_len, uint16_t *len)
{
const uint8_t app = key >> 8;
// APP == 0 is reserved for PIN related values
if (sectrue != initialized || app == APP_STORAGE) {
return secfalse;
}
// If the top bit of APP is set, then the value is not encrypted and can be read from a locked device.
secbool ret = secfalse;
if ((app & FLAG_PUBLIC) != 0) {
const void *val_stored = NULL;
if (sectrue != norcow_get(key, &val_stored, len)) {
return secfalse;
}
if (val_dest == NULL) {
return sectrue;
}
if (*len > max_len) {
return secfalse;
}
memcpy(val_dest, val_stored, *len);
ret = sectrue;
} else {
if (sectrue != unlocked) {
return secfalse;
}
ret = storage_get_encrypted(key, val_dest, max_len, len);
}
return ret;
}
/*
* Encrypts the data at val using cached_dek as the encryption key and stores the ciphertext under key.
*/
static secbool storage_set_encrypted(const uint16_t key, const void *val, const uint16_t len)
{
if (len > UINT16_MAX - CHACHA20_IV_SIZE - POLY1305_TAG_SIZE) {
return secfalse;
}
// Preallocate space on the flash storage.
if (sectrue != auth_set(key, NULL, CHACHA20_IV_SIZE + POLY1305_TAG_SIZE + len)) {
return secfalse;
}
// Write the IV to the flash.
uint8_t buffer[CHACHA20_BLOCK_SIZE];
random_buffer(buffer, CHACHA20_IV_SIZE);
uint16_t offset = 0;
if (sectrue != norcow_update_bytes(key, offset, buffer, CHACHA20_IV_SIZE)) {
return secfalse;
}
offset += CHACHA20_IV_SIZE + POLY1305_TAG_SIZE;
// Encrypt all blocks except for the last one.
chacha20poly1305_ctx ctx;
rfc7539_init(&ctx, cached_dek, buffer);
rfc7539_auth(&ctx, (const uint8_t*)&key, sizeof(key));
size_t i;
for (i = 0; i + CHACHA20_BLOCK_SIZE < len; i += CHACHA20_BLOCK_SIZE, offset += CHACHA20_BLOCK_SIZE) {
chacha20poly1305_encrypt(&ctx, ((const uint8_t*) val) + i, buffer, CHACHA20_BLOCK_SIZE);
if (sectrue != norcow_update_bytes(key, offset, buffer, CHACHA20_BLOCK_SIZE)) {
memzero(&ctx, sizeof(ctx));
memzero(buffer, sizeof(buffer));
return secfalse;
}
}
// Encrypt final block and compute message authentication tag.
chacha20poly1305_encrypt(&ctx, ((const uint8_t*) val) + i, buffer, len - i);
secbool ret = norcow_update_bytes(key, offset, buffer, len - i);
if (sectrue == ret) {
rfc7539_finish(&ctx, sizeof(key), len, buffer);
ret = norcow_update_bytes(key, CHACHA20_IV_SIZE, buffer, POLY1305_TAG_SIZE);
}
memzero(&ctx, sizeof(ctx));
memzero(buffer, sizeof(buffer));
return ret;
}
secbool storage_set(const uint16_t key, const void *val, const uint16_t len)
{
const uint8_t app = key >> 8;
// APP == 0 is reserved for PIN related values
if (sectrue != initialized || app == APP_STORAGE) {
return secfalse;
}
if (sectrue != unlocked && (app & FLAGS_WRITE) != FLAGS_WRITE) {
return secfalse;
}
secbool ret = secfalse;
if ((app & FLAG_PUBLIC) != 0) {
ret = norcow_set(key, val, len);
} else {
ret = storage_set_encrypted(key, val, len);
}
return ret;
}
secbool storage_delete(const uint16_t key)
{
const uint8_t app = key >> 8;
// APP == 0 is reserved for storage related values
if (sectrue != initialized || app == APP_STORAGE) {
return secfalse;
}
if (sectrue != unlocked && (app & FLAGS_WRITE) != FLAGS_WRITE) {
return secfalse;
}
secbool ret = norcow_delete(key);
if (sectrue == ret) {
ret = auth_update(key);
}
return ret;
}
secbool storage_set_counter(const uint16_t key, const uint32_t count)
{
const uint8_t app = key >> 8;
if ((app & FLAG_PUBLIC) == 0) {
return secfalse;
}
// The count is stored as a 32-bit integer followed by a tail of "1" bits,
// which is used as a tally.
uint32_t value[1 + COUNTER_TAIL_WORDS];
memset(value, 0xff, sizeof(value));
value[0] = count;
return storage_set(key, value, sizeof(value));
}
secbool storage_next_counter(const uint16_t key, uint32_t *count)
{
const uint8_t app = key >> 8;
// APP == 0 is reserved for PIN related values
if (sectrue != initialized || app == APP_STORAGE || (app & FLAG_PUBLIC) == 0) {
return secfalse;
}
if (sectrue != unlocked && (app & FLAGS_WRITE) != FLAGS_WRITE) {
return secfalse;
}
uint16_t len = 0;
const uint32_t *val_stored = NULL;
if (sectrue != norcow_get(key, (const void**)&val_stored, &len)) {
*count = 0;
return storage_set_counter(key, 0);
}
if (len < sizeof(uint32_t) || len % sizeof(uint32_t) != 0) {
return secfalse;
}
uint16_t len_words = len / sizeof(uint32_t);
uint16_t i = 1;
while (i < len_words && val_stored[i] == 0) {
++i;
}
*count = val_stored[0] + 1 + 32 * (i - 1);
if (i < len_words) {
*count += hamming_weight(~val_stored[i]);
return norcow_update_word(key, sizeof(uint32_t) * i, val_stored[i] >> 1);
} else {
return storage_set_counter(key, *count);
}
}
secbool storage_has_pin(void)
{
if (sectrue != initialized) {
return secfalse;
}
const void *val = NULL;
uint16_t len;
if (sectrue != norcow_get(PIN_NOT_SET_KEY, &val, &len) || (len > 0 && *(uint8_t*)val != FALSE_BYTE)) {
return secfalse;
}
return sectrue;
}
uint32_t storage_get_pin_rem(void)
{
if (sectrue != initialized) {
return 0;
}
uint32_t ctr = 0;
if (sectrue != pin_get_fails(&ctr)) {
return 0;
}
return PIN_MAX_TRIES - ctr;
}
secbool storage_change_pin(uint32_t oldpin, uint32_t newpin)
{
if (sectrue != initialized) {
return secfalse;
}
ui_total = 2 * DERIVE_SECS;
ui_rem = ui_total;
ui_message = (oldpin != PIN_EMPTY && newpin == PIN_EMPTY) ? VERIFYING_PIN_MSG : PROCESSING_MSG;
if (sectrue != unlock(oldpin)) {
return secfalse;
}
secbool ret = set_pin(newpin);
memzero(&oldpin, sizeof(oldpin));
memzero(&newpin, sizeof(newpin));
return ret;
}
void storage_wipe(void)
{
norcow_wipe();
norcow_active_version = NORCOW_VERSION;
memzero(authentication_sum, sizeof(authentication_sum));
memzero(cached_keys, sizeof(cached_keys));
init_wiped_storage();
}
static void __handle_fault(const char *msg, const char *file, int line, const char *func)
{
static secbool in_progress = secfalse;
// If fault handling is already in progress, then we are probably facing a fault injection attack, so wipe.
if (secfalse != in_progress) {
storage_wipe();
__fatal_error("Fault detected", msg, file, line, func);
}
// We use the PIN fail counter as a fault counter. Increment the counter, check that it was incremented and halt.
in_progress = sectrue;
uint32_t ctr;
if (sectrue != pin_get_fails(&ctr)) {
storage_wipe();
__fatal_error("Fault detected", msg, file, line, func);
}
if (sectrue != storage_pin_fails_increase()) {
storage_wipe();
__fatal_error("Fault detected", msg, file, line, func);
}
uint32_t ctr_new;
if (sectrue != pin_get_fails(&ctr_new) || ctr + 1 != ctr_new) {
storage_wipe();
}
__fatal_error("Fault detected", msg, file, line, func);
}
/*
* Reads the PIN fail counter in version 0 format. Returns the current number of failed PIN entries.
*/
static secbool v0_pin_get_fails(uint32_t *ctr)
{
const uint16_t V0_PIN_FAIL_KEY = 0x0001;
// The PIN_FAIL_KEY points to an area of words, initialized to
// 0xffffffff (meaning no PIN failures). The first non-zero word
// in this area is the current PIN failure counter. If PIN_FAIL_KEY
// has no configuration or is empty, the PIN failure counter is 0.
// We rely on the fact that flash allows to clear bits and we clear one
// bit to indicate PIN failure. On success, the word is set to 0,
// indicating that the next word is the PIN failure counter.
// Find the current pin failure counter
const void *val = NULL;
uint16_t len = 0;
if (secfalse != norcow_get(V0_PIN_FAIL_KEY, &val, &len)) {
for (unsigned int i = 0; i < len / sizeof(uint32_t); i++) {
uint32_t word = ((const uint32_t*)val)[i];
if (word != 0) {
*ctr = hamming_weight(~word);
return sectrue;
}
}
}
// No PIN failures
*ctr = 0;
return sectrue;
}
static secbool storage_upgrade(void)
{
const uint16_t V0_PIN_KEY = 0x0000;
const uint16_t V0_PIN_FAIL_KEY = 0x0001;
uint16_t key = 0;
uint16_t len = 0;
const void *val = NULL;
if (norcow_active_version == 0) {
random_buffer(cached_keys, sizeof(cached_keys));
// Initialize the storage authentication tag.
auth_init();
// Set the new storage version number.
uint32_t version = NORCOW_VERSION;
if (sectrue != storage_set_encrypted(VERSION_KEY, &version, sizeof(version))) {
return secfalse;
}
// Set EDEK_PVC_KEY and PIN_NOT_SET_KEY.
ui_total = DERIVE_SECS;
ui_rem = ui_total;
ui_message = PROCESSING_MSG;
if (sectrue == norcow_get(V0_PIN_KEY, &val, &len)) {
set_pin(*(const uint32_t*)val);
} else {
set_pin(PIN_EMPTY);
}
// Convert PIN failure counter.
uint32_t fails = 0;
v0_pin_get_fails(&fails);
pin_logs_init(fails);
// Copy the remaining entries (encrypting the protected ones).
uint32_t offset = 0;
while (sectrue == norcow_get_next(&offset, &key, &val, &len)) {
if (key == V0_PIN_KEY || key == V0_PIN_FAIL_KEY) {
continue;
}
secbool ret;
if (((key >> 8) & FLAG_PUBLIC) != 0) {
ret = norcow_set(key, val, len);
} else {
ret = storage_set_encrypted(key, val, len);
}
if (sectrue != ret) {
return secfalse;
}
}
unlocked = secfalse;
memzero(cached_keys, sizeof(cached_keys));
} else {
return secfalse;
}
norcow_active_version = NORCOW_VERSION;
return norcow_upgrade_finish();
}
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