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feat(core): make random delays use chacha_drbg

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This commit is contained in:
Ondřej Vejpustek 2021-03-25 19:33:21 +01:00
parent e1a5f42c81
commit 6fd4739c5c
13 changed files with 128 additions and 107 deletions
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1
core/.changelog.d/1554.changed Normal file
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@ -0,0 +1 @@
Random delays use ChaCha-based DRBG instead of HMAC-DRBG.

3
core/SConscript.bootloader
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@ -22,13 +22,14 @@ CPPDEFINES_MOD += [
]
SOURCE_MOD += [
'vendor/trezor-crypto/blake2s.c',
'vendor/trezor-crypto/chacha_drbg.c',
'vendor/trezor-crypto/chacha20poly1305/chacha_merged.c',
'vendor/trezor-crypto/ed25519-donna/curve25519-donna-32bit.c',
'vendor/trezor-crypto/ed25519-donna/curve25519-donna-helpers.c',
'vendor/trezor-crypto/ed25519-donna/ed25519.c',
'vendor/trezor-crypto/ed25519-donna/ed25519-donna-32bit-tables.c',
'vendor/trezor-crypto/ed25519-donna/ed25519-donna-impl-base.c',
'vendor/trezor-crypto/ed25519-donna/modm-donna-32bit.c',
'vendor/trezor-crypto/hmac_drbg.c',
'vendor/trezor-crypto/memzero.c',
'vendor/trezor-crypto/rand.c',
'vendor/trezor-crypto/sha2.c',

3
core/SConscript.bootloader_ci
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@ -22,13 +22,14 @@ CPPDEFINES_MOD += [
]
SOURCE_MOD += [
'vendor/trezor-crypto/blake2s.c',
'vendor/trezor-crypto/chacha_drbg.c',
'vendor/trezor-crypto/chacha20poly1305/chacha_merged.c',
'vendor/trezor-crypto/ed25519-donna/curve25519-donna-32bit.c',
'vendor/trezor-crypto/ed25519-donna/curve25519-donna-helpers.c',
'vendor/trezor-crypto/ed25519-donna/ed25519.c',
'vendor/trezor-crypto/ed25519-donna/ed25519-donna-32bit-tables.c',
'vendor/trezor-crypto/ed25519-donna/ed25519-donna-impl-base.c',
'vendor/trezor-crypto/ed25519-donna/modm-donna-32bit.c',
'vendor/trezor-crypto/hmac_drbg.c',
'vendor/trezor-crypto/memzero.c',
'vendor/trezor-crypto/rand.c',
'vendor/trezor-crypto/sha2.c',

3
core/SConscript.prodtest
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@ -14,7 +14,8 @@ CPPPATH_MOD += [
'vendor/trezor-crypto',
]
SOURCE_MOD += [
'vendor/trezor-crypto/hmac_drbg.c',
'vendor/trezor-crypto/chacha_drbg.c',
'vendor/trezor-crypto/chacha20poly1305/chacha_merged.c',
'vendor/trezor-crypto/memzero.c',
'vendor/trezor-crypto/rand.c',
'vendor/trezor-crypto/sha2.c',

4
core/embed/bootloader/main.c
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@ -26,7 +26,7 @@
#include "image.h"
#include "mini_printf.h"
#include "mpu.h"
#include "rng.h"
#include "random_delays.h"
#include "secbool.h"
#include "touch.h"
#include "usb.h"
@ -236,7 +236,7 @@ static void check_bootloader_version(void) {
#endif
int main(void) {
drbg_init();
random_delays_init();
// display_init_seq();
touch_init();
touch_power_on();

3
core/embed/bootloader_ci/main.c
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@ -26,6 +26,7 @@
#include "image.h"
#include "mini_printf.h"
#include "mpu.h"
#include "random_delays.h"
#include "rng.h"
#include "secbool.h"
#include "touch.h"
@ -214,7 +215,7 @@ static void check_bootloader_version(void) {
#endif
int main(void) {
drbg_init();
random_delays_init();
touch_init();
touch_power_on();

4
core/embed/firmware/main.c
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@ -52,8 +52,8 @@
#include "touch.h"
int main(void) {
// initialize pseudo-random number generator
drbg_init();
random_delays_init();
#ifdef RDI
rdi_start();
#endif

3
core/embed/prodtest/main.c
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@ -27,6 +27,7 @@
#include "display.h"
#include "flash.h"
#include "mini_printf.h"
#include "random_delays.h"
#include "rng.h"
#include "sbu.h"
#include "sdcard.h"
@ -371,7 +372,7 @@ static secbool startswith(const char *s, const char *prefix) {
int main(void) {
display_orientation(0);
drbg_init();
random_delays_init();
sdcard_init();
touch_init();
sbu_init();

23
core/embed/trezorhal/common.c
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@ -24,7 +24,6 @@
#include "common.h"
#include "display.h"
#include "flash.h"
#include "hmac_drbg.h"
#include "rand.h"
#include "stm32f4xx_ll_utils.h"
@ -32,8 +31,6 @@
// from util.s
extern void shutdown(void);
static HMAC_DRBG_CTX drbg_ctx;
#define COLOR_FATAL_ERROR RGB16(0x7F, 0x00, 0x00)
void __attribute__((noreturn))
@ -170,23 +167,3 @@ void collect_hw_entropy(void) {
FLASH_OTP_BLOCK_SIZE),
NULL);
}
void drbg_init(void) {
uint8_t entropy[48];
random_buffer(entropy, sizeof(entropy));
hmac_drbg_init(&drbg_ctx, entropy, sizeof(entropy), NULL, 0);
}
void drbg_reseed(const uint8_t *entropy, size_t len) {
hmac_drbg_reseed(&drbg_ctx, entropy, len, NULL, 0);
}
void drbg_generate(uint8_t *buf, size_t len) {
hmac_drbg_generate(&drbg_ctx, buf, len);
}
uint32_t drbg_random32(void) {
uint32_t value;
drbg_generate((uint8_t *)&value, sizeof(value));
return value;
}

5
core/embed/trezorhal/common.h
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@ -74,11 +74,6 @@ void collect_hw_entropy(void);
#define HW_ENTROPY_LEN (12 + 32)
extern uint8_t HW_ENTROPY_DATA[HW_ENTROPY_LEN];
void drbg_init(void);
void drbg_reseed(const uint8_t *entropy, size_t len);
void drbg_generate(uint8_t *buf, size_t len);
uint32_t drbg_random32(void);
// the following functions are defined in util.s
void memset_reg(volatile void *start, volatile void *stop, uint32_t val);

179
core/embed/trezorhal/random_delays.c
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@ -36,6 +36,7 @@ https://link.springer.com/content/pdf/10.1007%2F978-3-540-72354-7_3.pdf
#include "random_delays.h"
#include <stdatomic.h>
#include <stdbool.h>
#include "chacha_drbg.h"
@ -46,35 +47,125 @@ https://link.springer.com/content/pdf/10.1007%2F978-3-540-72354-7_3.pdf
// from util.s
extern void shutdown(void);
#define DRBG_RESEED_INTERVAL_CALLS 1000
#define DRBG_TRNG_ENTROPY_LENGTH 50
_Static_assert(CHACHA_DRBG_OPTIMAL_RESEED_LENGTH(1) == DRBG_TRNG_ENTROPY_LENGTH,
"");
#define BUFFER_LENGTH 64
#define RESEED_INTERVAL 65536
static CHACHA_DRBG_CTX drbg_ctx;
static uint8_t buffer[BUFFER_LENGTH];
static size_t buffer_index;
static secbool drbg_initialized = secfalse;
static uint8_t session_delay;
static bool refresh_session_delay;
static secbool rdi_disabled = sectrue;
static void rdi_reseed(void) {
uint8_t entropy[CHACHA_DRBG_SEED_LENGTH];
random_buffer(entropy, CHACHA_DRBG_SEED_LENGTH);
static void drbg_init() {
uint8_t entropy[DRBG_TRNG_ENTROPY_LENGTH] = {0};
random_buffer(entropy, sizeof(entropy));
chacha_drbg_init(&drbg_ctx, entropy, sizeof(entropy), NULL, 0);
memzero(entropy, sizeof(entropy));
drbg_initialized = sectrue;
}
static void drbg_reseed() {
ensure(drbg_initialized, NULL);
uint8_t entropy[DRBG_TRNG_ENTROPY_LENGTH] = {0};
random_buffer(entropy, sizeof(entropy));
chacha_drbg_reseed(&drbg_ctx, entropy, sizeof(entropy), NULL, 0);
memzero(entropy, sizeof(entropy));
}
static void buffer_refill(void) {
chacha_drbg_generate(&drbg_ctx, buffer, BUFFER_LENGTH);
}
static void drbg_generate(uint8_t *buffer, size_t length) {
ensure(drbg_initialized, NULL);
static uint32_t random8(void) {
buffer_index += 1;
if (buffer_index >= BUFFER_LENGTH) {
buffer_refill();
if (RESEED_INTERVAL != 0 && drbg_ctx.reseed_counter > RESEED_INTERVAL)
rdi_reseed();
buffer_index = 0;
if (drbg_ctx.reseed_counter > DRBG_RESEED_INTERVAL_CALLS) {
drbg_reseed();
}
chacha_drbg_generate(&drbg_ctx, buffer, length);
}
// WARNING: Returns a constant if the function's critical section is locked
static uint32_t drbg_random8(void) {
// Since the function is called both from an interrupt (rdi_handler,
// wait_random) and the main thread (wait_random), we use a lock to
// synchronise access to global variables
static volatile atomic_flag locked = ATOMIC_FLAG_INIT;
if (atomic_flag_test_and_set(&locked))
// locked_old = locked; locked = true; locked_old
{
// If the critical section is locked we return a non-random value, which
// should be ok for our purposes
return 128;
}
static size_t buffer_index = 0;
static uint8_t buffer[BUFFER_LENGTH] = {0};
if (buffer_index == 0) {
drbg_generate(buffer, sizeof(buffer));
}
// To be extra sure there is no buffer overflow, we use a local copy of
// buffer_index
size_t buffer_index_local = buffer_index % sizeof(buffer);
uint8_t value = buffer[buffer_index_local];
memzero(&buffer[buffer_index_local], 1);
buffer_index = (buffer_index_local + 1) % sizeof(buffer);
atomic_flag_clear(&locked); // locked = false
return value;
}
static void wait(uint32_t delay) {
// wait (30 + delay) ticks
asm volatile(
"ldr r0, %0;" // r0 = delay
"loop:"
"subs r0, $3;" // r0 -= 3
"bhs loop;" // if (r0 >= 3): goto loop
// loop (delay // 3) times
// every loop takes 3 ticks
// r0 == (delay % 3) - 3
"add r0, $3;" // r0 += 3
// r0 == delay % 3
"and r0, r0, $3;" // r0 %= 4, make sure that 0 <= r0 < 4
"ldr r1, =table;" // r1 = &table
"tbb [r1, r0];" // jump 2*r1[r0] bytes forward, that is goto wait_r0
"base:"
"table:" // table of branch lengths
".byte (wait_0 - base)/2;"
".byte (wait_1 - base)/2;"
".byte (wait_2 - base)/2;"
".byte (wait_2 - base)/2;" // next instruction must be 2-byte aligned
"wait_2:"
"add r0, $1;" // wait one tick
"wait_1:"
"add r0, $1;" // wait one tick
"wait_0:"
:
: "m"(delay)
: "r0", "r1");
}
void random_delays_init() { drbg_init(); }
void rdi_start(void) {
ensure(drbg_initialized, NULL);
if (rdi_disabled == sectrue) { // if rdi disabled
refresh_session_delay = true;
rdi_disabled = secfalse;
}
}
void rdi_stop(void) {
if (rdi_disabled == secfalse) { // if rdi enabled
rdi_disabled = sectrue;
session_delay = 0;
}
return buffer[buffer_index];
}
void rdi_refresh_session_delay(void) {
@ -85,71 +176,23 @@ void rdi_refresh_session_delay(void) {
void rdi_handler(uint32_t uw_tick) {
if (rdi_disabled == secfalse) { // if rdi enabled
if (refresh_session_delay) {
session_delay = random8();
session_delay = drbg_random8();
refresh_session_delay = false;
}
uint32_t delay = random8() + session_delay;
wait(drbg_random8() + session_delay);
// wait (30 + delay) ticks
asm volatile(
"ldr r0, %0;" // r0 = delay
"loop:"
"subs r0, $3;" // r0 -= 3
"bhs loop;" // if (r0 >= 3): goto loop
// loop (delay // 3) times
// every loop takes 3 ticks
// r0 == (delay % 3) - 3
"add r0, $3;" // r0 += 3
// r0 == delay % 3
"and r0, r0, $3;" // r0 %= 4, make sure that 0 <= r0 < 4
"ldr r1, =table;" // r1 = &table
"tbb [r1, r0];" // jump 2*r1[r0] bytes forward, that is goto wait_r0
"base:"
"table:" // table of branch lengths
".byte (wait_0 - base)/2;"
".byte (wait_1 - base)/2;"
".byte (wait_2 - base)/2;"
".byte (wait_2 - base)/2;" // next instruction must be 2-byte aligned
"wait_2:"
"add r0, $1;" // wait one tick
"wait_1:"
"add r0, $1;" // wait one tick
"wait_0:"
:
: "m"(delay)
: "r0", "r1");
} else { // if rdi disabled or rdi_disabled corrupted
ensure(rdi_disabled, "Fault detected");
}
}
void rdi_start(void) {
if (rdi_disabled == sectrue) { // if rdi disabled
uint8_t entropy[CHACHA_DRBG_SEED_LENGTH];
random_buffer(entropy, CHACHA_DRBG_SEED_LENGTH);
chacha_drbg_init(&drbg_ctx, entropy, sizeof(entropy), NULL, 0);
buffer_refill();
buffer_index = 0;
refresh_session_delay = true;
rdi_disabled = secfalse;
}
}
void rdi_stop(void) {
if (rdi_disabled == secfalse) { // if rdi enabled
rdi_disabled = sectrue;
session_delay = 0;
memzero(&drbg_ctx, sizeof(drbg_ctx));
}
}
/*
* Generates a delay of random length. Use this to protect sensitive code
* against fault injection.
*/
void wait_random(void) {
int wait = drbg_random32() & 0xff;
int wait = drbg_random8();
volatile int i = 0;
volatile int j = wait;
while (i < wait) {

2
core/embed/trezorhal/random_delays.h
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@ -22,6 +22,8 @@
#include <stdint.h>
void random_delays_init(void);
void rdi_start(void);
void rdi_stop(void);
void rdi_refresh_session_delay(void);

2
core/embed/unix/common.c
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@ -107,8 +107,6 @@ error_shutdown(const char *line1, const char *line2, const char *line3,
void hal_delay(uint32_t ms) { usleep(1000 * ms); }
void wait_random(void) {}
uint8_t HW_ENTROPY_DATA[HW_ENTROPY_LEN];
void collect_hw_entropy(void) { memzero(HW_ENTROPY_DATA, HW_ENTROPY_LEN); }