diff options
Diffstat (limited to 'src/rand_stm32.c')
| -rw-r--r-- | src/rand_stm32.c | 135 |
1 files changed, 0 insertions, 135 deletions
diff --git a/src/rand_stm32.c b/src/rand_stm32.c deleted file mode 100644 index 87bea8f..0000000 --- a/src/rand_stm32.c +++ /dev/null @@ -1,135 +0,0 @@ -/* Quick-and-dirty cryptographic RNG based on BLAKE2s - * - * This system uses a 32-byte BLAKE2s hash as internal state seeded by somewhat random post-powerup SRAM content, the - * unique device ID and the program flash contents. This seed state is mixed with values from the hardware RNG for each - * 32-byte block of output data. - * - * The RNG's chaining looks like the following, with H(...) being the BLAKE2s hash function, | being binary - * concatenation and hw_rng(...) being the hardware RNG. c and e are the fixed extraction and chain string constants - * defined below. - * - * Seed: state = H(SRAM | FLASH | hw_rng(64 byte)) - * - * Extract: state = H(state | c | hw_rng(64 byte)) block[0] = H(state | e) - * state = H(state | c | hw_rng(64 byte)) block[1] = H(state | e) - * [...] - * state = H(state | c | hw_rng(64 byte)) block[n] = H(state | e) - * state = H(state | c | hw_rng(64 byte)) - * - * - * Graphically, with C = H( state | c | rng ) being the chaining function - * and X = H( state | e ) being the extraction function - * this becomes: - * - * rng rng rng rng - * | | | | - * v v v v - * state ---> [C] ---> [C] -- . . . --> [C] ---> [C] ---> new state - * | | | - * v v v - * [X] [X] [X] - * | | | - * v v v - * out[0] out[1] . . . out[n] - * - */ - -#include <unistd.h> -#include <stdlib.h> -#include <string.h> - -#include <libopencm3/stm32/f4/rng.h> - -#include "usart_helpers.h" -#include "rand_stm32.h" -#include "tracing.h" - -#include "crypto/noise-c/src/protocol/internal.h" -#include "crypto/noise-c/src/crypto/blake2/blake2s.h" - -/* FIXME persist state in backup sram */ -extern unsigned _ram_start, _ram_end, _rom_start, _rom_end; -static uint8_t global_stm_rand_state[BLAKE2S_HASH_SIZE]; - -static uint32_t stm32_read_rng_raw(void) { - if ((RNG_SR & (RNG_SR_SEIS | RNG_SR_CEIS)) || !(RNG_CR & RNG_CR_RNGEN)) { - LOG_PRINTF("RNG error detected, bailing out.\n"); - exit(1); - } - - while (!(RNG_SR & RNG_SR_DRDY)) - ; - - return RNG_DR; -} - -static void rng_seed_blake(BLAKE2s_context_t *bc) { - /* This pulls out 64 bytes. Even though the resulting BLAKE2s hash only is 32 bytes large, the internal state of - * BLAKE2s is larger. Also I don't quite trust the STM32F4's hardware RNG. */ - for (int i=0; i<16; i++) { - uint32_t val = stm32_read_rng_raw(); - BLAKE2s_update(bc, &val, sizeof(val)); - } -} - -void rand_init() { - RNG_CR |= RNG_CR_RNGEN; - BLAKE2s_context_t bc; - BLAKE2s_reset(&bc); - - /* Seed with entire SRAM area */ - BLAKE2s_update(&bc, &_ram_start, &_ram_end - &_ram_start); - /* Seed with entire flash area. This includes the device unique ID if it has not been overwritten. */ - BLAKE2s_update(&bc, &_rom_start, &_rom_end - &_rom_start); - /* Seed with 64 bytes of handware RNG input */ - rng_seed_blake(&bc); - /* FIXME use ADC to seeed */ - - BLAKE2s_finish(&bc, global_stm_rand_state); - /* FIXME make sure this is not optimized out */ - memset(&bc, 0, sizeof(bc)); -} - -const char *extraction_constant = "Blake2 RNG extraction constant"; -const char *chain_constant = "Blake2 RNG chaining constant"; - -void noise_rand_bytes(void *bytes, size_t size) { - TRACING_SET(TR_RNG); - BLAKE2s_context_t out_ctx, chain_ctx; - uint8_t *out = (uint8_t *)bytes; - uint8_t hash_buf[BLAKE2S_HASH_SIZE]; - - for (size_t wr_pos = 0; wr_pos<size; wr_pos += BLAKE2S_HASH_SIZE) { - BLAKE2s_reset(&chain_ctx); - BLAKE2s_update(&chain_ctx, global_stm_rand_state, sizeof(global_stm_rand_state)); - BLAKE2s_update(&chain_ctx, chain_constant, strlen(chain_constant)); - rng_seed_blake(&chain_ctx); - BLAKE2s_finish(&chain_ctx, global_stm_rand_state); - - BLAKE2s_reset(&out_ctx); - BLAKE2s_update(&out_ctx, global_stm_rand_state, sizeof(global_stm_rand_state)); - BLAKE2s_update(&out_ctx, extraction_constant, strlen(extraction_constant)); - BLAKE2s_finish(&out_ctx, hash_buf); - - size_t rem = size-wr_pos; - memcpy(&out[wr_pos], hash_buf, rem < BLAKE2S_HASH_SIZE ? rem : BLAKE2S_HASH_SIZE); - } - - BLAKE2s_reset(&chain_ctx); - BLAKE2s_update(&chain_ctx, global_stm_rand_state, sizeof(global_stm_rand_state)); - BLAKE2s_update(&chain_ctx, chain_constant, strlen(chain_constant)); - rng_seed_blake(&chain_ctx); - BLAKE2s_finish(&chain_ctx, global_stm_rand_state); - - /* FIXME make sure this is not optimized out */ - memset(&out_ctx, 0, sizeof(out_ctx)); - memset(&chain_ctx, 0, sizeof(chain_ctx)); - memset(hash_buf, 0, sizeof(hash_buf)); - TRACING_CLEAR(TR_RNG); -} - -#ifdef ED25519_CUSTOMRANDOM /* We are building against ed25519-donna, which needs a random function */ -void ed25519_randombytes_unsafe(void *p, size_t len) { - noise_rand_bytes(p, len); -} -#endif |