diff options
Diffstat (limited to 'modexp.c')
| -rw-r--r-- | modexp.c | 104 |
1 files changed, 51 insertions, 53 deletions
@@ -91,60 +91,41 @@ static hal_error_t set_register(const off_t addr, } /* - * Get value of a block memory. + * Get value of a data buffer. We reverse the order of 32-bit words + * in the buffer during the transfer to match what the modexps6 core + * expects. */ -static hal_error_t get_blockmem(const off_t reset_addr, - const off_t data_addr, - uint8_t *value, - const size_t length, - const size_t io_len) +static hal_error_t get_buffer(const off_t data_addr, + uint8_t *value, + const size_t length) { - uint8_t discard[4]; size_t i; assert(value != NULL && length % 4 == 0); - assert(io_len >= length && io_len % 4 == 0); - - check(set_register(reset_addr, 1)); - - for (i = 0; i < io_len - length; i += 4) { - check(hal_io_read(data_addr, discard, 4)); - if (discard[0] != 0 || discard[1] != 0 || discard[2] != 0 || discard[3] != 0) - return HAL_ERROR_IO_UNEXPECTED; - } - for (i = 0; i < length; i += 4) - check(hal_io_read(data_addr, &value[i], 4)); + check(hal_io_read(data_addr + i/4, &value[length - 4 - i], 4)); return HAL_OK; } /* - * Set value of a block memory. + * Set value of a data buffer. We reverse the order of 32-bit words + * in the buffer during the transfer to match what the modexps6 core + * expects. */ -static hal_error_t set_blockmem(const off_t reset_addr, - const off_t data_addr, - const uint8_t * const value, - const size_t length, - const size_t io_len) +static hal_error_t set_buffer(const off_t data_addr, + const uint8_t * const value, + const size_t length) { - const uint8_t zero[4] = { 0, 0, 0, 0 }; size_t i; assert(value != NULL && length % 4 == 0); - assert(io_len >= length && io_len % 4 == 0); - - check(set_register(reset_addr, 1)); - - for (i = 0; i < io_len - length; i += 4) - check(hal_io_write(data_addr, zero, 4)); - for (i = 0; i < length; i += 4) - check(hal_io_write(data_addr, &value[i], 4)); + check(hal_io_write(data_addr + i/4, &value[length - 4 - i], 4)); return HAL_OK; } @@ -175,35 +156,52 @@ hal_error_t hal_modexp(const uint8_t * const msg, const size_t msg_len, /* Messa return HAL_ERROR_BAD_ARGUMENTS; /* - * This insanity is a work-around for a current bug in the ModExp - * core: we have to zero-pad everything out to the size of the - * modulus plus 32-bits. Some kind of overflow issue. All of this - * "io_len" nonsense can go away once that's fixed. + * We probably ought to take the mode (fast vs constant-time) as an + * argument, but for the moment we just guess that really short + * exponent means we're using the public key and can use fast mode, + * all other cases are something to do with the private key and + * therefore must use constant-time mode. + * + * Unclear whether it's worth trying to figure out exactly how long + * the operands are: assuming a multiple of eight is safe, but makes + * a bit more work for the core; checking to see how many bits are + * really set leaves the core sitting idle while the main CPU does + * these checks. No way to know which is faster without testing; + * take simple approach for the moment. */ - const size_t io_len = mod_len + 4; - assert((io_len & 3) == 0); + /* Select mode (1 = fast, 0 = safe) */ + check(set_register(MODEXPS6_ADDR_MODE, (exp_len <= 4))); - check(set_blockmem(MODEXP_MODULUS_PTR_RST, MODEXP_MODULUS_DATA, mod, mod_len, io_len)); - check(set_blockmem(MODEXP_MESSAGE_PTR_RST, MODEXP_MESSAGE_DATA, msg, msg_len, io_len)); - check(set_register(MODEXP_MODULUS_LENGTH, /* mod_len */ io_len / 4)); + /* Set modulus size in bits */ + check(set_register(MODEXPS6_ADDR_MODULUS_WIDTH, mod_len * 8)); - check(set_blockmem(MODEXP_EXPONENT_PTR_RST, MODEXP_EXPONENT_DATA, exp, exp_len, exp_len)); - check(set_register(MODEXP_EXPONENT_LENGTH, exp_len / 4)); + /* Write new modulus */ + check(set_buffer(MODEXPS6_ADDR_MODULUS, mod, mod_len)); - check(hal_io_wait_ready(MODEXP_ADDR_STATUS)); + /* Pre-calcuate speed-up coefficient */ + check(hal_io_init(MODEXPS6_ADDR_CTRL)); - check(set_register(MODEXP_ADDR_CTRL, 1)); + /* Wait for calculation to complete */ + check(hal_io_wait_ready(MODEXPS6_ADDR_STATUS)); - /* - * ModExp core is not very fast (yet), so wait a long time for a - * response, but not forever. - */ + /* Write new message */ + check(set_buffer(MODEXPS6_ADDR_MESSAGE, msg, msg_len)); + + /* Set new exponent length in bits */ + check(set_register(MODEXPS6_ADDR_EXPONENT_WIDTH, exp_len * 8)); + + /* Set new exponent */ + check(set_buffer(MODEXPS6_ADDR_EXPONENT, exp, exp_len)); + + /* Start calculation */ + check(hal_io_next(MODEXPS6_ADDR_CTRL)); - int timeout = 0x7FFFFFFF; - check(hal_io_wait(MODEXP_ADDR_STATUS, STATUS_READY, &timeout)); + /* Wait for result */ + check(hal_io_wait_valid(MODEXPS6_ADDR_STATUS)); - check(get_blockmem(MODEXP_RESULT_PTR_RST, MODEXP_RESULT_DATA, result, mod_len, io_len)); + /* Extract result */ + check(get_buffer(MODEXPS6_ADDR_RESULT, result, mod_len)); return HAL_OK; } |