/*
* modexp.c
* ----------
* Wrapper around Cryptech ModExp core.
*
* This doesn't do full RSA, that's another module. This module's job
* is just the I/O to get bits in and out of the ModExp core, including
* compensating for a few known bugs that haven't been resolved yet.
*
* If at some point the interface to the ModExp core becomes simple
* enough that this module is no longer needed, it will go away.
*
* Authors: Rob Austein
* Copyright (c) 2015, NORDUnet A/S
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are
* met:
* - Redistributions of source code must retain the above copyright notice,
* this list of conditions and the following disclaimer.
*
* - Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* - Neither the name of the NORDUnet nor the names of its contributors may
* be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
* IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
* TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
* PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
* HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED
* TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
* LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
* NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#include <stdio.h>
#include <stdint.h>
#include "hal.h"
#include "hal_internal.h"
/*
* Whether we want debug output.
*/
static int debug = 0;
void hal_modexp_set_debug(const int onoff)
{
debug = onoff;
}
/*
* Get value of an ordinary register.
*/
static hal_error_t inline get_register(const hal_core_t *core,
const hal_addr_t addr,
uint32_t *value)
{
hal_error_t err;
uint8_t w[4];
if (value == NULL)
return HAL_ERROR_IMPOSSIBLE;
if ((err = hal_io_read(core, addr, w, sizeof(w))) != HAL_OK)
return err;
*value = (w[0] << 0) | (w[1] << 8) | (w[2] << 16) | (w[3] << 24);
return HAL_OK;
}
/*
* Set value of an ordinary register.
*/
static hal_error_t inline set_register(const hal_core_t *core,
const hal_addr_t addr,
const uint32_t value)
{
const uint8_t w[4] = {
((value >> 24) & 0xFF),
((value >> 16) & 0xFF),
((value >> 8) & 0xFF),
((value >> 0) & 0xFF)
};
return hal_io_write(core, addr, w, sizeof(w));
}
/*
* Get value of a data buffer. We reverse the order of 32-bit words
* in the buffer during the transfer to match what the modexpa7 core
* expects.
*/
static inline hal_error_t get_buffer(const hal_core_t *core,
const hal_addr_t data_addr,
uint8_t *value,
const size_t length)
{
hal_error_t err;
size_t i;
if (value == NULL || length % 4 != 0)
return HAL_ERROR_IMPOSSIBLE;
for (i = 0; i < length; i += 4)
if ((err = hal_io_read(core, data_addr + i/4, &value[length - 4 - i], 4)) != HAL_OK)
return err;
return HAL_OK;
}
/*
* Set value of a data buffer. We reverse the order of 32-bit words
* in the buffer during the transfer to match what the modexpa7 core
* expects.
*
* Do we need to zero the portion of the buffer we're not using
* explictly (that is, the portion between `length` and the value of
* the core's MODEXPA7_ADDR_BUFFER_BITS register)? We've gotten away
* without doing this so far, but the core doesn't take an explicit
* length parameter for the message itself, instead it assumes that
* the message is either as long as or twice as long as the exponent,
* depending on the setting of the CRT mode bit. Maybe initializing
* the core clears the excess bits so there's no issue? Dunno. Have
* never seen a problem with this yet, just dont' know why not.
*/
static inline hal_error_t set_buffer(const hal_core_t *core,
const hal_addr_t data_addr,
const uint8_t * const value,
const size_t length)
{
hal_error_t err;
size_t i;
if (value == NULL || length % 4 != 0)
return HAL_ERROR_IMPOSSIBLE;
for (i = 0; i < length; i += 4)
if ((err = hal_io_write(core, data_addr + i/4, &value[length - 4 - i], 4)) != HAL_OK)
return err;
return HAL_OK;
}
/*
* Check a result, report on failure if debugging, pass failures up
* the chain.
*/
#define check(_expr_) \
do { \
hal_error_t _err = (_expr_); \
if (_err != HAL_OK && debug) \
hal_log(HAL_LOG_WARN, "%s failed: %s\n", #_expr_, hal_error_string(_err)); \
if (_err != HAL_OK) { \
hal_core_free(core); \
return _err; \
} \
} while (0)
/*
* Run one modexp operation.
*/
hal_error_t hal_modexp(hal_core_t *core,
const int precalc_done,
const uint8_t * const msg, const size_t msg_len, /* Message */
const uint8_t * const exp, const size_t exp_len, /* Exponent */
const uint8_t * const mod, const size_t mod_len, /* Modulus */
uint8_t *result, const size_t result_len, /* Result of exponentiation */
uint8_t *coeff, const size_t coeff_len, /* Modulus coefficient (r/w) */
uint8_t *mont, const size_t mont_len) /* Montgomery factor (r/w)*/
{
hal_error_t err;
/*
* All pointers must be set, exponent may not be longer than
* modulus, message may not be longer than twice the modulus (CRT
* mode), result buffer must not be shorter than modulus, and all
* input lengths must be a multiple of four bytes (the core is all
* about 32-bit words).
*/
if (msg == NULL || msg_len > MODEXPA7_OPERAND_BYTES || msg_len > mod_len * 2 ||
exp == NULL || exp_len > MODEXPA7_OPERAND_BYTES || exp_len > mod_len ||
mod == NULL || mod_len > MODEXPA7_OPERAND_BYTES ||
result == NULL || result_len > MODEXPA7_OPERAND_BYTES || result_len < mod_len ||
coeff == NULL || coeff_len > MODEXPA7_OPERAND_BYTES ||
mont == NULL || mont_len > MODEXPA7_OPERAND_BYTES ||
((msg_len | exp_len | mod_len) & 3) != 0)
return HAL_ERROR_BAD_ARGUMENTS;
/*
* Gonna need to think about running two modexpa7 cores in parallel
* in CRT mode for full speed signature.
*/
if (((err = hal_core_alloc(MODEXPA7_NAME, &core)) != HAL_OK))
return err;
/*
* Now that we have the core, check operand length against what it
* says it can handle.
*/
uint32_t operand_max = 0;
check(get_register(core, MODEXPA7_ADDR_BUFFER_BITS, &operand_max));
operand_max /= 8;
if (msg_len > operand_max ||
exp_len > operand_max ||
mod_len > operand_max ||
coeff_len > operand_max ||
mont_len > operand_max) {
hal_core_free(core);
return HAL_ERROR_BAD_ARGUMENTS;
}
/* Set modulus */
check(set_register(core, MODEXPA7_ADDR_MODULUS_BITS, mod_len * 8));
check(set_buffer(core, MODEXPA7_ADDR_MODULUS, mod, mod_len));
/*
* Calculate modulus-dependent speedup factors if needed. Buffer
* space is always caller's problem (because caller almost certainly
* wants to stash these values in the keystore anyway). Calculation
* is edge-triggered by "init" bit going from zero to one.
*/
if (!precalc_done) {
check(hal_io_zero(core));
check(hal_io_init(core));
check(hal_io_wait_ready(core));
check(get_buffer(core, MODEXPA7_ADDR_MODULUS_COEFF_OUT, coeff, coeff_len));
check(get_buffer(core, MODEXPA7_ADDR_MONTGOMERY_FACTOR_OUT, mont, mont_len));
}
/* Load modulus-dependent speedup factors (even if we just calculated them) */
check(set_buffer(core, MODEXPA7_ADDR_MODULUS_COEFF_IN, coeff, coeff_len));
check(set_buffer(core, MODEXPA7_ADDR_MONTGOMERY_FACTOR_IN, mont, mont_len));
/* Select CRT mode if and only if message is longer than exponent */
check(set_register(core, MODEXPA7_ADDR_MODE,
(msg_len > mod_len
? MODEXPA7_MODE_CRT
: MODEXPA7_MODE_PLAIN)));
/* Set message and exponent */
check(set_buffer(core, MODEXPA7_ADDR_MESSAGE, msg, msg_len));
check(set_buffer(core, MODEXPA7_ADDR_EXPONENT, exp, exp_len));
check(set_register(core, MODEXPA7_ADDR_EXPONENT_BITS, exp_len * 8));
/* Edge-trigger the "next" bit to start calculation, then wait for the result */
check(hal_io_zero(core));
check(hal_io_next(core));
check(hal_io_wait_valid(core));
/* Extract result, clean up, then done */
check(get_buffer(core, MODEXPA7_ADDR_RESULT, result, mod_len));
hal_core_free(core);
return HAL_OK;
}
/*
* Local variables:
* indent-tabs-mode: nil
* End:
*/
