graphene/Pal/lib/crypto/adapters/mbedtls_dh.c

/* Copyright (C) 2017 Fortanix, Inc.

   This file is part of Graphene Library OS.

   Graphene Library OS 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.

   Graphene Library OS 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 "pal.h"
#include "pal_crypto.h"
#include "pal_error.h"
#include "pal_debug.h"

/* This is declared in pal_internal.h, but that can't be included here. */
int _DkRandomBitsRead(void *buffer, int size);

/* Wrapper to provide mbedtls the RNG interface it expects. It passes an
 * extra context parameter, and expects a return value of 0 for success
 * and nonzero for failure. */
static int RandomWrapper(void *private, unsigned char *data, size_t size)
{
    return _DkRandomBitsRead(data, size) != size;
}

int lib_DhInit(LIB_DH_CONTEXT *context)
{
    int ret;
    mbedtls_dhm_init(context);

    /* Configure parameters. Note that custom Diffie-Hellman parameters 
     * are considered more secure, but require more data be exchanged
     * between the two parties to establish the parameters, so we haven't
     * implemented that yet. */
    ret = mbedtls_mpi_read_string(&context->P, 16 /* radix */,
                                  MBEDTLS_DHM_RFC3526_MODP_2048_P);
    if (ret != 0) {
        pal_printf("D-H initialization failed: %d\n", ret);
        return ret;
    }

    ret = mbedtls_mpi_read_string(&context->G, 16 /* radix */,
                                  MBEDTLS_DHM_RFC3526_MODP_2048_G);
    if (ret != 0) {
        pal_printf("D-H initialization failed: %d\n", ret);
        return ret;
    }

    context->len = mbedtls_mpi_size(&context->P);

    return 0;
}

int lib_DhCreatePublic(LIB_DH_CONTEXT *context, uint8_t *public,
                     uint64_t *public_size)
{
    int ret;

    if (*public_size != DH_SIZE)
        return -PAL_ERROR_INVAL;

    /* The RNG here is used to generate secret exponent X. */
    ret = mbedtls_dhm_make_public(context, context->len, public, *public_size,
                                  RandomWrapper, NULL);
    if (ret != 0)
        return ret;

    /* mbedtls writes leading zeros in the big-endian output to pad to
     * public_size, so leave caller's public_size unchanged */
    return 0;
}

int lib_DhCalcSecret(LIB_DH_CONTEXT *context, uint8_t *peer, uint64_t peer_size,
                   uint8_t *secret, uint64_t *secret_size)
{
    int ret;

    if (*secret_size != DH_SIZE)
        return -PAL_ERROR_INVAL;

    ret = mbedtls_dhm_read_public(context, peer, peer_size);
    if (ret != 0)
        return ret;

    /* The RNG here is used for blinding against timing attacks if X is
     * reused and not used otherwise. mbedtls recommends always passing
     * in an RNG. */
    return mbedtls_dhm_calc_secret(context, secret, *secret_size, secret_size,
                                   RandomWrapper, NULL);
}

void lib_DhFinal(LIB_DH_CONTEXT *context)
{
    /* This call zeros out context for us. */
    mbedtls_dhm_free(context);
}