/**
 * \file dhm.h
 *
 * \brief Diffie-Hellman-Merkle key exchange
 *
 *  Copyright (C) 2006-2010, Brainspark B.V.
 *
 *  This file is part of PolarSSL (http://www.polarssl.org)
 *  Lead Maintainer: Paul Bakker <polarssl_maintainer at polarssl.org>
 *
 *  All rights reserved.
 *
 *  This program 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 2 of the License, or
 *  (at your option) any later version.
 *
 *  This program 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, write to the Free Software Foundation, Inc.,
 *  51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 */
#ifndef POLARSSL_DHM_H
#define POLARSSL_DHM_H

#include "polarssl/bignum.h"

/*
 * DHM Error codes
 */
#define POLARSSL_ERR_DHM_BAD_INPUT_DATA                    0x0480
#define POLARSSL_ERR_DHM_READ_PARAMS_FAILED                0x0490
#define POLARSSL_ERR_DHM_MAKE_PARAMS_FAILED                0x04A0
#define POLARSSL_ERR_DHM_READ_PUBLIC_FAILED                0x04B0
#define POLARSSL_ERR_DHM_MAKE_PUBLIC_FAILED                0x04C0
#define POLARSSL_ERR_DHM_CALC_SECRET_FAILED                0x04D0

/**
 * \brief          DHM context structure
 */
typedef struct
{
    size_t len; /*!<  size(P) in chars  */
    mpi P;      /*!<  prime modulus     */
    mpi G;      /*!<  generator         */
    mpi X;      /*!<  secret value      */
    mpi GX;     /*!<  self = G^X mod P  */
    mpi GY;     /*!<  peer = G^Y mod P  */
    mpi K;      /*!<  key = GY^X mod P  */
    mpi RP;     /*!<  cached R^2 mod P  */
}
dhm_context;

#ifdef __cplusplus
extern "C" {
#endif

/**
 * \brief          Parse the ServerKeyExchange parameters
 *
 * \param ctx      DHM context
 * \param p        &(start of input buffer)
 * \param end      end of buffer
 *
 * \return         0 if successful, or an POLARSSL_ERR_DHM_XXX error code
 */
int dhm_read_params( dhm_context *ctx,
                     unsigned char **p,
                     const unsigned char *end );

/**
 * \brief          Setup and write the ServerKeyExchange parameters
 *
 * \param ctx      DHM context
 * \param x_size   private value size in bytes
 * \param output   destination buffer
 * \param olen     number of chars written
 * \param f_rng    RNG function
 * \param p_rng    RNG parameter
 *
 * \note           This function assumes that ctx->P and ctx->G
 *                 have already been properly set (for example
 *                 using mpi_read_string or mpi_read_binary).
 *
 * \return         0 if successful, or an POLARSSL_ERR_DHM_XXX error code
 */
int dhm_make_params( dhm_context *ctx, int x_size,
                     unsigned char *output, size_t *olen,
                     int (*f_rng)(void *), void *p_rng );

/**
 * \brief          Import the peer's public value G^Y
 *
 * \param ctx      DHM context
 * \param input    input buffer
 * \param ilen     size of buffer
 *
 * \return         0 if successful, or an POLARSSL_ERR_DHM_XXX error code
 */
int dhm_read_public( dhm_context *ctx,
                     const unsigned char *input, size_t ilen );

/**
 * \brief          Create own private value X and export G^X
 *
 * \param ctx      DHM context
 * \param x_size   private value size in bits
 * \param output   destination buffer
 * \param olen     must be equal to ctx->P.len
 * \param f_rng    RNG function
 * \param p_rng    RNG parameter
 *
 * \return         0 if successful, or an POLARSSL_ERR_DHM_XXX error code
 */
int dhm_make_public( dhm_context *ctx, int x_size,
                     unsigned char *output, size_t olen,
                     int (*f_rng)(void *), void *p_rng );

/**
 * \brief          Derive and export the shared secret (G^Y)^X mod P
 *
 * \param ctx      DHM context
 * \param output   destination buffer
 * \param olen     number of chars written
 *
 * \return         0 if successful, or an POLARSSL_ERR_DHM_XXX error code
 */
int dhm_calc_secret( dhm_context *ctx,
                     unsigned char *output, size_t *olen );

/*
 * \brief          Free the components of a DHM key
 */
void dhm_free( dhm_context *ctx );

/**
 * \brief          Checkup routine
 *
 * \return         0 if successful, or 1 if the test failed
 */
int dhm_self_test( int verbose );

#ifdef __cplusplus
}
#endif

#endif