/**
 * \file dhm.h
 */
#ifndef XYSSL_DHM_H
#define XYSSL_DHM_H

#include "bignum.h"

#define XYSSL_ERR_DHM_BAD_INPUT_DATA                    -0x0480
#define XYSSL_ERR_DHM_READ_PARAMS_FAILED                -0x0490
#define XYSSL_ERR_DHM_MAKE_PARAMS_FAILED                -0x04A0
#define XYSSL_ERR_DHM_READ_PUBLIC_FAILED                -0x04B0
#define XYSSL_ERR_DHM_MAKE_PUBLIC_FAILED                -0x04C0
#define XYSSL_ERR_DHM_CALC_SECRET_FAILED                -0x04D0

typedef struct
{
    int 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 XYSSL_ERR_DHM_XXX error code
 */
int dhm_read_params( dhm_context *ctx,
                     unsigned char **p,
                     unsigned char *end );

/**
 * \brief          Setup and write the ServerKeyExchange parameters
 *
 * \param ctx      DHM context
 * \param x_size   private value size in bits
 * \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 che_mpi_read_string or che_mpi_read_binary).
 *
 * \return         0 if successful, or an XYSSL_ERR_DHM_XXX error code
 */
int dhm_make_params( dhm_context *ctx, int s_size,
                     unsigned char *output, int *olen,
                     int (*f_rng)(void *), void *p_rng );

int dhm_make_params_internal( dhm_context *ctx, int x_size,
                              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 XYSSL_ERR_DHM_XXX error code
 */
int dhm_read_public( dhm_context *ctx,
                     unsigned char *input, int 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 XYSSL_ERR_DHM_XXX error code
 */
int dhm_make_public( dhm_context *ctx, int s_size,
                     unsigned char *output, int olen,
                     int (*f_rng)(void *), void *p_rng );
int dhm_make_public_internal( dhm_context *ctx, int x_size,
                              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 XYSSL_ERR_DHM_XXX error code
 */
int dhm_calc_secret( dhm_context *ctx,
                     unsigned char *output, int *olen );
int dhm_calc_secret_internal( dhm_context *ctx);

/*
 * \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