/*
* Create own private value X and export G^X
*/
int dhm_make_public (dhm_context * ctx, int x_size, unsigned char* output, int olen, int (*f_rng) (void* ), void* p_rng)
{
int ret, i, n;
unsigned char* p;
if (ctx == NULL || olen < 1 || olen > ctx->len)
return (POLARSSL_ERR_DHM_BAD_INPUT_DATA);
/*
* generate X and calculate GX = G^X mod P
*/
n = x_size / sizeof (t_int);
MPI_CHK (mpi_grow (&ctx->X, n));
MPI_CHK (mpi_lset (&ctx->X, 0));
n = x_size - 1;
p = (unsigned char *) ctx->X.p;
for (i = 0; i < n; i++)
*p++ = (unsigned char) f_rng (p_rng);
while (mpi_cmp_mpi (&ctx->X, &ctx->P) >= 0)
mpi_shift_r (&ctx->X, 1);
MPI_CHK (mpi_exp_mod (&ctx->GX, &ctx->G, &ctx->X, &ctx->P, &ctx->RP));
MPI_CHK (mpi_write_binary (&ctx->GX, output, olen));
cleanup:
if (ret != 0)
return (POLARSSL_ERR_DHM_MAKE_PUBLIC_FAILED | ret);
return (0);
}
/*
* Setup and write the ServerKeyExchange parameters
*/
int dhm_make_params( dhm_context *ctx, int x_size,
unsigned char *output, int *olen,
int (*f_rng)(void *), void *p_rng )
{
int i, ret, n, n1, n2, n3;
unsigned char *p;
/*
* generate X and calculate GX = G^X mod P
*/
n = x_size / sizeof( t_int );
MPI_CHK( mpi_grow( &ctx->X, n ) );
MPI_CHK( mpi_lset( &ctx->X, 0 ) );
n = x_size >> 3;
p = (unsigned char *) ctx->X.p;
for( i = 0; i < n; i++ )
*p++ = (unsigned char) f_rng( p_rng );
while( mpi_cmp_mpi( &ctx->X, &ctx->P ) >= 0 )
mpi_shift_r( &ctx->X, 1 );
MPI_CHK( mpi_exp_mod( &ctx->GX, &ctx->G, &ctx->X,
&ctx->P , &ctx->RP ) );
/*
* export P, G, GX
*/
#define DHM_MPI_EXPORT(X,n) \
MPI_CHK( mpi_write_binary( X, p + 2, n ) ); \
*p++ = (unsigned char)( n >> 8 ); \
*p++ = (unsigned char)( n ); p += n;
n1 = mpi_size( &ctx->P );
n2 = mpi_size( &ctx->G );
n3 = mpi_size( &ctx->GX );
p = output;
DHM_MPI_EXPORT( &ctx->P , n1 );
DHM_MPI_EXPORT( &ctx->G , n2 );
DHM_MPI_EXPORT( &ctx->GX, n3 );
*olen = p - output;
ctx->len = n1;
cleanup:
if( ret != 0 )
return( ret | XYSSL_ERR_DHM_MAKE_PARAMS_FAILED );
return( 0 );
}
