/*
* HMAC_DRBG update, using optional additional data (10.1.2.2)
*/
SSL_ROM_TEXT_SECTION
void hmac_drbg_update( hmac_drbg_context *ctx,
const unsigned char *additional, size_t add_len )
{
size_t md_len = ctx->md_ctx.md_info->size;
unsigned char rounds = ( additional != NULL && add_len != 0 ) ? 2 : 1;
unsigned char sep[1];
unsigned char K[POLARSSL_MD_MAX_SIZE];
for( sep[0] = 0; sep[0] < rounds; sep[0]++ )
{
/* Step 1 or 4 */
md_hmac_reset( &ctx->md_ctx );
md_hmac_update( &ctx->md_ctx, ctx->V, md_len );
md_hmac_update( &ctx->md_ctx, sep, 1 );
if( rounds == 2 )
md_hmac_update( &ctx->md_ctx, additional, add_len );
md_hmac_finish( &ctx->md_ctx, K );
/* Step 2 or 5 */
md_hmac_starts( &ctx->md_ctx, K, md_len );
md_hmac_update( &ctx->md_ctx, ctx->V, md_len );
md_hmac_finish( &ctx->md_ctx, ctx->V );
}
}
/*
* HMAC_DRBG random function with optional additional data:
* 10.1.2.5 (arabic) + 9.3 (Roman)
*/
SSL_ROM_TEXT_SECTION
int hmac_drbg_random_with_add( void *p_rng,
unsigned char *output, size_t out_len,
const unsigned char *additional, size_t add_len )
{
int ret;
hmac_drbg_context *ctx = (hmac_drbg_context *) p_rng;
size_t md_len = md_get_size( ctx->md_ctx.md_info );
size_t left = out_len;
unsigned char *out = output;
/* II. Check request length */
if( out_len > POLARSSL_HMAC_DRBG_MAX_REQUEST )
return( POLARSSL_ERR_HMAC_DRBG_REQUEST_TOO_BIG );
/* III. Check input length */
if( add_len > POLARSSL_HMAC_DRBG_MAX_INPUT )
return( POLARSSL_ERR_HMAC_DRBG_INPUT_TOO_BIG );
/* 1. (aka VII and IX) Check reseed counter and PR */
if( ctx->f_entropy != NULL && /* For no-reseeding instances */
( ctx->prediction_resistance == POLARSSL_HMAC_DRBG_PR_ON ||
ctx->reseed_counter > ctx->reseed_interval ) )
{
if( ( ret = hmac_drbg_reseed( ctx, additional, add_len ) ) != 0 )
return( ret );
add_len = 0; /* VII.4 */
}
/* 2. Use additional data if any */
if( additional != NULL && add_len != 0 )
hmac_drbg_update( ctx, additional, add_len );
/* 3, 4, 5. Generate bytes */
while( left != 0 )
{
size_t use_len = left > md_len ? md_len : left;
md_hmac_reset( &ctx->md_ctx );
md_hmac_update( &ctx->md_ctx, ctx->V, md_len );
md_hmac_finish( &ctx->md_ctx, ctx->V );
memcpy( out, ctx->V, use_len );
out += use_len;
left -= use_len;
}
/* 6. Update */
hmac_drbg_update( ctx, additional, add_len );
/* 7. Update reseed counter */
ctx->reseed_counter++;
/* 8. Done */
return( 0 );
}
void
hmac_ctx_reset (md_context_t *ctx)
{
ASSERT(0 == md_hmac_reset(ctx));
}