/**
* Instantiate HMAC_DRBG
*
* @v hash Underlying hash algorithm
* @v state HMAC_DRBG internal state to be initialised
* @v entropy Entropy input
* @v entropy_len Length of entropy input
* @v personal Personalisation string
* @v personal_len Length of personalisation string
*
* This is the HMAC_DRBG_Instantiate_algorithm function defined in ANS
* X9.82 Part 3-2007 Section 10.2.2.2.3 (NIST SP 800-90 Section
* 10.1.2.3).
*
* The nonce must be included within the entropy input (i.e. the
* entropy input must contain at least 3/2 * security_strength bits of
* entropy, as per ANS X9.82 Part 3-2007 Section 8.4.2 (NIST SP 800-90
* Section 8.6.7).
*
* The key, value and reseed counter are updated in-place within the
* HMAC_DRBG internal state.
*/
void hmac_drbg_instantiate ( struct digest_algorithm *hash,
struct hmac_drbg_state *state,
const void *entropy, size_t entropy_len,
const void *personal, size_t personal_len ){
size_t out_len = hash->digestsize;
DBGC ( state, "HMAC_DRBG_%s %p instantiate\n", hash->name, state );
/* Sanity checks */
assert ( hash != NULL );
assert ( state != NULL );
assert ( entropy != NULL );
assert ( ( personal != NULL ) || ( personal_len == 0 ) );
/* 1. seed_material = entropy_input || nonce ||
* personalisation_string
*/
/* 2. Key = 0x00 00..00 */
memset ( state->key, 0x00, out_len );
/* 3. V = 0x01 01...01 */
memset ( state->value, 0x01, out_len );
/* 4. ( Key, V ) = HMAC_DBRG_Update ( seed_material, Key, V )
* 5. reseed_counter = 1
* 6. Return V, Key and reseed_counter as the
* initial_working_state
*/
hmac_drbg_reseed ( hash, state, entropy, entropy_len,
personal, personal_len );
}
/*
* 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 );
}
/*
* HMAC_DRBG initialisation (10.1.2.3 + 9.1)
*/
SSL_ROM_TEXT_SECTION
int hmac_drbg_init( hmac_drbg_context *ctx,
const md_info_t * md_info,
int (*f_entropy)(void *, unsigned char *, size_t),
void *p_entropy,
const unsigned char *custom,
size_t len )
{
int ret;
size_t entropy_len;
memset( ctx, 0, sizeof( hmac_drbg_context ) );
md_init( &ctx->md_ctx );
if( ( ret = md_init_ctx( &ctx->md_ctx, md_info ) ) != 0 )
return( ret );
/*
* Set initial working state.
* Use the V memory location, which is currently all 0, to initialize the
* MD context with an all-zero key. Then set V to its initial value.
*/
md_hmac_starts( &ctx->md_ctx, ctx->V, md_info->size );
memset( ctx->V, 0x01, md_info->size );
ctx->f_entropy = f_entropy;
ctx->p_entropy = p_entropy;
ctx->reseed_interval = POLARSSL_HMAC_DRBG_RESEED_INTERVAL;
/*
* See SP800-57 5.6.1 (p. 65-66) for the security strength provided by
* each hash function, then according to SP800-90A rev1 10.1 table 2,
* min_entropy_len (in bits) is security_strength.
*
* (This also matches the sizes used in the NIST test vectors.)
*/
entropy_len = md_info->size <= 20 ? 16 : /* 160-bits hash -> 128 bits */
md_info->size <= 28 ? 24 : /* 224-bits hash -> 192 bits */
32; /* better (256+) -> 256 bits */
/*
* For initialisation, use more entropy to emulate a nonce
* (Again, matches test vectors.)
*/
ctx->entropy_len = entropy_len * 3 / 2;
if( ( ret = hmac_drbg_reseed( ctx, custom, len ) ) != 0 )
return( ret );
ctx->entropy_len = entropy_len;
return( 0 );
}
/*
* Checkup routine for HMAC_DRBG with SHA-1
*/
SSL_ROM_TEXT_SECTION
int hmac_drbg_self_test( int verbose )
{
hmac_drbg_context ctx;
unsigned char buf[OUTPUT_LEN];
const md_info_t *md_info = md_info_from_type( POLARSSL_MD_SHA1 );
/*
* PR = True
*/
if( verbose != 0 )
polarssl_printf( " HMAC_DRBG (PR = True) : " );
test_offset = 0;
CHK( hmac_drbg_init( &ctx, md_info,
hmac_drbg_self_test_entropy, entropy_pr,
NULL, 0 ) );
hmac_drbg_set_prediction_resistance( &ctx, POLARSSL_HMAC_DRBG_PR_ON );
CHK( hmac_drbg_random( &ctx, buf, OUTPUT_LEN ) );
CHK( hmac_drbg_random( &ctx, buf, OUTPUT_LEN ) );
CHK( memcmp( buf, result_pr, OUTPUT_LEN ) );
hmac_drbg_free( &ctx );
if( verbose != 0 )
polarssl_printf( "passed\n" );
/*
* PR = False
*/
if( verbose != 0 )
polarssl_printf( " HMAC_DRBG (PR = False) : " );
test_offset = 0;
CHK( hmac_drbg_init( &ctx, md_info,
hmac_drbg_self_test_entropy, entropy_nopr,
NULL, 0 ) );
CHK( hmac_drbg_reseed( &ctx, NULL, 0 ) );
CHK( hmac_drbg_random( &ctx, buf, OUTPUT_LEN ) );
CHK( hmac_drbg_random( &ctx, buf, OUTPUT_LEN ) );
CHK( memcmp( buf, result_nopr, OUTPUT_LEN ) );
hmac_drbg_free( &ctx );
if( verbose != 0 )
polarssl_printf( "passed\n" );
if( verbose != 0 )
polarssl_printf( "\n" );
return( 0 );
}
