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ctr_drbg: add comments relating the code with the NIST specification

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This commit is contained in:
Gilles Peskine 2018-08-03 20:16:52 +02:00 committed by Nir Sonnenschein
parent 954f9879e9
commit ed7da59798
2 changed files with 74 additions and 6 deletions
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63
library/ctr_drbg.c
View file

@ -66,6 +66,18 @@ void mbedtls_ctr_drbg_init( mbedtls_ctr_drbg_context *ctx )
* Non-public function wrapped by mbedtls_ctr_drbg_seed(). Necessary to allow
* NIST tests to succeed (which require known length fixed entropy)
*/
/* CTR_DRBG_Instantiate with derivation function (SP 800-90A §10.2.1.3.2)
* mbedtls_ctr_drbg_seed_entropy_len(ctx, f_entropy, p_entropy,
* custom, len, entropy_len)
* implements
* CTR_DRBG_Instantiate(entropy_input, nonce, personalization_string,
* security_strength) -> initial_working_state
* with inputs
* custom[:len] = nonce || personalization_string
* where entropy_input comes from f_entropy for entropy_len bytes
* and with outputs
* ctx = initial_working_state
*/
int mbedtls_ctr_drbg_seed_entropy_len(
mbedtls_ctr_drbg_context *ctx,
int (*f_entropy)(void *, unsigned char *, size_t),
@ -256,6 +268,14 @@ exit:
return( ret );
}
/* CTR_DRBG_Update (SP 800-90A §10.2.1.2)
* ctr_drbg_update_internal(ctx, provided_data)
* implements
* CTR_DRBG_Update(provided_data, Key, V)
* with inputs and outputs
* ctx->aes_ctx = Key
* ctx->counter = V
*/
static int ctr_drbg_update_internal( mbedtls_ctr_drbg_context *ctx,
const unsigned char data[MBEDTLS_CTR_DRBG_SEEDLEN] )
{
@ -301,6 +321,18 @@ static int ctr_drbg_update_internal( mbedtls_ctr_drbg_context *ctx,
return( 0 );
}
/* CTR_DRBG_Instantiate with derivation function (SP 800-90A §10.2.1.3.2)
* mbedtls_ctr_drbg_update(ctx, additional, add_len)
* implements
* CTR_DRBG_Instantiate(entropy_input, nonce, personalization_string,
* security_strength) -> initial_working_state
* with inputs
* ctx->counter = all-bits-0
* ctx->aes_ctx = context from all-bits-0 key
* additional[:add_len] = entropy_input || nonce || personalization_string
* and with outputs
* ctx = initial_working_state
*/
void mbedtls_ctr_drbg_update( mbedtls_ctr_drbg_context *ctx,
const unsigned char *additional, size_t add_len )
{
@ -318,6 +350,18 @@ void mbedtls_ctr_drbg_update( mbedtls_ctr_drbg_context *ctx,
}
}
/* CTR_DRBG_Reseed with derivation function (SP 800-90A §10.2.1.4.2)
* mbedtls_ctr_drbg_reseed(ctx, additional, len)
* implements
* CTR_DRBG_Reseed(working_state, entropy_input, additional_input)
* -> new_working_state
* with inputs
* ctx contains working_state
* additional[:len] = additional_input
* and entropy_input comes from calling ctx->f_entropy
* and with output
* ctx contains new_working_state
*/
int mbedtls_ctr_drbg_reseed( mbedtls_ctr_drbg_context *ctx,
const unsigned char *additional, size_t len )
{
@ -371,6 +415,25 @@ int mbedtls_ctr_drbg_reseed( mbedtls_ctr_drbg_context *ctx,
return( 0 );
}
/* CTR_DRBG_Generate with derivation function (SP 800-90A §10.2.1.5.2)
* mbedtls_ctr_drbg_random_with_add(ctx, output, output_len, additional, add_len)
* implements
* CTR_DRBG_Reseed(working_state, entropy_input, additional[:add_len])
* -> working_state_after_reseed
* if required, then
* CTR_DRBG_Generate(working_state_after_reseed,
* requested_number_of_bits, additional_input)
* -> status, returned_bits, new_working_state
* with inputs
* ctx contains working_state
* requested_number_of_bits = 8 * output_len
* additional[:add_len] = additional_input
* and entropy_input comes from calling ctx->f_entropy
* and with outputs
* status = SUCCESS (this function does the reseed internally)
* returned_bits = output[:output_len]
* ctx contains new_working_state
*/
int mbedtls_ctr_drbg_random_with_add( void *p_rng,
unsigned char *output, size_t output_len,
const unsigned char *additional, size_t add_len )

17
tests/suites/test_suite_ctr_drbg.function
View file

@ -62,12 +62,15 @@ void ctr_drbg_validate_pr( data_t * add_init, data_t * entropy,
test_offset_idx = 0;
TEST_ASSERT( mbedtls_ctr_drbg_seed_entropy_len( &ctx, mbedtls_test_entropy_func, entropy->x, add_init->x, add_init->len, 32 ) == 0 );
/* CTR_DRBG_Instantiate(entropy[:entropy_len/3], nonce, perso, <ignored>)
* where nonce||perso = add_init[add_init_len] */
mbedtls_ctr_drbg_set_prediction_resistance( &ctx, MBEDTLS_CTR_DRBG_PR_ON );
TEST_ASSERT( mbedtls_ctr_drbg_random_with_add( &ctx, buf, 16, add1->x, add1->len ) == 0 );
TEST_ASSERT( mbedtls_ctr_drbg_random_with_add( &ctx, buf, 16, add2->x, add2->len ) == 0 );
/* CTR_DRBG_Generate(result_len * 8 bits, add1[:add1_len]) -> buf */
/* Then reseed because of prediction resistance. */
TEST_ASSERT( hexcmp( buf, result_str->x, 16, result_str->len ) == 0 );
/* CTR_DRBG_Generate(result_len * 8 bits, add2[:add2_len]) -> buf */
/* Then reseed because of prediction resistance. */
exit:
mbedtls_ctr_drbg_free( &ctx );
@ -86,12 +89,14 @@ void ctr_drbg_validate_nopr( data_t * add_init, data_t * entropy,
test_offset_idx = 0;
TEST_ASSERT( mbedtls_ctr_drbg_seed_entropy_len( &ctx, mbedtls_test_entropy_func, entropy->x, add_init->x, add_init->len, 32 ) == 0 );
/* CTR_DRBG_Instantiate(entropy[:entropy_len/2], nonce, perso, <ignored>)
* where nonce||perso = add_init[add_init_len] */
TEST_ASSERT( mbedtls_ctr_drbg_random_with_add( &ctx, buf, 16, add1->x, add1->len ) == 0 );
/* CTR_DRBG_Generate(16 * 8 bits, add1[:add1_len]) -> buf */
TEST_ASSERT( mbedtls_ctr_drbg_reseed( &ctx, add_reseed->x, add_reseed->len ) == 0 );
TEST_ASSERT( mbedtls_ctr_drbg_random_with_add( &ctx, buf, 16, add2->x, add2->len ) == 0 );
/* CTR_DRBG_Reseed(entropy[entropy_len/2:entropy_len], add_reseed[:add_reseed_len]) */
TEST_ASSERT( hexcmp( buf, result_str->x, 16, result_str->len ) == 0 );
/* CTR_DRBG_Generate(16 * 8 bits, add2[:add2_len]) -> buf */
exit:
mbedtls_ctr_drbg_free( &ctx );