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CTR_DRBG: support set_entropy_len() before seed()

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mbedtls_ctr_drbg_seed() always set the entropy length to the default,
so a call to mbedtls_ctr_drbg_set_entropy_len() before seed() had no
effect. Change this to the more intuitive behavior that
set_entropy_len() sets the entropy length and seed() respects that and
only uses the default entropy length if there was no call to
set_entropy_len().

The former test-only function mbedtls_ctr_drbg_seed_entropy_len() is
no longer used, but keep it for strict ABI compatibility.
This commit is contained in:
Gilles Peskine 2019-10-04 12:15:55 +02:00 • committed by Simon Butcher
parent f0bf757f9c
commit 20dbfb9938
3 changed files with 35 additions and 40 deletions
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53
library/ctr_drbg.c
View file

@ -365,29 +365,22 @@ exit:
return( ret );
}
/*
* 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)
* mbedtls_ctr_drbg_seed(ctx, f_entropy, p_entropy, custom, 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
* where entropy_input comes from f_entropy for ctx->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),
void *p_entropy,
const unsigned char *custom,
size_t len,
size_t entropy_len )
int mbedtls_ctr_drbg_seed( mbedtls_ctr_drbg_context *ctx,
int (*f_entropy)(void *, unsigned char *, size_t),
void *p_entropy,
const unsigned char *custom,
size_t len )
{
int ret;
unsigned char key[MBEDTLS_CTR_DRBG_KEYSIZE];
@ -399,7 +392,8 @@ int mbedtls_ctr_drbg_seed_entropy_len(
ctx->f_entropy = f_entropy;
ctx->p_entropy = p_entropy;
ctx->entropy_len = entropy_len;
if( ctx->entropy_len == 0 )
ctx->entropy_len = MBEDTLS_CTR_DRBG_ENTROPY_LEN;
ctx->reseed_interval = MBEDTLS_CTR_DRBG_RESEED_INTERVAL;
/*
@ -417,14 +411,15 @@ int mbedtls_ctr_drbg_seed_entropy_len(
return( 0 );
}
int mbedtls_ctr_drbg_seed( mbedtls_ctr_drbg_context *ctx,
int (*f_entropy)(void *, unsigned char *, size_t),
void *p_entropy,
const unsigned char *custom,
size_t len )
/* Backward compatibility wrapper */
int mbedtls_ctr_drbg_seed_entropy_len(
mbedtls_ctr_drbg_context *ctx,
int (*f_entropy)(void *, unsigned char *, size_t), void *p_entropy,
const unsigned char *custom, size_t len,
size_t entropy_len )
{
return( mbedtls_ctr_drbg_seed_entropy_len( ctx, f_entropy, p_entropy, custom, len,
MBEDTLS_CTR_DRBG_ENTROPY_LEN ) );
mbedtls_ctr_drbg_set_entropy_len( ctx, entropy_len );
return( mbedtls_ctr_drbg_seed( ctx, f_entropy, p_entropy, custom, len ) );
}
/* CTR_DRBG_Generate with derivation function (SP 800-90A §10.2.1.5.2)
@ -678,8 +673,11 @@ int mbedtls_ctr_drbg_self_test( int verbose )
mbedtls_printf( " CTR_DRBG (PR = TRUE) : " );
test_offset = 0;
CHK( mbedtls_ctr_drbg_seed_entropy_len( &ctx, ctr_drbg_self_test_entropy,
(void *) entropy_source_pr, nonce_pers_pr, 16, 32 ) );
mbedtls_ctr_drbg_set_entropy_len( &ctx, 32 );
CHK( mbedtls_ctr_drbg_seed( &ctx,
ctr_drbg_self_test_entropy,
(void *) entropy_source_pr,
nonce_pers_pr, 16 ) );
mbedtls_ctr_drbg_set_prediction_resistance( &ctx, MBEDTLS_CTR_DRBG_PR_ON );
CHK( mbedtls_ctr_drbg_random( &ctx, buf, MBEDTLS_CTR_DRBG_BLOCKSIZE ) );
CHK( mbedtls_ctr_drbg_random( &ctx, buf, MBEDTLS_CTR_DRBG_BLOCKSIZE ) );
@ -699,8 +697,11 @@ int mbedtls_ctr_drbg_self_test( int verbose )
mbedtls_ctr_drbg_init( &ctx );
test_offset = 0;
CHK( mbedtls_ctr_drbg_seed_entropy_len( &ctx, ctr_drbg_self_test_entropy,
(void *) entropy_source_nopr, nonce_pers_nopr, 16, 32 ) );
mbedtls_ctr_drbg_set_entropy_len( &ctx, 32 );
CHK( mbedtls_ctr_drbg_seed( &ctx,
ctr_drbg_self_test_entropy,
(void *) entropy_source_nopr,
nonce_pers_nopr, 16 ) );
CHK( mbedtls_ctr_drbg_random( &ctx, buf, 16 ) );
CHK( mbedtls_ctr_drbg_reseed( &ctx, NULL, 0 ) );
CHK( mbedtls_ctr_drbg_random( &ctx, buf, 16 ) );