lib/mbedtls
1
0
Fork 0
mirror of https://github.com/Mbed-TLS/mbedtls.git synced 2025-07-29 11:41:15 +03:00
Code Activity

CTR_DRBG: add the possibility of grabbing entropy for a nonce

Browse Source 
Add a new function mbedtls_ctr_drbg_set_nonce_len() which configures
the DRBG instance to call f_entropy a second time during the initial
seeding to grab a nonce.

The default nonce length is 0, so there is no behavior change unless
the user calls the new function.
This commit is contained in:
Gilles Peskine
2019-10-22 18:42:27 +02:00
parent dbd3f7c68d
commit 9be5098061
2 changed files with 125 additions and 40 deletions
Download Patch File Download Diff File Expand all files Collapse all files

65
library/ctr_drbg.c
View File

@ -86,6 +86,32 @@ void mbedtls_ctr_drbg_set_entropy_len( mbedtls_ctr_drbg_context *ctx,
ctx->entropy_len = len;
}
int mbedtls_ctr_drbg_set_nonce_len( mbedtls_ctr_drbg_context *ctx,
size_t len )
{
/* If mbedtls_ctr_drbg_seed() has already been called, it's
* too late. Return the error code that's closest to making sense. */
if( ctx->f_entropy != NULL )
return( MBEDTLS_ERR_CTR_DRBG_ENTROPY_SOURCE_FAILED );
if( len > MBEDTLS_CTR_DRBG_MAX_SEED_INPUT )
return( MBEDTLS_ERR_CTR_DRBG_INPUT_TOO_BIG );
#if SIZE_MAX > INT_MAX
/* This shouldn't be an issue because
* MBEDTLS_CTR_DRBG_MAX_SEED_INPUT < INT_MAX in any sensible
* configuration, but make sure anyway. */
if( len > INT_MAX )
return( MBEDTLS_ERR_CTR_DRBG_INPUT_TOO_BIG );
#endif
/* For backward compatibility with Mbed TLS <= 2.19, store the
* entropy nonce length in a field that already exists, but isn't
* used until after the initial seeding. */
/* Due to the capping of len above, the value fits in an int. */
ctx->reseed_counter = (int) len;
return( 0 );
}
void mbedtls_ctr_drbg_set_reseed_interval( mbedtls_ctr_drbg_context *ctx,
int interval )
{
@ -319,7 +345,7 @@ void mbedtls_ctr_drbg_update( mbedtls_ctr_drbg_context *ctx,
#endif /* MBEDTLS_DEPRECATED_REMOVED */
/* CTR_DRBG_Reseed with derivation function (SP 800-90A &sect;10.2.1.4.2)
* mbedtls_ctr_drbg_reseed(ctx, additional, len)
* mbedtls_ctr_drbg_reseed(ctx, additional, len, nonce_len)
* implements
* CTR_DRBG_Reseed(working_state, entropy_input, additional_input)
* -> new_working_state
@ -327,11 +353,14 @@ void mbedtls_ctr_drbg_update( mbedtls_ctr_drbg_context *ctx,
* ctx contains working_state
* additional[:len] = additional_input
* and entropy_input comes from calling ctx->f_entropy
* for (ctx->entropy_len + nonce_len) bytes
* 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 )
int mbedtls_ctr_drbg_reseed_internal( mbedtls_ctr_drbg_context *ctx,
const unsigned char *additional,
size_t len,
size_t nonce_len )
{
unsigned char seed[MBEDTLS_CTR_DRBG_MAX_SEED_INPUT];
size_t seedlen = 0;
@ -339,7 +368,9 @@ int mbedtls_ctr_drbg_reseed( mbedtls_ctr_drbg_context *ctx,
if( ctx->entropy_len > MBEDTLS_CTR_DRBG_MAX_SEED_INPUT )
return( MBEDTLS_ERR_CTR_DRBG_INPUT_TOO_BIG );
if( len > MBEDTLS_CTR_DRBG_MAX_SEED_INPUT - ctx->entropy_len )
if( nonce_len > MBEDTLS_CTR_DRBG_MAX_SEED_INPUT - ctx->entropy_len )
return( MBEDTLS_ERR_CTR_DRBG_INPUT_TOO_BIG );
if( len > MBEDTLS_CTR_DRBG_MAX_SEED_INPUT - ctx->entropy_len - nonce_len )
return( MBEDTLS_ERR_CTR_DRBG_INPUT_TOO_BIG );
memset( seed, 0, MBEDTLS_CTR_DRBG_MAX_SEED_INPUT );
@ -351,6 +382,16 @@ int mbedtls_ctr_drbg_reseed( mbedtls_ctr_drbg_context *ctx,
}
seedlen += ctx->entropy_len;
/* Gather entropy for a nonce if requested. */
if( nonce_len != 0 )
{
if( 0 != ctx->f_entropy( ctx->p_entropy, seed, nonce_len ) )
{
return( MBEDTLS_ERR_CTR_DRBG_ENTROPY_SOURCE_FAILED );
}
seedlen += nonce_len;
}
/* Add additional data if provided. */
if( additional != NULL && len != 0 )
{
@ -372,6 +413,12 @@ exit:
return( ret );
}
int mbedtls_ctr_drbg_reseed( mbedtls_ctr_drbg_context *ctx,
const unsigned char *additional, size_t len )
{
return( mbedtls_ctr_drbg_reseed_internal( ctx, additional, len, 0 ) );
}
/* CTR_DRBG_Instantiate with derivation function (SP 800-90A &sect;10.2.1.3.2)
* mbedtls_ctr_drbg_seed(ctx, f_entropy, p_entropy, custom, len)
* implements
@ -403,16 +450,18 @@ int mbedtls_ctr_drbg_seed( mbedtls_ctr_drbg_context *ctx,
ctx->entropy_len = MBEDTLS_CTR_DRBG_ENTROPY_LEN;
ctx->reseed_interval = MBEDTLS_CTR_DRBG_RESEED_INTERVAL;
/*
* Initialize with an empty key
*/
/* Initialize with an empty key. */
if( ( ret = mbedtls_aes_setkey_enc( &ctx->aes_ctx, key,
MBEDTLS_CTR_DRBG_KEYBITS ) ) != 0 )
{
return( ret );
}
if( ( ret = mbedtls_ctr_drbg_reseed( ctx, custom, len ) ) != 0 )
/* Do the initial seeding.
* ctx->reseed_counter contains the desired amount of entropy to
* grab for a nonce (see mbedtls_ctr_drbg_set_nonce_len()). */
if( ( ret = mbedtls_ctr_drbg_reseed_internal( ctx, custom, len,
ctx->reseed_counter ) ) != 0 )
{
return( ret );
}