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Add hmac_drbg_reseed()

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Manuel Pégourié-Gonnard 2014-01-30 18:28:09 +01:00
parent 4e669c614d
commit 8fc484d1df
2 changed files with 69 additions and 42 deletions
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13
include/polarssl/hmac_drbg.h
View file

@ -135,6 +135,19 @@ void hmac_drbg_set_entropy_len( hmac_drbg_context *ctx,
void hmac_drbg_update( hmac_drbg_context *ctx,
const unsigned char *additional, size_t add_len );
/**
* \brief HMAC_DRBG reseeding (extracts data from entropy source)
*
* \param ctx HMAC_DRBG context
* \param additional Additional data to add to state (Can be NULL)
* \param len Length of additional data
*
* \return 0 if successful, or
* POLARSSL_ERR_HMAC_DRBG_ENTROPY_SOURCE_FAILED
*/
int hmac_drbg_reseed( hmac_drbg_context *ctx,
const unsigned char *additional, size_t len );
/**
* \brief HMAC_DRBG generate random with additional update input
*

98
library/hmac_drbg.c
View file

@ -84,6 +84,42 @@ int hmac_drbg_init_buf( hmac_drbg_context *ctx,
return( 0 );
}
/*
* HMAC_DRBG reseeding (10.1.2.4)
*/
int hmac_drbg_reseed( hmac_drbg_context *ctx,
const unsigned char *additional, size_t len )
{
unsigned char seed[HMAC_DRBG_MAX_SEED_INPUT];
size_t seedlen;
if( ctx->entropy_len + len > HMAC_DRBG_MAX_SEED_INPUT )
return( POLARSSL_ERR_HMAC_DRBG_INPUT_TOO_BIG );
memset( seed, 0, HMAC_DRBG_MAX_SEED_INPUT );
/* 1a. Gather entropy_len bytes of entropy for the seed */
if( ctx->f_entropy( ctx->p_entropy, seed, ctx->entropy_len ) != 0 )
return( POLARSSL_ERR_HMAC_DRBG_ENTROPY_SOURCE_FAILED );
seedlen = ctx->entropy_len;
/* 1b. Append additional data if any */
if( additional != NULL && len != 0 )
{
memcpy( seed + seedlen, additional, len );
seedlen += len;
}
/* 2. Update state */
hmac_drbg_update( ctx, seed, seedlen );
/* 3. Reset reseed_counter (TODO) */
/* 4. Done */
return( 0 );
}
/*
* HMAC_DRBG initialisation
*/
@ -95,63 +131,41 @@ int hmac_drbg_init( hmac_drbg_context *ctx,
size_t len )
{
int ret;
unsigned char seed[HMAC_DRBG_MAX_SEED_INPUT];
size_t seedlen, init_entropy_len;
size_t entropy_len;
memset( ctx, 0, sizeof( hmac_drbg_context ) );
if( ( ret = md_init_ctx( &ctx->md_ctx, md_info ) ) != 0 )
return( ret );
/*
* 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.
*/
ctx->entropy_len = md_info->size <= 20 ? 16 : /* 160-bits hash -> 128 */
md_info->size <= 28 ? 24 : /* 224-bits hash -> 192 */
32; /* better (256+) -> 256 */
/* Set initial working state */
memset( ctx->V, 0x01, md_info->size );
/* ctx->K is already 0 */
ctx->f_entropy = f_entropy;
ctx->p_entropy = p_entropy;
/*
* 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.)
*/
init_entropy_len = ctx->entropy_len * 3 / 2;
ctx->entropy_len = entropy_len * 3 / 2;
if( init_entropy_len + len > HMAC_DRBG_MAX_SEED_INPUT )
return( POLARSSL_ERR_HMAC_DRBG_INPUT_TOO_BIG );
if( ( ret = hmac_drbg_reseed( ctx, custom, len ) ) != 0 )
return( ret );
memset( seed, 0, HMAC_DRBG_MAX_SEED_INPUT );
/*
* Gather init_entropy_len bytes of entropy for initial seed
*/
if( 0 != ctx->f_entropy( ctx->p_entropy, seed,
init_entropy_len ) )
{
return( POLARSSL_ERR_HMAC_DRBG_ENTROPY_SOURCE_FAILED );
}
seedlen = init_entropy_len;
/*
* Add additional data
*/
if( custom != NULL && len != 0 )
{
memcpy( seed + seedlen, custom, len );
seedlen += len;
}
/*
* Set initial state and update it with initialisation data
*/
memset( ctx->V, 0x01, md_info->size );
/* ctx->K is already 0 */
hmac_drbg_update( ctx, seed, seedlen );
ctx->entropy_len = entropy_len;
return( 0 );
}