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Add automatic periodic reseeding

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This commit is contained in:
Manuel Pégourié-Gonnard 2014-01-30 19:03:45 +01:00
parent af786ff6cc
commit 658dbed080
2 changed files with 40 additions and 12 deletions
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31
include/polarssl/hmac_drbg.h
View file

@ -51,18 +51,22 @@ extern "C" {
/**
* HMAC_DRBG context.
* TODO: reseed counter.
*/
typedef struct
{
md_context_t md_ctx;
unsigned char V[POLARSSL_MD_MAX_SIZE];
unsigned char K[POLARSSL_MD_MAX_SIZE];
/* Working state */
md_context_t md_ctx; /*!< HMAC context */
unsigned char V[POLARSSL_MD_MAX_SIZE]; /*!< V in the spec */
unsigned char K[POLARSSL_MD_MAX_SIZE]; /*!< Key in the spec */
int reseed_counter; /*!< reseed counter */
/* Administrative state */
size_t entropy_len; /*!< entropy bytes grabbed on each (re)seed */
int prediction_resistance; /*!< enable prediction resistance (Automatic
reseed before every random generation) */
int reseed_interval; /*!< reseed interval */
/* Callbacks */
int (*f_entropy)(void *, unsigned char *, size_t); /*!< entropy function */
void *p_entropy; /*!< context for the entropy function */
} hmac_drbg_context;
@ -128,14 +132,25 @@ void hmac_drbg_set_prediction_resistance( hmac_drbg_context *ctx,
/**
* \brief Set the amount of entropy grabbed on each reseed
* (Default: HMAC_DRBG_ENTROPY_LEN)
* (Default: given by the security strength, which
* depends on the hash used, see \c hmac_drbg_init() )
*
* \param ctx HMAC_DRBG context
* \param len Amount of entropy to grab
* \param len Amount of entropy to grab, in bytes
*/
void hmac_drbg_set_entropy_len( hmac_drbg_context *ctx,
size_t len );
/**
* \brief Set the reseed interval
* (Default: HMAC_DRBG_RESEED_INTERVAL)
*
* \param ctx HMAC_DRBG context
* \param interval Reseed interval
*/
void hmac_drbg_set_reseed_interval( hmac_drbg_context *ctx,
int interval );
/**
* \brief HMAC_DRBG update state
*
@ -165,7 +180,7 @@ int hmac_drbg_reseed( hmac_drbg_context *ctx,
/**
* \brief HMAC_DRBG generate random with additional update input
*
* Note: Automatically reseeds if reseed_counter is reached.
* Note: Automatically reseeds if reseed_counter is reached or PR is enabled.
*
* \param p_rng HMAC_DRBG context
* \param output Buffer to fill
@ -185,7 +200,7 @@ int hmac_drbg_random_with_add( void *p_rng,
/**
* \brief HMAC_DRBG generate random
*
* Note: Automatically reseeds if reseed_counter is reached.
* Note: Automatically reseeds if reseed_counter is reached or PR is enabled.
*
* \param p_rng HMAC_DRBG context
* \param output Buffer to fill

21
library/hmac_drbg.c
View file

@ -114,7 +114,8 @@ int hmac_drbg_reseed( hmac_drbg_context *ctx,
/* 2. Update state */
hmac_drbg_update( ctx, seed, seedlen );
/* 3. Reset reseed_counter (TODO) */
/* 3. Reset reseed_counter */
ctx->reseed_counter = 1;
/* 4. Done */
return( 0 );
@ -145,6 +146,8 @@ int hmac_drbg_init( hmac_drbg_context *ctx,
ctx->f_entropy = f_entropy;
ctx->p_entropy = p_entropy;
ctx->reseed_interval = 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,
@ -187,6 +190,14 @@ void hmac_drbg_set_entropy_len( hmac_drbg_context *ctx, size_t len )
ctx->entropy_len = len;
}
/*
* Set reseed interval
*/
void hmac_drbg_set_reseed_interval( hmac_drbg_context *ctx, int interval )
{
ctx->reseed_interval = interval;
}
/*
* HMAC_DRBG random function with optional additional data (10.1.2.5)
*/
@ -200,9 +211,10 @@ int hmac_drbg_random_with_add( void *p_rng,
size_t left = out_len;
unsigned char *out = output;
/* 1. Check reseed counter (TODO) and PR */
/* 1. Check reseed counter and PR */
if( ctx->f_entropy != NULL &&
ctx->prediction_resistance == HMAC_DRBG_PR_ON )
( ctx->prediction_resistance == HMAC_DRBG_PR_ON ||
ctx->reseed_counter > ctx->reseed_interval ) )
{
if( ( ret = hmac_drbg_reseed( ctx, additional, add_len ) ) != 0 )
return( ret );
@ -229,7 +241,8 @@ int hmac_drbg_random_with_add( void *p_rng,
/* 6. Update */
hmac_drbg_update( ctx, additional, add_len );
/* 7. Update reseed counter (TODO) */
/* 7. Update reseed counter */
ctx->reseed_counter++;
/* 8. Done */
return( 0 );