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Add hmac_drbg_set_prediction_resistance()

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This commit is contained in:
Manuel Pégourié-Gonnard 2014-01-30 18:44:18 +01:00
parent 8fc484d1df
commit af786ff6cc
2 changed files with 37 additions and 7 deletions
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26
include/polarssl/hmac_drbg.h
View File

@ -42,13 +42,16 @@
#define HMAC_DRBG_MAX_REQUEST 1024 /**< Maximum number of requested bytes per call */
#define HMAC_DRBG_MAX_SEED_INPUT 384 /**< Maximum size of (re)seed buffer */
#define HMAC_DRBG_PR_OFF 0 /**< No prediction resistance */
#define HMAC_DRBG_PR_ON 1 /**< Prediction resistance enabled */
#ifdef __cplusplus
extern "C" {
#endif
/**
* HMAC_DRBG context.
* TODO: reseed counter, prediction resistance flag.
* TODO: reseed counter.
*/
typedef struct
{
@ -57,12 +60,11 @@ typedef struct
unsigned char K[POLARSSL_MD_MAX_SIZE];
size_t entropy_len; /*!< entropy bytes grabbed on each (re)seed */
int prediction_resistance; /*!< enable prediction resistance (Automatic
reseed before every random generation) */
/*
* Callbacks (Entropy)
*/
int (*f_entropy)(void *, unsigned char *, size_t);
void *p_entropy; /*!< context for the entropy function */
int (*f_entropy)(void *, unsigned char *, size_t); /*!< entropy function */
void *p_entropy; /*!< context for the entropy function */
} hmac_drbg_context;
/**
@ -112,6 +114,18 @@ int hmac_drbg_init_buf( hmac_drbg_context *ctx,
const md_info_t * md_info,
const unsigned char *data, size_t data_len );
/**
* \brief Enable / disable prediction resistance (Default: Off)
*
* Note: If enabled, entropy is used for ctx->entropy_len before each call!
* Only use this if you have ample supply of good entropy!
*
* \param ctx HMAC_DRBG context
* \param resistance HMAC_DRBG_PR_ON or HMAC_DRBG_PR_OFF
*/
void hmac_drbg_set_prediction_resistance( hmac_drbg_context *ctx,
int resistance );
/**
* \brief Set the amount of entropy grabbed on each reseed
* (Default: HMAC_DRBG_ENTROPY_LEN)

18
library/hmac_drbg.c
View File

@ -170,6 +170,15 @@ int hmac_drbg_init( hmac_drbg_context *ctx,
return( 0 );
}
/*
* Set prediction resistance
*/
void hmac_drbg_set_prediction_resistance( hmac_drbg_context *ctx,
int resistance )
{
ctx->prediction_resistance = resistance;
}
/*
* Set entropy length grabbed for reseeds
*/
@ -185,12 +194,19 @@ int hmac_drbg_random_with_add( void *p_rng,
unsigned char *output, size_t out_len,
const unsigned char *additional, size_t add_len )
{
int ret;
hmac_drbg_context *ctx = (hmac_drbg_context *) p_rng;
size_t md_len = md_get_size( ctx->md_ctx.md_info );
size_t left = out_len;
unsigned char *out = output;
/* 1. Check reseed counter (TODO) */
/* 1. Check reseed counter (TODO) and PR */
if( ctx->f_entropy != NULL &&
ctx->prediction_resistance == HMAC_DRBG_PR_ON )
{
if( ( ret = hmac_drbg_reseed( ctx, additional, add_len ) ) != 0 )
return( ret );
}
/* 2. Use additional data if any */
if( additional != NULL && add_len != 0 )