From fe34a5fb832defac003841502fbb343299b2594f Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Manuel=20P=C3=A9gouri=C3=A9-Gonnard?= <mpg@elzevir.fr>
Date: Thu, 30 Jan 2014 15:06:40 +0100
Subject: [PATCH] Add entropy callbacks to HMAC_DRBG
---
include/polarssl/hmac_drbg.h | 66 +++++++++++++++++++++++++----
library/ecdsa.c | 2 +-
library/hmac_drbg.c | 80 ++++++++++++++++++++++++++++++++++--
3 files changed, 135 insertions(+), 13 deletions(-)
diff --git a/include/polarssl/hmac_drbg.h b/include/polarssl/hmac_drbg.h
index b35d62b3d2..54aa9a4080 100644
--- a/include/polarssl/hmac_drbg.h
+++ b/include/polarssl/hmac_drbg.h
@@ -29,19 +29,40 @@
#include "md.h"
+/*
+ * ! Same values as ctr_drbg.h !
+ */
+#define POLARSSL_ERR_HMAC_DRBG_ENTROPY_SOURCE_FAILED -0x0034 /**< The entropy source failed. */
+#define POLARSSL_ERR_HMAC_DRBG_REQUEST_TOO_BIG -0x0036 /**< Too many random requested in single call. */
+#define POLARSSL_ERR_HMAC_DRBG_INPUT_TOO_BIG -0x0038 /**< Input too large (Entropy + additional). */
+#define POLARSSL_ERR_HMAC_DRBG_FILE_IO_ERROR -0x003A /**< Read/write error in file. */
+
+#define HMAC_DRBG_RESEED_INTERVAL 10000 /**< Interval before reseed is performed by default */
+#define HMAC_DRBG_MAX_INPUT 256 /**< Maximum number of additional input bytes */
+#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 */
+
#ifdef __cplusplus
extern "C" {
#endif
-/*
- * Simplified HMAC_DRBG context.
- * No reseed counter, no prediction resistance flag.
+/**
+ * HMAC_DRBG context.
+ * TODO: reseed counter, prediction resistance flag.
*/
typedef struct
{
md_context_t md_ctx;
unsigned char V[POLARSSL_MD_MAX_SIZE];
unsigned char K[POLARSSL_MD_MAX_SIZE];
+
+ size_t entropy_len; /*!< entropy bytes grabbed on each (re)seed */
+
+ /*
+ * Callbacks (Entropy)
+ */
+ int (*f_entropy)(void *, unsigned char *, size_t);
+ void *p_entropy; /*!< context for the entropy function */
} hmac_drbg_context;
/**
@@ -49,18 +70,47 @@ typedef struct
*
* \param ctx HMAC_DRBG context to be initialised
* \param md_info MD algorithm to use for HMAC_DRBG
- * \param data Concatenation of entropy string and additional data
- * \param data_len Length of data in bytes
+ * \param f_entropy Entropy callback (p_entropy, buffer to fill, buffer
+ * length)
+ * \param p_entropy Entropy context
+ * \param custom Personalization data (Device specific identifiers)
+ * (Can be NULL)
+ * \param len Length of personalization data
*
- * \todo Use entropy callback rather than buffer.
+ * \note The "security strength" as defined by NIST is set to:
+ * 128 bits if md_alg is SHA-1,
+ * 192 bits if md_alg is SHA-224,
+ * 256 bits if md_alg is SHA-256 or higher.
+ * Note that SHA-256 is just as efficient as SHA-224.
*
* \return 0 if successful, or
* POLARSSL_ERR_MD_BAD_INPUT_DATA, or
- * POLARSSL_ERR_MD_ALLOC_FAILED
+ * POLARSSL_ERR_MD_ALLOC_FAILED, or
+ * POLARSSL_ERR_CTR_DRBG_ENTROPY_SOURCE_FAILED.
*/
int hmac_drbg_init( hmac_drbg_context *ctx,
const md_info_t * md_info,
- const unsigned char *data, size_t data_len );
+ int (*f_entropy)(void *, unsigned char *, size_t),
+ void *p_entropy,
+ const unsigned char *custom,
+ size_t len );
+
+/**
+ * \brief Simplified HMAC_DRBG initialisation.
+ * (For use with deterministic ECDSA.)
+ *
+ * \param ctx HMAC_DRBG context to be initialised
+ * \param md_info MD algorithm to use for HMAC_DRBG
+ * \param data Concatenation of entropy string and additional data
+ * \param data_len Length of data in bytes
+ *
+ * \return 0 if successful, or
+ * POLARSSL_ERR_MD_BAD_INPUT_DATA, or
+ * POLARSSL_ERR_MD_ALLOC_FAILED.
+ */
+int hmac_drbg_init_buf( hmac_drbg_context *ctx,
+ const md_info_t * md_info,
+ const unsigned char *data, size_t data_len );
/**
* \brief HMAC_DRBG update state
diff --git a/library/ecdsa.c b/library/ecdsa.c
index 92f6eef1e3..12076d536f 100644
--- a/library/ecdsa.c
+++ b/library/ecdsa.c
@@ -193,7 +193,7 @@ int ecdsa_sign_det( ecp_group *grp, mpi *r, mpi *s,
MPI_CHK( mpi_write_binary( d, data, grp_len ) );
MPI_CHK( derive_mpi( grp, &h, buf, blen ) );
MPI_CHK( mpi_write_binary( &h, data + grp_len, grp_len ) );
- hmac_drbg_init( &rng_ctx, md_info, data, 2 * grp_len );
+ hmac_drbg_init_buf( &rng_ctx, md_info, data, 2 * grp_len );
ret = ecdsa_sign( grp, r, s, d, buf, blen,
hmac_drbg_random, &rng_ctx );
diff --git a/library/hmac_drbg.c b/library/hmac_drbg.c
index bc5b908162..a8fe486c85 100644
--- a/library/hmac_drbg.c
+++ b/library/hmac_drbg.c
@@ -63,11 +63,11 @@ void hmac_drbg_update( hmac_drbg_context *ctx,
}
/*
- * Simplified HMAC_DRBG initialisation.
+ * Simplified HMAC_DRBG initialisation (for use with deterministic ECDSA)
*/
-int hmac_drbg_init( hmac_drbg_context *ctx,
- const md_info_t * md_info,
- const unsigned char *data, size_t data_len )
+int hmac_drbg_init_buf( hmac_drbg_context *ctx,
+ const md_info_t * md_info,
+ const unsigned char *data, size_t data_len )
{
int ret;
@@ -84,6 +84,78 @@ int hmac_drbg_init( hmac_drbg_context *ctx,
return( 0 );
}
+/*
+ * HMAC_DRBG initialisation
+ */
+int hmac_drbg_init( hmac_drbg_context *ctx,
+ const md_info_t * md_info,
+ int (*f_entropy)(void *, unsigned char *, size_t),
+ void *p_entropy,
+ const unsigned char *custom,
+ size_t len )
+{
+ int ret;
+ unsigned char seed[HMAC_DRBG_MAX_SEED_INPUT];
+ size_t seedlen, init_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 */
+
+ ctx->f_entropy = f_entropy;
+ ctx->p_entropy = p_entropy;
+
+ /*
+ * For initialisation, use more entropy to emulate a nonce
+ */
+ init_entropy_len = ctx->entropy_len * 3 / 2;
+
+ if( init_entropy_len + len > HMAC_DRBG_MAX_SEED_INPUT )
+ return( POLARSSL_ERR_HMAC_DRBG_INPUT_TOO_BIG );
+
+ 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 );
+
+ return( 0 );
+}
+
/*
* HMAC_DRBG random function with optional additional data (10.1.2.5)
*/