library/hmac_drbg.c - security/mbedtls - Rivoreo Source Code Repositories

 /*
  *  HMAC_DRBG implementation (NIST SP 800-90)
  *
  *  Copyright (C) 2014, ARM Limited, All Rights Reserved
  *
  *  This file is part of mbed TLS (https://www.polarssl.org)
  *
  *  This program is free software; you can redistribute it and/or modify
  *  it under the terms of the GNU General Public License as published by
  *  the Free Software Foundation; either version 2 of the License, or
  *  (at your option) any later version.
  *
  *  This program is distributed in the hope that it will be useful,
  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  *  GNU General Public License for more details.
  *
  *  You should have received a copy of the GNU General Public License along
  *  with this program; if not, write to the Free Software Foundation, Inc.,
  *  51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */

 /*
  *  The NIST SP 800-90A DRBGs are described in the following publication.
  *  http://csrc.nist.gov/publications/nistpubs/800-90A/SP800-90A.pdf
  *  References below are based on rev. 1 (January 2012).
  */

 #if !defined(POLARSSL_CONFIG_FILE)
 #include "polarssl/config.h"
 #else
 #include POLARSSL_CONFIG_FILE
 #endif

 #if defined(POLARSSL_HMAC_DRBG_C)

 #include "polarssl/hmac_drbg.h"

 #if defined(POLARSSL_FS_IO)
 #include <stdio.h>
 #endif

 #if defined(POLARSSL_PLATFORM_C)
 #include "polarssl/platform.h"
 #else
 #define polarssl_printf printf
 #endif

 /* Implementation that should never be optimized out by the compiler */
 static void polarssl_zeroize( void *v, size_t n ) {
     volatile unsigned char *p = v; while( n-- ) *p++ = 0;
 }

 /*
  * HMAC_DRBG update, using optional additional data (10.1.2.2)
  */
 void hmac_drbg_update( hmac_drbg_context *ctx,
                        const unsigned char *additional, size_t add_len )
 {
     size_t md_len = ctx->md_ctx.md_info->size;
     unsigned char rounds = ( additional != NULL && add_len != 0 ) ? 2 : 1;
     unsigned char sep[1];
     unsigned char K[POLARSSL_MD_MAX_SIZE];

     for( sep[0] = 0; sep[0] < rounds; sep[0]++ )
     {
         /* Step 1 or 4 */
         md_hmac_reset( &ctx->md_ctx );
         md_hmac_update( &ctx->md_ctx, ctx->V, md_len );
         md_hmac_update( &ctx->md_ctx, sep, 1 );
         if( rounds == 2 )
             md_hmac_update( &ctx->md_ctx, additional, add_len );
         md_hmac_finish( &ctx->md_ctx, K );

         /* Step 2 or 5 */
         md_hmac_starts( &ctx->md_ctx, K, md_len );
         md_hmac_update( &ctx->md_ctx, ctx->V, md_len );
         md_hmac_finish( &ctx->md_ctx, ctx->V );
     }
 }

 /*
  * Simplified HMAC_DRBG initialisation (for use with deterministic ECDSA)
  */
 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;

     memset( ctx, 0, sizeof( hmac_drbg_context ) );

     md_init( &ctx->md_ctx );

     if( ( ret = md_init_ctx( &ctx->md_ctx, md_info ) ) != 0 )
         return( ret );

     /*
      * Set initial working state.
      * Use the V memory location, which is currently all 0, to initialize the
      * MD context with an all-zero key. Then set V to its initial value.
      */
     md_hmac_starts( &ctx->md_ctx, ctx->V, md_info->size );
     memset( ctx->V, 0x01, md_info->size );

     hmac_drbg_update( ctx, data, data_len );

     return( 0 );
 }

 /*
  * HMAC_DRBG reseeding: 10.1.2.4 (arabic) + 9.2 (Roman)
  */
 int hmac_drbg_reseed( hmac_drbg_context *ctx,
                       const unsigned char *additional, size_t len )
 {
     unsigned char seed[POLARSSL_HMAC_DRBG_MAX_SEED_INPUT];
     size_t seedlen;

     /* III. Check input length */
     if( len > POLARSSL_HMAC_DRBG_MAX_INPUT ||
         ctx->entropy_len + len > POLARSSL_HMAC_DRBG_MAX_SEED_INPUT )
     {
         return( POLARSSL_ERR_HMAC_DRBG_INPUT_TOO_BIG );
     }

     memset( seed, 0, POLARSSL_HMAC_DRBG_MAX_SEED_INPUT );

     /* IV. 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;

     /* 1. Concatenate entropy and 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 */
     ctx->reseed_counter = 1;

     /* 4. Done */
     return( 0 );
 }

 /*
  * HMAC_DRBG initialisation (10.1.2.3 + 9.1)
  */
 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;
     size_t entropy_len;

     memset( ctx, 0, sizeof( hmac_drbg_context ) );

     md_init( &ctx->md_ctx );

     if( ( ret = md_init_ctx( &ctx->md_ctx, md_info ) ) != 0 )
         return( ret );

     /*
      * Set initial working state.
      * Use the V memory location, which is currently all 0, to initialize the
      * MD context with an all-zero key. Then set V to its initial value.
      */
     md_hmac_starts( &ctx->md_ctx, ctx->V, md_info->size );
     memset( ctx->V, 0x01, md_info->size );

     ctx->f_entropy = f_entropy;
     ctx->p_entropy = p_entropy;

     ctx->reseed_interval = POLARSSL_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,
      * 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.)
      */
     ctx->entropy_len = entropy_len * 3 / 2;

     if( ( ret = hmac_drbg_reseed( ctx, custom, len ) ) != 0 )
         return( ret );

     ctx->entropy_len = entropy_len;

     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
  */
 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 (arabic) + 9.3 (Roman)
  */
 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;

     /* II. Check request length */
     if( out_len > POLARSSL_HMAC_DRBG_MAX_REQUEST )
         return( POLARSSL_ERR_HMAC_DRBG_REQUEST_TOO_BIG );

     /* III. Check input length */
     if( add_len > POLARSSL_HMAC_DRBG_MAX_INPUT )
         return( POLARSSL_ERR_HMAC_DRBG_INPUT_TOO_BIG );

     /* 1. (aka VII and IX) Check reseed counter and PR */
     if( ctx->f_entropy != NULL && /* For no-reseeding instances */
         ( ctx->prediction_resistance == POLARSSL_HMAC_DRBG_PR_ON ||
           ctx->reseed_counter > ctx->reseed_interval ) )
     {
         if( ( ret = hmac_drbg_reseed( ctx, additional, add_len ) ) != 0 )
             return( ret );

         add_len = 0; /* VII.4 */
     }

     /* 2. Use additional data if any */
     if( additional != NULL && add_len != 0 )
         hmac_drbg_update( ctx, additional, add_len );

     /* 3, 4, 5. Generate bytes */
     while( left != 0 )
     {
         size_t use_len = left > md_len ? md_len : left;

         md_hmac_reset( &ctx->md_ctx );
         md_hmac_update( &ctx->md_ctx, ctx->V, md_len );
         md_hmac_finish( &ctx->md_ctx, ctx->V );

         memcpy( out, ctx->V, use_len );
         out += use_len;
         left -= use_len;
     }

     /* 6. Update */
     hmac_drbg_update( ctx, additional, add_len );

     /* 7. Update reseed counter */
     ctx->reseed_counter++;

     /* 8. Done */
     return( 0 );
 }

 /*
  * HMAC_DRBG random function
  */
 int hmac_drbg_random( void *p_rng, unsigned char *output, size_t out_len )
 {
     return( hmac_drbg_random_with_add( p_rng, output, out_len, NULL, 0 ) );
 }

 /*
  * Free an HMAC_DRBG context
  */
 void hmac_drbg_free( hmac_drbg_context *ctx )
 {
     if( ctx == NULL )
         return;

     md_free_ctx( &ctx->md_ctx );

     polarssl_zeroize( ctx, sizeof( hmac_drbg_context ) );
 }

 #if defined(POLARSSL_FS_IO)
 int hmac_drbg_write_seed_file( hmac_drbg_context *ctx, const char *path )
 {
     int ret;
     FILE *f;
     unsigned char buf[ POLARSSL_HMAC_DRBG_MAX_INPUT ];

     if( ( f = fopen( path, "wb" ) ) == NULL )
         return( POLARSSL_ERR_HMAC_DRBG_FILE_IO_ERROR );

     if( ( ret = hmac_drbg_random( ctx, buf, sizeof( buf ) ) ) != 0 )
         goto exit;

     if( fwrite( buf, 1, sizeof( buf ), f ) != sizeof( buf ) )
     {
         ret = POLARSSL_ERR_HMAC_DRBG_FILE_IO_ERROR;
         goto exit;
     }

     ret = 0;

 exit:
     fclose( f );
     return( ret );
 }

 int hmac_drbg_update_seed_file( hmac_drbg_context *ctx, const char *path )
 {
     FILE *f;
     size_t n;
     unsigned char buf[ POLARSSL_HMAC_DRBG_MAX_INPUT ];

     if( ( f = fopen( path, "rb" ) ) == NULL )
         return( POLARSSL_ERR_HMAC_DRBG_FILE_IO_ERROR );

     fseek( f, 0, SEEK_END );
     n = (size_t) ftell( f );
     fseek( f, 0, SEEK_SET );

     if( n > POLARSSL_HMAC_DRBG_MAX_INPUT )
     {
         fclose( f );
         return( POLARSSL_ERR_HMAC_DRBG_INPUT_TOO_BIG );
     }

     if( fread( buf, 1, n, f ) != n )
     {
         fclose( f );
         return( POLARSSL_ERR_HMAC_DRBG_FILE_IO_ERROR );
     }

     fclose( f );

     hmac_drbg_update( ctx, buf, n );

     return( hmac_drbg_write_seed_file( ctx, path ) );
 }
 #endif /* POLARSSL_FS_IO */


 #if defined(POLARSSL_SELF_TEST)

 #include <stdio.h>

 #if !defined(POLARSSL_SHA1_C)
 /* Dummy checkup routine */
 int hmac_drbg_self_test( int verbose )
 {

     if( verbose != 0 )
         polarssl_printf( "\n" );

     return( 0 );
 }
 #else

 #define OUTPUT_LEN  80

 /* From a NIST PR=true test vector */
 static unsigned char entropy_pr[] = {
     0xa0, 0xc9, 0xab, 0x58, 0xf1, 0xe2, 0xe5, 0xa4, 0xde, 0x3e, 0xbd, 0x4f,
     0xf7, 0x3e, 0x9c, 0x5b, 0x64, 0xef, 0xd8, 0xca, 0x02, 0x8c, 0xf8, 0x11,
     0x48, 0xa5, 0x84, 0xfe, 0x69, 0xab, 0x5a, 0xee, 0x42, 0xaa, 0x4d, 0x42,
     0x17, 0x60, 0x99, 0xd4, 0x5e, 0x13, 0x97, 0xdc, 0x40, 0x4d, 0x86, 0xa3,
     0x7b, 0xf5, 0x59, 0x54, 0x75, 0x69, 0x51, 0xe4 };
 static const unsigned char result_pr[OUTPUT_LEN] = {
     0x9a, 0x00, 0xa2, 0xd0, 0x0e, 0xd5, 0x9b, 0xfe, 0x31, 0xec, 0xb1, 0x39,
     0x9b, 0x60, 0x81, 0x48, 0xd1, 0x96, 0x9d, 0x25, 0x0d, 0x3c, 0x1e, 0x94,
     0x10, 0x10, 0x98, 0x12, 0x93, 0x25, 0xca, 0xb8, 0xfc, 0xcc, 0x2d, 0x54,
     0x73, 0x19, 0x70, 0xc0, 0x10, 0x7a, 0xa4, 0x89, 0x25, 0x19, 0x95, 0x5e,
     0x4b, 0xc6, 0x00, 0x1d, 0x7f, 0x4e, 0x6a, 0x2b, 0xf8, 0xa3, 0x01, 0xab,
     0x46, 0x05, 0x5c, 0x09, 0xa6, 0x71, 0x88, 0xf1, 0xa7, 0x40, 0xee, 0xf3,
     0xe1, 0x5c, 0x02, 0x9b, 0x44, 0xaf, 0x03, 0x44 };

 /* From a NIST PR=false test vector */
 static unsigned char entropy_nopr[] = {
     0x79, 0x34, 0x9b, 0xbf, 0x7c, 0xdd, 0xa5, 0x79, 0x95, 0x57, 0x86, 0x66,
     0x21, 0xc9, 0x13, 0x83, 0x11, 0x46, 0x73, 0x3a, 0xbf, 0x8c, 0x35, 0xc8,
     0xc7, 0x21, 0x5b, 0x5b, 0x96, 0xc4, 0x8e, 0x9b, 0x33, 0x8c, 0x74, 0xe3,
     0xe9, 0x9d, 0xfe, 0xdf };
 static const unsigned char result_nopr[OUTPUT_LEN] = {
     0xc6, 0xa1, 0x6a, 0xb8, 0xd4, 0x20, 0x70, 0x6f, 0x0f, 0x34, 0xab, 0x7f,
     0xec, 0x5a, 0xdc, 0xa9, 0xd8, 0xca, 0x3a, 0x13, 0x3e, 0x15, 0x9c, 0xa6,
     0xac, 0x43, 0xc6, 0xf8, 0xa2, 0xbe, 0x22, 0x83, 0x4a, 0x4c, 0x0a, 0x0a,
     0xff, 0xb1, 0x0d, 0x71, 0x94, 0xf1, 0xc1, 0xa5, 0xcf, 0x73, 0x22, 0xec,
     0x1a, 0xe0, 0x96, 0x4e, 0xd4, 0xbf, 0x12, 0x27, 0x46, 0xe0, 0x87, 0xfd,
     0xb5, 0xb3, 0xe9, 0x1b, 0x34, 0x93, 0xd5, 0xbb, 0x98, 0xfa, 0xed, 0x49,
     0xe8, 0x5f, 0x13, 0x0f, 0xc8, 0xa4, 0x59, 0xb7 };

 /* "Entropy" from buffer */
 static size_t test_offset;
 static int hmac_drbg_self_test_entropy( void *data,
                                         unsigned char *buf, size_t len )
 {
     const unsigned char *p = data;
     memcpy( buf, p + test_offset, len );
     test_offset += len;
     return( 0 );
 }

 #define CHK( c )    if( (c) != 0 )                          \
                     {                                       \
                         if( verbose != 0 )                  \
                             polarssl_printf( "failed\n" );  \
                         return( 1 );                        \
                     }

 /*
  * Checkup routine for HMAC_DRBG with SHA-1
  */
 int hmac_drbg_self_test( int verbose )
 {
     hmac_drbg_context ctx;
     unsigned char buf[OUTPUT_LEN];
     const md_info_t *md_info = md_info_from_type( POLARSSL_MD_SHA1 );

     /*
      * PR = True
      */
     if( verbose != 0 )
         polarssl_printf( "  HMAC_DRBG (PR = True) : " );

     test_offset = 0;
     CHK( hmac_drbg_init( &ctx, md_info,
                          hmac_drbg_self_test_entropy, entropy_pr,
                          NULL, 0 ) );
     hmac_drbg_set_prediction_resistance( &ctx, POLARSSL_HMAC_DRBG_PR_ON );
     CHK( hmac_drbg_random( &ctx, buf, OUTPUT_LEN ) );
     CHK( hmac_drbg_random( &ctx, buf, OUTPUT_LEN ) );
     CHK( memcmp( buf, result_pr, OUTPUT_LEN ) );
     hmac_drbg_free( &ctx );

     if( verbose != 0 )
         polarssl_printf( "passed\n" );

     /*
      * PR = False
      */
     if( verbose != 0 )
         polarssl_printf( "  HMAC_DRBG (PR = False) : " );

     test_offset = 0;
     CHK( hmac_drbg_init( &ctx, md_info,
                          hmac_drbg_self_test_entropy, entropy_nopr,
                          NULL, 0 ) );
     CHK( hmac_drbg_reseed( &ctx, NULL, 0 ) );
     CHK( hmac_drbg_random( &ctx, buf, OUTPUT_LEN ) );
     CHK( hmac_drbg_random( &ctx, buf, OUTPUT_LEN ) );
     CHK( memcmp( buf, result_nopr, OUTPUT_LEN ) );
     hmac_drbg_free( &ctx );

     if( verbose != 0 )
         polarssl_printf( "passed\n" );

     if( verbose != 0 )
         polarssl_printf( "\n" );

     return( 0 );
 }
 #endif /* POLARSSL_SHA1_C */
 #endif /* POLARSSL_SELF_TEST */

 #endif /* POLARSSL_HMAC_DRBG_C */
	/*
	* HMAC_DRBG implementation (NIST SP 800-90)
	*
	* Copyright (C) 2014, ARM Limited, All Rights Reserved
	*
	* This file is part of mbed TLS (https://www.polarssl.org)
	*
	* This program is free software; you can redistribute it and/or modify
	* it under the terms of the GNU General Public License as published by
	* the Free Software Foundation; either version 2 of the License, or
	* (at your option) any later version.
	*
	* This program is distributed in the hope that it will be useful,
	* but WITHOUT ANY WARRANTY; without even the implied warranty of
	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
	* GNU General Public License for more details.
	*
	* You should have received a copy of the GNU General Public License along
	* with this program; if not, write to the Free Software Foundation, Inc.,
	* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
	*/

	/*
	* The NIST SP 800-90A DRBGs are described in the following publication.
	* http://csrc.nist.gov/publications/nistpubs/800-90A/SP800-90A.pdf
	* References below are based on rev. 1 (January 2012).
	*/

	#if !defined(POLARSSL_CONFIG_FILE)
	#include "polarssl/config.h"
	#else
	#include POLARSSL_CONFIG_FILE
	#endif

	#if defined(POLARSSL_HMAC_DRBG_C)

	#include "polarssl/hmac_drbg.h"

	#if defined(POLARSSL_FS_IO)
	#include <stdio.h>
	#endif

	#if defined(POLARSSL_PLATFORM_C)
	#include "polarssl/platform.h"
	#else
	#define polarssl_printf printf
	#endif

	/* Implementation that should never be optimized out by the compiler */
	static void polarssl_zeroize( void *v, size_t n ) {
	volatile unsigned char p = v; while( n-- ) p++ = 0;
	}

	/*
	* HMAC_DRBG update, using optional additional data (10.1.2.2)
	*/
	void hmac_drbg_update( hmac_drbg_context *ctx,
	const unsigned char *additional, size_t add_len )
	{
	size_t md_len = ctx->md_ctx.md_info->size;
	unsigned char rounds = ( additional != NULL && add_len != 0 ) ? 2 : 1;
	unsigned char sep[1];
	unsigned char K[POLARSSL_MD_MAX_SIZE];

	for( sep[0] = 0; sep[0] < rounds; sep[0]++ )
	{
	/* Step 1 or 4 */
	md_hmac_reset( &ctx->md_ctx );
	md_hmac_update( &ctx->md_ctx, ctx->V, md_len );
	md_hmac_update( &ctx->md_ctx, sep, 1 );
	if( rounds == 2 )
	md_hmac_update( &ctx->md_ctx, additional, add_len );
	md_hmac_finish( &ctx->md_ctx, K );

	/* Step 2 or 5 */
	md_hmac_starts( &ctx->md_ctx, K, md_len );
	md_hmac_update( &ctx->md_ctx, ctx->V, md_len );
	md_hmac_finish( &ctx->md_ctx, ctx->V );
	}
	}

	/*
	* Simplified HMAC_DRBG initialisation (for use with deterministic ECDSA)
	*/
	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;

	memset( ctx, 0, sizeof( hmac_drbg_context ) );

	md_init( &ctx->md_ctx );

	if( ( ret = md_init_ctx( &ctx->md_ctx, md_info ) ) != 0 )
	return( ret );

	/*
	* Set initial working state.
	* Use the V memory location, which is currently all 0, to initialize the
	* MD context with an all-zero key. Then set V to its initial value.
	*/
	md_hmac_starts( &ctx->md_ctx, ctx->V, md_info->size );
	memset( ctx->V, 0x01, md_info->size );

	hmac_drbg_update( ctx, data, data_len );

	return( 0 );
	}

	/*
	* HMAC_DRBG reseeding: 10.1.2.4 (arabic) + 9.2 (Roman)
	*/
	int hmac_drbg_reseed( hmac_drbg_context *ctx,
	const unsigned char *additional, size_t len )
	{
	unsigned char seed[POLARSSL_HMAC_DRBG_MAX_SEED_INPUT];
	size_t seedlen;

	/* III. Check input length */
	if( len > POLARSSL_HMAC_DRBG_MAX_INPUT \|\|
	ctx->entropy_len + len > POLARSSL_HMAC_DRBG_MAX_SEED_INPUT )
	{
	return( POLARSSL_ERR_HMAC_DRBG_INPUT_TOO_BIG );
	}

	memset( seed, 0, POLARSSL_HMAC_DRBG_MAX_SEED_INPUT );

	/* IV. 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;

	/* 1. Concatenate entropy and 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 */
	ctx->reseed_counter = 1;

	/* 4. Done */
	return( 0 );
	}

	/*
	* HMAC_DRBG initialisation (10.1.2.3 + 9.1)
	*/
	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;
	size_t entropy_len;

	memset( ctx, 0, sizeof( hmac_drbg_context ) );

	md_init( &ctx->md_ctx );

	if( ( ret = md_init_ctx( &ctx->md_ctx, md_info ) ) != 0 )
	return( ret );

	/*
	* Set initial working state.
	* Use the V memory location, which is currently all 0, to initialize the
	* MD context with an all-zero key. Then set V to its initial value.
	*/
	md_hmac_starts( &ctx->md_ctx, ctx->V, md_info->size );
	memset( ctx->V, 0x01, md_info->size );

	ctx->f_entropy = f_entropy;
	ctx->p_entropy = p_entropy;

	ctx->reseed_interval = POLARSSL_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,
	* 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.)
	*/
	ctx->entropy_len = entropy_len * 3 / 2;

	if( ( ret = hmac_drbg_reseed( ctx, custom, len ) ) != 0 )
	return( ret );

	ctx->entropy_len = entropy_len;

	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
	*/
	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 (arabic) + 9.3 (Roman)
	*/
	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;

	/* II. Check request length */
	if( out_len > POLARSSL_HMAC_DRBG_MAX_REQUEST )
	return( POLARSSL_ERR_HMAC_DRBG_REQUEST_TOO_BIG );

	/* III. Check input length */
	if( add_len > POLARSSL_HMAC_DRBG_MAX_INPUT )
	return( POLARSSL_ERR_HMAC_DRBG_INPUT_TOO_BIG );

	/* 1. (aka VII and IX) Check reseed counter and PR */
	if( ctx->f_entropy != NULL && /* For no-reseeding instances */
	( ctx->prediction_resistance == POLARSSL_HMAC_DRBG_PR_ON \|\|
	ctx->reseed_counter > ctx->reseed_interval ) )
	{
	if( ( ret = hmac_drbg_reseed( ctx, additional, add_len ) ) != 0 )
	return( ret );

	add_len = 0; /* VII.4 */
	}

	/* 2. Use additional data if any */
	if( additional != NULL && add_len != 0 )
	hmac_drbg_update( ctx, additional, add_len );

	/* 3, 4, 5. Generate bytes */
	while( left != 0 )
	{
	size_t use_len = left > md_len ? md_len : left;

	md_hmac_reset( &ctx->md_ctx );
	md_hmac_update( &ctx->md_ctx, ctx->V, md_len );
	md_hmac_finish( &ctx->md_ctx, ctx->V );

	memcpy( out, ctx->V, use_len );
	out += use_len;
	left -= use_len;
	}

	/* 6. Update */
	hmac_drbg_update( ctx, additional, add_len );

	/* 7. Update reseed counter */
	ctx->reseed_counter++;

	/* 8. Done */
	return( 0 );
	}

	/*
	* HMAC_DRBG random function
	*/
	int hmac_drbg_random( void p_rng, unsigned char output, size_t out_len )
	{
	return( hmac_drbg_random_with_add( p_rng, output, out_len, NULL, 0 ) );
	}

	/*
	* Free an HMAC_DRBG context
	*/
	void hmac_drbg_free( hmac_drbg_context *ctx )
	{
	if( ctx == NULL )
	return;

	md_free_ctx( &ctx->md_ctx );

	polarssl_zeroize( ctx, sizeof( hmac_drbg_context ) );
	}

	#if defined(POLARSSL_FS_IO)
	int hmac_drbg_write_seed_file( hmac_drbg_context ctx, const char path )
	{
	int ret;
	FILE *f;
	unsigned char buf[ POLARSSL_HMAC_DRBG_MAX_INPUT ];

	if( ( f = fopen( path, "wb" ) ) == NULL )
	return( POLARSSL_ERR_HMAC_DRBG_FILE_IO_ERROR );

	if( ( ret = hmac_drbg_random( ctx, buf, sizeof( buf ) ) ) != 0 )
	goto exit;

	if( fwrite( buf, 1, sizeof( buf ), f ) != sizeof( buf ) )
	{
	ret = POLARSSL_ERR_HMAC_DRBG_FILE_IO_ERROR;
	goto exit;
	}

	ret = 0;

	exit:
	fclose( f );
	return( ret );
	}

	int hmac_drbg_update_seed_file( hmac_drbg_context ctx, const char path )
	{
	FILE *f;
	size_t n;
	unsigned char buf[ POLARSSL_HMAC_DRBG_MAX_INPUT ];

	if( ( f = fopen( path, "rb" ) ) == NULL )
	return( POLARSSL_ERR_HMAC_DRBG_FILE_IO_ERROR );

	fseek( f, 0, SEEK_END );
	n = (size_t) ftell( f );
	fseek( f, 0, SEEK_SET );

	if( n > POLARSSL_HMAC_DRBG_MAX_INPUT )
	{
	fclose( f );
	return( POLARSSL_ERR_HMAC_DRBG_INPUT_TOO_BIG );
	}

	if( fread( buf, 1, n, f ) != n )
	{
	fclose( f );
	return( POLARSSL_ERR_HMAC_DRBG_FILE_IO_ERROR );
	}

	fclose( f );

	hmac_drbg_update( ctx, buf, n );

	return( hmac_drbg_write_seed_file( ctx, path ) );
	}
	#endif /* POLARSSL_FS_IO */


	#if defined(POLARSSL_SELF_TEST)

	#include <stdio.h>

	#if !defined(POLARSSL_SHA1_C)
	/* Dummy checkup routine */
	int hmac_drbg_self_test( int verbose )
	{

	if( verbose != 0 )
	polarssl_printf( "\n" );

	return( 0 );
	}
	#else

	#define OUTPUT_LEN 80

	/* From a NIST PR=true test vector */
	static unsigned char entropy_pr[] = {
	0xa0, 0xc9, 0xab, 0x58, 0xf1, 0xe2, 0xe5, 0xa4, 0xde, 0x3e, 0xbd, 0x4f,
	0xf7, 0x3e, 0x9c, 0x5b, 0x64, 0xef, 0xd8, 0xca, 0x02, 0x8c, 0xf8, 0x11,
	0x48, 0xa5, 0x84, 0xfe, 0x69, 0xab, 0x5a, 0xee, 0x42, 0xaa, 0x4d, 0x42,
	0x17, 0x60, 0x99, 0xd4, 0x5e, 0x13, 0x97, 0xdc, 0x40, 0x4d, 0x86, 0xa3,
	0x7b, 0xf5, 0x59, 0x54, 0x75, 0x69, 0x51, 0xe4 };
	static const unsigned char result_pr[OUTPUT_LEN] = {
	0x9a, 0x00, 0xa2, 0xd0, 0x0e, 0xd5, 0x9b, 0xfe, 0x31, 0xec, 0xb1, 0x39,
	0x9b, 0x60, 0x81, 0x48, 0xd1, 0x96, 0x9d, 0x25, 0x0d, 0x3c, 0x1e, 0x94,
	0x10, 0x10, 0x98, 0x12, 0x93, 0x25, 0xca, 0xb8, 0xfc, 0xcc, 0x2d, 0x54,
	0x73, 0x19, 0x70, 0xc0, 0x10, 0x7a, 0xa4, 0x89, 0x25, 0x19, 0x95, 0x5e,
	0x4b, 0xc6, 0x00, 0x1d, 0x7f, 0x4e, 0x6a, 0x2b, 0xf8, 0xa3, 0x01, 0xab,
	0x46, 0x05, 0x5c, 0x09, 0xa6, 0x71, 0x88, 0xf1, 0xa7, 0x40, 0xee, 0xf3,
	0xe1, 0x5c, 0x02, 0x9b, 0x44, 0xaf, 0x03, 0x44 };

	/* From a NIST PR=false test vector */
	static unsigned char entropy_nopr[] = {
	0x79, 0x34, 0x9b, 0xbf, 0x7c, 0xdd, 0xa5, 0x79, 0x95, 0x57, 0x86, 0x66,
	0x21, 0xc9, 0x13, 0x83, 0x11, 0x46, 0x73, 0x3a, 0xbf, 0x8c, 0x35, 0xc8,
	0xc7, 0x21, 0x5b, 0x5b, 0x96, 0xc4, 0x8e, 0x9b, 0x33, 0x8c, 0x74, 0xe3,
	0xe9, 0x9d, 0xfe, 0xdf };
	static const unsigned char result_nopr[OUTPUT_LEN] = {
	0xc6, 0xa1, 0x6a, 0xb8, 0xd4, 0x20, 0x70, 0x6f, 0x0f, 0x34, 0xab, 0x7f,
	0xec, 0x5a, 0xdc, 0xa9, 0xd8, 0xca, 0x3a, 0x13, 0x3e, 0x15, 0x9c, 0xa6,
	0xac, 0x43, 0xc6, 0xf8, 0xa2, 0xbe, 0x22, 0x83, 0x4a, 0x4c, 0x0a, 0x0a,
	0xff, 0xb1, 0x0d, 0x71, 0x94, 0xf1, 0xc1, 0xa5, 0xcf, 0x73, 0x22, 0xec,
	0x1a, 0xe0, 0x96, 0x4e, 0xd4, 0xbf, 0x12, 0x27, 0x46, 0xe0, 0x87, 0xfd,
	0xb5, 0xb3, 0xe9, 0x1b, 0x34, 0x93, 0xd5, 0xbb, 0x98, 0xfa, 0xed, 0x49,
	0xe8, 0x5f, 0x13, 0x0f, 0xc8, 0xa4, 0x59, 0xb7 };

	/* "Entropy" from buffer */
	static size_t test_offset;
	static int hmac_drbg_self_test_entropy( void *data,
	unsigned char *buf, size_t len )
	{
	const unsigned char *p = data;
	memcpy( buf, p + test_offset, len );
	test_offset += len;
	return( 0 );
	}

	#define CHK( c ) if( (c) != 0 ) \
	{ \
	if( verbose != 0 ) \
	polarssl_printf( "failed\n" ); \
	return( 1 ); \
	}

	/*
	* Checkup routine for HMAC_DRBG with SHA-1
	*/
	int hmac_drbg_self_test( int verbose )
	{
	hmac_drbg_context ctx;
	unsigned char buf[OUTPUT_LEN];
	const md_info_t *md_info = md_info_from_type( POLARSSL_MD_SHA1 );

	/*
	* PR = True
	*/
	if( verbose != 0 )
	polarssl_printf( " HMAC_DRBG (PR = True) : " );

	test_offset = 0;
	CHK( hmac_drbg_init( &ctx, md_info,
	hmac_drbg_self_test_entropy, entropy_pr,
	NULL, 0 ) );
	hmac_drbg_set_prediction_resistance( &ctx, POLARSSL_HMAC_DRBG_PR_ON );
	CHK( hmac_drbg_random( &ctx, buf, OUTPUT_LEN ) );
	CHK( hmac_drbg_random( &ctx, buf, OUTPUT_LEN ) );
	CHK( memcmp( buf, result_pr, OUTPUT_LEN ) );
	hmac_drbg_free( &ctx );

	if( verbose != 0 )
	polarssl_printf( "passed\n" );

	/*
	* PR = False
	*/
	if( verbose != 0 )
	polarssl_printf( " HMAC_DRBG (PR = False) : " );

	test_offset = 0;
	CHK( hmac_drbg_init( &ctx, md_info,
	hmac_drbg_self_test_entropy, entropy_nopr,
	NULL, 0 ) );
	CHK( hmac_drbg_reseed( &ctx, NULL, 0 ) );
	CHK( hmac_drbg_random( &ctx, buf, OUTPUT_LEN ) );
	CHK( hmac_drbg_random( &ctx, buf, OUTPUT_LEN ) );
	CHK( memcmp( buf, result_nopr, OUTPUT_LEN ) );
	hmac_drbg_free( &ctx );

	if( verbose != 0 )
	polarssl_printf( "passed\n" );

	if( verbose != 0 )
	polarssl_printf( "\n" );

	return( 0 );
	}
	#endif /* POLARSSL_SHA1_C */
	#endif /* POLARSSL_SELF_TEST */

	#endif /* POLARSSL_HMAC_DRBG_C */