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      1 /*	$NetBSD: crypto-rand.c,v 1.2 2017/01/28 21:31:49 christos Exp $	*/
      2 
      3 /*
      4  * Copyright (c) 1997 - 2008 Kungliga Tekniska Hgskolan
      5  * (Royal Institute of Technology, Stockholm, Sweden).
      6  * All rights reserved.
      7  *
      8  * Redistribution and use in source and binary forms, with or without
      9  * modification, are permitted provided that the following conditions
     10  * are met:
     11  *
     12  * 1. Redistributions of source code must retain the above copyright
     13  *    notice, this list of conditions and the following disclaimer.
     14  *
     15  * 2. Redistributions in binary form must reproduce the above copyright
     16  *    notice, this list of conditions and the following disclaimer in the
     17  *    documentation and/or other materials provided with the distribution.
     18  *
     19  * 3. Neither the name of the Institute nor the names of its contributors
     20  *    may be used to endorse or promote products derived from this software
     21  *    without specific prior written permission.
     22  *
     23  * THIS SOFTWARE IS PROVIDED BY THE INSTITUTE AND CONTRIBUTORS ``AS IS'' AND
     24  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     25  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     26  * ARE DISCLAIMED.  IN NO EVENT SHALL THE INSTITUTE OR CONTRIBUTORS BE LIABLE
     27  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     28  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     29  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     30  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     31  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     32  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     33  * SUCH DAMAGE.
     34  */
     35 
     36 #include "krb5_locl.h"
     37 
     38 #undef HEIMDAL_WARN_UNUSED_RESULT_ATTRIBUTE
     39 #define HEIMDAL_WARN_UNUSED_RESULT_ATTRIBUTE
     40 
     41 #define ENTROPY_NEEDED 128
     42 
     43 static HEIMDAL_MUTEX crypto_mutex = HEIMDAL_MUTEX_INITIALIZER;
     44 
     45 static int
     46 seed_something(void)
     47 {
     48 #ifndef NO_RANDFILE
     49     char buf[1024], seedfile[256];
     50 
     51     /* If there is a seed file, load it. But such a file cannot be trusted,
     52        so use 0 for the entropy estimate */
     53     if (RAND_file_name(seedfile, sizeof(seedfile))) {
     54 	int fd;
     55 	fd = open(seedfile, O_RDONLY | O_BINARY | O_CLOEXEC);
     56 	if (fd >= 0) {
     57 	    ssize_t ret;
     58 	    rk_cloexec(fd);
     59 	    ret = read(fd, buf, sizeof(buf));
     60 	    if (ret > 0)
     61 		RAND_add(buf, ret, 0.0);
     62 	    close(fd);
     63 	} else
     64 	    seedfile[0] = '\0';
     65     } else
     66 	seedfile[0] = '\0';
     67 #endif
     68 
     69     /* Calling RAND_status() will try to use /dev/urandom if it exists so
     70        we do not have to deal with it. */
     71     if (RAND_status() != 1) {
     72 	/* TODO: Once a Windows CryptoAPI RAND method is defined, we
     73 	   can use that and failover to another method. */
     74     }
     75 
     76     if (RAND_status() == 1)	{
     77 #ifndef NO_RANDFILE
     78 	/* Update the seed file */
     79 	if (seedfile[0])
     80 	    RAND_write_file(seedfile);
     81 #endif
     82 
     83 	return 0;
     84     } else
     85 	return -1;
     86 }
     87 
     88 /**
     89  * Fill buffer buf with len bytes of PRNG randomness that is ok to use
     90  * for key generation, padding and public diclosing the randomness w/o
     91  * disclosing the randomness source.
     92  *
     93  * This function can fail, and callers must check the return value.
     94  *
     95  * @param buf a buffer to fill with randomness
     96  * @param len length of memory that buf points to.
     97  *
     98  * @return return 0 on success or HEIM_ERR_RANDOM_OFFLINE if the
     99  * funcation failed to initialize the randomness source.
    100  *
    101  * @ingroup krb5_crypto
    102  */
    103 
    104 HEIMDAL_WARN_UNUSED_RESULT_ATTRIBUTE
    105 KRB5_LIB_FUNCTION krb5_error_code KRB5_LIB_CALL
    106 krb5_generate_random(void *buf, size_t len)
    107 {
    108     static int rng_initialized = 0;
    109     int ret;
    110 
    111     HEIMDAL_MUTEX_lock(&crypto_mutex);
    112     if (!rng_initialized) {
    113 	if (seed_something()) {
    114             HEIMDAL_MUTEX_unlock(&crypto_mutex);
    115 	    return HEIM_ERR_RANDOM_OFFLINE;
    116         }
    117 	rng_initialized = 1;
    118     }
    119     if (RAND_bytes(buf, len) <= 0)
    120 	ret = HEIM_ERR_RANDOM_OFFLINE;
    121     else
    122 	ret = 0;
    123     HEIMDAL_MUTEX_unlock(&crypto_mutex);
    124 
    125     return ret;
    126 }
    127 
    128 /**
    129  * Fill buffer buf with len bytes of PRNG randomness that is ok to use
    130  * for key generation, padding and public diclosing the randomness w/o
    131  * disclosing the randomness source.
    132  *
    133  * This function can NOT fail, instead it will abort() and program will crash.
    134  *
    135  * If this function is called after a successful krb5_init_context(),
    136  * the chance of it failing is low due to that krb5_init_context()
    137  * pulls out some random, and quite commonly the randomness sources
    138  * will not fail once it have started to produce good output,
    139  * /dev/urandom behavies that way.
    140  *
    141  * @param buf a buffer to fill with randomness
    142  * @param len length of memory that buf points to.
    143  *
    144  * @ingroup krb5_crypto
    145  */
    146 
    147 
    148 KRB5_LIB_FUNCTION void KRB5_LIB_CALL
    149 krb5_generate_random_block(void *buf, size_t len)
    150 {
    151     int ret = krb5_generate_random(buf, len);
    152     if (ret)
    153 	krb5_abortx(NULL, "Failed to generate random block");
    154 }
    155