include/crypto/rand_pool.h

   1 /*
   2  * Copyright 1995-2021 The OpenSSL Project Authors. All Rights Reserved.
   3  *
   4  * Licensed under the Apache License 2.0 (the "License").  You may not use
   5  * this file except in compliance with the License.  You can obtain a copy
   6  * in the file LICENSE in the source distribution or at
   7  * https://www.openssl.org/source/license.html
   8  */
   9
  10 #ifndef OSSL_PROVIDER_RAND_POOL_H
  11 # define OSSL_PROVIDER_RAND_POOL_H
  12 # pragma once
  13
  14 # include <stdio.h>
  15 # include <openssl/rand.h>
  16
  17 /*
  18  * Maximum allocation size for RANDOM_POOL buffers
  19  *
  20  * The max_len value for the buffer provided to the rand_drbg_get_entropy()
  21  * callback is currently 2^31 bytes (2 gigabytes), if a derivation function
  22  * is used. Since this is much too large to be allocated, the rand_pool_new()
  23  * function chooses more modest values as default pool length, bounded
  24  * by RAND_POOL_MIN_LENGTH and RAND_POOL_MAX_LENGTH
  25  *
  26  * The choice of the RAND_POOL_FACTOR is large enough such that the
  27  * RAND_POOL can store a random input which has a lousy entropy rate of
  28  * 8/256 (= 0.03125) bits per byte. This input will be sent through the
  29  * derivation function which 'compresses' the low quality input into a
  30  * high quality output.
  31  *
  32  * The factor 1.5 below is the pessimistic estimate for the extra amount
  33  * of entropy required when no get_nonce() callback is defined.
  34  */
  35 # define RAND_POOL_FACTOR        256
  36 # define RAND_POOL_MAX_LENGTH    (RAND_POOL_FACTOR * \
  37                                   3 * (RAND_DRBG_STRENGTH / 16))
  38 /*
  39  *                             = (RAND_POOL_FACTOR * \
  40  *                                1.5 * (RAND_DRBG_STRENGTH / 8))
  41  */
  42
  43 /*
  44  * Initial allocation minimum.
  45  *
  46  * There is a distinction between the secure and normal allocation minimums.
  47  * Ideally, the secure allocation size should be a power of two.  The normal
  48  * allocation size doesn't have any such restriction.
  49  *
  50  * The secure value is based on 128 bits of secure material, which is 16 bytes.
  51  * Typically, the DRBGs will set a minimum larger than this so optimal
  52  * allocation ought to take place (for full quality seed material).
  53  *
  54  * The normal value has been chosen by noticing that the rand_drbg_get_nonce
  55  * function is usually the largest of the built in allocation (twenty four
  56  * bytes and then appending another sixteen bytes).  This means the buffer ends
  57  * with 40 bytes.  The value of forty eight is comfortably above this which
  58  * allows some slack in the platform specific values used.
  59  */
  60 # define RAND_POOL_MIN_ALLOCATION(secure) ((secure) ? 16 : 48)
  61
  62 /*
  63  * The 'random pool' acts as a dumb container for collecting random
  64  * input from various entropy sources. It is the callers duty to 1) initialize
  65  * the random pool, 2) pass it to the polling callbacks, 3) seed the RNG, and
  66  * 4) cleanup the random pool again.
  67  *
  68  * The random pool contains no locking mechanism because its scope and
  69  * lifetime is intended to be restricted to a single stack frame.
  70  */
  71 typedef struct rand_pool_st {
  72     unsigned char *buffer;  /* points to the beginning of the random pool */
  73     size_t len; /* current number of random bytes contained in the pool */
  74
  75     int attached;  /* true pool was attached to existing buffer */
  76     int secure;    /* 1: allocated on the secure heap, 0: otherwise */
  77
  78     size_t min_len; /* minimum number of random bytes requested */
  79     size_t max_len; /* maximum number of random bytes (allocated buffer size) */
  80     size_t alloc_len; /* current number of bytes allocated */
  81     size_t entropy; /* current entropy count in bits */
  82     size_t entropy_requested; /* requested entropy count in bits */
  83 } RAND_POOL;
  84
  85 RAND_POOL *rand_pool_new(int entropy_requested, int secure,
  86                          size_t min_len, size_t max_len);
  87 RAND_POOL *rand_pool_attach(const unsigned char *buffer, size_t len,
  88                             size_t entropy);
  89 void rand_pool_free(RAND_POOL *pool);
  90
  91 const unsigned char *rand_pool_buffer(RAND_POOL *pool);
  92 unsigned char *rand_pool_detach(RAND_POOL *pool);
  93 void rand_pool_reattach(RAND_POOL *pool, unsigned char *buffer);
  94
  95 size_t rand_pool_entropy(RAND_POOL *pool);
  96 size_t rand_pool_length(RAND_POOL *pool);
  97
  98 size_t rand_pool_entropy_available(RAND_POOL *pool);
  99 size_t rand_pool_entropy_needed(RAND_POOL *pool);
 100 /* |entropy_factor| expresses how many bits of data contain 1 bit of entropy */
 101 size_t rand_pool_bytes_needed(RAND_POOL *pool, unsigned int entropy_factor);
 102 size_t rand_pool_bytes_remaining(RAND_POOL *pool);
 103
 104 int rand_pool_add(RAND_POOL *pool,
 105                   const unsigned char *buffer, size_t len, size_t entropy);
 106 unsigned char *rand_pool_add_begin(RAND_POOL *pool, size_t len);
 107 int rand_pool_add_end(RAND_POOL *pool, size_t len, size_t entropy);
 108
 109 #endif /* OSSL_PROVIDER_RAND_POOL_H */