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1 | =pod |
2 | ||
3 | =head1 NAME | |
4 | ||
5 | RAND_DRBG_set_callbacks, | |
6 | RAND_DRBG_get_entropy_fn, | |
7 | RAND_DRBG_cleanup_entropy_fn, | |
8 | RAND_DRBG_get_nonce_fn, | |
9 | RAND_DRBG_cleanup_nonce_fn | |
10 | - set callbacks for reseeding | |
11 | ||
12 | =head1 SYNOPSIS | |
13 | ||
14 | #include <openssl/rand_drbg.h> | |
15 | ||
16 | ||
17 | int RAND_DRBG_set_callbacks(RAND_DRBG *drbg, | |
18 | RAND_DRBG_get_entropy_fn get_entropy, | |
19 | RAND_DRBG_cleanup_entropy_fn cleanup_entropy, | |
20 | RAND_DRBG_get_nonce_fn get_nonce, | |
21 | RAND_DRBG_cleanup_nonce_fn cleanup_nonce); | |
22 | ||
23 | ||
24 | =head2 Callback Functions | |
25 | ||
26 | typedef size_t (*RAND_DRBG_get_entropy_fn)( | |
27 | RAND_DRBG *drbg, | |
28 | unsigned char **pout, | |
29 | int entropy, | |
30 | size_t min_len, size_t max_len, | |
31 | int prediction_resistance); | |
32 | ||
33 | typedef void (*RAND_DRBG_cleanup_entropy_fn)( | |
34 | RAND_DRBG *drbg, | |
35 | unsigned char *out, size_t outlen); | |
36 | ||
37 | typedef size_t (*RAND_DRBG_get_nonce_fn)( | |
38 | RAND_DRBG *drbg, | |
39 | unsigned char **pout, | |
40 | int entropy, | |
41 | size_t min_len, size_t max_len); | |
42 | ||
43 | typedef void (*RAND_DRBG_cleanup_nonce_fn)( | |
44 | RAND_DRBG *drbg, | |
45 | unsigned char *out, size_t outlen); | |
46 | ||
47 | ||
48 | ||
49 | =head1 DESCRIPTION | |
50 | ||
51 | RAND_DRBG_set_callbacks() sets the callbacks for obtaining fresh entropy and | |
52 | the nonce when reseeding the given B<drbg>. | |
53 | The callback functions are implemented and provided by the caller. | |
54 | Their parameter lists need to match the function prototypes above. | |
55 | ||
56 | Setting the callbacks is allowed only if the DRBG has not been initialized yet. | |
57 | Otherwise, the operation will fail. | |
58 | To change the settings for one of the three shared DRBGs it is necessary to call | |
59 | RAND_DRBG_uninstantiate() first. | |
60 | ||
61 | The B<get_entropy>() callback is called by the B<drbg> when it requests fresh | |
62 | random input. | |
63 | It is expected that the callback allocates and fills a random buffer of size | |
64 | B<min_len> <= size <= B<max_len> (in bytes) which contains at least B<entropy> | |
65 | bits of randomness. | |
66 | The B<prediction_resistance> flag indicates whether the reseeding was | |
67 | triggered by a prediction resistance request. | |
68 | ||
69 | The buffer's address is to be returned in *B<pout> and the number of collected | |
70 | randomness bytes as return value. | |
71 | ||
72 | If the callback fails to acquire at least B<entropy> bits of randomness, | |
73 | it must indicate an error by returning a buffer length of 0. | |
74 | ||
75 | If B<prediction_resistance> was requested and the random source of the DRBG | |
76 | does not satisfy the conditions requested by [NIST SP 800-90C], then | |
77 | it must also indicate an error by returning a buffer length of 0. | |
78 | See NOTES section for more details. | |
79 | ||
80 | The B<cleanup_entropy>() callback is called from the B<drbg> to to clear and | |
81 | free the buffer allocated previously by get_entropy(). | |
f7bef277 | 82 | The values B<out> and B<outlen> are the random buffer's address and length, |
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83 | as returned by the get_entropy() callback. |
84 | ||
85 | The B<get_nonce>() and B<cleanup_nonce>() callbacks are used to obtain a nonce | |
86 | and free it again. A nonce is only required for instantiation (not for reseeding) | |
87 | and only in the case where the DRBG uses a derivation function. | |
88 | The callbacks are analogous to get_entropy() and cleanup_entropy(), | |
89 | except for the missing prediction_resistance flag. | |
90 | ||
91 | If the derivation function is disabled, then no nonce is used for instantiation, | |
92 | and the B<get_nonce>() and B<cleanup_nonce>() callbacks can be omitted by | |
93 | setting them to NULL. | |
94 | ||
95 | ||
96 | =head1 RETURN VALUES | |
97 | ||
98 | RAND_DRBG_set_callbacks() return 1 on success, and 0 on failure | |
99 | ||
100 | =head1 NOTES | |
101 | ||
102 | It is important that B<cleanup_entropy>() and B<cleanup_nonce>() clear the buffer | |
103 | contents safely before freeing it, in order not to leave sensitive information | |
104 | about the DRBG's state in memory. | |
105 | ||
106 | A request for prediction resistance can only be satisfied by pulling fresh | |
65175163 P |
107 | entropy from a live entropy source (section 5.5.2 of [NIST SP 800-90C]). |
108 | It is up to the user to ensure that a live entropy source is configured | |
109 | and is being used. | |
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110 | |
111 | The derivation function is disabled during initialization by calling the | |
112 | RAND_DRBG_set() function with the RAND_DRBG_FLAG_CTR_NO_DF flag. | |
113 | For more information on the derivation function and when it can be omitted, | |
114 | see [NIST SP 800-90A Rev. 1]. Roughly speeking it can be omitted if the random | |
115 | source has "full entropy", i.e., contains 8 bits of entropy per byte. | |
116 | ||
117 | Even if a nonce is required, the B<get_nonce>() and B<cleanup_nonce>() | |
118 | callbacks can be omitted by setting them to NULL. | |
119 | In this case the DRBG will automatically request an extra amount of entropy | |
120 | (using the B<get_entropy>() and B<cleanup_entropy>() callbacks) which it will | |
121 | utilize for the nonce, following the recommendations of [NIST SP 800-90A Rev. 1], | |
122 | section 8.6.7. | |
123 | ||
124 | ||
125 | =head1 HISTORY | |
126 | ||
127 | The RAND_DRBG functions were added in OpenSSL 1.1.1. | |
128 | ||
129 | =head1 SEE ALSO | |
130 | ||
131 | L<RAND_DRBG_new(3)>, | |
132 | L<RAND_DRBG_reseed(3)>, | |
133 | L<RAND_DRBG(7)> | |
134 | ||
135 | =head1 COPYRIGHT | |
136 | ||
137 | Copyright 2017-2018 The OpenSSL Project Authors. All Rights Reserved. | |
138 | ||
4746f25a | 139 | Licensed under the Apache License 2.0 (the "License"). You may not use |
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140 | this file except in compliance with the License. You can obtain a copy |
141 | in the file LICENSE in the source distribution or at | |
142 | L<https://www.openssl.org/source/license.html>. | |
143 | ||
144 | =cut |