5 BN_generate_prime_ex, BN_is_prime_ex, BN_is_prime_fasttest_ex, BN_GENCB_call,
6 BN_GENCB_new, BN_GENCB_free, BN_GENCB_set_old, BN_GENCB_set, BN_GENCB_get_arg,
7 BN_generate_prime, BN_is_prime, BN_is_prime_fasttest - generate primes and test
12 #include <openssl/bn.h>
14 int BN_generate_prime_ex(BIGNUM *ret, int bits, int safe, const BIGNUM *add,
15 const BIGNUM *rem, BN_GENCB *cb);
17 int BN_is_prime_ex(const BIGNUM *p, int nchecks, BN_CTX *ctx, BN_GENCB *cb);
19 int BN_is_prime_fasttest_ex(const BIGNUM *p, int nchecks, BN_CTX *ctx,
20 int do_trial_division, BN_GENCB *cb);
22 int BN_GENCB_call(BN_GENCB *cb, int a, int b);
24 BN_GENCB *BN_GENCB_new(void);
26 void BN_GENCB_free(BN_GENCB *cb);
28 void BN_GENCB_set_old(BN_GENCB *gencb,
29 void (*callback)(int, int, void *), void *cb_arg);
31 void BN_GENCB_set(BN_GENCB *gencb,
32 int (*callback)(int, int, BN_GENCB *), void *cb_arg);
34 void *BN_GENCB_get_arg(BN_GENCB *cb);
38 #if OPENSSL_API_COMPAT < 0x00908000L
39 BIGNUM *BN_generate_prime(BIGNUM *ret, int num, int safe, BIGNUM *add,
40 BIGNUM *rem, void (*callback)(int, int, void *),
43 int BN_is_prime(const BIGNUM *a, int checks,
44 void (*callback)(int, int, void *), BN_CTX *ctx, void *cb_arg);
46 int BN_is_prime_fasttest(const BIGNUM *a, int checks,
47 void (*callback)(int, int, void *), BN_CTX *ctx,
48 void *cb_arg, int do_trial_division);
53 BN_generate_prime_ex() generates a pseudo-random prime number of
54 at least bit length B<bits>.
55 If B<ret> is not B<NULL>, it will be used to store the number.
57 If B<cb> is not B<NULL>, it is used as follows:
63 B<BN_GENCB_call(cb, 0, i)> is called after generating the i-th
64 potential prime number.
68 While the number is being tested for primality,
69 B<BN_GENCB_call(cb, 1, j)> is called as described below.
73 When a prime has been found, B<BN_GENCB_call(cb, 2, i)> is called.
77 The prime may have to fulfill additional requirements for use in
78 Diffie-Hellman key exchange:
80 If B<add> is not B<NULL>, the prime will fulfill the condition p % B<add>
81 == B<rem> (p % B<add> == 1 if B<rem> == B<NULL>) in order to suit a given
84 If B<safe> is true, it will be a safe prime (i.e. a prime p so
85 that (p-1)/2 is also prime).
87 The PRNG must be seeded prior to calling BN_generate_prime_ex().
88 The prime number generation has a negligible error probability.
90 BN_is_prime_ex() and BN_is_prime_fasttest_ex() test if the number B<p> is
91 prime. The following tests are performed until one of them shows that
92 B<p> is composite; if B<p> passes all these tests, it is considered
95 BN_is_prime_fasttest_ex(), when called with B<do_trial_division == 1>,
96 first attempts trial division by a number of small primes;
97 if no divisors are found by this test and B<cb> is not B<NULL>,
98 B<BN_GENCB_call(cb, 1, -1)> is called.
99 If B<do_trial_division == 0>, this test is skipped.
101 Both BN_is_prime_ex() and BN_is_prime_fasttest_ex() perform a Miller-Rabin
102 probabilistic primality test with B<nchecks> iterations. If
103 B<nchecks == BN_prime_checks>, a number of iterations is used that
104 yields a false positive rate of at most 2^-64 for random input.
105 The error rate depends on the size of the prime and goes down for bigger primes.
106 The rate is 2^-80 starting at 308 bits, 2^-112 at 852 bit, 2^-128 at 1080 bits,
107 2^-192 at 3747 bit and 2^-256 at 6394 bit.
109 When the source of the prime is not random or not trusted, the number
110 of checks needs to be much higher to reach the same level of assurance:
111 It should equal half of the targeted security level in bits (rounded up to the
112 next integer if necessary).
113 For instance, to reach the 128 bit security level, B<nchecks> should be set to
116 If B<cb> is not B<NULL>, B<BN_GENCB_call(cb, 1, j)> is called
117 after the j-th iteration (j = 0, 1, ...). B<ctx> is a
118 pre-allocated B<BN_CTX> (to save the overhead of allocating and
119 freeing the structure in a loop), or B<NULL>.
121 BN_GENCB_call() calls the callback function held in the B<BN_GENCB> structure
122 and passes the ints B<a> and B<b> as arguments. There are two types of
123 B<BN_GENCB> structure that are supported: "new" style and "old" style. New
124 programs should prefer the "new" style, whilst the "old" style is provided
125 for backwards compatibility purposes.
127 A B<BN_GENCB> structure should be created through a call to BN_GENCB_new(),
128 and freed through a call to BN_GENCB_free().
130 For "new" style callbacks a BN_GENCB structure should be initialised with a
131 call to BN_GENCB_set(), where B<gencb> is a B<BN_GENCB *>, B<callback> is of
132 type B<int (*callback)(int, int, BN_GENCB *)> and B<cb_arg> is a B<void *>.
133 "Old" style callbacks are the same except they are initialised with a call
134 to BN_GENCB_set_old() and B<callback> is of type
135 B<void (*callback)(int, int, void *)>.
137 A callback is invoked through a call to B<BN_GENCB_call>. This will check
138 the type of the callback and will invoke B<callback(a, b, gencb)> for new
139 style callbacks or B<callback(a, b, cb_arg)> for old style.
141 It is possible to obtained the argument associated with a BN_GENCB structure
142 (set via a call to BN_GENCB_set or BN_GENCB_set_old) using BN_GENCB_get_arg.
144 BN_generate_prime() (deprecated) works in the same way as
145 BN_generate_prime_ex() but expects an old-style callback function
146 directly in the B<callback> parameter, and an argument to pass to it in
147 the B<cb_arg>. BN_is_prime() and BN_is_prime_fasttest()
148 can similarly be compared to BN_is_prime_ex() and
149 BN_is_prime_fasttest_ex(), respectively.
153 BN_generate_prime_ex() return 1 on success or 0 on error.
155 BN_is_prime_ex(), BN_is_prime_fasttest_ex(), BN_is_prime() and
156 BN_is_prime_fasttest() return 0 if the number is composite, 1 if it is
157 prime with an error probability of less than 0.25^B<nchecks>, and
160 BN_generate_prime() returns the prime number on success, B<NULL> otherwise.
162 BN_GENCB_new returns a pointer to a BN_GENCB structure on success, or B<NULL>
165 BN_GENCB_get_arg returns the argument previously associated with a BN_GENCB
168 Callback functions should return 1 on success or 0 on error.
170 The error codes can be obtained by L<ERR_get_error(3)>.
172 =head1 REMOVED FUNCTIONALITY
174 As of OpenSSL 1.1.0 it is no longer possible to create a BN_GENCB structure
179 Instead applications should create a BN_GENCB structure using BN_GENCB_new:
182 callback = BN_GENCB_new();
186 BN_GENCB_free(callback);
190 L<ERR_get_error(3)>, L<RAND_bytes(3)>
194 BN_GENCB_new(), BN_GENCB_free(),
195 and BN_GENCB_get_arg() were added in OpenSSL 1.1.0
199 Copyright 2000-2017 The OpenSSL Project Authors. All Rights Reserved.
201 Licensed under the OpenSSL license (the "License"). You may not use
202 this file except in compliance with the License. You can obtain a copy
203 in the file LICENSE in the source distribution or at
204 L<https://www.openssl.org/source/license.html>.