5 BN_generate_prime_ex2, BN_generate_prime_ex, BN_is_prime_ex, BN_check_prime,
6 BN_is_prime_fasttest_ex, BN_GENCB_call, BN_GENCB_new, BN_GENCB_free,
7 BN_GENCB_set_old, BN_GENCB_set, BN_GENCB_get_arg, BN_generate_prime,
8 BN_is_prime, BN_is_prime_fasttest - generate primes and test for primality
12 #include <openssl/bn.h>
14 int BN_generate_prime_ex2(BIGNUM *ret, int bits, int safe,
15 const BIGNUM *add, const BIGNUM *rem, BN_GENCB *cb,
18 int BN_generate_prime_ex(BIGNUM *ret, int bits, int safe, const BIGNUM *add,
19 const BIGNUM *rem, BN_GENCB *cb);
21 int BN_check_prime(const BIGNUM *p, BN_CTX *ctx, BN_GENCB *cb);
23 int BN_GENCB_call(BN_GENCB *cb, int a, int b);
25 BN_GENCB *BN_GENCB_new(void);
27 void BN_GENCB_free(BN_GENCB *cb);
29 void BN_GENCB_set_old(BN_GENCB *gencb,
30 void (*callback)(int, int, void *), void *cb_arg);
32 void BN_GENCB_set(BN_GENCB *gencb,
33 int (*callback)(int, int, BN_GENCB *), void *cb_arg);
35 void *BN_GENCB_get_arg(BN_GENCB *cb);
37 The following functions have been deprecated since OpenSSL 0.9.8, and can be
38 hidden entirely by defining B<OPENSSL_API_COMPAT> with a suitable version value,
39 see L<openssl_user_macros(7)>:
41 BIGNUM *BN_generate_prime(BIGNUM *ret, int num, int safe, BIGNUM *add,
42 BIGNUM *rem, void (*callback)(int, int, void *),
45 int BN_is_prime(const BIGNUM *p, int nchecks,
46 void (*callback)(int, int, void *), BN_CTX *ctx, void *cb_arg);
48 int BN_is_prime_fasttest(const BIGNUM *p, int nchecks,
49 void (*callback)(int, int, void *), BN_CTX *ctx,
50 void *cb_arg, int do_trial_division);
52 The following functions have been deprecated since OpenSSL 3.0, and can be
53 hidden entirely by defining B<OPENSSL_API_COMPAT> with a suitable version value,
54 see L<openssl_user_macros(7)>:
56 int BN_is_prime_ex(const BIGNUM *p, int nchecks, BN_CTX *ctx, BN_GENCB *cb);
58 int BN_is_prime_fasttest_ex(const BIGNUM *p, int nchecks, BN_CTX *ctx,
59 int do_trial_division, BN_GENCB *cb);
63 BN_generate_prime_ex2() generates a pseudo-random prime number of
64 at least bit length B<bits> using the BN_CTX provided in B<ctx>. The value of
65 B<ctx> must not be NULL.
67 The returned number is probably prime with a negligible error.
68 The maximum error rate is 2^-128.
69 It's 2^-287 for a 512 bit prime, 2^-435 for a 1024 bit prime,
70 2^-648 for a 2048 bit prime, and lower than 2^-882 for primes larger
73 If B<add> is B<NULL> the returned prime number will have exact bit
74 length B<bits> with the top most two bits set.
76 If B<ret> is not B<NULL>, it will be used to store the number.
78 If B<cb> is not B<NULL>, it is used as follows:
84 B<BN_GENCB_call(cb, 0, i)> is called after generating the i-th
85 potential prime number.
89 While the number is being tested for primality,
90 B<BN_GENCB_call(cb, 1, j)> is called as described below.
94 When a prime has been found, B<BN_GENCB_call(cb, 2, i)> is called.
98 The callers of BN_generate_prime_ex() may call B<BN_GENCB_call(cb, i, j)> with
99 other values as described in their respective man pages; see L</SEE ALSO>.
103 The prime may have to fulfill additional requirements for use in
104 Diffie-Hellman key exchange:
106 If B<add> is not B<NULL>, the prime will fulfill the condition p % B<add>
107 == B<rem> (p % B<add> == 1 if B<rem> == B<NULL>) in order to suit a given
110 If B<safe> is true, it will be a safe prime (i.e. a prime p so
111 that (p-1)/2 is also prime). If B<safe> is true, and B<rem> == B<NULL>
112 the condition will be p % B<add> == 3.
113 It is recommended that B<add> is a multiple of 4.
115 The random generator must be seeded prior to calling BN_generate_prime_ex().
116 If the automatic seeding or reseeding of the OpenSSL CSPRNG fails due to
117 external circumstances (see L<RAND(7)>), the operation will fail.
118 The random number generator configured for the OSSL_LIB_CTX associated with
121 BN_generate_prime_ex() is the same as BN_generate_prime_ex2() except that no
122 B<ctx> parameter is passed.
123 In this case the random number generator associated with the default OSSL_LIB_CTX
126 BN_check_prime(), BN_is_prime_ex(), BN_is_prime_fasttest_ex(), BN_is_prime()
127 and BN_is_prime_fasttest() test if the number B<p> is prime.
128 The functions tests until one of the tests shows that B<p> is composite,
129 or all the tests passed.
130 If B<p> passes all these tests, it is considered a probable prime.
132 The test performed on B<p> are trial division by a number of small primes
133 and rounds of the of the Miller-Rabin probabilistic primality test.
135 The functions do at least 64 rounds of the Miller-Rabin test giving a maximum
136 false positive rate of 2^-128.
137 If the size of B<p> is more than 2048 bits, they do at least 128 rounds
138 giving a maximum false positive rate of 2^-256.
140 If B<nchecks> is larger than the minimum above (64 or 128), B<nchecks>
141 rounds of the Miller-Rabin test will be done.
143 If B<do_trial_division> set to B<0>, the trial division will be skipped.
144 BN_is_prime_ex() and BN_is_prime() always skip the trial division.
146 BN_is_prime_ex(), BN_is_prime_fasttest_ex(), BN_is_prime()
147 and BN_is_prime_fasttest() are deprecated.
149 BN_is_prime_fasttest() and BN_is_prime() behave just like
150 BN_is_prime_fasttest_ex() and BN_is_prime_ex() respectively, but with the old
153 B<ctx> is a preallocated B<BN_CTX> (to save the overhead of allocating and
154 freeing the structure in a loop), or B<NULL>.
156 If the trial division is done, and no divisors are found and B<cb>
157 is not B<NULL>, B<BN_GENCB_call(cb, 1, -1)> is called.
159 After each round of the Miller-Rabin probabilistic primality test,
160 if B<cb> is not B<NULL>, B<BN_GENCB_call(cb, 1, j)> is called
161 with B<j> the iteration (j = 0, 1, ...).
163 BN_GENCB_call() calls the callback function held in the B<BN_GENCB> structure
164 and passes the ints B<a> and B<b> as arguments. There are two types of
165 B<BN_GENCB> structure that are supported: "new" style and "old" style. New
166 programs should prefer the "new" style, whilst the "old" style is provided
167 for backwards compatibility purposes.
169 A B<BN_GENCB> structure should be created through a call to BN_GENCB_new(),
170 and freed through a call to BN_GENCB_free().
172 For "new" style callbacks a BN_GENCB structure should be initialised with a
173 call to BN_GENCB_set(), where B<gencb> is a B<BN_GENCB *>, B<callback> is of
174 type B<int (*callback)(int, int, BN_GENCB *)> and B<cb_arg> is a B<void *>.
175 "Old" style callbacks are the same except they are initialised with a call
176 to BN_GENCB_set_old() and B<callback> is of type
177 B<void (*callback)(int, int, void *)>.
179 A callback is invoked through a call to B<BN_GENCB_call>. This will check
180 the type of the callback and will invoke B<callback(a, b, gencb)> for new
181 style callbacks or B<callback(a, b, cb_arg)> for old style.
183 It is possible to obtain the argument associated with a BN_GENCB structure
184 (set via a call to BN_GENCB_set or BN_GENCB_set_old) using BN_GENCB_get_arg.
186 BN_generate_prime() (deprecated) works in the same way as
187 BN_generate_prime_ex() but expects an old-style callback function
188 directly in the B<callback> parameter, and an argument to pass to it in
189 the B<cb_arg>. BN_is_prime() and BN_is_prime_fasttest()
190 can similarly be compared to BN_is_prime_ex() and
191 BN_is_prime_fasttest_ex(), respectively.
195 BN_generate_prime_ex() return 1 on success or 0 on error.
197 BN_is_prime_ex(), BN_is_prime_fasttest_ex(), BN_is_prime(),
198 BN_is_prime_fasttest() and BN_check_prime return 0 if the number is composite,
199 1 if it is prime with an error probability of less than 0.25^B<nchecks>, and
202 BN_generate_prime() returns the prime number on success, B<NULL> otherwise.
204 BN_GENCB_new returns a pointer to a BN_GENCB structure on success, or B<NULL>
207 BN_GENCB_get_arg returns the argument previously associated with a BN_GENCB
210 Callback functions should return 1 on success or 0 on error.
212 The error codes can be obtained by L<ERR_get_error(3)>.
214 =head1 REMOVED FUNCTIONALITY
216 As of OpenSSL 1.1.0 it is no longer possible to create a BN_GENCB structure
221 Instead applications should create a BN_GENCB structure using BN_GENCB_new:
224 callback = BN_GENCB_new();
228 BN_GENCB_free(callback);
232 L<DH_generate_parameters(3)>, L<DSA_generate_parameters(3)>,
233 L<RSA_generate_key(3)>, L<ERR_get_error(3)>, L<RAND_bytes(3)>,
238 The BN_is_prime_ex() and BN_is_prime_fasttest_ex() functions were
239 deprecated in OpenSSL 3.0.
241 The BN_GENCB_new(), BN_GENCB_free(),
242 and BN_GENCB_get_arg() functions were added in OpenSSL 1.1.0.
244 BN_check_prime() was added in OpenSSL 3.0.
248 Copyright 2000-2021 The OpenSSL Project Authors. All Rights Reserved.
250 Licensed under the Apache License 2.0 (the "License"). You may not use
251 this file except in compliance with the License. You can obtain a copy
252 in the file LICENSE in the source distribution or at
253 L<https://www.openssl.org/source/license.html>.