fc5ecaddd0
While stereotyped repetitions are frowned upon in literature, they serve a useful purpose in manual pages, because it is easier for the user to find certain information if it is always presented in the same way. For that reason, this commit harmonizes the varying formulations in the HISTORY section about which functions, flags, etc. were added in which OpenSSL version. It also attempts to make the pod files more grep friendly by avoiding to insert line breaks between the symbol names and the corresponding version number in which they were introduced (wherever possible). Some punctuation and typographical errors were fixed on the way. Reviewed-by: Tim Hudson <tjh@openssl.org> (Merged from https://github.com/openssl/openssl/pull/7854)
212 lines
7.4 KiB
Text
212 lines
7.4 KiB
Text
=pod
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=head1 NAME
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BN_generate_prime_ex, BN_is_prime_ex, BN_is_prime_fasttest_ex, BN_GENCB_call,
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BN_GENCB_new, BN_GENCB_free, BN_GENCB_set_old, BN_GENCB_set, BN_GENCB_get_arg,
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BN_generate_prime, BN_is_prime, BN_is_prime_fasttest - generate primes and test
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for primality
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=head1 SYNOPSIS
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#include <openssl/bn.h>
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int BN_generate_prime_ex(BIGNUM *ret, int bits, int safe, const BIGNUM *add,
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const BIGNUM *rem, BN_GENCB *cb);
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int BN_is_prime_ex(const BIGNUM *p, int nchecks, BN_CTX *ctx, BN_GENCB *cb);
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int BN_is_prime_fasttest_ex(const BIGNUM *p, int nchecks, BN_CTX *ctx,
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int do_trial_division, BN_GENCB *cb);
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int BN_GENCB_call(BN_GENCB *cb, int a, int b);
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BN_GENCB *BN_GENCB_new(void);
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void BN_GENCB_free(BN_GENCB *cb);
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void BN_GENCB_set_old(BN_GENCB *gencb,
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void (*callback)(int, int, void *), void *cb_arg);
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void BN_GENCB_set(BN_GENCB *gencb,
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int (*callback)(int, int, BN_GENCB *), void *cb_arg);
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void *BN_GENCB_get_arg(BN_GENCB *cb);
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Deprecated since OpenSSL 0.9.8, can be hidden entirely by defining
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B<OPENSSL_API_COMPAT> with a suitable version value, see
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L<openssl_user_macros(7)>:
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BIGNUM *BN_generate_prime(BIGNUM *ret, int num, int safe, BIGNUM *add,
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BIGNUM *rem, void (*callback)(int, int, void *),
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void *cb_arg);
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int BN_is_prime(const BIGNUM *a, int checks,
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void (*callback)(int, int, void *), BN_CTX *ctx, void *cb_arg);
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int BN_is_prime_fasttest(const BIGNUM *a, int checks,
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void (*callback)(int, int, void *), BN_CTX *ctx,
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void *cb_arg, int do_trial_division);
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=head1 DESCRIPTION
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BN_generate_prime_ex() generates a pseudo-random prime number of
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at least bit length B<bits>.
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If B<ret> is not B<NULL>, it will be used to store the number.
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If B<cb> is not B<NULL>, it is used as follows:
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=over 2
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=item *
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B<BN_GENCB_call(cb, 0, i)> is called after generating the i-th
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potential prime number.
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=item *
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While the number is being tested for primality,
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B<BN_GENCB_call(cb, 1, j)> is called as described below.
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=item *
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When a prime has been found, B<BN_GENCB_call(cb, 2, i)> is called.
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=item *
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The callers of BN_generate_prime_ex() may call B<BN_GENCB_call(cb, i, j)> with
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other values as described in their respective man pages; see L</SEE ALSO>.
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=back
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The prime may have to fulfill additional requirements for use in
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Diffie-Hellman key exchange:
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If B<add> is not B<NULL>, the prime will fulfill the condition p % B<add>
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== B<rem> (p % B<add> == 1 if B<rem> == B<NULL>) in order to suit a given
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generator.
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If B<safe> is true, it will be a safe prime (i.e. a prime p so
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that (p-1)/2 is also prime).
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The PRNG must be seeded prior to calling BN_generate_prime_ex().
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The prime number generation has a negligible error probability.
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BN_is_prime_ex() and BN_is_prime_fasttest_ex() test if the number B<p> is
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prime. The following tests are performed until one of them shows that
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B<p> is composite; if B<p> passes all these tests, it is considered
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prime.
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BN_is_prime_fasttest_ex(), when called with B<do_trial_division == 1>,
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first attempts trial division by a number of small primes;
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if no divisors are found by this test and B<cb> is not B<NULL>,
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B<BN_GENCB_call(cb, 1, -1)> is called.
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If B<do_trial_division == 0>, this test is skipped.
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Both BN_is_prime_ex() and BN_is_prime_fasttest_ex() perform a Miller-Rabin
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probabilistic primality test with B<nchecks> iterations. If
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B<nchecks == BN_prime_checks>, a number of iterations is used that
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yields a false positive rate of at most 2^-64 for random input.
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The error rate depends on the size of the prime and goes down for bigger primes.
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The rate is 2^-80 starting at 308 bits, 2^-112 at 852 bits, 2^-128 at 1080 bits,
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2^-192 at 3747 bits and 2^-256 at 6394 bits.
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When the source of the prime is not random or not trusted, the number
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of checks needs to be much higher to reach the same level of assurance:
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It should equal half of the targeted security level in bits (rounded up to the
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next integer if necessary).
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For instance, to reach the 128 bit security level, B<nchecks> should be set to
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64.
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If B<cb> is not B<NULL>, B<BN_GENCB_call(cb, 1, j)> is called
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after the j-th iteration (j = 0, 1, ...). B<ctx> is a
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pre-allocated B<BN_CTX> (to save the overhead of allocating and
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freeing the structure in a loop), or B<NULL>.
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BN_GENCB_call() calls the callback function held in the B<BN_GENCB> structure
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and passes the ints B<a> and B<b> as arguments. There are two types of
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B<BN_GENCB> structure that are supported: "new" style and "old" style. New
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programs should prefer the "new" style, whilst the "old" style is provided
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for backwards compatibility purposes.
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A B<BN_GENCB> structure should be created through a call to BN_GENCB_new(),
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and freed through a call to BN_GENCB_free().
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For "new" style callbacks a BN_GENCB structure should be initialised with a
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call to BN_GENCB_set(), where B<gencb> is a B<BN_GENCB *>, B<callback> is of
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type B<int (*callback)(int, int, BN_GENCB *)> and B<cb_arg> is a B<void *>.
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"Old" style callbacks are the same except they are initialised with a call
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to BN_GENCB_set_old() and B<callback> is of type
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B<void (*callback)(int, int, void *)>.
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A callback is invoked through a call to B<BN_GENCB_call>. This will check
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the type of the callback and will invoke B<callback(a, b, gencb)> for new
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style callbacks or B<callback(a, b, cb_arg)> for old style.
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It is possible to obtain the argument associated with a BN_GENCB structure
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(set via a call to BN_GENCB_set or BN_GENCB_set_old) using BN_GENCB_get_arg.
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BN_generate_prime() (deprecated) works in the same way as
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BN_generate_prime_ex() but expects an old-style callback function
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directly in the B<callback> parameter, and an argument to pass to it in
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the B<cb_arg>. BN_is_prime() and BN_is_prime_fasttest()
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can similarly be compared to BN_is_prime_ex() and
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BN_is_prime_fasttest_ex(), respectively.
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=head1 RETURN VALUES
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BN_generate_prime_ex() return 1 on success or 0 on error.
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BN_is_prime_ex(), BN_is_prime_fasttest_ex(), BN_is_prime() and
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BN_is_prime_fasttest() return 0 if the number is composite, 1 if it is
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prime with an error probability of less than 0.25^B<nchecks>, and
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-1 on error.
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BN_generate_prime() returns the prime number on success, B<NULL> otherwise.
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BN_GENCB_new returns a pointer to a BN_GENCB structure on success, or B<NULL>
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otherwise.
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BN_GENCB_get_arg returns the argument previously associated with a BN_GENCB
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structure.
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Callback functions should return 1 on success or 0 on error.
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The error codes can be obtained by L<ERR_get_error(3)>.
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=head1 REMOVED FUNCTIONALITY
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As of OpenSSL 1.1.0 it is no longer possible to create a BN_GENCB structure
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directly, as in:
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BN_GENCB callback;
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Instead applications should create a BN_GENCB structure using BN_GENCB_new:
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BN_GENCB *callback;
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callback = BN_GENCB_new();
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if (!callback)
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/* error */
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...
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BN_GENCB_free(callback);
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=head1 SEE ALSO
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L<DH_generate_parameters(3)>, L<DSA_generate_parameters(3)>,
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L<RSA_generate_key(3)>, L<ERR_get_error(3)>, L<RAND_bytes(3)>
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=head1 HISTORY
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The BN_GENCB_new(), BN_GENCB_free(),
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and BN_GENCB_get_arg() functions were added in OpenSSL 1.1.0.
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=head1 COPYRIGHT
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Copyright 2000-2018 The OpenSSL Project Authors. All Rights Reserved.
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Licensed under the Apache License 2.0 (the "License"). You may not use
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this file except in compliance with the License. You can obtain a copy
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in the file LICENSE in the source distribution or at
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L<https://www.openssl.org/source/license.html>.
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=cut
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