NetBSD/lib/libcrypto/man/BN_generate_prime.3

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.TH BN_generate_prime 3 "0.9.5a" "22/Jul/100" "OpenSSL"
.UC
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.rm #[ #] #H #V #F C
.SH "NAME"
BN_generate_prime, BN_is_prime, BN_is_prime_fasttest \- generate primes and test for primality
.SH "LIBRARY"
libcrypto, -lcrypto
.SH "SYNOPSIS"
.PP
.Vb 1
\& #include <openssl/bn.h>
.Ve
.Vb 2
\& BIGNUM *BN_generate_prime(BIGNUM *ret, int num, int safe, BIGNUM *add,
\& BIGNUM *rem, void (*callback)(int, int, void *), void *cb_arg);
.Ve
.Vb 2
\& int BN_is_prime(const BIGNUM *a, int checks, void (*callback)(int, int,
\& void *), BN_CTX *ctx, void *cb_arg);
.Ve
.Vb 3
\& int BN_is_prime_fasttest(const BIGNUM *a, int checks,
\& void (*callback)(int, int, void *), BN_CTX *ctx, void *cb_arg,
\& int do_trial_division);
.Ve
.SH "DESCRIPTION"
\fIBN_generate_prime()\fR generates a pseudo-random prime number of \fBnum\fR
bits.
If \fBret\fR is not \fBNULL\fR, it will be used to store the number.
.PP
If \fBcallback\fR is not \fBNULL\fR, it is called as follows:
.Ip "\(bu" 4
\fBcallback(0, i, cb_arg)\fR is called after generating the i-th
potential prime number.
.Ip "\(bu" 4
While the number is being tested for primality, \fBcallback(1, j,
cb_arg)\fR is called as described below.
.Ip "\(bu" 4
When a prime has been found, \fBcallback(2, i, cb_arg)\fR is called.
.PP
The prime may have to fulfill additional requirements for use in
Diffie-Hellman key exchange:
.PP
If \fBadd\fR is not \fB\s-1NULL\s0\fR, the prime will fulfill the condition p % \fBadd\fR
== \fBrem\fR (p % \fBadd\fR == 1 if \fBrem\fR == \fB\s-1NULL\s0\fR) in order to suit a given
generator.
.PP
If \fBsafe\fR is true, it will be a safe prime (i.e. a prime p so
that (p-1)/2 is also prime).
.PP
The \s-1PRNG\s0 must be seeded prior to calling \fIBN_generate_prime()\fR.
The prime number generation has a negligible error probability.
.PP
\fIBN_is_prime()\fR and \fIBN_is_prime_fasttest()\fR test if the number \fBa\fR is
prime. The following tests are performed until one of them shows that
\fBa\fR is composite; if \fBa\fR passes all these tests, it is considered
prime.
.PP
\fIBN_is_prime_fasttest()\fR, when called with \fBdo_trial_division == 1\fR,
first attempts trial division by a number of small primes;
if no divisors are found by this test and \fBcallback\fR is not \fB\s-1NULL\s0\fR,
\fBcallback(1, \-1, cb_arg)\fR is called.
If \fBdo_trial_division == 0\fR, this test is skipped.
.PP
Both \fIBN_is_prime()\fR and \fIBN_is_prime_fasttest()\fR perform a Miller-Rabin
probabilistic primality test with \fBchecks\fR iterations. If
\fBchecks == BN_prime_check\fR, a number of iterations is used that
yields a false positive rate of at most 2^\-80 for random input.
.PP
If \fBcallback\fR is not \fB\s-1NULL\s0\fR, \fBcallback(1, j, cb_arg)\fR is called
after the j-th iteration (j = 0, 1, ...). \fBctx\fR is a
pre-allocated \fB\s-1BN_CTX\s0\fR (to save the overhead of allocating and
freeing the structure in a loop), or \fB\s-1NULL\s0\fR.
.SH "RETURN VALUES"
\fIBN_generate_prime()\fR returns the prime number on success, \fBNULL\fR otherwise.
.PP
\fIBN_is_prime()\fR returns 0 if the number is composite, 1 if it is
prime with an error probability of less than 0.25^\fBchecks\fR, and
\-1 on error.
.PP
The error codes can be obtained by the \fIERR_get_error(3)|ERR_get_error(3)\fR manpage.
.SH "SEE ALSO"
the \fIbn(3)|bn(3)\fR manpage, the \fIerr(3)|err(3)\fR manpage, the \fIrand(3)|rand(3)\fR manpage
.SH "HISTORY"
The \fBcb_arg\fR arguments to \fIBN_generate_prime()\fR and to \fIBN_is_prime()\fR
were added in SSLeay 0.9.0. The \fBret\fR argument to \fIBN_generate_prime()\fR
was added in SSLeay 0.9.1.
\fIBN_is_prime_fasttest()\fR was added in OpenSSL 0.9.5.
.rn }` ''
.IX Title "BN_generate_prime 3"
.IX Name "BN_generate_prime, BN_is_prime, BN_is_prime_fasttest - generate primes and test for primality"
.IX Header "NAME"
.IX Header "SYNOPSIS"
.IX Header "DESCRIPTION"
.IX Item "\(bu"
.IX Item "\(bu"
.IX Item "\(bu"
.IX Header "RETURN VALUES"
.IX Header "SEE ALSO"
.IX Header "HISTORY"