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[dragonfly.git] / secure / lib / libcrypto / man / BN_generate_prime.3
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80.\" If the F register is turned on, we'll generate
81.\" index entries out stderr for the following things:
82.\" TH Title
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96.TH BN_generate_prime 3 "0.9.7d" "2/Sep/2004" "OpenSSL"
97.UC
98.if n .hy 0
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189.rm #[ #] #H #V #F C
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190.SH "NAME"
191BN_generate_prime, BN_is_prime, BN_is_prime_fasttest \- generate primes and test for primality
192.SH "SYNOPSIS"
74dab6c2 193.PP
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194.Vb 1
195\& #include <openssl/bn.h>
196.Ve
197.Vb 2
198\& BIGNUM *BN_generate_prime(BIGNUM *ret, int num, int safe, BIGNUM *add,
199\& BIGNUM *rem, void (*callback)(int, int, void *), void *cb_arg);
200.Ve
201.Vb 2
202\& int BN_is_prime(const BIGNUM *a, int checks, void (*callback)(int, int,
203\& void *), BN_CTX *ctx, void *cb_arg);
204.Ve
205.Vb 3
206\& int BN_is_prime_fasttest(const BIGNUM *a, int checks,
207\& void (*callback)(int, int, void *), BN_CTX *ctx, void *cb_arg,
208\& int do_trial_division);
209.Ve
210.SH "DESCRIPTION"
74dab6c2 211\fIBN_generate_prime()\fR generates a pseudo-random prime number of \fBnum\fR
984263bc 212bits.
74dab6c2 213If \fBret\fR is not \fBNULL\fR, it will be used to store the number.
984263bc 214.PP
74dab6c2 215If \fBcallback\fR is not \fBNULL\fR, it is called as follows:
984263bc 216.Ip "\(bu" 4
74dab6c2 217\fBcallback(0, i, cb_arg)\fR is called after generating the i-th
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218potential prime number.
219.Ip "\(bu" 4
220While the number is being tested for primality, \fBcallback(1, j,
221cb_arg)\fR is called as described below.
222.Ip "\(bu" 4
223When a prime has been found, \fBcallback(2, i, cb_arg)\fR is called.
224.PP
225The prime may have to fulfill additional requirements for use in
226Diffie-Hellman key exchange:
227.PP
228If \fBadd\fR is not \fB\s-1NULL\s0\fR, the prime will fulfill the condition p % \fBadd\fR
229== \fBrem\fR (p % \fBadd\fR == 1 if \fBrem\fR == \fB\s-1NULL\s0\fR) in order to suit a given
230generator.
231.PP
232If \fBsafe\fR is true, it will be a safe prime (i.e. a prime p so
233that (p-1)/2 is also prime).
234.PP
235The \s-1PRNG\s0 must be seeded prior to calling \fIBN_generate_prime()\fR.
236The prime number generation has a negligible error probability.
237.PP
74dab6c2 238\fIBN_is_prime()\fR and \fIBN_is_prime_fasttest()\fR test if the number \fBa\fR is
984263bc 239prime. The following tests are performed until one of them shows that
74dab6c2 240\fBa\fR is composite; if \fBa\fR passes all these tests, it is considered
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241prime.
242.PP
74dab6c2 243\fIBN_is_prime_fasttest()\fR, when called with \fBdo_trial_division == 1\fR,
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244first attempts trial division by a number of small primes;
245if no divisors are found by this test and \fBcallback\fR is not \fB\s-1NULL\s0\fR,
74dab6c2 246\fBcallback(1, \-1, cb_arg)\fR is called.
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247If \fBdo_trial_division == 0\fR, this test is skipped.
248.PP
249Both \fIBN_is_prime()\fR and \fIBN_is_prime_fasttest()\fR perform a Miller-Rabin
250probabilistic primality test with \fBchecks\fR iterations. If
74dab6c2 251\fBchecks == BN_prime_checks\fR, a number of iterations is used that
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252yields a false positive rate of at most 2^\-80 for random input.
253.PP
254If \fBcallback\fR is not \fB\s-1NULL\s0\fR, \fBcallback(1, j, cb_arg)\fR is called
255after the j-th iteration (j = 0, 1, ...). \fBctx\fR is a
256pre-allocated \fB\s-1BN_CTX\s0\fR (to save the overhead of allocating and
257freeing the structure in a loop), or \fB\s-1NULL\s0\fR.
258.SH "RETURN VALUES"
74dab6c2 259\fIBN_generate_prime()\fR returns the prime number on success, \fBNULL\fR otherwise.
984263bc 260.PP
74dab6c2 261\fIBN_is_prime()\fR returns 0 if the number is composite, 1 if it is
984263bc 262prime with an error probability of less than 0.25^\fBchecks\fR, and
74dab6c2 263\-1 on error.
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264.PP
265The error codes can be obtained by ERR_get_error(3).
266.SH "SEE ALSO"
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267bn(3), ERR_get_error(3), rand(3)
268.SH "HISTORY"
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269The \fBcb_arg\fR arguments to \fIBN_generate_prime()\fR and to \fIBN_is_prime()\fR
270were added in SSLeay 0.9.0. The \fBret\fR argument to \fIBN_generate_prime()\fR
271was added in SSLeay 0.9.1.
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272\fIBN_is_prime_fasttest()\fR was added in OpenSSL 0.9.5.
273
274.rn }` ''
275.IX Title "BN_generate_prime 3"
276.IX Name "BN_generate_prime, BN_is_prime, BN_is_prime_fasttest - generate primes and test for primality"
277
278.IX Header "NAME"
279
280.IX Header "SYNOPSIS"
281
282.IX Header "DESCRIPTION"
283
284.IX Item "\(bu"
285
286.IX Item "\(bu"
287
288.IX Item "\(bu"
289
290.IX Header "RETURN VALUES"
291
292.IX Header "SEE ALSO"
293
294.IX Header "HISTORY"
295