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[dragonfly.git] / secure / lib / libcrypto / man / BN_generate_prime.3
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129.\" ========================================================================
130.\"
131.IX Title "BN_generate_prime 3"
aac4ff6f 132.TH BN_generate_prime 3 "2008-09-06" "0.9.8h" "OpenSSL"
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133.SH "NAME"
134BN_generate_prime, BN_is_prime, BN_is_prime_fasttest \- generate primes and test for primality
135.SH "SYNOPSIS"
8b0cefbb 136.IX Header "SYNOPSIS"
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137.Vb 1
138\& #include <openssl/bn.h>
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139.Ve
140.PP
141.Vb 2
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142\& BIGNUM *BN_generate_prime(BIGNUM *ret, int num, int safe, BIGNUM *add,
143\& BIGNUM *rem, void (*callback)(int, int, void *), void *cb_arg);
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144.Ve
145.PP
146.Vb 2
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147\& int BN_is_prime(const BIGNUM *a, int checks, void (*callback)(int, int,
148\& void *), BN_CTX *ctx, void *cb_arg);
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149.Ve
150.PP
151.Vb 3
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152\& int BN_is_prime_fasttest(const BIGNUM *a, int checks,
153\& void (*callback)(int, int, void *), BN_CTX *ctx, void *cb_arg,
154\& int do_trial_division);
155.Ve
156.SH "DESCRIPTION"
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157.IX Header "DESCRIPTION"
158\&\fIBN_generate_prime()\fR generates a pseudo-random prime number of \fBnum\fR
984263bc 159bits.
8b0cefbb 160If \fBret\fR is not \fB\s-1NULL\s0\fR, it will be used to store the number.
984263bc 161.PP
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162If \fBcallback\fR is not \fB\s-1NULL\s0\fR, it is called as follows:
163.IP "\(bu" 4
164\&\fBcallback(0, i, cb_arg)\fR is called after generating the i\-th
984263bc 165potential prime number.
8b0cefbb 166.IP "\(bu" 4
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167While the number is being tested for primality, \fBcallback(1, j,
168cb_arg)\fR is called as described below.
8b0cefbb 169.IP "\(bu" 4
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170When a prime has been found, \fBcallback(2, i, cb_arg)\fR is called.
171.PP
172The prime may have to fulfill additional requirements for use in
173Diffie-Hellman key exchange:
174.PP
175If \fBadd\fR is not \fB\s-1NULL\s0\fR, the prime will fulfill the condition p % \fBadd\fR
176== \fBrem\fR (p % \fBadd\fR == 1 if \fBrem\fR == \fB\s-1NULL\s0\fR) in order to suit a given
177generator.
178.PP
179If \fBsafe\fR is true, it will be a safe prime (i.e. a prime p so
8b0cefbb 180that (p\-1)/2 is also prime).
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181.PP
182The \s-1PRNG\s0 must be seeded prior to calling \fIBN_generate_prime()\fR.
183The prime number generation has a negligible error probability.
184.PP
8b0cefbb 185\&\fIBN_is_prime()\fR and \fIBN_is_prime_fasttest()\fR test if the number \fBa\fR is
984263bc 186prime. The following tests are performed until one of them shows that
8b0cefbb 187\&\fBa\fR is composite; if \fBa\fR passes all these tests, it is considered
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188prime.
189.PP
8b0cefbb 190\&\fIBN_is_prime_fasttest()\fR, when called with \fBdo_trial_division == 1\fR,
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191first attempts trial division by a number of small primes;
192if no divisors are found by this test and \fBcallback\fR is not \fB\s-1NULL\s0\fR,
8b0cefbb 193\&\fBcallback(1, \-1, cb_arg)\fR is called.
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194If \fBdo_trial_division == 0\fR, this test is skipped.
195.PP
196Both \fIBN_is_prime()\fR and \fIBN_is_prime_fasttest()\fR perform a Miller-Rabin
197probabilistic primality test with \fBchecks\fR iterations. If
8b0cefbb 198\&\fBchecks == BN_prime_checks\fR, a number of iterations is used that
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199yields a false positive rate of at most 2^\-80 for random input.
200.PP
201If \fBcallback\fR is not \fB\s-1NULL\s0\fR, \fBcallback(1, j, cb_arg)\fR is called
8b0cefbb 202after the j\-th iteration (j = 0, 1, ...). \fBctx\fR is a
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203pre-allocated \fB\s-1BN_CTX\s0\fR (to save the overhead of allocating and
204freeing the structure in a loop), or \fB\s-1NULL\s0\fR.
205.SH "RETURN VALUES"
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206.IX Header "RETURN VALUES"
207\&\fIBN_generate_prime()\fR returns the prime number on success, \fB\s-1NULL\s0\fR otherwise.
984263bc 208.PP
8b0cefbb 209\&\fIBN_is_prime()\fR returns 0 if the number is composite, 1 if it is
984263bc 210prime with an error probability of less than 0.25^\fBchecks\fR, and
8b0cefbb 211\&\-1 on error.
984263bc 212.PP
8b0cefbb 213The error codes can be obtained by \fIERR_get_error\fR\|(3).
984263bc 214.SH "SEE ALSO"
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215.IX Header "SEE ALSO"
216\&\fIbn\fR\|(3), \fIERR_get_error\fR\|(3), \fIrand\fR\|(3)
984263bc 217.SH "HISTORY"
8b0cefbb 218.IX Header "HISTORY"
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219The \fBcb_arg\fR arguments to \fIBN_generate_prime()\fR and to \fIBN_is_prime()\fR
220were added in SSLeay 0.9.0. The \fBret\fR argument to \fIBN_generate_prime()\fR
221was added in SSLeay 0.9.1.
8b0cefbb 222\&\fIBN_is_prime_fasttest()\fR was added in OpenSSL 0.9.5.