Update files for OpenSSL-1.0.0f import.
[dragonfly.git] / secure / lib / libcrypto / man / BN_generate_prime.3
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124.\" ========================================================================
125.\"
126.IX Title "BN_generate_prime 3"
e3261593 127.TH BN_generate_prime 3 "2012-01-04" "1.0.0f" "OpenSSL"
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128.\" For nroff, turn off justification. Always turn off hyphenation; it makes
129.\" way too many mistakes in technical documents.
130.if n .ad l
131.nh
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132.SH "NAME"
133BN_generate_prime, BN_is_prime, BN_is_prime_fasttest \- generate primes and test for primality
134.SH "SYNOPSIS"
8b0cefbb 135.IX Header "SYNOPSIS"
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136.Vb 1
137\& #include <openssl/bn.h>
e257b235 138\&
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139\& BIGNUM *BN_generate_prime(BIGNUM *ret, int num, int safe, BIGNUM *add,
140\& BIGNUM *rem, void (*callback)(int, int, void *), void *cb_arg);
e257b235 141\&
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142\& int BN_is_prime(const BIGNUM *a, int checks, void (*callback)(int, int,
143\& void *), BN_CTX *ctx, void *cb_arg);
e257b235 144\&
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145\& int BN_is_prime_fasttest(const BIGNUM *a, int checks,
146\& void (*callback)(int, int, void *), BN_CTX *ctx, void *cb_arg,
147\& int do_trial_division);
148.Ve
149.SH "DESCRIPTION"
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150.IX Header "DESCRIPTION"
151\&\fIBN_generate_prime()\fR generates a pseudo-random prime number of \fBnum\fR
984263bc 152bits.
8b0cefbb 153If \fBret\fR is not \fB\s-1NULL\s0\fR, it will be used to store the number.
984263bc 154.PP
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155If \fBcallback\fR is not \fB\s-1NULL\s0\fR, it is called as follows:
156.IP "\(bu" 4
157\&\fBcallback(0, i, cb_arg)\fR is called after generating the i\-th
984263bc 158potential prime number.
8b0cefbb 159.IP "\(bu" 4
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160While the number is being tested for primality, \fBcallback(1, j,
161cb_arg)\fR is called as described below.
8b0cefbb 162.IP "\(bu" 4
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163When a prime has been found, \fBcallback(2, i, cb_arg)\fR is called.
164.PP
165The prime may have to fulfill additional requirements for use in
166Diffie-Hellman key exchange:
167.PP
168If \fBadd\fR is not \fB\s-1NULL\s0\fR, the prime will fulfill the condition p % \fBadd\fR
169== \fBrem\fR (p % \fBadd\fR == 1 if \fBrem\fR == \fB\s-1NULL\s0\fR) in order to suit a given
170generator.
171.PP
172If \fBsafe\fR is true, it will be a safe prime (i.e. a prime p so
8b0cefbb 173that (p\-1)/2 is also prime).
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174.PP
175The \s-1PRNG\s0 must be seeded prior to calling \fIBN_generate_prime()\fR.
176The prime number generation has a negligible error probability.
177.PP
8b0cefbb 178\&\fIBN_is_prime()\fR and \fIBN_is_prime_fasttest()\fR test if the number \fBa\fR is
984263bc 179prime. The following tests are performed until one of them shows that
8b0cefbb 180\&\fBa\fR is composite; if \fBa\fR passes all these tests, it is considered
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181prime.
182.PP
8b0cefbb 183\&\fIBN_is_prime_fasttest()\fR, when called with \fBdo_trial_division == 1\fR,
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184first attempts trial division by a number of small primes;
185if no divisors are found by this test and \fBcallback\fR is not \fB\s-1NULL\s0\fR,
8b0cefbb 186\&\fBcallback(1, \-1, cb_arg)\fR is called.
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187If \fBdo_trial_division == 0\fR, this test is skipped.
188.PP
189Both \fIBN_is_prime()\fR and \fIBN_is_prime_fasttest()\fR perform a Miller-Rabin
190probabilistic primality test with \fBchecks\fR iterations. If
8b0cefbb 191\&\fBchecks == BN_prime_checks\fR, a number of iterations is used that
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192yields a false positive rate of at most 2^\-80 for random input.
193.PP
194If \fBcallback\fR is not \fB\s-1NULL\s0\fR, \fBcallback(1, j, cb_arg)\fR is called
8b0cefbb 195after the j\-th iteration (j = 0, 1, ...). \fBctx\fR is a
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196pre-allocated \fB\s-1BN_CTX\s0\fR (to save the overhead of allocating and
197freeing the structure in a loop), or \fB\s-1NULL\s0\fR.
198.SH "RETURN VALUES"
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199.IX Header "RETURN VALUES"
200\&\fIBN_generate_prime()\fR returns the prime number on success, \fB\s-1NULL\s0\fR otherwise.
984263bc 201.PP
8b0cefbb 202\&\fIBN_is_prime()\fR returns 0 if the number is composite, 1 if it is
984263bc 203prime with an error probability of less than 0.25^\fBchecks\fR, and
8b0cefbb 204\&\-1 on error.
984263bc 205.PP
8b0cefbb 206The error codes can be obtained by \fIERR_get_error\fR\|(3).
984263bc 207.SH "SEE ALSO"
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208.IX Header "SEE ALSO"
209\&\fIbn\fR\|(3), \fIERR_get_error\fR\|(3), \fIrand\fR\|(3)
984263bc 210.SH "HISTORY"
8b0cefbb 211.IX Header "HISTORY"
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212The \fBcb_arg\fR arguments to \fIBN_generate_prime()\fR and to \fIBN_is_prime()\fR
213were added in SSLeay 0.9.0. The \fBret\fR argument to \fIBN_generate_prime()\fR
214was added in SSLeay 0.9.1.
8b0cefbb 215\&\fIBN_is_prime_fasttest()\fR was added in OpenSSL 0.9.5.