1DH_generate_parameters(3)           OpenSSL          DH_generate_parameters(3)
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NAME

6       DH_generate_parameters_ex, DH_generate_parameters, DH_check - generate
7       and check Diffie-Hellman parameters
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SYNOPSIS

10        #include <openssl/dh.h>
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12        int DH_generate_parameters_ex(DH *dh, int prime_len,int generator, BN_GENCB *cb);
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14        int DH_check(DH *dh, int *codes);
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16       Deprecated:
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18        DH *DH_generate_parameters(int prime_len, int generator,
19            void (*callback)(int, int, void *), void *cb_arg);
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DESCRIPTION

22       DH_generate_parameters_ex() generates Diffie-Hellman parameters that
23       can be shared among a group of users, and stores them in the provided
24       DH structure. The pseudo-random number generator must be seeded prior
25       to calling DH_generate_parameters().
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27       prime_len is the length in bits of the safe prime to be generated.
28       generator is a small number > 1, typically 2 or 5.
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30       A callback function may be used to provide feedback about the progress
31       of the key generation. If cb is not NULL, it will be called as
32       described in BN_generate_prime(3) while a random prime number is
33       generated, and when a prime has been found, BN_GENCB_call(cb, 3, 0) is
34       called. See BN_generate_prime(3) for information on the BN_GENCB_call()
35       function.
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37       DH_check() validates Diffie-Hellman parameters. It checks that p is a
38       safe prime, and that g is a suitable generator. In the case of an
39       error, the bit flags DH_CHECK_P_NOT_SAFE_PRIME or
40       DH_NOT_SUITABLE_GENERATOR are set in *codes.
41       DH_UNABLE_TO_CHECK_GENERATOR is set if the generator cannot be checked,
42       i.e. it does not equal 2 or 5.
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RETURN VALUES

45       DH_generate_parameters_ex() and DH_check() return 1 if the check could
46       be performed, 0 otherwise.
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48       DH_generate_parameters() (deprecated) returns a pointer to the DH
49       structure, or NULL if the parameter generation fails.
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51       The error codes can be obtained by ERR_get_error(3).
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NOTES

54       DH_generate_parameters_ex() and DH_generate_parameters() may run for
55       several hours before finding a suitable prime.
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57       The parameters generated by DH_generate_parameters_ex() and
58       DH_generate_parameters() are not to be used in signature schemes.
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BUGS

61       If generator is not 2 or 5, dh->g=generator is not a usable generator.
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SEE ALSO

64       dh(3), ERR_get_error(3), rand(3), DH_free(3)
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HISTORY

67       DH_check() is available in all versions of SSLeay and OpenSSL.  The
68       cb_arg argument to DH_generate_parameters() was added in SSLeay 0.9.0.
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70       In versions before OpenSSL 0.9.5, DH_CHECK_P_NOT_STRONG_PRIME is used
71       instead of DH_CHECK_P_NOT_SAFE_PRIME.
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751.0.2k                            2017-01-26         DH_generate_parameters(3)
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