1DH_generate_parameters(3)           OpenSSL          DH_generate_parameters(3)
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NAME

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

10        #include <openssl/dh.h>
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12        DH *DH_generate_parameters(int prime_len, int generator,
13            void (*callback)(int, int, void *), void *cb_arg);
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15        int DH_check(DH *dh, int *codes);
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DESCRIPTION

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

40       DH_generate_parameters() returns a pointer to the DH structure, or NULL
41       if the parameter generation fails. The error codes can be obtained by
42       ERR_get_error(3).
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44       DH_check() returns 1 if the check could be performed, 0 otherwise.
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NOTES

47       DH_generate_parameters() may run for several hours before finding a
48       suitable prime.
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50       The parameters generated by DH_generate_parameters() are not to be used
51       in signature schemes.
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BUGS

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

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

60       DH_check() is available in all versions of SSLeay and OpenSSL.  The
61       cb_arg argument to DH_generate_parameters() was added in SSLeay 0.9.0.
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63       In versions before OpenSSL 0.9.5, DH_CHECK_P_NOT_STRONG_PRIME is used
64       instead of DH_CHECK_P_NOT_SAFE_PRIME.
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681.0.1e                            2013-02-11         DH_generate_parameters(3)