1DH_generate_parameters(3)           OpenSSL          DH_generate_parameters(3)
2
3
4

NAME

6       DH_generate_parameters, DH_check - generate and check Diffie-Hellman
7       parameters
8

SYNOPSIS

10        #include <openssl/dh.h>
11
12        DH *DH_generate_parameters(int prime_len, int generator,
13            void (*callback)(int, int, void *), void *cb_arg);
14
15        int DH_check(DH *dh, int *codes);
16

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().
22
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.
25
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 gener‐
29       ated, and when a prime has been found, callback(3, 0, cb_arg) is
30       called.
31
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 DH_NOT_SUITABLE_GEN‐
35       ERATOR are set in *codes.  DH_UNABLE_TO_CHECK_GENERATOR is set if the
36       generator cannot be checked, i.e. it does not equal 2 or 5.
37

RETURN VALUES

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

NOTES

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

BUGS

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

SEE ALSO

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

HISTORY

59       DH_check() is available in all versions of SSLeay and OpenSSL.  The
60       cb_arg argument to DH_generate_parameters() was added in SSLeay 0.9.0.
61
62       In versions before OpenSSL 0.9.5, DH_CHECK_P_NOT_STRONG_PRIME is used
63       instead of DH_CHECK_P_NOT_SAFE_PRIME.
64
65
66
670.9.8b                            2002-09-25         DH_generate_parameters(3)