DH_GENERATE_PARAMETERS(3)  Library Functions Manual  DH_GENERATE_PARAMETERS(3)

NAME
     DH_generate_parameters_ex, DH_check, DH_check_pub_key,
     DH_generate_parameters - generate and check Diffie-Hellman parameters

SYNOPSIS
     #include <openssl/dh.h>

     int
     DH_generate_parameters_ex(DH *dh, int prime_len, int generator,
         BN_GENCB *cb);

     int
     DH_check(DH *dh, int *codes);

     int
     DH_check_pub_key(const DH *dh, const BIGNUM *pub_key, int *codes);

     Deprecated:

     DH *
     DH_generate_parameters(int prime_len, int generator,
         void (*callback)(int, int, void *), void *cb_arg);

DESCRIPTION
     DH_generate_parameters_ex() generates Diffie-Hellman parameters that can
     be shared among a group of users, and stores them in the provided DH
     structure.

     prime_len is the length in bits of the safe prime to be generated.
     generator is a small number > 1, typically 2 or 5.

     A callback function may be used to provide feedback about the progress of
     the key generation.  If cb is not NULL, it will be called as described in
     BN_generate_prime(3) while a random prime number is generated, and when a
     prime has been found, BN_GENCB_call(cb, 3, 0) is called; see
     BN_GENCB_call(3).

     DH_check() validates Diffie-Hellman parameters.  If no problems are
     found, *codes is set to zero.  Otherwise, one or more of the following
     bits are set:

     DH_CHECK_P_NOT_PRIME
             The parameter dh->p is not prime.

     DH_CHECK_P_NOT_SAFE_PRIME
             The parameter dh->p is not a safe prime.

     DH_UNABLE_TO_CHECK_GENERATOR
             The generator dh->g cannot be checked for suitability: it is
             neither 2 nor 5.

     DH_NOT_SUITABLE_GENERATOR
             The generator dh->g is not suitable.

     DH_check_pub_key() checks whether pub_key is a valid public key when
     using the domain parameters contained in dh.  If no problems are found,
     *codes is set to zero.  Otherwise, one or more of the following bits are
     set:

     DH_CHECK_PUBKEY_TOO_SMALL
             pub_key is less than or equal to 1.

     DH_CHECK_PUBKEY_TOO_LARGE
             pub_key is greater than or equal to dh->p - 1.

     DH_CHECK_PUBKEY_INVALID
             dh->q is set but pub_key to the power of dh->q is not 1 modulo
             dh->p.

RETURN VALUES
     DH_generate_parameters_ex(), DH_check(), and DH_check_pub_key() return 1
     if the check could be performed or 0 otherwise.

     DH_generate_parameters() (deprecated) returns a pointer to the DH
     structure, or NULL if the parameter generation fails.

     The error codes can be obtained by ERR_get_error(3).

SEE ALSO
     DH_get0_pqg(3), DH_new(3)

HISTORY
     DH_check() and DH_generate_parameters() first appeared in SSLeay 0.5.1
     and have been available since OpenBSD 2.4.

     The cb_arg argument to DH_generate_parameters() was added in SSLeay
     0.9.0.

     DH_check_pub_key() first appeared in OpenSSL 0.9.8a and has been
     available since OpenBSD 4.0.

     DH_generate_parameters_ex() first appeared in OpenSSL 0.9.8 and has been
     available since OpenBSD 4.5.

CAVEATS
     DH_generate_parameters_ex() and DH_generate_parameters() may run for
     several hours before finding a suitable prime.

     The parameters generated by DH_generate_parameters_ex() and
     DH_generate_parameters() are not to be used in signature schemes.

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

Linux 6.8.2-arch2-1              July 13, 2022             Linux 6.8.2-arch2-1