NAME

       DH_generate_parameters_ex, DH_generate_parameters, DH_check, DH_check_params, DH_check_ex,
       DH_check_params_ex, DH_check_pub_key_ex - 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_params(DH *dh, int *codes);

        int DH_check_ex(const DH *dh);
        int DH_check_params_ex(const DH *dh);
        int DH_check_pub_key_ex(const DH *dh, const BIGNUM *pub_key);

       Deprecated:

        #if OPENSSL_API_COMPAT < 0x00908000L
        DH *DH_generate_parameters(int prime_len, int generator,
                                   void (*callback)(int, int, void *), void *cb_arg);
        #endif

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. The pseudo-random number generator must be seeded
       before calling it.  The parameters generated by DH_generate_parameters_ex() should not be used in
       signature schemes.

       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_generate_prime_ex(3) for information on the BN_GENCB_call() function.

       DH_generate_parameters() is similar to DH_generate_prime_ex() but expects an old-style callback function;
       see BN_generate_prime(3) for information on the old-style callback.

       DH_check_params() confirms that the p and g are likely enough to be valid.  This is a lightweight check,
       if a more thorough check is needed, use DH_check().  The value of *codes is updated with any problems
       found.  If *codes is zero then no problems were found, otherwise the following bits may be set:

       DH_CHECK_P_NOT_PRIME
           The  parameter  p  has  been  determined  to  not being an odd prime.  Note that the lack of this bit
           doesn't guarantee that p is a prime.

       DH_NOT_SUITABLE_GENERATOR
           The generator g is not suitable.  Note that the  lack  of  this  bit  doesn't  guarantee  that  g  is
           suitable, unless p is known to be a strong prime.

       DH_check()  confirms that the Diffie-Hellman parameters dh are valid. The value of *codes is updated with
       any problems found. If *codes is zero then no problems were found, otherwise the following  bits  may  be
       set:

       DH_CHECK_P_NOT_PRIME
           The parameter p is not prime.

       DH_CHECK_P_NOT_SAFE_PRIME
           The parameter p is not a safe prime and no q value is present.

       DH_UNABLE_TO_CHECK_GENERATOR
           The generator g cannot be checked for suitability.

       DH_NOT_SUITABLE_GENERATOR
           The generator g is not suitable.

       DH_CHECK_Q_NOT_PRIME
           The parameter q is not prime.

       DH_CHECK_INVALID_Q_VALUE
           The parameter q is invalid.

       DH_CHECK_INVALID_J_VALUE
           The parameter j is invalid.

       DH_check_ex(),    DH_check_params()   and   DH_check_pub_key_ex()   are   similar   to   DH_check()   and
       DH_check_params() respectively, but the error reasons are added to the thread's error  queue  instead  of
       provided as return values from the function.

RETURN VALUES

       DH_generate_parameters_ex(), DH_check() and DH_check_params() return 1 if the check could be performed, 0
       otherwise.

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

       DH_check_ex(),  DH_check_params()  and  DH_check_pub_key_ex()  return 1 if the check is successful, 0 for
       failed.

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

SEE ALSO

       DH_new(3), ERR_get_error(3), RAND_bytes(3), DH_free(3)

HISTORY

       DH_generate_parameters() was deprecated in OpenSSL 0.9.8; use DH_generate_parameters_ex() instead.

COPYRIGHT

       Copyright 2000-2018 The OpenSSL Project Authors. All Rights Reserved.

       Licensed under the OpenSSL license (the "License").  You may not use this file except in compliance  with
       the   License.   You  can  obtain  a  copy  in  the  file  LICENSE  in  the  source  distribution  or  at
       <https://www.openssl.org/source/license.html>.

1.1.1f                                             2025-02-05                       DH_GENERATE_PARAMETERS(3SSL)