DH_GENERATE_PARAMETERS(3)

NAME
DH_generate_parameters_ex, DH_generate_parameters, DH_check, DH_check_params, DH_check_pub_key, DH_check_ex, DH_check_params_ex, DH_check_pub_key_ex - generate and check Diffie-Hellman parameters

SYNOPSIS
 #include <openssl/dh.h>

The following functions have been deprecated since OpenSSL 3.0, and can be hidden entirely by defining OPENSSL_API_COMPAT with a suitable version value, see openssl_user_macros(7):

 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_pub_key(const DH *dh, const BIGNUM *pub_key, 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);

The following functions have been deprecated since OpenSSL 0.9.8, and can be hidden entirely by defining OPENSSL_API_COMPAT with a suitable version value, see openssl_user_macros(7):

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

DESCRIPTION
All of the functions described on this page are deprecated. Applications should instead use EVP_PKEY_check(3), EVP_PKEY_public_check(3), EVP_PKEY_private_check(3) and EVP_PKEY_param_check(3).

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_MODULUS_TOO_SMALL
    The modulus is too small.

DH_MODULUS_TOO_LARGE
    The modulus is too large.

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.

If 0 is returned or *codes is set to a nonzero value the supplied parameters should not be used for Diffie-Hellman operations otherwise the security properties of the key exchange are not guaranteed.

DH_check_ex(), DH_check_params_ex() and DH_check_pub_key_ex() are similar to DH_check(), DH_check_params() and DH_check_pub_key() 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
All of these functions were deprecated in OpenSSL 3.0.

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

COPYRIGHT
Copyright 2000-2026 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the Apache License 2.0 (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>.