DH_GENERATE_PARAMETERS(3ossl)

📦 version 3.5.0, in opensuse-leap 16.0

💅 DH_GENERATE_PARAMETERS 💅

okay so bestie, buckle up — this is the 3ossl manual page for the Diffie-Hellman parameter girlies ✨ (DH_generate_parameters_ex, DH_generate_parameters, DH_check, DH_check_params, DH_check_ex, DH_check_params_ex, DH_check_pub_key_ex). It's a lot of names, I know, but we're gonna get through it together 🫶

🌸 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. that's the whole gig 💖

✨ SYNOPSIS ✨

#include <openssl/dh.h>

so first off, heads up: the following functions have been deprecated since OpenSSL 3.0 💀 and you can hide them 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_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);

and then there's this one, which has been deprecated since OpenSSL 0.9.8 (yes, ancient, it's giving vintage 😭) and can also 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 🦋

okay so the vibes here are complicated: all of the functions described on this page are deprecated. like, every single one. no cap 🫠 applications should instead use EVP_PKEY_check(3), EVP_PKEY_public_check(3), EVP_PKEY_private_check(3) and EVP_PKEY_param_check(3). that's the glow-up, bestie.

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 ⚠️ (yes that means you, main character, seed it first). also important: the parameters generated by DH_generate_parameters_ex() should not be used in signature schemes. periodt.

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.
🚨 do not skip this one: 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. like, fr fr. don't do it. 💀

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 👑

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 2000-2020 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>.

k that's literally it, bestie — go forth and check your params 🦋✨

signed off with love from version 3.5.0, dated 2026-09-25 — mwah 💋

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