DH_METH_NEW(3ossl)

📦
version 3.5.9 · 8 versions
, in fedora 43, fedora 44

🌸 DH_METH_NEW 🌸

okay bestie, so this is the 3ossl manual page, and the whole vibe is "how do I build my own DH method from scratch" — it's giving very DIY, very customizable, very much for the OpenSSL girlies who want to roll their own DH implementation. 💅

✨ NAME ✨

DH_meth_new, DH_meth_free, DH_meth_dup, DH_meth_get0_name, DH_meth_set1_name, DH_meth_get_flags, DH_meth_set_flags, DH_meth_get0_app_data, DH_meth_set0_app_data, DH_meth_get_generate_key, DH_meth_set_generate_key, DH_meth_get_compute_key, DH_meth_set_compute_key, DH_meth_get_bn_mod_exp, DH_meth_set_bn_mod_exp, DH_meth_get_init, DH_meth_set_init, DH_meth_get_finish, DH_meth_set_finish, DH_meth_get_generate_params, DH_meth_set_generate_params — the routines that build up DH methods 🛠️✨

💖 SYNOPSIS 💖

#include <openssl/dh.h>
⚠️ bestie listen. 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). Not me warning you, just saying. 🙈
DH_METHOD *DH_meth_new(const char *name, int flags);

void DH_meth_free(DH_METHOD *dhm);

DH_METHOD *DH_meth_dup(const DH_METHOD *dhm);

const char *DH_meth_get0_name(const DH_METHOD *dhm);
int DH_meth_set1_name(DH_METHOD *dhm, const char *name);

int DH_meth_get_flags(const DH_METHOD *dhm);
int DH_meth_set_flags(DH_METHOD *dhm, int flags);

void *DH_meth_get0_app_data(const DH_METHOD *dhm);
int DH_meth_set0_app_data(DH_METHOD *dhm, void *app_data);

int (*DH_meth_get_generate_key(const DH_METHOD *dhm))(DH *);
int DH_meth_set_generate_key(DH_METHOD *dhm, int (*generate_key)(DH *));

int (*DH_meth_get_compute_key(const DH_METHOD *dhm))
    (unsigned char *key, const BIGNUM *pub_key, DH *dh);
int DH_meth_set_compute_key(DH_METHOD *dhm,
    int (*compute_key)(unsigned char *key, const BIGNUM *pub_key, DH *dh));

int (*DH_meth_get_bn_mod_exp(const DH_METHOD *dhm))
    (const DH *dh, BIGNUM *r, const BIGNUM *a, const BIGNUM *p,
     const BIGNUM *m, BN_CTX *ctx, BN_MONT_CTX *m_ctx);
int DH_meth_set_bn_mod_exp(DH_METHOD *dhm,
    int (*bn_mod_exp)(const DH *dh, BIGNUM *r, const BIGNUM *a,
                      const BIGNUM *p, const BIGNUM *m, BN_CTX *ctx,
                      BN_MONT_CTX *m_ctx));

int (*DH_meth_get_init(const DH_METHOD *dhm))(DH *);
int DH_meth_set_init(DH_METHOD *dhm, int (*init)(DH *));

int (*DH_meth_get_finish(const DH_METHOD *dhm))(DH *);
int DH_meth_set_finish(DH_METHOD *dhm, int (*finish)(DH *));

int (*DH_meth_get_generate_params(const DH_METHOD *dhm))
    (DH *, int, int, BN_GENCB *);
int DH_meth_set_generate_params(DH_METHOD *dhm,
    int (*generate_params)(DH *, int, int, BN_GENCB *));

look at those function pointers, she's layered 💅

🌈 DESCRIPTION 🌈

okay first thing, and I need you to hear me on this one:

🚨 All of the functions described on this page are deprecated. Applications should instead use the provider APIs. that's the whole tea. periodt.

So the DH_METHOD type is a structure used for the provision of custom DH implementations. Basically it hands OpenSSL a whole little bundle of functions, and OpenSSL uses that bundle to make the various DH capabilities happen. it's like a little toolbox you hand over 🧰✨

DH_meth_new() creates a new DH_METHOD structure. You gotta give it a unique name and a set of flags. The name should be a NULL terminated string, and here's the thing — it gets duplicated and stored in the DH_METHOD object, so it is the callers responsibility to free the original string. The flags get used during the construction of a new DH object based on this DH_METHOD, and any new DH object will have those flags set by default. lowkey convenient 💖

DH_meth_dup() creates a duplicate copy of the DH_METHOD object passed as a parameter. This might be useful for creating a new DH_METHOD based on an existing one, but with some differences. it's giving inspired by, but make it different 🦋

DH_meth_free() destroys a DH_METHOD structure and frees up any memory associated with it. And if the argument is NULL, nothing is done. no drama, no crash, we love a graceful exit 👑

DH_meth_get0_name() will return a pointer to the name of this DH_METHOD. Important: this is a pointer to the internal name string, so it should not be freed by the caller. Do not touch, do not free, just admire. 🙅‍♀️

DH_meth_set1_name() sets the name of the DH_METHOD to name. The string is duplicated and the copy is stored in the DH_METHOD structure, so the caller remains responsible for freeing the memory associated with the name. (yes you still own the original, she just made a copy for herself ✨)

DH_meth_get_flags() returns the current value of the flags associated with this DH_METHOD. DH_meth_set_flags() provides the ability to set these flags.

The functions DH_meth_get0_app_data() and DH_meth_set0_app_data() provide the ability to associate implementation specific data with the DH_METHOD. Heads up though: it is the application's responsibility to free this data before the DH_METHOD is freed via a call to DH_meth_free(). your data, your problem bestie 💀

DH_meth_get_generate_key() and DH_meth_set_generate_key() get and set the function used for generating a new DH key pair respectively. This function will be called in response to the application calling DH_generate_key(). The parameter for the function has the same meaning as for DH_generate_key().

DH_meth_get_compute_key() and DH_meth_set_compute_key() get and set the function used for computing a new DH shared secret respectively. This function will be called in response to the application calling DH_compute_key(). The parameters for the function have the same meaning as for DH_compute_key().

DH_meth_get_bn_mod_exp() and DH_meth_set_bn_mod_exp() get and set the function used for computing the following value:

r = a ^ p mod m

This function will be called by the default OpenSSL function for DH_generate_key(). The result is stored in the r parameter. This function may be NULL — unless you're using the default generate key function, in which case it must be present. read that twice, bestie, it's conditional 👀

DH_meth_get_init() and DH_meth_set_init() get and set the function used for creating a new DH instance respectively. This function will be called in response to the application calling DH_new() (if the current default DH_METHOD is this one) or DH_new_method(). The DH_new() and DH_new_method() functions will allocate the memory for the new DH object, and a pointer to this newly allocated structure will be passed as a parameter to the function. This function may be NULL. ✅

DH_meth_get_finish() and DH_meth_set_finish() get and set the function used for destroying an instance of a DH object respectively. This function will be called in response to the application calling DH_free(). A pointer to the DH to be destroyed is passed as a parameter. The destroy function should be used for DH implementation specific clean up. The memory for the DH itself should not be freed by this function. This function may be NULL.

🫶 okay that last one is important — the destroy function is for your cleanup, not for freeing the DH itself. OpenSSL handles that. don't double-free, we're not doing that today.

DH_meth_get_generate_params() and DH_meth_set_generate_params() get and set the function used for generating DH parameters respectively. This function will be called in response to the application calling DH_generate_parameters_ex() (or DH_generate_parameters()). The parameters for the function have the same meaning as for DH_generate_parameters_ex(). This function may be NULL.

🎀 RETURN VALUES 🎀

DH_meth_new() and DH_meth_dup() return the newly allocated DH_METHOD object, or NULL on failure. (failure? never heard of her 💅)

DH_meth_get0_name() and DH_meth_get_flags() return the name and flags associated with the DH_METHOD respectively.

All other DH_meth_get_*() functions return the appropriate function pointer that has been set in the DH_METHOD, or NULL if no such pointer has yet been set.

DH_meth_set1_name() and all DH_meth_set_*() functions return 1 on success or 0 on failure.

🔥 SEE ALSO 🔥

(and yes, DH_new(3) really is listed twice in the original — we keep it exactly as she came, no edits, no notes 😌✨)

⭐ HISTORY ⭐

All of these functions were deprecated in OpenSSL 3.0.

The functions described here were added in OpenSSL 1.1.0.

it's giving legacy icon, honestly 🌸

Copyright 2016-2024 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>.

okay that's the whole page bestie, go forth and build your custom DH methods (or, y'know, use the provider APIs like the deprecation warning is literally begging you to 🙈) — much love from OpenSSL 3.5.9, dated 2026-09-29, signing off 🦋💜✨

📦 where this page comes from