DH_GET0_PQG(3SSL)

📦

version 4.0.3 · 14 versions

🎀 NAME 🎀

hiii bestie 💖 so this page — DH_GET0_PQG(3SSL), yes that's the whole vibe — is the lowdown on all the lil routines that get and set data inside a DH object. Think of it as the group chat where p, q, g, your keys, your flags and your length all hang out ✨

The whole squad on this page:

DH_get0_pqg, DH_set0_pqg
DH_get0_key, DH_set0_key
DH_get0_p, DH_get0_q, DH_get0_g
DH_get0_priv_key, DH_get0_pub_key
DH_clear_flags, DH_test_flags, DH_set_flags
DH_get_length, DH_set_length

and together they're the Routines for getting and setting data in a DH object. no cap 💅

✨ SYNOPSIS ✨

#include <openssl/dh.h>

okay so real talk: 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):

 void DH_get0_pqg(const DH *dh,
                  const BIGNUM **p, const BIGNUM **q, const BIGNUM **g);
 int DH_set0_pqg(DH *dh, BIGNUM *p, BIGNUM *q, BIGNUM *g);
 void DH_get0_key(const DH *dh,
                  const BIGNUM **pub_key, const BIGNUM **priv_key);
 int DH_set0_key(DH *dh, BIGNUM *pub_key, BIGNUM *priv_key);
 const BIGNUM *DH_get0_p(const DH *dh);
 const BIGNUM *DH_get0_q(const DH *dh);
 const BIGNUM *DH_get0_g(const DH *dh);
 const BIGNUM *DH_get0_priv_key(const DH *dh);
 const BIGNUM *DH_get0_pub_key(const DH *dh);
 void DH_clear_flags(DH *dh, int flags);
 int DH_test_flags(const DH *dh, int flags);
 void DH_set_flags(DH *dh, int flags);

 long DH_get_length(const DH *dh);
 int DH_set_length(DH *dh, long length);

💅 DESCRIPTION 💅

first thing first, and I need you to hear me on this: all of the functions described on this page are deprecated 😭. Like, every single one. Applications should instead use EVP_PKEY_get_bn_param(3) for any methods that return a BIGNUM, and you should refer to EVP_PKEY-DH(7) for more information. it's giving "we moved on, bestie" 🦋

so, a DH object contains the parameters p, q and g. heads up: the q parameter is optional. it also contains a public key (pub_key) and (optionally) a private key (priv_key). main character energy for the whole struct tbh 👑

getting and setting p, q, g 🌸

DH_get0_pqg() — this is how you get the p, q and g params. If the parameters have not yet been set then *p, *q and *g will be set to NULL. Otherwise they are set to pointers to their respective values. These point directly to the internal representations of the values and therefore should not be freed directly. 🙈 Any of the out parameters p, q, and g can be NULL, in which case no value will be returned for that parameter.
DH_set0_pqg() — sets the p, q and g values, by passing the new values for p, q and g as parameters to the function. Calling this function transfers the memory management of the values to the DH object, and therefore the values that have been passed in should not be freed directly after this function has been called. The q parameter may be NULL. DH_set0_pqg() also checks if the parameters associated with p and g and optionally q are associated with known safe prime groups. If it is a safe prime group then the value of q will be set to q = (p - 1) / 2 if q is NULL. The optional length parameter will be set to BN_num_bits(q) if q is not NULL. ate that logic, honestly 🔥

keys 🔑

DH_get0_key() — to get the public and private key values, use this. A pointer to the public key will be stored in *pub_key, and a pointer to the private key will be stored in *priv_key. Either may be NULL if they have not been set yet, although if the private key has been set then the public key must be. The values point to the internal representation of the public key and private key values. This memory should not be freed directly. Any of the out parameters pub_key and priv_key can be NULL, in which case no value will be returned for that parameter.
DH_set0_key() — sets the public and private key values. Either parameter may be NULL, which means the corresponding DH field is left untouched. As with DH_set0_pqg() this function transfers the memory management of the key values to the DH object, and therefore they should not be freed directly after this function has been called.

the solo getters 🎀

any of the values p, q, g, priv_key, and pub_key can also be retrieved separately by the corresponding function, respectively:

DH_get0_p()
DH_get0_q()
DH_get0_g()
DH_get0_priv_key()
DH_get0_pub_key()

like, one at a time, no group project required 🫶

flags 🚩

DH_set_flags() — sets the flags in the flags parameter on the DH object. Multiple flags can be passed in one go (bitwise ORed together). Any flags that are already set are left set.
DH_test_flags() — tests to see whether the flags passed in the flags parameter are currently set in the DH object. Multiple flags can be tested in one go. All flags that are currently set are returned, or zero if none of the flags are set.
DH_clear_flags() — clears the specified flags within the DH object. bye felicia 💀

length 📏

DH_get_length() and DH_set_length() — get and set the optional length parameter associated with this DH object. If the length is nonzero then it is used, otherwise it is ignored. The length parameter indicates the length of the secret exponent (private key) in bits. For safe prime groups the optional length parameter length can be set to a value greater or equal to 2 * maximum_target_security_strength(BN_num_bits(p)) as listed in SP800-56Ar3 Table(s) 25 & 26.

not me reminding you again: these functions are deprecated and should be replaced with EVP_PKEY_CTX_set_params() and EVP_PKEY_get_int_param() using the parameter key OSSL_PKEY_PARAM_DH_PRIV_LEN as described in EVP_PKEY-DH(7) ✨

📝 NOTES 📝

values retrieved with DH_get0_key() are owned by the DH object used in the call and may therefore not be passed to DH_set0_key(). If needed, duplicate the received value using BN_dup() and pass the duplicate. The same applies to DH_get0_pqg() and DH_set0_pqg(). no borrowing without copying, bestie, that's the rule 🌸

🔢 RETURN VALUES 🔢

DH_set0_pqg() and DH_set0_key() return 1 on success or 0 on failure.
DH_get0_p(), DH_get0_q(), DH_get0_g(), DH_get0_priv_key(), and DH_get0_pub_key() return the respective value, or NULL if it is unset.
DH_test_flags() returns the current state of the flags in the DH object.
DH_get_length() returns the length of the secret exponent (private key) in bits, or zero if no such length has been explicitly set.

👀 SEE ALSO 👀

(yes DH_new(3) is listed twice in the original and I am not the one who's gonna erase it 💖)

📜 HISTORY 📜

The functions described here were added in OpenSSL 1.1.0.
All of these functions were deprecated in OpenSSL 3.0.
The DH_get0_engine() was removed in OpenSSL 4.0.

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>.

and that's the whole page, bestie 🫶 this was DH_GET0_PQG(3SSL) from OpenSSL, version 4.0.3, dated 2026-09-29 — thanks for reading my lil TedTalk, you're literally iconic for making it to the end 👑💖 slay, periodt, drink water ✨🌸

📦 where this page comes from

ubuntu stonking: libssl-doc 4.0.3-1ubuntu1 · Apache-2.0
💖 girlified by deepseek-ai/DeepSeek-V4.1-Flash on 2026-11-03: a language model's rewrite of the original, under its terms