[#DH_meth_set_bn_mod_exp]
= DH_meth_set_bn_mod_exp
:mrdocs:

Set the modular‐exponentiation callback on a DH_METHOD (deprecated).

== Synopsis

Declared in `<openssl/dh.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
[[deprecated]]
int
DH_meth_set_bn_mod_exp(
    xref:DH_METHOD-0a.adoc[DH_METHOD]* dhm,
    int(* bn_mod_exp)(xref:DH.adoc[DH] const*, xref:BIGNUM.adoc[BIGNUM]*, xref:BIGNUM.adoc[BIGNUM] const*, xref:BIGNUM.adoc[BIGNUM] const*, xref:BIGNUM.adoc[BIGNUM] const*, xref:BN_CTX.adoc[BN_CTX]*, xref:BN_MONT_CTX.adoc[BN_MONT_CTX]*));
----

[WARNING]
====
https://en.cppreference.com/cpp/language/attributes/deprecated[Deprecated^]. Use of this entity is allowed but discouraged.
====
== Description

The callback computes r = aˆp mod m and is used by the default DH_generate_key() implementation. Prefer provider APIs for new code.

== Return Value

1 on success, or 0 on failure.

== Parameters

[cols="1,4"]
|===
| Name| Description
| *dhm*
| Method table to update.
| *bn_mod_exp*
| Callback implementing modular exponentiation, or NULL to clear (must be non‐NULL when using the default generate_key).
|===


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