[#ECDH_compute_key]
= ECDH_compute_key
:mrdocs:

Perform ECDH and optionally apply a KDF to the shared secret (deprecated).

== Synopsis

Declared in `<openssl/ec.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
[[deprecated]]
int
ECDH_compute_key(
    void* out,
    size_t outlen,
    xref:EC_POINT.adoc[EC_POINT] const* pub_key,
    xref:EC_KEY.adoc[EC_KEY] const* ecdh,
    void*(* KDF)(void const*, size_t, void*, size_t*));
----

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

Number of bytes written to `out` on success, or 0 on error.

== Parameters

[cols="1,4"]
|===
| Name| Description
| *out*
| Buffer that receives the derived key material (or KDF output).
| *outlen*
| Size of `out` in bytes; also passed to `KDF` as initial output capacity.
| *pub_key*
| Peer's public EC point.
| *ecdh*
| Local private EC_KEY used for the agreement.
| *KDF*
| Optional key‐derivation callback; if NULL, copies min(`outlen,` secret length) raw shared secret bytes into `out.`
|===


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