[#EVP_PKEY_CTX_set_ecdh_kdf_outlen]
= EVP&lowbar;PKEY&lowbar;CTX&lowbar;set&lowbar;ecdh&lowbar;kdf&lowbar;outlen
:mrdocs:

Set the ECDH key&hyphen;derivation output length for a key&hyphen;exchange context&period;

== Synopsis

Declared in `&lt;openssl&sol;ec&period;h&gt;`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
int
EVP&lowbar;PKEY&lowbar;CTX&lowbar;set&lowbar;ecdh&lowbar;kdf&lowbar;outlen(
    xref:EVP_PKEY_CTX.adoc[EVP&lowbar;PKEY&lowbar;CTX]* ctx,
    int len);
----

== Return Value

1 on success, or a negative value on failure&period;

== Parameters

[cols="1,4"]
|===
| Name| Description
| *ctx*
| EVP&lowbar;PKEY context configured for ECDH with a KDF&period;
| *len*
| Desired derived&hyphen;key length in bytes&period;
|===


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