[#EVP_PKEY_CTX_set_mac_key]
= EVP_PKEY_CTX_set_mac_key
:mrdocs:

Set the MAC key bytes on a keygen/paramgen EVP_PKEY_CTX (for example HMAC or Poly1305).

== Synopsis

Declared in `<openssl/evp.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
int
EVP_PKEY_CTX_set_mac_key(
    xref:EVP_PKEY_CTX.adoc[EVP_PKEY_CTX]* ctx,
    unsigned char const* key,
    int keylen);
----

== Return Value

1 on success, or a negative value / 0 on failure.

== Parameters

[cols="1,4"]
|===
| Name| Description
| *ctx*
| Key generation context for a MAC algorithm.
| *key*
| MAC key octets; may be NULL when `keylen` is 0.
| *keylen*
| Length of `key` in bytes.
|===


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