[#EVP_MAC_init]
= EVP_MAC_init
:mrdocs:

Initialize a MAC context with a key and optional algorithm parameters.

== Synopsis

Declared in `<openssl/evp.h>`

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

== Return Value

1 on success, or 0 on failure.

== Parameters

[cols="1,4"]
|===
| Name| Description
| *ctx*
| MAC context created with EVP_MAC_CTX_new().
| *key*
| MAC key octets.
| *keylen*
| Length of `key` in bytes.
| *params*
| Optional OSSL_PARAM array (for example digest selection), or NULL.
|===


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