[#HMAC_Init_ex]
= HMAC_Init_ex
:mrdocs:

(Re)initialize an HMAC_CTX with key and digest (deprecated; prefer EVP_MAC).

== Synopsis

Declared in `<openssl/hmac.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
[[deprecated]]
int
HMAC_Init_ex(
    xref:HMAC_CTX.adoc[HMAC_CTX]* ctx,
    void const* key,
    int len,
    xref:EVP_MD.adoc[EVP_MD] const* md,
    xref:ENGINE.adoc[ENGINE]* impl);
----

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

1 on success, or 0 on failure.

== Parameters

[cols="1,4"]
|===
| Name| Description
| *ctx*
| HMAC context to initialize.
| *key*
| HMAC key bytes, or NULL to reuse the previous key when only `md` changes.
| *len*
| Length of `key` in bytes (ignored when `key` is NULL).
| *md*
| Message digest used as the HMAC hash, or NULL to keep the previous digest.
| *impl*
| Optional ENGINE implementing `md,` or NULL.
|===


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