[#EVP_Q_mac]
= EVP_Q_mac
:mrdocs:

One‐shot MAC computation: fetch the algorithm, process `data,` and write the tag.

== Synopsis

Declared in `<openssl/evp.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
unsigned char*
EVP_Q_mac(
    xref:OSSL_LIB_CTX.adoc[OSSL_LIB_CTX]* libctx,
    char const* name,
    char const* propq,
    char const* subalg,
    xref:OSSL_PARAM.adoc[OSSL_PARAM] const* params,
    void const* key,
    size_t keylen,
    unsigned char const* data,
    size_t datalen,
    unsigned char* out,
    size_t outsize,
    size_t* outlen);
----

== Return Value

Pointer to `out` on success, or NULL on failure.

== Parameters

[cols="1,4"]
|===
| Name| Description
| *libctx*
| Library context used to fetch the MAC, or NULL for the default.
| *name*
| MAC algorithm name (for example "HMAC" or "CMAC").
| *propq*
| Property query for the MAC fetch, or NULL.
| *subalg*
| Optional sub‐algorithm name (for example the HMAC digest), or NULL.
| *params*
| Optional OSSL_PARAM array for algorithm setup, or NULL.
| *key*
| MAC key octets.
| *keylen*
| Length of `key` in bytes.
| *data*
| Message bytes to authenticate.
| *datalen*
| Length of `data` in bytes.
| *out*
| Buffer that receives the MAC, or NULL to query the required size via `outlen.`
| *outsize*
| Size of `out` in bytes when `out` is non‐NULL.
| *outlen*
| On success, receives the number of MAC bytes written (or required if `out` is NULL).
|===


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