[#CRYPTO_ccm128_tag]
= CRYPTO_ccm128_tag
:mrdocs:

Write the computed CCM authentication tag into `tag.`

== Synopsis

Declared in `<openssl/modes.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
size_t
CRYPTO_ccm128_tag(
    xref:CCM128_CONTEXT-0c.adoc[CCM128_CONTEXT]* ctx,
    unsigned char* tag,
    size_t len);
----

== Return Value

Number of tag bytes written (`len),` or 0 if `len` does not match M.

== Parameters

[cols="1,4"]
|===
| Name| Description
| *ctx*
| CCM context after encryption (and optional AAD) processing.
| *tag*
| Destination buffer for the tag; `len` must equal the configured M tag length.
| *len*
| Number of tag bytes requested (must match the M value from CRYPTO_ccm128_init()).
|===


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