[#CRYPTO_gcm128_tag]
= CRYPTO_gcm128_tag
:mrdocs:

Write the computed GCM authentication tag into `tag.`

== Synopsis

Declared in `<openssl/modes.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
void
CRYPTO_gcm128_tag(
    xref:GCM128_CONTEXT-04.adoc[GCM128_CONTEXT]* ctx,
    unsigned char* tag,
    size_t len);
----

== Parameters

[cols="1,4"]
|===
| Name| Description
| *ctx*
| GCM context after encryption (typically after CRYPTO_gcm128_finish with NULL tag).
| *tag*
| Destination buffer for the tag.
| *len*
| Number of tag bytes to write (commonly 16).
|===


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