[#CRYPTO_gcm128_aad]
= CRYPTO&lowbar;gcm128&lowbar;aad
:mrdocs:

Absorb additional authenticated data into a GCM context before ciphertext&period;

== Synopsis

Declared in `&lt;openssl&sol;modes&period;h&gt;`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
int
CRYPTO&lowbar;gcm128&lowbar;aad(
    xref:GCM128_CONTEXT-04.adoc[GCM128&lowbar;CONTEXT]* ctx,
    unsigned char const* aad,
    size&lowbar;t len);
----

== Return Value

1 on success, or 0 on failure&period;

== Parameters

[cols="1,4"]
|===
| Name| Description
| *ctx*
| GCM context with IV already set&period;
| *aad*
| Additional authenticated data octets&period;
| *len*
| Length of `aad` in bytes&period;
|===


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