[#CRYPTO_gcm128_aad]
= CRYPTO_gcm128_aad
:mrdocs:

Absorb additional authenticated data into a GCM context before ciphertext.

== Synopsis

Declared in `<openssl/modes.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
int
CRYPTO_gcm128_aad(
    xref:GCM128_CONTEXT-04.adoc[GCM128_CONTEXT]* ctx,
    unsigned char const* aad,
    size_t len);
----

== Return Value

1 on success, or 0 on failure.

== Parameters

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


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