[#CRYPTO_ccm128_init]
= CRYPTO_ccm128_init
:mrdocs:

Initialise a CCM128_CONTEXT with tag length, length‐field size, and block cipher.

== Synopsis

Declared in `<openssl/modes.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
void
CRYPTO_ccm128_init(
    xref:CCM128_CONTEXT-0c.adoc[CCM128_CONTEXT]* ctx,
    unsigned int M,
    unsigned int L,
    void* key,
    xref:block128_f.adoc[block128_f] block);
----

== Parameters

[cols="1,4"]
|===
| Name| Description
| *ctx*
| Context storage to initialise.
| *M*
| Authentication tag length in bytes (for example 8 or 16).
| *L*
| Size of the message‐length field in bytes (nonce length is 15 ‐ L).
| *key*
| Cipher‐specific expanded key for `block.`
| *block*
| Block‐encrypt function for the underlying cipher.
|===


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