---
name: "EVP_MAC-GMAC"
section: "7ssl"
platform: "linux"
package: "openssl"
version: "3.6.5-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/EVP_MAC-GMAC"
---

# EVP\_MAC-GMAC(7ssl)

The GMAC EVP\_MAC implementation

## NAME

EVP\_MAC-GMAC - The GMAC EVP\_MAC implementation

## DESCRIPTION

Support for computing GMAC MACs through the **EVP\_MAC** API.

This implementation uses EVP\_CIPHER functions to get access to the underlying cipher.

### Identity

This implementation is identified with this name and properties, to be used with **EVP\_MAC\_fetch()**:

- "GMAC", "provider=default" or "provider=fips"

  ### Supported parameters

The general description of these parameters can be found in "PARAMETERS" in **EVP\_MAC**(3).

The following parameter can be set with **EVP\_MAC\_CTX\_set\_params()**:

- "key" (**OSSL\_MAC\_PARAM\_KEY**) \<octet string\>

  Sets the MAC key. Setting this parameter is identical to passing a *key* to **EVP\_MAC\_init**(3).

- "iv" (**OSSL\_MAC\_PARAM\_IV**) \<octet string\>

  Sets the IV of the underlying cipher, when applicable.

- "cipher" (**OSSL\_MAC\_PARAM\_CIPHER**) \<UTF8 string\>

  Sets the name of the underlying cipher to be used.

- "properties" (**OSSL\_MAC\_PARAM\_PROPERTIES**) \<UTF8 string\>

  Sets the properties to be queried when trying to fetch the underlying cipher. This must be given together with the cipher naming parameter to be considered valid.

The following parameters can be retrieved with **EVP\_MAC\_CTX\_get\_params()**:

- "size" (**OSSL\_MAC\_PARAM\_SIZE**) \<unsigned integer\>

  Gets the MAC size.

- "fips-indicator" (**OSSL\_MAC\_PARAM\_FIPS\_APPROVED\_INDICATOR**) \<integer\>

  The OpenSSL FIPS provider returns 1 if the operation is FIPS approved, or 0 otherwise.  See "FIPS indicators" in **fips\_module**(7) for more information.

The "size" parameter can also be retrieved with **EVP\_MAC\_CTX\_get\_mac\_size()**. The length of the "size" parameter is equal to that of an **unsigned int**.

## SEE ALSO

**EVP\_MAC\_CTX\_get\_params**(3), **EVP\_MAC\_CTX\_set\_params**(3), "PARAMETERS" in **EVP\_MAC**(3), **OSSL\_PARAM**(3)

## COPYRIGHT

Copyright 2018-2026 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the Apache License 2.0 (the "License").  You may not use this file except in compliance with the License.  You can obtain a copy in the file LICENSE in the source distribution or at \<https://www.openssl.org/source/license.html\>.