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📖 NAME

EVP_MAC-GMAC - The GMAC EVP_MAC implementation

🚀 Quick Reference

Use Case	Command	Description
Compute GMAC	EVP_MAC_fetch(NULL, "GMAC", "provider=default")	📌 Fetch the GMAC MAC implementation
Set cipher	EVP_MAC_CTX_set_params(ctx, {OSSL_MAC_PARAM_CIPHER, "AES-128-GCM", ...})	🔑 Set the underlying cipher (e.g., AES-128-GCM)
Set key	EVP_MAC_CTX_set_params(ctx, {OSSL_MAC_PARAM_KEY, key_data, ...})	🔐 Set the MAC key
Set IV	EVP_MAC_CTX_set_params(ctx, {OSSL_MAC_PARAM_IV, iv_data, ...})	🧪 Set the initialization vector
Get MAC size	EVP_MAC_CTX_get_mac_size(ctx)	📏 Retrieve the MAC length

📝 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.

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 2018-2021 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.

3.0.2 2026-06-02 EVP_MAC-GMAC(7SSL)

📖 NAME 🚀 Quick Reference 📝 DESCRIPTION 📚 SEE ALSO ©️ COPYRIGHT