EVP_MAC-GMAC(7ossl)

💅 EVP_MAC-GMAC

okay so bestie, welcome to the glow-up page for EVP_MAC-GMAC — it's one of the OpenSSL manual pages (the 7ossl girlies, you know the ones), and it's literally all about the GMAC implementation of EVP_MAC. grab a strawberry drink 🍓 and let's get into it.

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✨ NAME ✨

EVP_MAC-GMAC — the GMAC EVP_MAC implementation. that's it, that's the vibe. 🎀

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🌸 DESCRIPTION 🌸

So. This bad boy gives you support for computing GMAC MACs through the EVP_MAC API. iconic behaviour, no cap. 👑

And lowkey the way it works is: this implementation uses EVP_CIPHER functions to get access to the underlying cipher. that's the whole trick, and it ate. 🔥

🦋 Identity

This implementation is identified with this name and these properties, to be used with EVP_MAC_fetch():

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

so yeah — that's how you find her. provider=default or provider=fips, pick your fighter. 💅

🌈 Supported parameters

The general description of these parameters can be found in "PARAMETERS" in EVP_MAC(3). go check that out if you want the full lore, iykyk.

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). same energy, different entrance. 🫶
• "iv" (OSSL_MAC_PARAM_IV) <octet string> — sets the IV of the underlying cipher, when applicable. "when applicable" is doing a lot of heavy lifting there, respect. 🧚
• "cipher" (OSSL_MAC_PARAM_CIPHER) <UTF8 string> — sets the name of the underlying cipher to be used. main character cipher energy. 👑
• "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 — so like, they're a package deal, bestie, don't try to separate them. 😭

The following parameters can be retrieved with EVP_MAC_CTX_get_params():

• "size" (OSSL_MAC_PARAM_SIZE) <unsigned integer> — gets the MAC size. that's the tea. 💖

Also, the "size" parameter can also be retrieved with EVP_MAC_CTX_get_mac_size(). and just so you know, the length of the "size" parameter is equal to that of an unsigned int. noted, fr fr. ⭐

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🔍 SEE ALSO 🔍

EVP_MAC_CTX_get_params(3), EVP_MAC_CTX_set_params(3), "PARAMETERS" in EVP_MAC(3), OSSL_PARAM(3)

go read those next, bestie, they're the supporting cast and honestly they serve. 💜

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📜 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>.

ok important note bestie: this is the legal bit, so like, don't skip it — use it only in compliance with the License, periodt. 🎀

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and that's the page!! 💫 this one came from version 3.5.6, dated 2026-04-07 — so go forth, compute those GMACs, and slay. 🌈💅🦋