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🏷️ NAME

EVP_MAC-Poly1305 - The Poly1305 EVP_MAC implementation

🚀 Quick Reference

Use Case	Command	Description
🔍 Fetch MAC	EVP_MAC_fetch(NULL, "POLY1305", NULL)	Acquire the Poly1305 MAC implementation
🔑 Set Key	EVP_MAC_CTX_set_params(ctx, params) with OSSL_MAC_PARAM_KEY	Set the 256-bit key (must be unique per message)
🚀 Init MAC	EVP_MAC_init(ctx, key, keylen, NULL)	Initialize MAC context with key
📥 Update MAC	EVP_MAC_update(ctx, data, datalen)	Feed data to authenticate
✅ Finalize	EVP_MAC_final(ctx, out, &outlen, outsize)	Compute the 16-byte authentication tag
📏 Get Size	EVP_MAC_CTX_get_mac_size(ctx) or EVP_MAC_CTX_get_params(ctx, params) with OSSL_MAC_PARAM_SIZE	Retrieve MAC output size (16 bytes)

📖 Description

Support for computing Poly1305 MACs through the EVP_MAC API.

🔑 Identity

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

"POLY1305", "provider=default"

⚙️ 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():

• OSSL_MAC_PARAM_KEY (<octet string>) — Sets the MAC key. Setting this parameter is identical to passing a key to EVP_MAC_init(3).

The following parameters can be retrieved with EVP_MAC_CTX_get_params():

• 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 should not exceed that of an unsigned int.

📝 Notes

The OpenSSL implementation of the Poly 1305 MAC corresponds to RFC 7539.

It is critical to never reuse the key. The security implication noted in RFC 8439 applies equally to the OpenSSL implementation.

📚 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-POLY1305(7SSL)

🏷️ NAME 🚀 Quick Reference 📖 Description 📝 Notes 📚 See Also ©️ Copyright