Message authentication code

In cryptography, a message authentication code (MAC), sometimes known as an authentication tag, is a short piece of information used for authenticating and integrity-checking a message. In other words, it is used to confirm that the message came from the stated sender (its authenticity) and has not been changed (its integrity). The MAC value allows verifiers (who also possess a secret key) to detect any changes to the message content.

Pr [ k ← G(1), V( k, x, S(k, x) ) = accepted ] = 1.

A MAC is unforgeable if for every efficient adversary A

tag = (am + b) mod p, where p is prime.

More generally, k-independent hashing functions provide a secure message authentication code as long as the key is used less than k times for k-ways independent hashing functions.

Message authentication codes and data origin authentication have been also discussed in the framework of quantum cryptography. By contrast to other cryptographic tasks, such as key distribution, for a rather broad class of quantum MACs it has been shown that quantum resources do not offer any advantage over unconditionally secure one-time classical MACs.

Standards

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Various standards exist that define MAC algorithms. These include:

• FIPS PUB 113 Computer Data Authentication, withdrawn in 2002, defines an algorithm based on DES.
• FIPS PUB 198-1 The Keyed-Hash Message Authentication Code (HMAC)
• NIST SP800-185 SHA-3 Derived Functions: cSHAKE, KMAC, TupleHash, and ParallelHash
• ISO/IEC 9797-1 Mechanisms using a block cipher
• ISO/IEC 9797-2 Mechanisms using a dedicated hash-function
• ISO/IEC 9797-3 Mechanisms using a universal hash-function
• ISO/IEC 29192-6 Lightweight cryptography - Message authentication codes

ISO/IEC 9797-1 and -2 define generic models and algorithms that can be used with any block cipher or hash function, and a variety of different parameters. These models and parameters allow more specific algorithms to be defined by nominating the parameters. For example, the FIPS PUB 113 algorithm is functionally equivalent to ISO/IEC 9797-1 MAC algorithm 1 with padding method 1 and a block cipher algorithm of DES.

An example of MAC use

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In this example, the sender of a message runs it through a MAC algorithm to produce a MAC data tag. The message and the MAC tag are then sent to the receiver. The receiver in turn runs the message portion of the transmission through the same MAC algorithm using the same key, producing a second MAC data tag. The receiver then compares the first MAC tag received in the transmission to the second generated MAC tag. If they are identical, the receiver can safely assume that the message was not altered or tampered with during transmission (data integrity).

However, to allow the receiver to be able to detect replay attacks, the message itself must contain data that assures that this same message can only be sent once (e.g. time stamp, sequence number or use of a one-time MAC). Otherwise an attacker could – without even understanding its content – record this message and play it back at a later time, producing the same result as the original sender.

See also

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• Checksum
• CMAC
• HMAC (hash-based message authentication code)
• MAA
• MMH-Badger MAC
• Poly1305
• Authenticated encryption
• UMAC
• VMAC
• SipHash
• KMAC

Notes

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R. Shirey (August 2007). Internet Security Glossary, Version 2. Network Working Group. doi:10.17487/RFC4949. Jean-Philippe Aumasson & Daniel J. Bernstein (18 September 2012). "SipHash: a fast short-input PRF" (PDF).
1. ↑ "FIPS PUB 113 Computer Data Authentication". Archived from the original on 27 September 2011. Retrieved 10 October 2010.
2. ↑ "ISO/IEC 9797-1:2011". ISO. Retrieved 20 December 2023.
3. ↑ "ISO/IEC 29192-6:2019". ISO. Retrieved 20 December 2023.
4. ↑

   References

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   • Pass, Rafael, A Course in Cryptography (PDF), retrieved 31 December 2015

   External links

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   • RSA Laboratories entry on MACs
   • Ron Rivest lecture on MACs

   v t e Cryptographic hash functions and message authentication codes List Comparison Known attacks Common functions MD5 (compromised) SHA-1 (compromised) SHA-2 SHA-3 BLAKE2 SHA-3 finalists BLAKE Grøstl JH Skein Keccak (winner) Other functions BLAKE3 CubeHash ECOH FSB Fugue GOST HAS-160 HAVAL Kupyna LSH Lane MASH-1 MASH-2 MD2 MD4 MD6 MDC-2 N-hash RIPEMD RadioGatún SIMD SM3 SWIFFT Shabal Snefru Streebog Tiger VSH Whirlpool Password hashing/ key stretching functions Argon2 Balloon bcrypt Catena crypt LM hash Lyra2 Makwa PBKDF2 scrypt yescrypt General purpose key derivation functions HKDF KDF1/KDF2 MAC functions CBC-MAC DAA GMAC HMAC NMAC OMAC/CMAC PMAC Poly1305 SipHash UMAC VMAC Authenticated encryption modes CCM ChaCha20-Poly1305 CWC EAX GCM IAPM OCB Attacks Collision attack Preimage attack Birthday attack Brute-force attack Rainbow table Side-channel attack Length extension attack Design Avalanche effect Hash collision Merkle–Damgård construction Sponge function HAIFA construction Standardization CAESAR Competition CRYPTREC NESSIE NIST hash function competition Password Hashing Competition NSA Suite B CNSA Utilization Hash-based cryptography Merkle tree Message authentication Proof of work Salt Pepper

   v t e Cryptography
   General	History of cryptography Outline of cryptography Classical cipher Cryptographic protocol Authentication protocol Cryptographic primitive Cryptanalysis Cryptocurrency Cryptosystem Cryptographic nonce Cryptovirology Hash function Cryptographic hash function Key derivation function Secure Hash Algorithms Digital signature Kleptography Key (cryptography) Key exchange Key generator Key schedule Key stretching Keygen Machines Ransomware Random number generation Cryptographically secure pseudorandom number generator (CSPRNG) Pseudorandom noise (PRN) Secure channel Insecure channel Subliminal channel Encryption Decryption End-to-end encryption Harvest now, decrypt later Information-theoretic security Plaintext Codetext Ciphertext Shared secret Trapdoor function Trusted timestamping Key-based routing Onion routing Garlic routing Kademlia Mix network
   Mathematics	Cryptographic hash function Block cipher Stream cipher Symmetric-key algorithm Authenticated encryption Public-key cryptography Quantum key distribution Quantum cryptography Post-quantum cryptography Message authentication code Random numbers Steganography
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