EAX mode

This article is about the mode of operation. For Creative EAX, see Environmental Audio Extensions.

EAX mode is a mode of operation for cryptographic block ciphers. It is an Authenticated Encryption with Associated Data (AEAD) algorithm designed to simultaneously provide both authentication and privacy of the message (authenticated encryption) with a two-pass scheme, one pass for achieving privacy and one for authenticity for each block.

EAX mode was submitted on October 3, 2003 to the attention of NIST in order to replace CCM as standard AEAD mode of operation, since CCM mode lacks some desirable attributes of EAX and is more complex.

Encryption and authentication

EAX is a flexible nonce-using two-pass AEAD scheme with no restrictions on block cipher primitive to be used, nor on block size, and supports arbitrary-length messages. Authentication tag length is arbitrarily sizeable up to the used cipher's block size.

The block cipher primitive is used in CTR mode for encryption and as OMAC for authentication over each block through the EAX composition method, that may be seen as a particular case of a more general algorithm called EAX2 and described in "The EAX Mode of Operation" paper.

The reference implementation in the aforementioned paper uses AES in CTR mode for encryption combined with AES OMAC for authentication.

Performance

Being a two-pass scheme, EAX mode is slower than a well designed one-pass scheme based on the same primitives.

EAX mode has several desirable attributes, notably:

provable security (dependent on the security of the underlying primitive cipher);
message expansion is minimal, being limited to the overhead of the tag length;
using CTR mode means the cipher need be implemented only for encryption, in simplifying implementation of some ciphers (especially desirable attribute for hardware implementation);
the algorithm is "on-line", that means that can process a stream of data, using constant memory, without knowing total data length in advance;
the algorithm can pre-process static Associated Data (AD), useful for encryption/decryption of communication session parameters (where session parameters may represent the Associated Data).

Notably, CCM mode lacks the last 2 attributes (CCM can process Associated Data, it can't pre-process it).

Patent status

The authors of EAX mode, Mihir Bellare, Phillip Rogaway, and David Wagner placed the work under public domain and have stated that they were unaware of any patents covering this technology. Thus, EAX mode of operation is believed to be free and unencumbered for any use.

Use

A modification of the EAX mode, so called EAX′ or EAXprime, is used in the ANSI C12.22 standard for transport of meter-based data over a network. In 2012 Kazuhiko Minematsu, Hiraku Morita and Tetsu Iwata published a flaw in this mode that breaks the security.^[1]

References

↑ Cryptanalysis of EAXprime

External links

Software implementations

Hardware implementations

Block ciphers (security summary)

Common algorithms	AES (Implementations) Blowfish DES (Internal Mechanics, Triple DES) Serpent Twofish

Less common algorithms	Camellia CAST-128 IDEA RC2 RC5 SEED Skipjack TEA XTEA

Other algorithms	3-Way Akelarre Anubis ARIA BaseKing BassOmatic BATON BEAR and LION CAST-256 Chiasmus CIKS-1 CIPHERUNICORN-A CIPHERUNICORN-E CLEFIA CMEA Cobra COCONUT98 Crab Cryptomeria/C2 CRYPTON CS-Cipher DEAL DES-X DFC E2 FEAL FEA-M FROG G-DES GOST Grand Cru Hasty Pudding cipher Hierocrypt ICE IDEA NXT Intel Cascade Cipher Iraqi KASUMI KeeLoq KHAZAD Khufu and Khafre KN-Cipher Ladder-DES Libelle LOKI (97, 89/91) Lucifer M6 M8 MacGuffin Madryga MAGENTA MARS Mercy MESH MISTY1 MMB MULTI2 MultiSwap New Data Seal NewDES Nimbus NOEKEON NUSH PRESENT Q RC6 REDOC Red Pike S-1 SAFER SAVILLE SC2000 SHACAL SHARK Simon SMS4 Speck Spectr-H64 Square SXAL/MBAL Threefish Treyfer UES Xenon xmx XXTEA Zodiac

Design	Feistel network Key schedule Lai-Massey scheme Product cipher S-box P-box SPN Avalanche effect Block size Key size Key whitening (Whitening transformation)

Attack (cryptanalysis)	Brute-force (EFF DES cracker) MITM (Biclique attack, 3-Subset MITM attack) Linear (Piling-up lemma) Differential (Impossible Truncated Higher-order) Differential-linear Integral/Square Boomerang Mod n Related-key Slide Rotational Timing XSL Interpolation Partitioning Davies' Rebound Weak key Tau Chi-square Time/memory/data tradeoff

Standardization	AES process CRYPTREC NESSIE

Utilization	Initialization vector Mode of operation Padding

Hash functions & message authentication codes

Security summary

Common functions	MD5 SHA-1 SHA-2 SHA-3/Keccak

SHA-3 finalists	BLAKE Grøstl JH Skein Keccak (winner)

Other functions	FSB ECOH GOST HAS-160 HAVAL LM hash MDC-2 MD2 MD4 MD6 N-Hash RadioGatún RIPEMD SipHash Snefru SWIFFT Tiger VSH WHIRLPOOL crypt(3) (DES)

MAC algorithms	DAA CBC-MAC HMAC OMAC/CMAC PMAC VMAC UMAC Poly1305-AES

Authenticated encryption modes	CCM CWC EAX GCM IAPM OCB

Attacks	Collision attack Preimage attack Birthday attack Brute force attack Rainbow table Distinguishing attack Side-channel attack Length extension attack

Design	Avalanche effect Hash collision Merkle–Damgård construction

Standardization	CRYPTREC NESSIE NIST hash function competition

Utilization	Salt Key stretching

Cryptography

History of cryptography Cryptanalysis Cryptography portal Outline of cryptography

Symmetric-key algorithm Block cipher Stream cipher Public-key cryptography Cryptographic hash function Message authentication code Random numbers Steganography