Mercy (cipher) - Wikipedia

Mercy
General
Designers	Paul Crowley
First published	April 2000^[1]
Derived from	WAKE
Cipher detail
Key sizes	128 bits
Block sizes	4096 bits
Structure	Feistel network
Rounds	6
Best public cryptanalysis
Scott Fluhrer's differential attack breaks the cipher.^[2]

In cryptography, Mercy is a tweakable block cipher designed by Paul Crowley for disk encryption.

The block size is 4096 bits—unusually large for a block cipher, but a standard disk sector size. Mercy uses a 128-bit secret key, along with a 128-bit non-secret tweak for each block. In disk encryption, the sector number would be used as a tweak. Mercy uses a 6-round Feistel network structure with partial key whitening. The round function uses a key-dependent state machine which borrows some structure from the stream cipher WAKE, with key-dependent S-boxes based on the Nyberg S-boxes also used in AES.

Scott Fluhrer has discovered a differential attack that works against the full 6 rounds of Mercy. This attack can even be extended to a seven-round variant.^[2]

References

^ Paul Crowley, Mercy: A fast large block cipher for disk sector encryption. In Bruce Schneier, editor, Fast Software Encryption: 7th International Workshop, volume 1978 of Lecture Notes in Computer Science, pages 49-63, New York City, USA, April 2000. Springer-Verlag.
^ ^a ^b Scott Fluhrer (2 April 2006). Cryptanalysis of the Mercy Block Cipher (PostScript). Fast Software Encryption Workshop 2001. Royal Park Hotel Nikko, Yokohama, Japan: Cisco Systems, Inc. Retrieved 15 December 2006.

v t e Block ciphers (security summary)
Common algorithms	AES Blowfish DES (internal mechanics, Triple DES) Serpent SM4 Twofish
Less common algorithms	ARIA Camellia CAST-128 GOST IDEA LEA RC5 RC6 SEED Skipjack TEA XTEA
Other algorithms	3-Way Adiantum Akelarre Anubis Ascon 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 Grand Cru Hasty Pudding cipher Hierocrypt ICE IDEA NXT Intel Cascade Cipher Iraqi Kalyna KASUMI KeeLoq KHAZAD Khufu and Khafre KN-Cipher Kuznyechik Ladder-DES 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 Prince Q RC2 REDOC Red Pike S-1 SAFER SAVILLE SC2000 SHACAL SHARK Simon Speck Spectr-H64 Square SXAL/MBAL Threefish Treyfer UES xmx XXTEA Zodiac
Design	Feistel network Key schedule Lai–Massey scheme Product cipher S-box P-box SPN Confusion and diffusion Round 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 Distinguishing (Known-key) Integral/Square Boomerang Mod n Related-key Slide Rotational Side-channel Timing Power-monitoring Electromagnetic Acoustic Differential-fault XSL Interpolation Partitioning Rubber-hose Black-bag Davies Rebound Weak key Tau Chi-square Time/memory/data tradeoff
Standardization	AES process CRYPTREC NESSIE NSA Suite B CNSA
Utilization	Initialization vector Mode of operation Padding

v t e Cryptography
General	History of cryptography Outline of cryptography Cryptographic protocol Authentication protocol Cryptographic primitive Cryptanalysis Cryptocurrency Cryptosystem Cryptographic nonce Cryptovirology Hash function Cryptographic hash function Key derivation function Digital signature Kleptography Key (cryptography) Key exchange Key generator Key schedule Key stretching Keygen Cryptojacking malware 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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