BassOmatic

BassOmatic
General
Designers	Phil Zimmermann
First published	1991
Cipher detail
Key sizes	8 to 2048 bits
Block sizes	2048 bits
Rounds	1–8

In cryptography, BassOmatic was the symmetric-key cipher designed by Phil Zimmermann as part of his email encryption software PGP (in the first release, version 1.0). Comments in the source code indicate that he had been designing the cipher since as early as 1988, but it was not publicly released until 1991. After Eli Biham pointed out to him several serious weaknesses in the BassOmatic algorithm over lunch at the 1991 CRYPTO conference,^[1] Zimmermann replaced it with IDEA in subsequent versions of PGP.

The name is explained in this comment from the source code: "BassOmatic gets its name from an old Dan Aykroyd Saturday Night Live skit involving a blender and a whole fish. The BassOmatic algorithm does to data what the original BassOmatic did to the fish."

Algorithm

The algorithm operates on blocks of 256 bytes (or 2048 bits). The actual key size can be anywhere from 8 to 2048 bits. The 6 least-significant bits of the key are control bits, used to choose between several possible variations. The number of rounds is 1 to 8, depending on the 3 lowest control bits. Bit 4 selects between two possible key schedules: one using the key to seed a pseudorandom number generator, the other using BassOmatic itself. Making such variations key-dependent means that some keys must be weaker than others; the key space is not flat.

The chosen key schedule produces a total of 8 permutation tables, each a permutation of the numbers 0 to 255. Each round consists of 4 operations: XORing the block with one of the permutation tables, shredding or permuting individual bits throughout the block, an unkeyed diffusion called raking, and a substitution step using the permutation tables as S-boxes. The shredding step can either permute all 8 bit-planes independently, or in groups of 4, depending on control bit 3. The permutation tables stay the same through all rounds of encryption on a given block, but if control bit 5 is set, then the tables are regenerated after each block.

References

↑ Garfinkel, Simson (December 1, 1994). PGP: Pretty Good Privacy. O'Reilly Media. pp. 101–102. ISBN 978-1-56592-098-9.

External links

PGPkeys.org – downloads of older PGP software, including version 1.0 source
The Super Bass-O-Matic '76 – Saturday Night Live episode originally aired on April 17, 1976.

Block ciphers (security summary)
Common algorithms	AES Blowfish DES (Internal Mechanics, Triple DES) Serpent Twofish
Less common algorithms	Camellia CAST-128 IDEA RC2 RC5 RC6 SEED ARIA Skipjack TEA XTEA
Other algorithms	3-Way Akelarre Anubis 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 Kalyna KASUMI KeeLoq KHAZAD Khufu and Khafre KN-Cipher Kuznyechik 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 Prince Q RC6 REDOC Red Pike S-1 SAFER SAVILLE SC2000 SHACAL SHARK Simon SM4 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 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
Utilization	Initialization vector Mode of operation Padding

Cryptography
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