- BassOmatic
Infobox block cipher
name = BassOmatic
caption =
designers =Phil Zimmermann
publish date = 1991
derived from =
derived to =
related to =
key size = 8 to 2048 bits
block size = 2048 bits
structure =
rounds = 1–8
cryptanalysis =In
cryptography , BassOmatic was thesymmetric-key cipher designed byPhil Zimmermann as part of his email encryption software, PGP (in the first release, version 1.0). Comments in thesource code indicate that he had been designing the cipher since as early as 1988, but it was not publicly released until 1991. AfterEli Biham pointed out to him several serious weaknesses in the BassOmatic algorithm over lunch at the 1991CRYPTO conference, [cite book | last = Garfinkel | first = Simson | authorlink = Simson Garfinkel | title = PGP: Pretty Good Privacy | publisher =O'Reilly Media | date =December 1 1994 | location = | pages = pp.101–102 | isbn = 978-1565920989] 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."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 possiblekey schedule s: one using the key to seed apseudorandom number generator , the other using BassOmatic itself. Making such variations key-dependent means some keys are surely weaker than others; thekey 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:XOR ing 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 8bit-plane s 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
External links
* [http://www.pgpkeys.org/software.html PGPkeys.org] - downloads of older PGP software, including version 1.0 source
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