Editing SEED (section)

== Design ==

SEED is a 16-round [[Feistel network]] with [[block size (cryptography)|128-bit blocks]] and a [[key size|128-bit key]]. It uses two 8 × 8 [[S-box]]es which, like those of [[Secure and Fast Encryption Routine|SAFER]], are derived from discrete [[exponentiation]] (in this case, x<sup>247</sup> and x<sup>251</sup> &ndash; plus some "incompatible operations"). It also has some resemblance to [[MISTY1]] in the recursiveness of its structure: the 128-bit full cipher is a Feistel network with an F-function operating on 64-bit halves, while the F-function itself is a Feistel network composed of a G-function operating on 32-bit halves. However the recursion does not extend further because the G-function is not a Feistel network. In the G-function, the 32-bit word is considered as four 8-bit bytes, each of which is passed through one or the other of the S-boxes, then combined in a moderately complex set of [[boolean function]]s such that each output bit depends on 3 of the 4 input bytes.

SEED has a fairly complex [[key schedule]], generating its thirty-two 32-bit subkeys through application of its G-function on a series of rotations of the raw key, combined with round constants derived (as in [[Tiny Encryption Algorithm|TEA]]) from the [[Golden ratio]].