Zodiac uses a 16-round Feistel network structure with key whitening. The round function uses only XORs and S-box lookups. There are two 8×8-bit S-boxes: one based on the discrete exponentiation 45x as in SAFER, the other using the multiplicative inverse in the finite field GF(28), as introduced by SHARK.
Zodiac is theoretically vulnerable to impossible differential cryptanalysis, which can recover a 128-bit key in 2119 encryptions.
Further reading Edit