Once a permutation has been generated from the link, its application to the block as a reversible cellular automaton follows directly. As mentioned above (section 2.1.2), block encryption uses a 6-cell frame to transform states of the irreversible cellular automaton of the diffusion phase to states of the reversible cellular automaton for the substitution phase. The reversible cellular automaton is applied only to the 384 bits of ciphertext from the previous round which are a function of the block. Thus, when interpreted as the block for a 64-state reversible CA, the block contains but 64 cells. These 64 cells can be updated in parallel by 64 processors executing the permutation. After each update, the reading frame shifts by one (2-state) cell (to the right during encryption, and to the left during decryption). This permits the reversible rules to perform some local diffusion in addition to its primary function of substitution.
Decryption works exactly like encryption. Note that during decryption the link is extracted in 10-bit pieces from the block during the diffusion phase. The link must be link-decrypted before the permutation corresponding to the reversible rule for the subround substitution phase can be generated. This permutation must be inverted before it is applied to the block for the decryption substitution phase.