Fractionate

verb

1. To separate (a mixture) into its individual constituents by exploiting differences in some chemical or physical property, such as boiling point, particle size, solubility etc.

   "Crude oil is fractionated in a refinery to produce a number of different petroleum products."

2. To divide each plaintext symbol into several ciphertext symbols as a preliminary stage of encryption.
3. To use the technique of fractionation in hypnosis.