One difference between the proposed embedding method and the translation-based embedding methods is that the former restricts the length of a permutation to be the same as the cover sentence so that the receiver is able to recover the list of permutations; while the latter allows a permutation to only include a subset of the input words and therefore provides more choices for a given cover sentence.
dropping words introduces the risk of deleting information in the cover sentence and may lead to incoherence in the resulting text.