Specifically catalyzes the degradation of N,N'-diacetylchitobiose. Key enzyme in the chitin catabolic cascade. H2O + N,N'-diacetylchitobiose = acetate + N-acetyl-beta-D-glucosaminyl-(1->4)-D-glucosamine Glycan degradation; chitin degradation. Belongs to the polysaccharide deacetylase family. Carbohydrate-binding module 12 subfamily.