Sentence:  In particular we study the case where cryptographic primitives are modelled using a <WSD>"group theory</WSD>". <WSD>Group theories</WSD> are a special case of monoidal theories which have been extensively studied by F. Baader and W. Nutt [20,6] who have provided a complete survey of unification in these theories. <WSD>Group theories</WSD> include theories for exclusive or and Abelian groups. 
Meaning of the word marked with <WSD> tags:  (nodot=1); a theory about (particular kinds of) groups.