  In this paper, we show a new tagging scheme for cryptographic protocol
messages. Under this tagging, equational theories of operators such as
exclusive-or, binary addition etc. are effectively disabled, when terms are
unified. We believe that this result has a significant impact on protocol
analysis and security, since unification is at the heart of symbolic protocol
analysis. Hence, disabling equational theories in unification implies disabling
them altogether in protocol analysis for most operators and theories.
