A type flaw attack on a security protocol is an attack where a field in a message that was originally intended to have one type is subsequently interpreted as having another type. Heather et al. proves that type flaw attacks can be prevented with the technique of tagging each field with the information that indicates its intended type. We simplify Heather et al.'s tagging scheme by combining all the tags inside each encrypted component into a single tag and by omitting the tags on the outmost level. The simplification reduces the sizes of messages in the security protocol. We also formally prove our simplified tagging scheme is as secure as Heather et al.'s with the strand space method. Note that Heather et al.'s tagging scheme and our simplified tagging are applicable to, not just one protocol, but a variety of security protocols.
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