By configuring an adequate set of messages obtained by an adversary and analyzing the information which can be obtained by an adversary, it is possible to verify the secrecy of cryptography protocols. We have already proposed a deduction system for analyzing whether an adversary can obtain relational information between contents or keys of two ciphertexts, such as "the contents of two ciphertexts are equal" or "the keys of two cipehrtexts are different". We have also proposed the semantics of this system. In the semantics, acquisition of relational information by an adversary is intuitionistically defined as his ability to show the evidence to succeed in obtaining the information. In this paper, we reconsider the deduction system as a kind of epistemic logic, and give Kripke semantics for the system. In Kripke semantics, acquisition of relational information by an adversary can be naturally defined as his knowledge of relational information. We also make a comparison between the two semantics.