Security Analysis of Two Authenticated Encryption Schemes

Authenticated encryption scheme is very useful for transmitting a confidential message in insecure networks. Recently, Li et al. give a new forward-security authenticated encryption scheme, and Hung-Yu Chien also give a convertible authenticated encryption scheme. However, our analysis shows that the two schemes are extremely insecure. The common flaw of the two schemes is forgeability and repudiation. After we give the corresponding attack to the two authenticated encryption schemes respectively, we propose two secure publicly verifiable authenticated encryption schemes to overcome the flaws of Li et al. scheme and Hung-Yu Chien scheme. As for efficiency, the computation cost and communication overhead of our proposed schemes are about as small as the two original schemes: Li et al. scheme and Hung-Yu Chien scheme. In second improved scheme, we do not use hash function yet, and the scheme satisfies forward security. Finally, secure proof of the scheme is given.