Unconditionally Secure Authenticated Encryption

Junji SHIKATA  Goichiro HANAOKA  Yuliang ZHENG  Tsutomu MATSUMOTO  Hideki IMAI  

IEICE TRANSACTIONS on Fundamentals of Electronics, Communications and Computer Sciences   Vol.E87-A   No.5   pp.1119-1131
Publication Date: 2004/05/01
Online ISSN: 
Print ISSN: 0916-8508
Type of Manuscript: Special Section LETTER (Special Section on Discrete Mathematics and Its Applications)
unconditional security,  encryption,  authenticated encryption,  signcryption,  

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In this paper, we formally define and analyze the security notions of authenticated encryption in unconditional security setting. For confidentiality, we define the notions, APS (almost perfect secrecy) and NM (non-malleability), in terms of an information-theoretic viewpoint along with our model where multiple senders and receivers exist. For authenticity, we define the notions, IntC (integrity of ciphertexts) and IntP (integrity of plaintexts), from a view point of information theory. And then we combine the above notions to define the security notions of unconditionally secure authenticated encryption. Then, we analyze relations among the security notions. In particular, it is shown that the strongest security notion is the combined notion of APS and IntC. Finally, we formally define and analyze the following generic composition methods in the unconditional security setting along with our model: Encrypt-and-Sign, Sign-then-Encrypt and Encrypt-then-Sign. Consequently, it is shown that: the Encrypt-and-Sign composition method is not always secure; the Sign-then-Encrypt composition method is not always secure; and the Encrypt-then-Sign composition method is always secure, if a given encryption meets APS and a given signature is secure.