How to Shorten a Ciphertext of Reproducible Key Encapsulation Mechanisms in the Random Oracle Model

Yusuke SAKAI  Goichiro HANAOKA  Kaoru KUROSAWA  Kazuo OHTA  

IEICE TRANSACTIONS on Fundamentals of Electronics, Communications and Computer Sciences   Vol.E94-A   No.6   pp.1293-1305
Publication Date: 2011/06/01
Online ISSN: 1745-1337
DOI: 10.1587/transfun.E94.A.1293
Print ISSN: 0916-8508
Type of Manuscript: Special Section PAPER (Special Section on Discrete Mathematics and Its Applications)
public key encryption,  chosen-ciphertext security,  key encapsulation mechanism,  

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This paper shows a simple methodology for shortening a ciphertext of reproducible key encapsulation mechanisms. Specifically, it transforms a key encapsulation mechanism having OW-CCCA security and reproducibility into that of IND-CCA secure in the random oracle model whose ciphertext is shorter. Various existing chosen-ciphertext secure key encapsulation mechanisms (in the standard model) are reproducible, and thus their ciphertext can be shortened by the proposed transformation. The transformed scheme requires only one additional hashing for encryption. This property enables us to implement both the original scheme and the transformed scheme into a single chip simultaneously with small gate-size overhead. Using this chip, a sender can flexibly switch schemes to encrypt a message in a message-by-message manner. Such a use of schemes is also analyzed.