Ku-Young Chang

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We determine all the non-abelian normal CM-fields of degree 24 with class number one, provided that the Galois group of their maximal real subfields is isomorphic to A4, the alternating group of degree 4 and order 12. There are two such fields with Galois group A4 × C2 (see Theorem 14) and at most one with Galois group SL2(F3) (see Theorem 18); if the(More)
In this paper we propose an efficient OT N 1 scheme in the bounded storage model, which is provably secure without complexity assumptions. Under the assumption that a public random string of M bits is broadcasted, the protocol is secure against any computationally unbounded dishonest receiver who can store τ M bits, τ < 1. The protocol requires the sender(More)
Let N be an imaginary abelian number field. We know that h − N , the relative class number of N , goes to infinity as f N , the conductor of N , approaches infinity, so that there are only finitely many imaginary abelian number fields with given relative class number. First of all, we have found all imaginary abelian number fields with relative class number(More)
In this paper, we consider some aspects of binding properties that bind an anonymous user with messages. According to whether all the messages or some part of the messages are bound with an anonymous user, the protocol is said to satisfy the full binding property or the partial binding property, respectively. We propose methods to combine binding properties(More)
In this paper, we discuss a simple encryption scheme in which a secret file is encrypted twice: one by a common encryption algorithm like AES and another by XOR. Despite the first key is revealed by guessing or dictionary-based attack, the attacker can not reconstruct the original secret until knows the files used to derive the second key block according to(More)
Homomorphic encryption scheme is one of the useful tools for handling encrypted information in storage services. However, most of existing schemes have not been used in practical applications due to their inefficiency or lack of functionalities. For example, fully homomorphic encryption, which can provide arbitrary operations, is inefficient. On the other(More)