Yamaguchi, Okayama, and Miyahara proposed a simple but efficient authentication system, SPLICE/AS. In this article, we show that their method is vulnerable to the guessing attack. An attacker can obtain the password, private-key, and public-key of the user. To overcome the vulnerability of SPLICE/AS to the guessing attack, we propose an improvement of their system. In our scheme, we not only pr...

In this paper, we describe efficient forgery and full-key recovery attacks on the `-IC− signature scheme recently proposed at PKC 2007. This cryptosystem is a multivariate scheme based on a new internal quadratic primitive which avoids some drawbacks of previous multivariate schemes: the scheme is extremely fast since it requires one exponentiation in a finite field of medium size and the publi...

At Crypto’98, Cramer and Shoup [1] proposed a public key cryptosystem that is provably secure against the adaptive chosen ciphertext attacks. Recently, Zhu, Chan, and Deng [2] proposed a variation of Cramer and Shoup’s scheme (the Zhu-Chan-Deng scheme in short) which attempts to reduce Cramer and Shoup’s public key cryptosystem in terms of both the size of the ciphertext and the computation req...

The security of two public key encryption schemes relying on the hardness of different computational problems in non-abelian groups is investigated. First, an attack on a conceptual public key scheme based on Grigorchuk groups is presented: We show that from the public data one can easily derive an ‘equivalent’ secret key that allows the decryption of arbitrary messages encrypted under the publ...

In this paper we present a new practical key-recovery attack on the SFLASH signature scheme. SFLASH is a derivative of the older C∗ encryption and signature scheme that was broken in 1995 by Patarin. In SFLASH, the public key is truncated, and this simple countermeasure prevents Patarin’s attack. The scheme is well-known for having been considered secure and selected in 2004 by the NESSIE proje...

In applications of public-key encryption schemes, anonymity(key-privacy) as well as security(data-privacy) is useful and widely desired. In this paper some new and general concepts in public-key encryption, i.e., “master-key anonymity”, “relevant master-key anonymity” and “key-integrity”, are introduced(the former two are defined for IBE schemes and the latter one is for any public-key encrypti...

NTRU is an efficient public-key cryptosystem proposed by Hoffstein, Pipher, and Silverman. Assuming access to a decryption oracle, we show ways to recover the private key of NTRU systems that do not include a ciphertext validating procedure. The strongest of our methods will employ just a single call to the oracle, and in all cases, the number of calls needed will be small enough to be realistic.

In this paper, we address the Authenticated Key Agreement(AKA) between actor and sensor nodes in Wireless Sensor and Actor Network (WSAN). We propose DoS-resilient AKA scheme between Actor and Sensor nodes in WSAN. The proposed scheme utilizes the IDbased cyrptosystem to reduce a need to transmit public-key certificates. The proposed scheme is resilient against the Denial of Service (DoS) attac...

In this paper we propose, in a methodological manner, four different applications of Wavelet transforms in the Side-channel context. The proposed applications are involved in several Side-channel analysis aspects: acquisition of traces, patterns detection, noise filtering and secret-key recovery.

Let N = pq be the product of two large unknown primes of equal bit-size. Wiener’s famous attack on RSA shows that using a public key (N, e) satisfying ed− k(N + 1− (p+ q)) = 1 with d < 1 3 N makes RSA completely insecure. The number of such weak keys can be estimated as N 1 4−ε. In this paper, we present a generalization of Wiener’s attack. We study two new classes of exponents satisfying an eq...