In this paper we revisit the security models of certificateless signatures and propose two new constructions which are provably secure in the random oracle model. We divide the potential adversaries according to their attack power, and for the first time, three new kinds of adversaries are introduced into certificateless signatures. They are Normal Adversary, Strong Adversary and Super Adversar...

Based on a novel proof model we prove security for simple discrete log cryptosystems for which security has been an open problem. We consider a combination of the random oracle (RO) model and the generic model. This corresponds to assuming an ideal hash function H given by an oracle and an ideal group of prime order q, where the binary encoding of the group elements is useless for cryptographic...

In 2003, Boneh, Gentry, Lynn and Shacham (BGLS) devised the first provably-secure aggregate signature scheme. Their scheme uses bilinear pairings and their security proof is in the random oracle model. The first pairing-based aggregate signature scheme which has a security proof that does not make the random oracle assumption was proposed in 2006 by Lu, Ostrovsky, Sahai, Shacham and Waters (LOS...

To date, there exist three short signature schemes from bilinear pairings. In this paper, we propose a new signature scheme that is existentially unforgeable under a chosen message attack without random oracle. The security of our scheme depends on a new complexity assumption called the k+1 square roots assumption. We also discuss the relationship between the k+1 square roots assumption and som...

A protocol compiler is described, that transforms any provably secure authenticated 2-party key establishment into a provably secure authenticated group key establishment with 2 more rounds of communication. The compiler introduces neither idealizing assumptions nor high-entropy secrets, e. g., for signing. In particular, applying the compiler to a password-authenticated 2-party key establishme...

Ring signature enables an user to anonymously sign a message on behalf of a group of users termed as ‘ring’ formed in an ‘ad-hoc’ manner. A naive scheme produces a signature linear in the size of the ring, but this is extremely inefficient when ring size is large. Dodis et al. proposed a constant size scheme in EUROCRYPT’13, but provably secure in random oracle model. Best known result without ...

We investigate a new notion of security for “cryptographic functions” that we term seed incompressibility (SI). We argue that this notion captures some of the intuition for the alleged security of constructions in the random-oracle model, and indeed we show that seed incompressibility suffices for some applications of the random oracle methodology. Very roughly, a function family fs(·) with |s|...

A security proof in the Bellare–Rogaway model and the random oracle model is provided for a protocol closely based on one originally proposed by Boyd (1996), which enjoys some remarkable efficiency properties. The model is extended so that it can detect a known weakness of the protocol that cannot be captured in the original model. An alternative protocol, provably secure in the extended model ...