Identity-based key-insulated proxy signature without random oracles

In an identity based proxy signature (IBPS) scheme, a designated proxy signer can generate the signature on behalf of an original signer. Traditional IBPS schemes normally rely on the assumption that private keys are kept perfectly secure. However, due to viruses, worms or other break-ins allowed by operating-system holes, key exposure seems inevitable. To minimize the damage caused by key exposure in IBPS, we propose an identity-based key-insulated proxy signature (IBKIPS) scheme in the standard model, i.e. without random oracles.     

Identity-based verifiably committed signature scheme without random oracles

An identity-based verifiably committed signature scheme （IB-VCS） was proposed, which is proved secure in the standard model （i.e., without random oracles）. It enjoys the setup-free property and stand-alone property, both of which make an exchange protocol more practical. The scheme is unconditionally secure against the cheating signer, its security against the cheating verifier is reduced to the computational Diffie-Hellman （CDH） problem in the underlying group, it is secure against the cheating trusted third party if the underlying Paterson Schuldt＇s identity based signature （IBS） scheme is secure, which is proven true based on the CDH assumption in the standard model.     

An efficient threshold key-insulated signature scheme

To tackle the key-exposure problem in signature settings, this paper introduces a new cryptographic primitive named threshold key-insulated signature (TKIS) and proposes a concrete TKIS scheme. For a TKIS system, at least k out of n helpers are needed to update a user’s temporary private key. On the one hand, even if up to k−1 helpers are compromised in addition to the exposure of any of temporary private keys, security of the non-exposed periods is still assured. On the other hand, even if all the n helpers are compromised, we can still ensure the security of all periods as long as none of temporary private keys is exposed. Compared with traditional key-insulated signature (KIS) schemes, the proposed TKIS scheme not only greatly enhances the security of the system, but also provides flexibility and efficiency.     

Parallel Key-insulated Signature： Framework and Construction

To deal with the key-exposure problem in signature systems, a new framework named parallel key-insulated signature （PKIS） was introduced, and a concrete PKIS scheme was proposed. Compared with traditional key-insulated signature （KIS） schemes, the proposed PKIS scheme allows a frequent updating for temporary secret keys without increasing the risk of helper key-exposure. Moreover, the proposed PKIS scheme does not collapse even if some （not all） of the helper keys and some of the temporary secret keys are simultaneously exposed. As a result, the security of the PKIS scheme is greatly enhanced, and the damage caused by key-exposure is successfully minimized.     

Strong key-insulated signature in the standard model

The only known construction of key-insulated signature (KIS) that can be proven secure in the standard model is based on the approach of using double signing. That is, the scheme requires two signatures: a signature with a master key and a signature with the signer’s secret key. This folklore construction method leads to an inefficient scheme. Therefore it is desirable to devise an efficient KIS scheme. We present the first scheme with such a construction. Our construction derives from some variations of the Waters’ signature scheme. It is computationally efficient and the signatures are short. The scheme is provably secure based on the difficulty of computational Diffie-Hellman (CDH) problem in the standard model.     

一种基于无双线性对映射的无证书代理签密方案

无证书签密是公钥密码体制的一个重要应用,与传统的先签名后加密相比,其计算量和通信成本都要低。借鉴国密SM2标准签名方案设计技巧,提出了一个新的基于无双线性对映射的无证书代理签密方案。随后对协议的正确性、安全性、参数选择和效率进行分析,在适应性选择消息和存在第二类攻击者给出了随机预言机模型下的安全性证明。新方案基于离散对数问题困难假设,由于避免了使用双线性对,因此性能良好;通过与其它方案的对比,计算开销明显低于其它签密方案,分析表明新方案具备较高安全性和效率。     

An improved ring signature scheme without trusted key generation center for wireless sensor network

Security of wireless sensor network (WSN) is a considerable challenge, because of limitation in energy, communication bandwidth and storage. ID-based cryptosystem without checking and storing certificate is a suitable way used in WSN. But key escrow is an inherent disadvantage for traditional ID-based cryptosystem, i.e., the dishonest key generation center (KGC) can forge the signature of any node and on the other hand the node can deny the signature actually signed by him/herself. To solving this problem, we propose an ID-based ring signature scheme without trusted KGC. We also present the accurate secure proof to prove that our scheme is secure against existential forgery on adaptively chosen message and ID attacks assuming the complexity of computational Diffie-Hellman (CDH) problem. Compared with other ring signature schemes, we think proposed scheme is more efficient.