Related-key attack (RKA) is a kind of side-channel attack considered for kinds of cryptographic primitives, such as public key encryption, digital signature, pseudorandom functions etc. However, we note that the RKA-security seems to be not considered for identity-based signature (IBS), which is an important primitive for identity-based cryptography and proposed by Shamir in 1984. In this paper, for the first time, we introduce the RKA security into IBS schemes and try to define the security model for it. More specifically, we consider the RKA occurs in the users' signing key or the master key of the key-generation center (KGC), which derives two kinds of RKA securities for IBS. Meanwhile, we illustrate that the most efficient Schnorr-like IBS scheme proposed by Galindo and Garcia is RKA-insecure by launching a simple RKA. However, a slight modification of it yields a RKA-secure IBS scheme, for which we give the detailed security proof in the random oracle. Finally, the performance analysis shows that the modified scheme is still extremely efficient but has higher security.

Homomorphic signature is an extremely important public key authentication technique for network coding to defend against pollution attacks. As a public key cryptographic primitive, it also encounters the same problem of how to confirm the relationship between some public key pk and the identity ID of its owner. In the setting of distributed network coding, the intermediate and destination nodes need to use the public key of source node S to check the validity of vector-signature pairs. Therefore, the binding of S and its corresponding public key becomes crucial. The popular and traditional solution is based on certificates which are issued by a trusted certification authority (CA) center. However, the generation and management of certificates is extremely cumbersome. Hence, in recent work, Lin et al. proposed a new notion of identity-based homomorphic signature, which intends to avoid using certificates. But the key escrow problem is inevitable for identity-based primitives. In this article, we propose another new notion (for network coding): certificateless homomorphic signature (CLHS), which is a compromise for the above two techniques. In particular, we first describe the definition and security model of certificateless homomorphic signature. Then based on bilinear map and the computational Diffie-Hellman (CDH) assumption, give a concrete implementation and detailedly analyze its security. Finally, performance analysis illustrates that our construction is practical.

Storing multi-copy of data file on multi-cloud may be useful in some practical contexts. How to ensure the integrity of a user’s multi-copy becomes very important in this case. In recent work, Li et al. proposed an efficient “identity-based” auditing protocol (LYZ-protocol, for short) to achieve this goal. The “identity-based” property guarantees that the resulting primitive does not rely on PKI to manage certificates. However, in this letter, we note that the performances of this protocol can be further improved. More precisely, by introducing a new hash function modeled as a random oracle, the communication costs of original LYZ-protocol can be greatly reduced. In addition, the building block of a traditional signature scheme used in this protocol results in the entire protocol not being completely identity-based, and thus it may still bear the burden of managing certificates. Therefore, by replacing this signature with an identity-based scheme, we can obtain a completely identity-based protocol. Finally, the performance analysis shows that the modified LYZ-protocol outperforms the original one.

In recent years, how to design secure and efficient cloud storage auditing (CSA) protocols, which enable users to verify whether the cloud server still keeps their stored data undamaged, is a research hotspot, and many candidates were proposed. Recently, Chen et al. (2020) just suggested a usable CSA (UCSA) protocol by combining error correcting codes with homomorphic authentication technique, and claimed that their protocol is secure. However, in this article, we analyze the security of Chen et al. ’s construction and find that this protocol is completely insecure. In particular, after receiving data owner’s authenticated data, the cloud server only needs to compute and store the much shorter parity codes (derived from all the data blocks) instead of the blocks themselves. Then, it can correctly forge and return a proof, which is able to pass the checking of the verifier, even if it does not truly store original data blocks. In addition, we provide an improved UCSA (iUCSA) protocol on the remedy of the weaknesses of Chen et al. ’s scheme. A detailed security analysis is also performed within the framework of Chen et al. Finally, the performance analysis shows that the protocol iUCSA is practical.