Analysis of Collusion-Attack Free ID-Based Non-Interactive Key Sharing.

Oscar García Morchon, Ludo M. G. M. Tolhuizen, Domingo Gómez‐Pérez +1 more

Yun Wei, Fushan Wei, Chuangui Ma

Non-interactive key exchange (NIKE) allows two parties to establish a shared key without communications. In ID-based non-interactive key exchange (ID-NIKE) protocols, private key generator (PKG) knows user's private key, so it can calculate the shared key between two participants, and most constructions of ID-NIKE need expensive pairing operation. To overcome these disadvantages, a security model of certificateless non-interactive key exchange (CL-NIKE) is proposed in this paper. And a scheme without pairings is also given. The proposed protocol is proved secure in the Random Oracle Model (ROM) based on the gap Diffie-Hellman (GDH) and computational Diffie-Hellman (CDH) problem. In the new protocol, key generation center (KGC) only knows user's partial key and is not able to calculate the shared key. Moreover, the new protocol is more efficient than the existing ID-NIKE schemes because it is pairing-free.

Woo Kwon Koo, Jungyeon Hwang, Hyoung-Joong Kim +1 more

A proxy re-encryption scheme allows Alice to temporarily delegate the decryption rights to Bob via a proxy. Alice gives the proxy a re-encryption key so that the proxy can convert a ciphertext for Alice into the ciphertext for Bob. Recently, ID-based proxy re-encryption schemes are receiving considerable attention for a variety of applications such as distributed storage, DRM, and email-forwarding system. And a non-interactive identity-based proxy re-encryption scheme was proposed for achieving CCA-security by Green and Ateniese. In the paper, we show that the identity-based proxy re-encryption scheme is unfortunately vulnerable to a collusion attack. The collusion of a proxy and a malicious user enables two parties to derive other honest users' private keys and thereby decrypt ciphertexts intended for only the honest user. To solve this problem, we propose two ID-based proxy re-encryption scheme schemes, which are proved secure under CPA and CCA in the random oracle model. For achieving CCA-security, we present self-authentication tag based on short signature. Important features of proposed scheme is that ciphertext structure is preserved after the ciphertext is re-encrypted. Therefore it does not lead to ciphertext expansion. And there is no limitation on the number of re-encryption.

Hatsukazu Tanaka

Hatsukazu Tanaka

Qianqian Xing, Baosheng Wang, Xiaofeng Wang +2 more

We present the first selectively secure hierarchical identity-based non-interactive key agreement (HIB-NIKA) in the standard model that does not explicitly require multilinear maps. We give a novel solution for resilience called "shadowing factor" to improve the security of HIB-NIKA and present a practical attack model of hierarchical key agreement to analyze the anti-forgery and anti-collusion properties of key agreements in the real situation. Through the theoretical proof and practical analysis, our HIB-NIKA has been proved anti-collusion and resilient against the compromises from intermediate and leaf nodes in the hierarchy, which covers the shortage of the trial of Guo and solves the open problem posed by Gennaro in-the-true-sense.