A paper I wrote with Kenneth G. Paterson just became available on e-print. here’s the abstract:
We present collusion attacks against an Identity-based Encryption scheme based on DHIES that was proposed by Chen et al. at ASIACCS 2010. Our attacks recover the master secret key of the scheme, so invalidating the security analysis of Chen et al. For the concrete scheme of Chen et al., our attack requires a collusion of 213 parties, 243.3 evaluations of a hash function and 230 field operations.