International Association
for Cryptologic Research

In this work, we propose the first identity-based matchmaking encryption (IB-ME) scheme under the standard assumptions in the standard model. This scheme is proven to be secure under the symmetric external Diffie-Hellman (SXDH) assumption in prime order bilinear pairing groups. In our IB-ME scheme, all parameters have constant number of group elements and are simpler than those of previous constructions. Previous works are either in the random oracle model or based on the q-type assumptions, while ours is built directly in the standard model and based on static assumptions, and does not rely on other crypto tools. More concretely, our IB-ME scheme is constructed from a variant of two-level anonymous IBE. We observed that this two-level IBE with anonymity and unforgeability satisfies the same functionality of IB-ME, and its security properties cleverly meet the two requirements of IB-ME (Privacy and Authenticity). The privacy property of IB-ME relies on the anonymity of this two-level IBE, while the authenticity property is corresponding to the unforgeability in the 2nd level. This variant of two-level IBE is built from dual pairing vector spaces, and both security reductions rely on dual system encryption.

In this paper, we propose the first generic framework for attribute-based encryptions (ABE) with master-secret-key-dependent-message security (mKDM security) for affine functions via predicate encodings by Chen, Gay and Wee [Eurocrypt 2015]. The construction is adaptively secure under standard $k$-Lin assumption in prime-order bilinear groups. By this, we obtain a set of new mKDM-secure ABE schemes with high expressiveness that have never been reached before: we get the first hierarchical IBE (HIBE) scheme and the first ABE scheme for arithmetic branching program (ABP) with mKDM security for affine functions. Thanks to the expressiveness (more concretely, delegability like HIBE), we can obtain mKDM-secure ABE against chosen-ciphertext attack (i.e., CCA security) via a classical CPA-to-CCA transformation that works well in the context of mKDM.

In this work, we propose two IPE schemes achieving both adaptive security and full attribute-hiding in the prime-order bilinear group, which improve upon the unique existing result satisfying both features from Okamoto and Takashima [Eurocrypt ’12] in terms of efficiency. Our first IPE scheme is based on the standard $$k\textsc {-lin}$$ assumption and has shorter master public key and shorter secret keys than Okamoto and Takashima’s IPE under weaker $${\textsc {dlin} }=2\textsc {-lin}$$ assumption.Our second IPE scheme is adapted from the first one; the security is based on the $${\textsc {xdlin}}$$ assumption (as Okamoto and Takashima’s IPE) but now it also enjoys shorter ciphertexts. Technically, instead of starting from composite-order IPE and applying existing transformation, we start from an IPE scheme in a very restricted setting but already in the prime-order group, and then gradually upgrade it to our full-fledged IPE scheme. This method allows us to integrate Chen et al.’s framework [Eurocrypt ’15] with recent new techniques [TCC ’17, Eurocrypt ’18] in an optimized way.