Christoph Striecks

Programmable Hash Functions in the Multilinear Setting

We adapt the concept of a programmable hash function (PHF, Crypto 2008) to a setting in which a multilinear map is available. This enables new PHFs with previously unachieved parameters.

Identity-Based Encryption with (Almost) Tight Security in the Multi-instance, Multi-ciphertext Setting

We construct an identity-based encryption (IBE) scheme that is tightly secure in a very strong sense. Specifically, we consider a setting with many instances of the scheme and many encryptions per instance. In this setting, we reduce the security of our scheme to a variant of a simple assumption used for a similar purpose by Chen and Wee (Crypto 2013). The security loss of our reduction is (\(\mathbf {O}\) (\(k\)) ) (where \(k \) is the security parameter). Our scheme is the first IBE scheme to achieve this strong flavor of tightness under a simple assumption.

Practical Signatures from Standard Assumptions

We put forward new techniques for designing signature schemes. As a result, we present practical signature schemes based on the CDH, the RSA, and the SIS assumptions. Our schemes compare favorably with existing schemes based on these assumptions.

Confined Guessing: New Signatures From Standard Assumptions

We put forward a new technique to construct very efficient and compact signature schemes. Our technique combines several instances of only a mildly secure signature scheme to obtain a fully secure scheme. Since the mild security notion we require is much easier to achieve than full security, we can combine our strategy with existing techniques to obtain a number of interesting new (stateless and fully secure) signature schemes. Concretely, we get (1) A scheme based on the computational Diffie–Hellman (CDH) assumption in pairing-friendly groups. Signatures contain

Bloom Filter Encryption and Applications to Efficient Forward-Secret 0-RTT Key Exchange

\mathbf {O}(1)

Revisiting Proxy Re-encryption: Forward Secrecy, Improved Security, and Applications

O(1) and verification keys

A Generic View on Trace-and-Revoke Broadcast Encryption Schemes

\mathbf {O}(\log k)