Information-theoretic Key Encapsulation and its Applications

TL;DR

This paper introduces an information-theoretic approach to key encapsulation in hybrid encryption, analyzing security in a preprocessing model with correlated variables, and proves a composition theorem ensuring security under certain conditions.

Contribution

It defines the concept of information-theoretic KEM (iKEM), establishes its security properties, and demonstrates how it can be realized using a one-way SKA protocol with a revised security definition.

Findings

iKEM can be constructed from a one-way SKA protocol.

The hybrid encryption scheme achieves qe-CPA security under specified conditions.

The composition theorem guarantees security when building blocks meet certain security criteria.

Abstract

A hybrid encryption scheme is a public-key encryption system that consists of a public-key part called the key encapsulation mechanism (KEM), and a (symmetric) secret-key part called data encapsulation mechanism (DEM): the public-key part is used to generate a shared secret key between two parties, and the symmetric key part is used to encrypt the message using the generated key. Hybrid encryption schemes are widely used for secure communication over the Internet. In this paper, we initiate the study of hybrid encryption in preprocessing model which assumes access to initial correlated variables by all parties (including the eavesdropper). We define information-theoretic KEM (iKEM) that, together with a (computationally) secure DEM, results in a hybrid encryption scheme in preprocessing model. We define the security of each building block, and prove a composition theorem that guarantees (computational) qe-chosen plaintext (CPA) security of the hybrid encryption system if the iKEM and the DEM satisfy qe-chosen encapculation attack and one-time security, respectively. We show that iKEM can be realized by a one-way SKA (OW-SKA) protocol with a revised security definition. Using an OW-SKA that satisfies this revised definition of security effectively allows the secret key that is generated by the OW-SKA to be used with a one-time symmetric key encryption system such as XORing a pseudorandom string with the message, and provide qe-CPA security for the hybrid encryption system.We discuss our results and directions for future work.