On Compression of Cryptographic Keys

TL;DR

This paper investigates methods to minimize key storage in secure systems with resource constraints by deriving theoretical bounds and proposing a secure key linking scheme based on pseudorandom functions.

Contribution

It establishes a lower bound on key storage for systems with key derivation and introduces a secure key linking scheme using pseudorandom functions.

Findings

Derived a lower bound on key storage for systems with key derivation

Proposed a provably secure key linking scheme based on pseudorandom functions

Analyzed existing key pre-distribution schemes within the key linking framework

Abstract

Any secured system can be modeled as a capability-based access control system in which each user is given a set of secret keys of the resources he is granted access to. In some large systems with resource-constrained devices, such as sensor networks and RFID systems, the design is sensitive to memory or key storage cost. With a goal to minimize the maximum users' key storage, key compression based on key linking, that is, deriving one key from another without compromising security, is studied. A lower bound on key storage needed for a general access structure with key derivation is derived. This bound demonstrates the theoretic limit of any systems which do not trade off security and can be treated as a negative result to provide ground for designs with security tradeoff. A concrete, provably secure key linking scheme based on pseudorandom functions is given. Using the key linking framework, a number of key pre-distribution schemes in the literature are analyzed.