Leakage-Resilient Authentication and Encryption from Symmetric Cryptographic Primitives

Abstract

Leakage-resilient cryptosystems aim to maintain security in situations where their implementation leaks physical information about their internal secrets. Because of their efficiency and usability on a wide range of platforms, solutions based on symmetric primitives (such as block ciphers) are particularly attractive in this context. So far, the literature has mostly focused on the design of leakage-resilient pseudorandom objects (e.g. PRGs, PRFs, PRPs). In this paper, we consider the complementary and practically important problem of designing secure authentication and encryption schemes. For this purpose, we follow a pragmatic approach based on the advantages and limitations of existing leakageresilient pseudorandom objects, and rely on the (arguably necessary, yet minimal) use of a leak-free component. The latter can typically be instantiated with a block cipher implementation protected by traditional countermeasures, and we investigate how to combine it with the more intensive use of a much more efficient (less protected) block cipher implementation. Based on these premises, we propose and analyse new constructions of leakage-resilient MAC and encryption schemes, which allow fixing security and efficiency drawbacks of previous proposals in this direction. For encryption, we additionally provide a detailed discussion of why previously proposed (indistinguishability based) security definitions cannot capture actual side-channel attacks, and suggest a relaxed and more realistic way to quantify leakage-resilience in this case, by reducing the security of many iterations of the primitive to the security of a single iteration, independent of the security notion guaranteed by this single iteration (that remains hard to define).

MEAS: memory encryption and authentication secure against side-channel attacks

“…1 to design DPA-secure schemes from unprotected primitives are the leakage-resilient encryption schemes in [46,53,56] and the leakage-resilient MAC in [45]. Block-cipher-based instantiations of these schemes have a data complexity of q = 2 in order to prohibit successful key recovery via DPA attacks.…”

“…Using existing proposals of leakage-resilient block encryption [56] and a leakage-resilient MAC [45], both E NC and AE can be easily obtained from unprotected cryptographic implementations of standard primitives like AES and SHA-2 and the generic composition encrypt-then-MAC [8]. However, for the encryption and authentication of RAM, more lightweight constructions for E NC and AE are desirable.…”

“…Using existing memory encryption and authentication schemes with DPA-protected implementations, on the other hand, would result in overheads of a factor of four to a few hundred [6,10,42,45] and thus be far more expensive, eventually rendering memory encryption and authentication in many applications impractical.…”

“…However, protecting implementations of cryptographic primitives against DPA is expensive and a tough problem in an active field of research existing for almost two decades. The massive overheads for DPA-protected implementations range between a factor of four and a few hundred [6,10,42,45] and would thus render current memory encryption and authentication schemes in latency sensitive applications impractical. In contrast, more efficient solutions are in sight when considering side-channel protection throughout the cryptographic design and looking for potential synergies.…”

Authenticated Encryption in the Face of Protocol and Side Channel Leakage

“…In the bounded retrieval model, Bellare et al [7] proved the security of a symmetric encryption scheme that provides authenticated encryption in the leak free case, and indistinguishability when leakage is involved. Pereira et al [43] proposed what is, to our knowledge, the first and only leakage resilient encryption scheme in the simulatable leakage model. However, the construction requires a leak free component and in practice relies on the existence of efficient simulators of the leakage from (e.g.)…”