TEC-Tree: A Low-Cost, Parallelizable Tree for Efficient Defense Against Memory Replay Attacks

Abstract

Abstract. Replay attacks are often the most costly attacks to thwart when dealing with off-chip memory integrity. With a trusted System-on-Chip, the existing countermeasures against replay require a large amount of on-chip memory to provide tamper-proof storage for metadata such as hash values or nonces. Tree-based strategies can be deployed to reduce this unacceptable overhead; for example, the well-known Merkle tree technique decreases this overhead to a single hash value. However, it comes at the cost of performancekilling characteristics for embedded systems -e.g. non-parallelizable hash computations on tree updates. In this paper, we propose an alternative solution: the Tamper-Evident Counter Tree (TEC-Tree). It allows for tamper-evident offchip storage of the nonces involved in a replay countermeasure; TEC-Tree parallelizes the computations involved in both the authentication and tree update processes. Moreover, because our tree relies on block encryption, it provides data confidentiality at no extra cost. TEC-Tree is a deployable solution for memory integrity, with low performance hit and hardware cost.

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

“…The scheme is suitable for all kinds of memory including random access memory (RAM) and non-volatile memory (NVM). By making use of synergies between fresh re-keying and authentication trees [18,27,40], Meas simultaneously offers security against first-order DPA and random access to all memory blocks. In more detail, Meas uses separate keys for each memory block that are stored in a tree structure and changed on every write access in order to strictly limit the use of each key to the encryption of two different plaintexts at most.…”

“…Authentication trees over m memory blocks with arity a have logarithmic height l = log a (m). Three prominent examples of authentication trees are Merkle trees [40], Parallelizable Authentication Trees [27] (PAT), and Tamper Evident Counter [18] (TEC) trees. We give a detailed description of them in Appendix A.…”

“…Hereby, the authenticity is ensured by the diffusion of the block cipher as it makes it hard for the adversary to modify the encrypted nonce n l,i . The nonce n l,i is formed from the memory block address and a counter ctr l,i [18]. The nonce counters are recursively authenticated using AREA codes in a tree structure.…”

“…In the following we describe three prominent examples of authentication trees, namely Merkle trees [40], Parallelizable Authentication Trees [27] (PAT), and Tamper Evident Counter [18] (TEC) trees. Note, however, that there are also hybrid variants like Bonsai Merkle trees [49], which use elements from both Merkle trees and PATs.…”

“…In these cases, the attacker can, for example, observe and tamper with data in RAM. As a result, memory encryption and tree-based authentication techniques, e.g., Merkle trees [40], Parallelizable Authentication Trees [27] (PAT) and Tamper Evident Counter [18] (TEC) trees, are increasingly deployed to protect data in RAM. As one prominent example, RAM encryption and authentication was only recently adopted in consumer products with Intel SGX [25].…”