Full-State Keyed Duplex With Built-In Multi-User Support

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Generalized Initialization of the Duplex Construction

The duplex construction is already well analyzed with many papers proving its security in the random permutation model. However, so far, the first phase of the duplex, where the state is initialized with a secret key and an initialization vector ($\mathit{IV}$), is typically analyzed in a worst case manner. More detailed, it is always assumed that the adversary is allowed to choose the $\mathit{IV}$ on its will. In this paper, we analyze how the security changes if restrictions on the choice of the $\mathit{IV}$ are imposed, varying from the global nonce case over the random $\mathit{IV}$ case to the $\mathit{IV}$ on key case. The last one, in particular, is the duplex analogue of the use of a nonce masked with a secret in AES-GCM in TLS 1.3. We apply our findings to duplex-based encryption and authenticated encryption, and discuss the practical applications of our results

Security Proof of JAMBU under Nonce Respecting and Nonce Misuse Cases

JAMBU is an AEAD mode of operation which entered the third round of CAESAR competition. However, it does not have a security proof like other modes of operation do, and there was a cryptanalysis result that has overthrown the security claim under nonce misuse case by the designers. In this paper, we complement the shortage of the scheme by giving security proofs of JAMBU both under nonce respecting case and nonce misuse case. We prove that JAMBU under nonce respecting case has a slightly lower security than the birthday bound of $n$ bits, and JAMBU under nonce misuse case has a tight security bound of $n/2$ bits

Generic Security of the SAFE API and Its Applications

We provide security foundations for SAFE, a recently introduced API framework for sponge-based hash functions tailored to prime-field-based protocols. SAFE aims to provide a robust and foolproof interface, has been implemented in the Neptune hash framework and some zero-knowledge proof projects, but currently lacks any security proof. In this work we identify the SAFECore as versatile variant sponge construction underlying SAFE, we prove indifferentiability of SAFECore for all (binary and prime) fields up to around $|\mathbb{F}_p|^{c/2}$ queries, where $\mathbb{F}_p$ is the underlying field and $c$ the capacity, and we apply this security result to various use cases. We show that the SAFE-based protocols of plain hashing, authenticated encryption, verifiable computation, non-interactive proofs, and commitment schemes are secure against a wide class of adversaries, including those dealing with multiple invocations of a sponge in a single application. Our results pave the way of using SAFE with the full taxonomy of hash functions, including SNARK-, lattice-, and x86-friendly hashes

Security analysis of NIST-LWC contest finalists

Dissertação de mestrado integrado em Informatics EngineeringTraditional cryptographic standards are designed with a desktop and server environment in mind, so, with the relatively recent proliferation of small, resource constrained devices in the Internet of Things, sensor networks, embedded systems, and more, there has been a call for lightweight cryptographic standards with security, performance and resource requirements tailored for the highly-constrained environments these devices find themselves in. In 2015 the National Institute of Standards and Technology began a Standardization Process in order to select one or more Lightweight Cryptographic algorithms. Out of the original 57 submissions ten finalists remain, with ASCON and Romulus being among the most scrutinized out of them. In this dissertation I will introduce some concepts required for easy understanding of the body of work, do an up-to-date revision on the current situation on the standardization process from a security and performance standpoint, a description of ASCON and Romulus, and new best known analysis, and a comparison of the two, with their advantages, drawbacks, and unique traits.Os padrões criptográficos tradicionais foram elaborados com um ambiente de computador e servidor em mente. Com a proliferação de dispositivos de pequenas dimensões tanto na Internet of Things, redes de sensores e sistemas embutidos, apareceu uma necessidade para se definir padrões para algoritmos de criptografia leve, com prioridades de segurança, performance e gasto de recursos equilibrados para os ambientes altamente limitados em que estes dispositivos operam. Em 2015 o National Institute of Standards and Technology lançou um processo de estandardização com o objectivo de escolher um ou mais algoritmos de criptografia leve. Das cinquenta e sete candidaturas originais sobram apenas dez finalistas, sendo ASCON e Romulus dois desses finalistas mais examinados. Nesta dissertação irei introduzir alguns conceitos necessários para uma fácil compreensão do corpo deste trabalho, assim como uma revisão atualizada da situação atual do processo de estandardização de um ponto de vista tanto de segurança como de performance, uma descrição do ASCON e do Romulus assim como as suas melhores análises recentes e uma comparação entre os dois, frisando as suas vantagens, desvantagens e aspectos únicos

Release of Unverified Plaintext: Tight Unified Model and Application to ANYDAE

International audienceAuthenticated encryption schemes are usually expected to offer confidentiality and authenticity. In case of release of unverified plaintext (RUP), an adversary gets separated access to the decryption and verification functionality, and has more power in breaking the scheme. Andreeva et al. (ASIACRYPT 2014) formalized RUP security using plaintext awareness, informally meaning that the decryption functional-ity gives no extra power in breaking confidentiality, and INT-RUP security, covering authenticity in case of RUP. We describe a single, unified model, called AERUP security, that ties together these notions: we prove that an authenticated encryption scheme is AERUP secure if and only if it is conventionally secure, plaintext aware, and INT-RUP secure. We next present ANYDAE, a generalization of SUNDAE of Banik et al. (ToSC 2018/3). ANYDAE is a lightweight deterministic scheme that is based on a block cipher with block size n and arbitrary mixing functions that all operate on an n-bit state. It is particularly efficient for short messages, it does not rely on a nonce, and it provides maximal robustness to a lack of secure state. Whereas SUNDAE is not secure under release of unverified plaintext (a fairly simple attack can be mounted in constant time), ANYDAE is. We make handy use of the AERUP security model to prove that ANYDAE achieves both conventional security as RUP security, provided that certain modest conditions on the mixing functions are met. We describe two simple instances, called MONDAE and TUESDAE, that conform to these conditions and that are competitive with SUNDAE, in terms of efficiency and optimality

Generic Security of the Ascon Mode: On the Power of Key Blinding

The Ascon authenticated encryption scheme has recently been selected as winner of the NIST Lightweight Cryptography competition. Despite its fame, however, there is no known generic security analysis of its mode: most importantly, all related generic security results only use the key to initialize the state and do not take into account key blinding internally and at the end. In this work we present a thorough multi-user security analysis of the Ascon mode, where particularly the key blinding is taken into account. Most importantly, our analysis includes an authenticity study in various attack settings. This analysis includes a description of a new security model of authenticity under state recovery, that captures the idea that the mode aims to still guarantee authenticity and security against key recovery even if an inner state is revealed to the adversary in some way, for instance through leakage. We prove that Ascon satisfies this security property, thanks to its unique key blinding technique

Can Caesar Beat Galois?

The Competition for Authenticated Encryption: Security, Applicability and Robustness (CAESAR) has as its official goal to “identify a portfolio of authenticated ciphers that offer advantages over [the Galois-Counter Mode with AES]” and are suitable for widespread adoption.” Each of the 15 candidate schemes competing in the currently ongoing 3rd round of CAESAR must clearly declare its security claims, i.e. whether it can tolerate nonce misuse, and what is the maximal data complexity for which security is guaranteed. These claims appear to be valid for all 15 candidates. Interpreting “Robustness” in CAESAR as the ability to mitigate damage when security guarantees are void, we describe attacks with 64-bit complexity or above, and/or with nonce reuse for each of the 15 candidates. We then classify the candidates depending on how powerful does an attacker need to be to mount (semi-)universal forgeries, decryption attacks, or key recoveries. Rather than invalidating the security claims of any of the candidates, our results provide an additional criterion for evaluating the security that candidates deliver, which can be useful for e.g. breaking ties in the final CAESAR discussions

Improving Generic Attacks Using Exceptional Functions

Over the past ten years, there have been many attacks on symmetric constructions using the statistical properties of random functions. Initially, these attacks targeted iterated hash constructions and their combiners, developing a wide array of methods based on internal collisions and on the average behavior of iterated random functions. More recently, Gilbert et al. (EUROCRYPT 2023) introduced a forgery attack on so-called duplex-based Authenticated Encryption modes which was based on exceptional random functions, i.e., functions whose graph admits a large component with an exceptionally small cycle. In this paper, we expand the use of such functions in generic cryptanalysis with several new attacks. First, we improve the attack of Gilbert et al. from $\mathcal{O}(2^{3c/4})$ to $\mathcal{O}(2^{2c/3})$, where $c$ is the capacity. This new attack uses a nested pair of functions with exceptional behavior, where the second function is defined over the cycle of the first one. Next, we introduce several new generic attacks against hash combiners, notably using small cycles to improve the complexities of the best existing attacks on the XOR combiner, Zipper Hash and Hash-Twice. Last but not least, we propose the first quantum second preimage attack against Hash-Twice, reaching a quantum complexity $\mathcal{O}(2^{3n/7})$