Blink: Breaking Lattice-Based Schemes Implemented in Parallel with Chosen-Ciphertext Attack

As the message recovery-based attack poses a serious threat to lattice-based schemes, we conducted a study on the side-channel secu- rity of parallel implementations of lattice-based key encapsulation mech- anisms. Initially, we developed a power model to describe the power leakage during message encoding. Utilizing this power model, we pro- pose a multi-ciphertext message recovery attack, which can retrieve the required messages for a chosen ciphertext attack through a suitable mes- sage recovery oracle. Building upon the successful message recovery, we further develop a key recovery method based on a ciphertext-choosing strategy that maximizes key recovery accuracy, as well as a lattice reduc- tion attack capable of solving the whole private key from the target LWE instance. To assess the effectiveness of the attack, we conducted experi- ments using Kyber768 implemented on a Xilinx FPGA board. The exper- imental results demonstrate that our attack could successfully recover the private key with 9600 power traces and a computational complexity of 100 bikz, which is a significant advantage over existing attacks. Notably, our attack remains effective despite countermeasures such as masking and shuffling being implemented. This study reveals that parallel im- plementations remain vulnerable to side-channel attacks, and highlights the necessity of additional analysis and countermeasures for lattice-based schemes implemented in parallel

Cryptology in the Crowd

Uhell skjer: Kanskje mistet du nøkkelen til huset, eller hadde PIN-koden til innbruddsalarmen skrevet på en dårlig plassert post-it lapp. Og kanskje endte de slik opp i hendene på feil person, som nå kan påføre livet ditt all slags ugagn: Sikkerhetssystemer gir ingen garantier når nøkler blir stjålet og PIN-koder lekket. Likevel burde naboen din, hvis nøkkel-og-PIN-kode rutiner er heller vanntette, kunne føle seg trygg i vissheten om at selv om du ikke evner å sikre huset ditt mot innbrudd, så forblir deres hjem trygt. Det er tilsvarende for kryptologi, som også lener seg på at nøkkelmateriale hemmeligholdes for å kunne garantere sikkerhet: Intuitivt forventer man at kjennskap til ett systems hemmelige nøkkel ikke burde være til hjelp for å bryte inn i andre, urelaterte systemer. Men det har vist seg overraskende vanskelig å sette denne intuisjonen på formell grunn, og flere konkurrerende sikkerhetsmodeller av varierende styrke har oppstått. Det blir dermed naturlig å spørre seg: Hvilken formalisme er den riktige når man skal modellere realistiske scenarioer med mange brukere og mulige lekkasjer? Eller: hvordan bygger man kryptografi i en folkemengde? Artikkel I begir seg ut på reisen mot et svar ved å sammenligne forskjellige flerbrukervarianter av sikkerhetsmodellen IND-CCA, med og uten evnen til å motta hemmelige nøkler tilhørende andre brukere. Vi finner et delvis svar ved å vise at uten denne evnen, så er noen modeller faktisk å foretrekke over andre. Med denne evnen, derimot, forblir situasjonen uavklart. Artikkel II tar et sidesteg til et sett relaterte sikkerhetsmodeller hvor, heller enn å angripe én enkelt bruker (ut fra en mengde av mulige ofre), angriperen ønsker å bryte kryptografien til så mange brukere som mulig på én gang. Man ser for seg en uvanlig mektig motstander, for eksempel en statssponset aktør, som ikke har problemer med å bryte kryptografien til en enkelt bruker: Målet skifter dermed fra å garantere trygghet for alle brukerne, til å gjøre masseovervåking så vanskelig som mulig, slik at det store flertall av brukere kan forbli sikret. Artikkel III fortsetter der Artikkel I slapp ved å sammenligne og systematisere de samme IND-CCA sikkerhetsmodellene med en større mengde med sikkerhetsmodeller, med det til felles at de alle modellerer det samme (eller lignende) scenarioet. Disse modellene, som går under navnene SOA (Selective Opening Attacks; utvalgte åpningsangrep) og NCE (Non-Committing Encryption; ikke-bindende kryptering), er ofte vesentlig sterkere enn modellene studert i Artikkel I. Med et system på plass er vi i stand til å identifisere en rekke hull i litteraturen; og dog vi tetter noen, etterlater vi mange som åpne problemer.Accidents happen: you may misplace the key to your home, or maybe the PIN to your home security system was written on an ill-placed post-it note. And so they end up in the hands of a bad actor, who is then granted the power to wreak all kinds of havoc in your life: the security of your home grants no guarantees when keys are stolen and PINs are leaked. Nonetheless your neighbour, whose key-and-pin routines leave comparatively little to be desired, should feel safe that just because you can’t keep your house safe from intruders, their home remains secured. It is likewise with cryptography, whose security also relies on the secrecy of key material: intuitively, the ability to recover the secret keys of other users should not help an adversary break into an uncompromised system. Yet formalizing this intuition has turned out tricky, with several competing notions of security of varying strength. This begs the question: when modelling a real-world scenario with many users, some of which may be compromised, which formalization is the right one? Or: how do we build cryptology in a crowd? Paper I embarks on the quest to answer the above questions by studying how various notions of multi-user IND-CCA compare to each other, with and without the ability to adaptively compromise users. We partly answer the question by showing that, without compromise, some notions of security really are preferable over others. Still, the situation is left largely open when compromise is accounted for. Paper II takes a detour to a related set of security notions in which, rather than attacking a single user, an adversary seeks to break the security of many. One imagines an unusually powerful adversary, for example a state-sponsored actor, for whom brute-forcing a single system is not a problem. Our goal then shifts from securing every user to making mass surveillance as difficult as possible, so that the vast majority of uncompromised users can remain secure. Paper III picks up where Paper I left off by comparing and systemizing the same security notions with a wider array of security notions that aim to capture the same (or similar) scenarios. These notions appear under the names of Selective Opening Attacks (SOA) and Non-Committing Encryption (NCE), and are typically significantly stronger than the notions of IND-CCA studied in Paper I. With a system in place, we identify and highlight a number of gaps, some of which we close, and many of which are posed as open problems.Doktorgradsavhandlin

A Closer Look at the Belief Propagation Algorithm in Side-Channel-Assisted Chosen-Ciphertext Attacks

The implementation security of post-quantum cryptography (PQC) algorithms has emerged as a critical concern with the PQC standardization process reaching its end. In a side-channel-assisted chosen-ciphertext attack, the attacker builds linear inequalities on secret key components and uses the belief propagation (BP) algorithm to solve. The number of inequalities leverages the query complexity of the attack, so the fewer the better. In this paper, we use the PQC standard algorithm Kyber512 as a study case to construct bilateral inequalities on key variables with substantially narrower intervals using a side-channel-assisted oracle. The number of such inequalities required to recover the key with probability 1 utilizing the BP algorithm is reduced relative to previous unilateral inequalities. Furthermore, we introduce strategies aimed at further refining the interval of inequalities. Diving into the BP algorithm, we discover a measure metric named JSD-metric that can gauge the tightness of an inequality. We then develop a heuristic strategy and a machine learning-based strategy to utilize the JSD-metrics to contract boundaries of inequalities even with fewer inequalities given, thus improving the information carried by the system of linear inequalities. This contraction strategy is at the algorithmic level and has the potential to be employed in all attacks endeavoring to establish a system of inequalities concerning key variables

Sponge based CCA2 secure asymmetric encryption for arbitrary length message

OAEP and other similar schemes proven secure in Random-Oracle Model require one or more hash functions with output size larger than those of standard hash functions. In this paper, we show that by utilizing popular Sponge constructions in OAEP framework, we can eliminate the need of such hash functions. We provide a new scheme in OAEP framework based on Sponge construction and call our scheme \textit{Sponge based asymmetric encryption padding} (SpAEP). SpAEP is based on 2 functions: Sponge and SpongeWrap, and requires only standard output sizes proposed and standardized for Sponge functions. Our scheme is CCA2 secure for any trapdoor one-way permutation in the ideal permutation model for arbitrary length messages. Our scheme utilizes the versatile Sponge function to enhance the capability and efficiency of the OAEP framework. SpAEP with any trapdoor one-way permutation can also be used as a key encapsulation mechanism and a tag-based key encapsulation mechanism for hybrid encryption. Our scheme SpAEP utilizes the permutation model efficiently in the setting of public key encryption in a novel manner

Decryption Failure Attacks on Post-Quantum Cryptography

This dissertation discusses mainly new cryptanalytical results related to issues of securely implementing the next generation of asymmetric cryptography, or Public-Key Cryptography (PKC).PKC, as it has been deployed until today, depends heavily on the integer factorization and the discrete logarithm problems.Unfortunately, it has been well-known since the mid-90s, that these mathematical problems can be solved due to Peter Shor's algorithm for quantum computers, which achieves the answers in polynomial time.The recently accelerated pace of R&D towards quantum computers, eventually of sufficient size and power to threaten cryptography, has led the crypto research community towards a major shift of focus.A project towards standardization of Post-quantum Cryptography (PQC) was launched by the US-based standardization organization, NIST. PQC is the name given to algorithms designed for running on classical hardware/software whilst being resistant to attacks from quantum computers.PQC is well suited for replacing the current asymmetric schemes.A primary motivation for the project is to guide publicly available research toward the singular goal of finding weaknesses in the proposed next generation of PKC.For public key encryption (PKE) or digital signature (DS) schemes to be considered secure they must be shown to rely heavily on well-known mathematical problems with theoretical proofs of security under established models, such as indistinguishability under chosen ciphertext attack (IND-CCA).Also, they must withstand serious attack attempts by well-renowned cryptographers both concerning theoretical security and the actual software/hardware instantiations.It is well-known that security models, such as IND-CCA, are not designed to capture the intricacies of inner-state leakages.Such leakages are named side-channels, which is currently a major topic of interest in the NIST PQC project.This dissertation focuses on two things, in general:1) how does the low but non-zero probability of decryption failures affect the cryptanalysis of these new PQC candidates?And 2) how might side-channel vulnerabilities inadvertently be introduced when going from theory to the practice of software/hardware implementations?Of main concern are PQC algorithms based on lattice theory and coding theory.The primary contributions are the discovery of novel decryption failure side-channel attacks, improvements on existing attacks, an alternative implementation to a part of a PQC scheme, and some more theoretical cryptanalytical results

Envisioning the Future of Cyber Security in Post-Quantum Era: A Survey on PQ Standardization, Applications, Challenges and Opportunities

The rise of quantum computers exposes vulnerabilities in current public key cryptographic protocols, necessitating the development of secure post-quantum (PQ) schemes. Hence, we conduct a comprehensive study on various PQ approaches, covering the constructional design, structural vulnerabilities, and offer security assessments, implementation evaluations, and a particular focus on side-channel attacks. We analyze global standardization processes, evaluate their metrics in relation to real-world applications, and primarily focus on standardized PQ schemes, selected additional signature competition candidates, and PQ-secure cutting-edge schemes beyond standardization. Finally, we present visions and potential future directions for a seamless transition to the PQ era

Overview and Discussion of Attacks on CRYSTALS-Kyber

This paper reviews common attacks in classical cryptography and plausible attacks in the post-quantum era targeted at CRYSTALS-Kyber. Kyber is a recently standardized post-quantum cryptography scheme that relies on the hardness of lattice problems. Although it has undergone rigorous testing by the National Institute of Standards and Technology (NIST), there have recently been studies that have successfully executed attacks against Kyber while showing their applicability outside of controlled settings. The attacks discussed in the paper include common attacks, side-channel attacks, SCA-assisted CCA, and fault injections. In the common attacks section, attacks on symmetric primitives, multi-target attacks, and attacks exploiting decryption failures can all be deemed inviable, while recent data on attacks on module-LWE questions Kyber\u27s security level. In the side-channel attacks section, timing attacks are proven useless due to the constant-time nature of Kyber, but SASCA attacks are still viable, though easily defended against with minimal drawbacks. Attacks targeting message encoding and attacks using deep learning, however, both prove effective, even with high-order masking. LDPC has also been proposed as a new framework for attack, proving itself potent with room for growth. In the SCA-assisted CCA section, EM attacks and CPA attacks have also both shown potential while remaining difficult to defend against. In the fault injection section, Roulette and error-tolerant key recovery have both recently been proposed, with data demonstrating their effectiveness and difficulty to defend against. This paper aims to provide future researchers insight into what areas should be focused on to strengthen current as well as future cryptosystems

SCA-LDPC: A Code-Based Framework for Key-Recovery Side-Channel Attacks on Post-Quantum Encryption Schemes

Whereas theoretical attacks on standardized crypto primitives rarely lead to actual practical attacks, the situation is different for side-channel attacks. Improvements in the performance of side-channel attacks are of utmost importance. In this paper, we propose a framework to be used in key-recovery side-channel attacks on CCA-secure post-quantum encryption schemes. The basic idea is to construct chosen ciphertext queries to a plaintext checking oracle that collects information on a set of secret variables in a single query. Then a large number of such queries is considered, each related to a different set of secret variables, and they are modeled as a low-density parity-check code (LDPC code). Secret variables are finally determined through efficient iterative decoding methods, such as belief propagation, using soft information. The utilization of LDPC codes offers efficient decoding, source compression, and error correction benefits. It has been demonstrated that this approach provides significant improvements compared to previous work by reducing the required number of queries, such as the number of traces in a power attack. The framework is demonstrated and implemented in two different cases. On one hand, we attack implementations of HQC in a timing attack, lowering the number of required traces considerably compared to attacks in previous work. On the other hand, we describe and implement a full attack on a masked implementation of Kyber using power analysis. Using the ChipWhisperer evaluation platform, our real-world attacks recover the long-term secret key of a first-order masked implementation of Kyber-768 with an average of only 12 power traces

Pairing-based cryptosystems and key agreement protocols.

For a long time, pairings on elliptic curves have been considered to be destructive in elliptic curve cryptography. Only recently after some pioneering works, particularly the well-known Boneh-Franklin identity-based encryption (IBE), pairings have quickly become an important tool to construct novel cryptographic schemes. In this thesis, several new cryptographic schemes with pairings are proposed, which are both efficient and secure with respect to a properly defined security model, and some relevant previous schemes are revisited. IBE provides a public key encryption mechanism where a public key can be an arbitrary string such as an entity identifier and unwieldy certificates are unnecessary. Based on the Sakai-Kasahara key construction, an IBE scheme which is secure in the Boneh-Franklin IBE model is constructed, and two identity-based key encapsulation mechanisms are proposed. These schemes achieve the best efficiency among the existing schemes to date. Recently Al-Riyami and Paterson introduced the certificateless public key encryption (CL-PKE) paradigm, which eliminates the need of certificates and at the same time retains the desirable properties of IBE without the key escrow problem. The security formulation of CL-PKE is revisited and a strong security model for this type of mechanism is defined. Following a heuristic approach, three efficient CL-PKE schemes which are secure in the defined strong security model are proposed. Identity-based two-party key agreement protocols from pairings are also investigated. The Bellare-Rogaway key agreement model is enhanced and within the model several previously unproven protocols in the literature are formally analysed. In considering that the user identity may be sensitive information in many environments, an identity-based key agreement protocol with unilateral identity privacy is proposed