The Simon and Speck families of block ciphers were designed specifically to offer security on constrained devices, where simplicity of design is crucial. However, the intended use cases are diverse and demand flexibility in implementation. Simplicity, security, and flexibility are ever-present yet conflicting goals in cryptographic design. This paper outlines how these goals were balanced in the design of Simon and Speck.

The SIMON and SPECK lightweight block ciphers

We give a provable-security treatment for the key-wrap problem, providing definitions, constructions, and proofs. We suggest that key-wrap's goal is security in the sense of deterministic authenticated-encryption (DAE), a notion that we put forward. We also provide an alternative notion, a pseudorandom injection (PRI), which we prove to be equivalent. We provide a DAE construction, SIV, analyze its concrete security, develop a blockcipher-based instantiation of it, and suggest that the method makes a desirable alternative to the schemes of the X9.102 draft standard. The construction incorporates a method to turn a PRF that operates on a string into an equally efficient PRF that operates on a vector of strings, a problem of independent interest. Finally, we consider IV-based authenticated-encryption (AE) schemes that are maximally forgiving of repeated IVs, a goal we formalize as misuse-resistant AE. We show that a DAE scheme with a vector-valued header, such as SIV, directly realizes this goal.

A provable-security treatment of the key-wrap problem

We propose two systematic methods to describe the differential property of an S-box with linear inequalities based on logical condition modelling and computational geometry respectively. In one method, inequalities are generated according to some conditional differential properties of the S-box; in the other method, inequalities are extracted from the H-representation of the convex hull of all possible differential patterns of the S-box. For the second method, we develop a greedy algorithm for selecting a given number of inequalities from the convex hull. Using these inequalities combined with Mixed-integer Linear Programming (MILP) technique, we propose an automatic method for evaluating the security of bit-oriented block ciphers against the (related-key) differential attack with several techniques for obtaining tighter security bounds, and a new tool for finding (related-key) differential characteristics automatically for bit-oriented block ciphers.

/pdf/automatic-security-evaluation-and-related-key-differential-5erle8kbwv.pdf

Automatic Security Evaluation and (Related-key) Differential Characteristic Search: Application to SIMON, PRESENT, LBlock, DES(L) and Other Bit-Oriented Block Ciphers

Due to Shor's algorithm, quantum computers are a severe threat for public key cryptography. This motivated the cryptographic community to search for quantum-safe solutions. On the other hand, the impact of quantum computing on secret key cryptography is much less understood. In this paper, we consider attacks where an adversary can query an oracle implementing a cryptographic primitive in a quantum superposition of different states. This model gives a lot of power to the adversary, but recent results show that it is nonetheless possible to build secure cryptosystems in it.

We study applications of a quantum procedure called Simon's algorithm the simplest quantum period finding algorithm in order to attack symmetric cryptosystems in this model. Following previous works in this direction, we show that several classical attacks based on finding collisions can be dramatically sped up using Simon's algorithm: finding a collision requires $$\varOmega 2^{n/2}$$ queries in the classical setting, but when collisions happen with some hidden periodicity, they can be found with only On queries in the quantum model.

We obtain attacks with very strong implications. First, we show that the most widely used modes of operation for authentication and authenticated encryption e.g. CBC-MAC, PMAC, GMAC, GCM, and OCB are completely broken in this security model. Our attacks are also applicable to many CAESAR candidates: CLOC, AEZ, COPA, OTR, POET, OMD, and Minalpher. This is quite surprising compared to the situation with encryption modes: Anand et al. show that standard modes are secure with a quantum-secure PRF.

Second, we show that Simon's algorithm can also be applied to slide attacks, leading to an exponential speed-up of a classical symmetric cryptanalysis technique in the quantum model.

/pdf/breaking-symmetric-cryptosystems-usingzquantumzperiod-40xjh0ou6p.pdf

Breaking Symmetric Cryptosystems UsingźQuantumźPeriod Finding

The U.S. National Security Agency (NSA) developed the Simon and Speck families of lightweight block ciphers as an aid for securing applications in very constrained environments where AES may not be suitable. This paper summarizes the algorithms, their design rationale, along with current cryptanalysis and implementation results.

/pdf/simon-and-speck-block-ciphers-for-the-internet-of-things-2vkz23sw1g.pdf

SIMON and SPECK: Block Ciphers for the Internet of Things.

Recent developments in multi party computation (MPC) and fully homomorphic encryption (FHE) promoted the design and analysis of symmetric cryptographic schemes that minimize multiplications in one way or another. In this paper, we propose with Rastaa design strategy for symmetric encryption that has ANDdepth d and at the same time only needs d ANDs per encrypted bit. Even for very low values of d between 2 and 6 we can give strong evidence that attacks may not exist. This contributes to a better understanding of the limits of what concrete symmetric-key constructions can theoretically achieve with respect to AND-related metrics, and is to the best of our knowledge the first attempt that minimizes both metrics simultaneously. Furthermore, we can give evidence that for choices of d between 4 and 6 the resulting implementation properties may well be competitive by testing our construction in the use-case of removing the large ciphertext-expansion when using the BGV scheme.

/pdf/rasta-a-cipher-with-low-anddepth-and-few-ands-per-bit-a7f1g0nenc.pdf

Rasta: A cipher with low ANDdepth and few ANDs per bit.

Typical AE schemes are supposed to be secure when used as specified. However, they can --- and often do --- fail miserably when used improperly. As a partial remedy, Rogaway and Shrimpton proposed nonce-misuse-resistant AE MRAE and the first MRAE scheme SIV "Synthetic Initialization Vector". This paper proposes RIV "Robust Initialization Vector", which extends the generic SIV construction by an additional call to the internal PRF. RIV inherits the full security assurance from SIV, but unlike SIV and other MRAE schemes, RIV is also provably secure when releasing unverified plaintexts. This follows a recent line of research on "Robust Authenticated Encryption", similar to the CAESAR candidate AEZ.

An AES-based instantiation of RIV runs at less than 1.5 cpb on current x64 processors. Unlike the proposed instantiation of AEZ, which gains speed by relying on reduced-round AES, our instantiation of RIV is provably secure under the single assumption of the AES being secure.

/pdf/riv-for-robust-authenticated-encryption-4mzw3yfdzr.pdf

RIV for Robust Authenticated Encryption

Tweakable block ciphers are important primitives for designing cryptographic schemes with high security. In the absence of a standardized tweakable block cipher, constructions built from classical block ciphers remain an interesting research topic in both theory and practice. Motivated by Mennink’s $\widetilde{F}[2]$ publication from 2015, Wang et al. proposed 32 optimally secure constructions at ASIACRYPT’16, all of which employ two calls to a classical block cipher each. Yet, those constructions were still limited to n-bit keys and n-bit tweaks. Thus, applications with more general key or tweak lengths still lack support. This work proposes the XHX family of tweakable block ciphers from a classical block cipher and a family of universal hash functions, which generalizes the constructions by Wang et al. First, we detail the generic XHX construction with three independently keyed calls to the hash function. Second, we show that we can derive the hash keys in efficient manner from the block cipher, where we generalize the constructions by Wang et al.; finally, we propose efficient instantiations for the used hash functions.

XHX - A Framework for Optimally Secure Tweakable Block Ciphers from Classical Block Ciphers and Universal Hashing.

There is an ongoing trend in the symmetric-key cryptographic community to construct highly secure modes and message authentication codes based on tweakable block ciphers (TBCs). Recent constructions, such as Cogliati et al.’s HaT or Iwata et al.’s ZMAC, employ both the n -bit plaintext and the t -bit tweak simultaneously for higher performance. This work revisits ZMAC, and proposes a simpler alternative finalization based on HaT. As a result, we propose HtTBC, and call its instantiation with ZHash as a hash function ZMAC + . Compared to HaT, ZMAC + (1) requires only a single key and a single primitive. Compared to ZMAC, our construction (2) allows variable, per-query parametrizable output lengths. Moreover, ZMAC + (3) avoids the complex finalization of ZMAC and (4) improves the security bound from Ο ( σ 2 /2 n + min ( n , t ) ) to Ο ( q /2 n + q ( q + σ )/2 n + min ( n , t ) ) while retaining a practical tweak space.

ZMAC+ – An Efficient Variable-output-length Variant of ZMAC

In this work we provide an overview of the candidates of the Password Hashing Competition (PHC) regarding to their functionality, e.g., client-independent update and server relief, their security, e.g., memory-hardness and side-channel resistance, and its general properties, e.g., memory usage and flexibility of the underlying primitives. Furthermore, we formally introduce two kinds of attacks, called GarbageCollector and Weak Garbage-Collector Attack, exploiting the memory management of a candidate. Note that we consider all candidates which are not yet withdrawn from the competition.

/pdf/overview-of-the-candidates-for-the-password-hashing-5fguefb527.pdf

Eik List

Papers

Rasta: A cipher with low ANDdepth and few ANDs per bit.

RIV for Robust Authenticated Encryption

XHX - A Framework for Optimally Secure Tweakable Block Ciphers from Classical Block Ciphers and Universal Hashing.

ZMAC+ – An Efficient Variable-output-length Variant of ZMAC

Overview of the Candidates for the Password Hashing Competition - And their Resistance against Garbage-Collector Attacks.