## CryptoDB

### Joan Daemen

#### Publications

**Year**

**Venue**

**Title**

2022

TOSC

Differential Trail Search in Cryptographic Primitives with Big-Circle Chi:: Application to Subterranean
Abstract

Proving upper bounds for the expected differential probability (DP) of differential trails is a standard requirement when proposing a new symmetric primitive. In the case of cryptographic primitives with a bit-oriented round function, such as Keccak, Xoodoo and Subterranean, computer assistance is required in order to prove strong upper bounds on the probability of differential trails. The techniques described in the literature make use of the fact that the non-linear step of the round function is an S-box layer. In the case of Keccak and Xoodoo, the S-boxes are instances of the chi mapping operating on l-bit circles with l equal to 5 and 3 respectively. In that case the differential propagation properties of the non-linear layer can be evaluated efficiently by the use of pre-computed difference distribution tables.Subterranean 2.0 is a recently proposed cipher suite that has exceptionally good energy-efficiency when implemented in hardware (ASIC and FPGA). The non-linear step of its round function is also based on the chi mapping, but operating on an l = 257-bit circle, comprising all the state bits. This making the brute-force approach proposed and used for Keccak and Xoodoo infeasible to apply. Difference propagation through the chi mapping from input to output can be treated using linear algebra thanks to the fact that chi has algebraic degree 2. However, difference propagation from output to input is problematic for big-circle chi. In this paper, we tackle this problem, and present new techniques for the analysis of difference propagation for big-circle chi.We implemented these techniques in a dedicated program to perform differential trail search in Subterranean. Thanks to this, we confirm the maximum DP of 3-round trails found by the designers, we determine the maximum DP of 4-round trails and we improve the upper bounds for the DP of trails over 5, 6, 7 and 8 rounds.

2022

ASIACRYPT

Jammin' on the deck
📺
Abstract

Currently, a vast majority of symmetric-key cryptographic schemes are built as block cipher modes. The block cipher is designed to be hard to distinguish from a random permutation and this is supported by cryptanalysis, while (good) modes can be proven secure if a random permutation takes the place of the block cipher. As such, block ciphers form an abstraction level that marks the border between cryptanalysis and security proofs. In this paper, we investigate a re-factored version of symmetric-key cryptography built not around the block ciphers but rather the deck function: a keyed function with arbitrary input and output length and incrementality properties. This allows for modes of use that are simpler to analyze and still very efficient thanks to the excellent performance of currently proposed deck functions. We focus on authenticated encryption (AE) modes with varying levels of robustness. Our modes have built-in support for sessions, but are also efficient without them.
As a by-product, we define a new ideal model for AE dubbed the jammin cipher. Unlike the OAE2 security models, the jammin cipher is both a operational ideal scheme and a security reference, and addresses real-world use cases such as bi-directional communication and multi-key security.

2022

TCHES

BipBip: A Low-Latency Tweakable Block Cipher with Small Dimensions
Abstract

Recently, a memory safety concept called Cryptographic Capability Computing (C3) has been proposed. C3 is the first memory safety mechanism that works without requiring extra storage for metadata and hence, has the potential to significantly enhance the security of modern IT-systems at a rather low cost. To achieve this, C3 heavily relies on ultra-low-latency cryptographic primitives. However, the most crucial primitive required by C3 demands uncommon dimensions. To partially encrypt 64-bit pointers, a 24-bit tweakable block cipher with a 40-bit tweak is needed. The research on low-latency tweakable block ciphers with such small dimensions is not very mature. Therefore, designing such a cipher provides a great research challenge, which we take on with this paper. As a result, we present BipBip, a 24-bit tweakable block cipher with a 40-bit tweak that allows for ASIC implementations with a latency of 3 cycles at a 4.5 GHz clock frequency on a modern 10 nm CMOS technology.

2022

TOSC

Improved Differential and Linear Trail Bounds for ASCON
Abstract

Ascon is a family of cryptographic primitives for authenticated encryption and hashing introduced in 2015. It is selected as one of the ten finalists in the NIST Lightweight Cryptography competition. Since its introduction, Ascon has been extensively cryptanalyzed, and the results of these analyses can indicate the good resistance of this family of cryptographic primitives against known attacks, like differential and linear cryptanalysis.Proving upper bounds for the differential probability of differential trails and for the squared correlation of linear trails is a standard requirement to evaluate the security of cryptographic primitives. It can be done analytically for some primitives like AES. For other primitives, computer assistance is required to prove strong upper bounds for differential and linear trails. Computer-aided tools can be classified into two categories: tools based on general-purpose solvers and dedicated tools. General-purpose solvers such as SAT and MILP are widely used to prove these bounds, however they seem to have lower capabilities and thus yield less powerful bounds compared to dedicated tools.In this work, we present a dedicated tool for trail search in Ascon. We arrange 2-round trails in a tree and traverse this tree in an efficient way using a number of new techniques we introduce. Then we extend these trails to more rounds, where we also use the tree traversal technique to do it efficiently. This allows us to scan much larger spaces of trails faster than the previous methods using general-purpose solvers. As a result, we prove tight bounds for 3-rounds linear trails, and for both differential and linear trails, we improve the existing upper bounds for other number of rounds. In particular, for the first time, we prove bounds beyond 2−128 for 6 rounds and beyond 2−256 for 12 rounds of both differential and linear trails.

2021

CRYPTO

Thinking Outside the Superbox
📺
Abstract

Designing a block cipher or cryptographic permutation can be approached in many different ways. One such approach, popularized by AES, consists in grouping the bits along the S-box boundaries, e.g., in bytes, and in consistently processing them in these groups. This aligned approach leads to hierarchical structures like superboxes that make it possible to reason about the differential and linear propagation properties using combinatorial arguments. In contrast, an unaligned approach avoids any such grouping in the design of transformations. However, without hierarchical structure, sophisticated computer programs are required to investigate the differential and linear propagation properties of the primitive. In this paper, we formalize this notion of alignment and study four primitives that are exponents of different design strategies. We propose a way to analyze the interactions between the linear and the nonlinear layers w.r.t. the differential and linear propagation, and we use it to systematically compare the four primitives using non-trivial computer experiments. We show that alignment naturally leads to different forms of clustering, e.g., of active bits in boxes, of two-round trails in activity patterns, and of trails in differentials and linear approximations.

2020

TOSC

The Subterranean 2.0 Cipher Suite
📺
Abstract

This paper presents the Subterranean 2.0 cipher suite that can be used for hashing, MAC computation, stream encryption and several types of authenticated encryption schemes. At its core it has a duplex object with a 257-bit state and a lightweight single-round permutation. This makes Subterranean 2.0 very well suited for low-area and low-energy implementations in dedicated hardware.

2020

TOSC

Errata to Sound Hashing Modes of Arbitrary Functions, Permutations, and Block Ciphers
Abstract

In ToSC 2018(4), Daemen et al. performed an in-depth investigation of sound hashing modes based on arbitrary functions, permutations, or block ciphers. However, for the case of invertible primitives, there is a glitch. In this errata, we formally fix this glitch by adding an extra term to the security bound, q/2b−n, where q is query complexity, b the width of the permutation or the block size of the block cipher, and n the size of the hash digest. For permutations that are wider than two times the chaining value this term is negligible. For block cipher based hashing modes where the block size is close to the digest size, the term degrades the security significantly.

2020

TOSC

Deck-Based Wide Block Cipher Modes and an Exposition of the Blinded Keyed Hashing Model
📺
Abstract

We present two tweakable wide block cipher modes from doubly-extendable cryptographic keyed (deck) functions and a keyed hash function: double-decker and docked-double-decker. Double-decker is a direct generalization of Farfalle-WBC of Bertoni et al. (ToSC 2017(4)), and is a four-round Feistel network on two arbitrarily large branches, where the middle two rounds call deck functions and the first and last rounds call the keyed hash function. Docked-double-decker is a variant of double-decker where the bulk of the input to the deck functions is moved to the keyed hash functions. We prove that the distinguishing advantage of the resulting wide block ciphers is simply two times the sum of the pseudorandom function distinguishing advantage of the deck function and the blinded keyed hashing distinguishing advantage of the keyed hash functions. We demonstrate that blinded keyed hashing is more general than the conventional notion of XOR-universality, and that it allows us to instantiate our constructions with keyed hash functions that have a very strong claim on bkh security but not necessarily on XOR-universality, such as Xoofffie (ePrint 2018/767). The bounds of double-decker and docked-double-decker are moreover reduced tweak-dependent, informally meaning that collisions on the keyed hash function for different tweaks only have a limited impact. We describe two use cases that can exploit this property opportunistically to get stronger security than what would be achieved with prior solutions: SSD encryption, where each sector can only be written to a limited number of times, and incremental tweaks, where one includes the state of the system in the variable-length tweak and appends new data incrementally.

2020

EUROCRYPT

Friet: an Authenticated Encryption Scheme with Built-in Fault Detection
📺
Abstract

In this work we present a duplex-based authenticated encryption scheme Friet based on a new permutation called Friet-P. We designed Friet-P with a novel approach for cryptographic permutations and block ciphers that takes fault-attack resistance into account and that we introduce in this paper.
In this method, we build a permutation f_C to be embedded in a larger one f. First, we define f as a sequence of steps that all abide a chosen error-correcting code C, i.e., that map C-codewords to C-codewords. Then, we embed f_C in f by first encoding its input to an element of C, applying f and then decoding back from C. This last step detects a fault when the output of f is not in C.
We motivate the design of the permutation we use in Friet and report on performance in soft- and hardware. We evaluate the fault-detection capabilities of the software and simulated hardware implementations with attacks. Finally, we perform a leakage evaluation.
Our code is available at https://github.com/thisimon/Friet.git.

2020

TCHES

Protecting against Statistical Ineffective Fault Attacks
📺
Abstract

Statistical Ineffective Fault Attacks (SIFA) pose a threat for many practical implementations of symmetric primitives. Countermeasures against both power analysis and fault attacks typically do not prevent straightforward SIFA attacks, which require only very limited knowledge about the concrete implementation. Therefore, the exploration of countermeasures against SIFA that do not rely on protocols or physical protection mechanisms is of great interest. In this paper, we describe different countermeasure strategies against SIFA. First, we introduce an abstraction layer between the algorithmic specification of a cipher and its implementation in hardware or software to study and describe resistance against SIFA. We then show that by basing the masked implementation on permutations as building blocks, we can build circuits that withstand single-fault SIFA and DPA attacks. We show how this approach can be applied to 3-bit, 4-bit, and 5-bit S-boxes and the AES S-box. Additionally, we present a strategy based on fine-grained fault detection suitable for protecting any circuit against SIFA attacks. Although this approach may lead to a higher implementation cost due to the fine-grained detection needed, it can be used to protect arbitrary circuits and can be generalized to cover multi-fault SIFA. For single-fault SIFA protection, our countermeasures only have a small computational overhead compared to a simple combination of masking and duplication.

2020

TOSC

Xoodyak, a lightweight cryptographic scheme
📺
Abstract

In this paper, we present Xoodyak, a cryptographic primitive that can be used for hashing, encryption, MAC computation and authenticated encryption. Essentially, it is a duplex object extended with an interface that allows absorbing strings of arbitrary length, their encryption and squeezing output of arbitrary length. It inherently hashes the history of all operations in its state, allowing to derive its resistance against generic attacks from that of the full-state keyed duplex. Internally, it uses the Xoodoo[12] permutation that, with its width of 48 bytes, allows for very compact implementations. The choice of 12 rounds justifies a security claim in the hermetic philosophy: It implies that there are no shortcut attacks with higher success probability than generic attacks. The claimed security strength is 128 bits. We illustrate the versatility of Xoodyak by describing a number of use cases, including the ones requested by NIST in the lightweight competition. For those use cases, we translate the relatively detailed security claim that we make for Xoodyak into simple ones.

2018

TOSC

Column Parity Mixers
Abstract

We present column parity mixers (CPM), a generalization of the Θ mixing layer that is used in Keccak. Thanks to our description using matrix arithmetic, we can easily derive algebraic, diffusion, and mask propagation properties, leading to a surprising distinction between two types of CPMs. We compare CPMs to other popular types of mixing layers and argue that CPMs can be more efficient. While Keccak has a bit-oriented structure, we make the case that CPMs are also suitable for nibble- or byte-oriented designs. We outline a general substitution-permutation-network-based design strategy using a CPM, for which we show how one can attain strong bounds for differential and linear trails. We apply this strategy concretely to design a 256-bit permutation with an efficient inverse and strong trail bounds. Our permutation design uses a number of ideas that are of independent interest and allows a fast bitsliced implementation that compares quite well with other established ciphers and permutations.

2018

TOSC

The design of Xoodoo and Xoofff
📺
Abstract

This paper presents Xoodoo, a 48-byte cryptographic permutation with excellent propagation properties. Its design approach is inspired by Keccak-p, while it is dimensioned like Gimli for efficiency on low-end processors. The structure consists of three planes of 128 bits each, which interact per 3-bit columns through mixing and nonlinear operations, and which otherwise move as three independent rigid objects. We analyze its differential and linear propagation properties and, in particular, prove lower bounds on the weight of trails using the tree search-based technique of Mella et al. (ToSC 2017). Xoodoo’s primary target application is in the Farfalle construction that we instantiate for the doubly-extendable cryptographic keyed (or deck) function Xoofff. Combining a relatively narrow permutation with the parallelism of Farfalle results in very efficient schemes on a wide range of platforms, from low-end devices to high-end processors with vector instructions.

2018

TOSC

Sound Hashing Modes of Arbitrary Functions, Permutations, and Block Ciphers
📺
Abstract

Cryptographic hashing modes come in many flavors, including Merkle-Damgård with various types of strengthening, Merkle trees, and sponge functions. As underlying primitives, these functions use arbitrary functions, permutations, or block ciphers. In this work we provide three simple proofs, one per primitive type, that cover all modes where the input to the primitive consists of message bits, chaining value bits, and bits that only depend on the mode and message length. Our approach generalizes and simplifies over earlier attempts of Dodis et al. (FSE 2009) and Bertoni et al. (Int. J. Inf. Sec. 2014). We prove tight indifferentiability bounds for modes using each of these three primitive types provided that the mode satisfies some easy to verify conditions.

2017

TOSC

New techniques for trail bounds and application to differential trails in Keccak
Abstract

We present new techniques to efficiently scan the space of high-probability differential trails in bit-oriented ciphers. Differential trails consist in sequences of state patterns that we represent as ordered lists of basic components in order to arrange them in a tree. The task of generating trails with probability above some threshold starts with the traversal of the tree. Our choice of basic components allows us to efficiently prune the tree based on the fact that we can tightly bound the probability of all descendants for any node. Then we extend the state patterns resulting from the tree traversal into longer trails using similar bounding techniques. We apply these techniques to the 4 largest Keccak-f permutations, for which we are able to scan the space of trails with weight per round of 15. This space is orders of magnitude larger than previously best result published on Keccak-f[1600] that reached 12, which in turn is orders of magnitude larger than any published results achieved with standard tools, that reached at most 9. As a result we provide new and improved bounds for the minimum weight of differential trails on 3, 4, 5 and 6 rounds. We also report on new trails that are, to the best of our knowledge, the ones with the highest known probability.

2017

TOSC

Farfalle: parallel permutation-based cryptography
Abstract

In this paper, we introduce Farfalle, a new permutation-based construction for building a pseudorandom function (PRF). The PRF takes as input a key and a sequence of arbitrary-length data strings, and returns an arbitrary-length output. It has a compression layer and an expansion layer, each involving the parallel application of a permutation. The construction also makes use of LFSR-like rolling functions for generating input and output masks and for updating the inner state during expansion. On top of the inherent parallelism, Farfalle instances can be very efficient because the construction imposes less requirements on the underlying primitive than, e.g., the duplex construction or typical block cipher modes. Farfalle has an incremental property: compression of common prefixes of inputs can be factored out. Thanks to its input-output characteristics, Farfalle is really versatile. We specify simple modes on top of it for authentication, encryption and authenticated encryption, as well as a wide block cipher mode. As a showcase, we present Kravatte, a very efficient instance of Farfalle based on Keccak-p[1600, nr] permutations and formulate concrete security claims against classical and quantum adversaries. The permutations in the compression and expansion layers of Kravatte have only 6 rounds apiece and the rolling functions are lightweight. We provide a rationale for our choices and report on software performance.

2017

CHES

Changing of the Guards: A Simple and Efficient Method for Achieving Uniformity in Threshold Sharing
Abstract

Since they were first proposed as a countermeasure against differential power analysis (DPA) and differential electromagnetic analysis (DEMA) in 2006, threshold schemes have attracted a lot of attention from the community concentrating on cryptographic implementations. What makes threshold schemes so attractive from an academic point of view is that they come with an information-theoretic proof of resistance against a specific subset of side-channel attacks: first-order DPA. From an industrial point of view they are attractive as a careful threshold implementation forces adversaries to DPA of higher order, with all its problems such as noise amplification. A threshold scheme that offers the mentioned provable security must exhibit three properties: correctness, incompleteness and uniformity. A threshold scheme becomes more expensive with the number of shares that must be implemented and the required number of shares is lower bound by the algebraic degree of the function being shared plus 1. Defining a correct and incomplete sharing of a function of degree d in $$d+1$$ shares is straightforward. However, up to now there is no generic method to achieve uniformity and finding uniform sharings of degree-d functions with $$d+1$$ shares has been an active research area. In this paper we present a generic, simple and potentially cheap method to find a correct, incomplete and uniform $$d+1$$-share threshold scheme of any S-box layer consisting of degree-d invertible S-boxes. The uniformity is not implemented in the sharings of the individual S-boxes but rather at the S-box layer level by the use of feedforward and some expansion of shares. When applied to the Keccak-$$p$$ nonlinear step $$\chi $$, its cost is very small.

#### Program Committees

- Eurocrypt 2020
- Crypto 2020
- FSE 2020
- FSE 2019
- Eurocrypt 2018
- FSE 2018
- Crypto 2016
- FSE 2015
- Crypto 2015
- FSE 2014
- Asiacrypt 2014
- Asiacrypt 2012
- FSE 2010
- CHES 2009
- FSE 2009
- FSE 2008
- CHES 2007
- Asiacrypt 2007
- FSE 2007
- FSE 2006
- CHES 2006
- FSE 2005
- Eurocrypt 2003
- FSE 2003
- FSE 2002 (Program chair)

#### Coauthors

- Elena Andreeva (1)
- Gilles Van Assche (15)
- Norica Băcuieți (1)
- Lejla Batina (1)
- Yanis Belkheyar (1)
- Guido Bertoni (4)
- Nicolas Bordes (1)
- Antoon Bosselaers (2)
- Craig S. K. Clapp (1)
- Christoph Dobraunig (2)
- Maria Eichsleder (1)
- Solane El Hirch (1)
- Santosh Ghosh (1)
- René Govaerts (6)
- Lorenzo Grassi (1)
- Hannes Gross (1)
- Vincent Grosso (1)
- Aldo Gunsing (2)
- Seth Hoffert (4)
- Ronny Van Keer (4)
- Lars R. Knudsen (1)
- Daniël Kuijsters (1)
- Pedro Maat Costa Massolino (2)
- Alireza Mehrdad (3)
- Silvia Mella (3)
- Florian Mendel (1)
- Bart Mennink (5)
- Kostas Papagiannopoulos (1)
- Michael Peeters (5)
- Michaël Peeters (1)
- Bart Preneel (1)
- Robert Primas (1)
- Shahram Rasoolzadeh (1)
- Francesco Regazzoni (1)
- Vincent Rijmen (4)
- Yann Rotella (1)
- Niels Samwel (1)
- Daniel R. Simon (1)
- Ko Stoffelen (1)
- Joos Vandewalle (6)
- Erik De Win (1)