Research Highlights

Christof Beierle, Gregor Leander, Yosuke Todo

Improved Differential-Linear Attacks with Applications to ARX Ciphers

BEST PAPER AWARD

40th International Cryptology Conference (IACR Crypto), Santa Barbara, CA, USA, August 2020

We present several improvements to the framework of differential-linear attacks with a special focus on ARX ciphers. As a demonstration of their impact, we apply them to Chaskey and ChaCha and we are able to significantly improve upon the best attacks published so far. (...)

Maik Ender, Amir Moradi, Christof Paar

The Unpatchable Silicon: A Full Break of the Bitstream Encryption of Xilinx 7-Series FPGAs

DISTINGUISHED PAPER AWARD

29th USE­NIX Se­cu­ri­ty Sym­po­si­um, Bos­ton, MA, USA, Au­gust 2020

In this paper, we introduce novel low-cost attacks against the Xilinx 7-Series (and Virtex-6) bitstream encryption, resulting in the total loss of authenticity and confidentiality. We exploit a design flaw which piecewise leaks the decrypted bitstream. (...)

David Rupprecht, Katharina Kohls, Thorsten Holz

Call Me Maybe: Eavesdropping Encrypted LTE Calls With ReVoLTE

29th USE­NIX Se­cu­ri­ty Sym­po­si­um, Bos­ton, MA, USA, Au­gust 2020

Voice over LTE (VoLTE) is a packet-based telephony service seamlessly integrated into the Long Term Evolution (LTE) standard and deployed by most telecommunication providers in practice. Due to this widespread use, successful attacks against VoLTE can affect a large number of users worldwide. In this work, we introduce ReVoLTE, an attack that exploits an LTE implementation flaw to recover the contents of an encrypted VoLTE call, hence enabling an adversary to eavesdrop on phone calls. ReVoLTE makes use of a predictable keystream reuse on the radio layer that allows an adversary to decrypt a recorded call with minimal resources.

Tim Bla­zyt­ko, Mo­ritz Schlö­gel, Cor­ne­li­us Ascher­mann, Ali Ab­ba­si, Joel Frank, Simon Wör­ner, Thors­ten Holz

Au­ro­ra: Sta­tis­ti­cal Crash Ana­ly­sis for Au­to­ma­ted Root Cause Ex­pla­na­ti­on

29th USE­NIX Se­cu­ri­ty Sym­po­si­um, Bos­ton, MA, USA, Au­gust 2020

(...) In this paper, we propose an automated analysis approach that does not only identify the root cause of a given crashing input for a binary executable, but also provides the analyst with context information on the erroneous behavior that characterizes crashing inputs. (...)

Joel Frank, Cornelius Aschermann, Thorsten Holz

ETHBMC: A Bounded Model Checker for Smart Contracts

29th USE­NIX Se­cu­ri­ty Sym­po­si­um, Bos­ton, MA, USA, Au­gust 2020

(...) we present the design and implementation of, a bounded model checker based on symbolic execution which provides a precise model of the Ethereum network. We demonstrate its capabilities in a series of experiments. (...)

Paul Fiterau-Brostean, Bengt Jonsson, Robert Merget, Joeri de Ruiter,  Konstantinos Sagonas, Juraj Somorovsky

Analysis of DTLS Implementations Using Protocol State Fuzzing

29th USE­NIX Se­cu­ri­ty Sym­po­si­um, Bos­ton, MA, USA, Au­gust 2020

We present the first comprehensive analysis of DTLS implementations using protocol state fuzzing. To that end, we extend TLS-Attacker, an open source framework for analyzing TLS implementations, with support for DTLS tailored to the stateless and unreliable nature of the underlying UDP layer. (...)

Abraham A Clements, Eric Gustafson, Tobias Scharnowski, Paul Grosen, David Fritz, Christopher Kruegel, Giovanni Vigna, Saurabh Bagchi, Mathias Payer

HALucinator: Firmware Re-hosting Through Abstraction Layer Emulation

29th USE­NIX Se­cu­ri­ty Sym­po­si­um, Bos­ton, MA, USA, Au­gust 2020

Given the increasing ubiquity of online embedded devices, analyzing their firmware is important to security, privacy, and safety. The tight coupling between hardware and firmware and the diversity found in embedded systems makes it hard to perform dynamic analysis on firmware. (...)

Dominik Hartmann, Geoffroy Couteau

Shorter Non-Interactive Zero-Knowledge Arguments and ZAPs for Algebraic Languages

40th International Cryptology Conference (IACR Crypto), Santa Barbara, CA, USA, August 2020

We put forth a new framework for building pairing-based non-interactive zero- knowledge (NIZK) arguments for a wide class of algebraic languages, which are an extension of linear languages, containing disjunctions of linear languages and more. (...)

Christof Beierle, Alex Biryukov, Luan Cardoso dos Santos, Johann Großschädl, Léo Perrin, Aleksei Udovenko, Vesselin Velichkov, Qingju Wang

Alzette: a 64-bit ARX-box (feat. CRAX and TRAX)

40th International Cryptology Conference (IACR Crypto), Santa Barbara, CA, USA, August 2020

In this paper, we present a 64-bit ARX-based S-box called Alzette, which can be evaluated in constant time using only 12 instructions on modern CPUs. Its parallel application can also leverage vector (SIMD) instructions. (...)

Tim Beyne, Anne Canteaut, Itai Dinur, Maria Eichlseder, Gregor Leander, Gaëtan Leurent, Léo Perrin, María Naya Plasencia, Yu Sasaki, Yosuke Todo, Friedrich Wiemer

Out of Oddity -- New Cryptanalytic Techniques against Symmetric Primitives Optimized for Integrity Proof Systems

40th International Cryptology Conference (IACR Crypto), Santa Barbara, CA, USA, August 2020

This work compares the security levels offered by two recent families of such primitives, namely GMiMC and HadesMiMC. We exhibit low-complexity distinguishers against the GMiMC and HadesMiMC permutations for most parameters proposed in recently launched public challenges for STARK-friendly hash functions. (...)

Eduard Hauck, Eike Kiltz, Julian Loss, Ngoc Khanh Nguyen

Lattice-Based Blind Signatures, Revisited

40th International Cryptology Conference (IACR Crypto), Santa Barbara, CA, USA, August 2020

We observe that all previously known lattice-based blind signature schemes contain subtle flaws in their security proofs (e.g., R\"uckert, ASIACRYPT '08) or can be attacked (e.g., BLAZE by Alkadri et al., FC '20). Motivated by this, we revisit the problem of constructing blind signatures from standard lattice assumptions. (...)

Benedikt Auerbach, Federico Giacon, and Eike Kiltz.

Everybody’s a Target: Scalability in Public-Key Encryption

39th Annual International Conference on the Theory and Applications of Cryptographic, 2020

For 1≤m≤n, we consider a natural m-out-of-n multi-instance scenario for a public-key encryption (PKE) scheme. An adversary, given n independent instances of PKE, wins if he breaks at least m out of the n instances. In this work, we are interested in the scaling factor of PKE schemes, SF, which measures how well the difficulty of breaking m out of the n instances scales in m. (...)

Cor­ne­li­us Ascher­mann, Ser­gej Schu­mi­lo, Ali Ab­ba­si, Thors­ten Holz

IJON: Ex­plo­ring Deep State Spaces via Fuz­zing

IEEE Sym­po­si­um on Se­cu­ri­ty and Pri­va­cy ("Oak­land"), San Jose, CA, May 2020

In this paper, we propose IJON, an annotation mechanism that a human analyst can use to guide the fuzzer. In contrast to the two aforementioned techniques, this approach allows a more systematic exploration of the program’s behavior based on the data representing the internal state of the program. As a consequence, using only a small (usually one line) annotation, a user can help the fuzzer to solve previously unsolvable challenges. (...)

Erwin Quiring, Alwin Maier, and Konrad Rieck, TU Braunschweig

Misleading Authorship Attribution of Source Code using Adversarial Learning

29th USENIX Security Symposium, 2019

In this paper, we present a novel attack against authorship attribution of source code. We exploit that recent attribution methods rest on machine learning and thus can be deceived by adversarial examples of source code. Our attack performs a series of semantics-preserving code transformations that mislead learning-based attribution but appear plausible to a developer. (...)

Daniel J. Bernstein and Andreas Hülsing and Stefan Kölbl and Ruben Niederhagen and Joost Rijneveld and Peter Schwabe

The SPHINCS+ Signature Framework

ACM SIGSAC Conference on Computer and Communications Security 2019

We introduce SPHINCS+, a stateless hash-based signature framework. SPHINCS+ has significant advantages over the state of the art in terms of speed, signature size, and security, and is among the nine remaining signature schemes in the second round of the NIST PQC standardization project. One of our main contributions in this context is a new few-time signature scheme that we call FORS. (...)

Phil­ipp Mar­kert, Da­ni­el V. Bai­ley, Ma­xi­mi­li­an Golla, Mar­kus Dür­muth, Adam J. Aviv

This PIN Can Be Ea­si­ly Gues­sed: Ana­ly­zing the Se­cu­ri­ty of Smart­pho­ne Un­lock PINs

IEEE Sym­po­si­um on Se­cu­ri­ty and Pri­va­cy (SP '20). San Fran­cis­co, Ca­li­for­nia, May, 2020

In this paper, we provide the first comprehensive study of user-chosen 4- and 6-digit PINs (n=1220) collected on smartphones with participants being explicitly primed for device unlocking. We find that against a throttled attacker (with 10, 30, or 100 guesses, matching the smartphone unlock setting), using 6-digit PINs instead of 4-digit PINs provides little to no increase in security, and surprisingly may even decrease security.

Ser­gej Schu­mi­lo, Cor­ne­li­us Ascher­mann, Ali Ab­ba­si, Simon Wör­ner, Thors­ten Holz

Hy­per-Cu­be: High-Di­men­sio­nal Hy­per­vi­sor Fuz­zing

Net­work and Di­stri­bu­ted Sys­tem Se­cu­ri­ty Sym­po­si­um (NDSS), San Diego, Ca­li­for­nia, USA, Fe­bru­ary 2020

In this paper, we present the design and implementation of HYPER-CUBE, a novel fuzzer that aims explicitly at testing hypervisors in an efficient, effective, and precise way. Our approach is based on a custom operating system that implements a custom bytecode interpreter. This high-throughput design for long-running, interactive targets allows us to fuzz a large number of both open source and proprietary hypervisors.

Daniel J. Bernstein and Tanja Lange

McTiny: fast high-confidence post-quantum key erasure for tiny network servers

29th USENIX Security Symposium, 2019

This paper describes a protocol, suitable for today's networks and tiny servers, in which clients transmit their code-based one-time public keys to servers. Servers never store full client public keys but work on parts provided by the clients, without having to maintain any per-client state. Intermediate results are stored on the client side in the form of encrypted cookies and are eventually combined by the server to obtain the ciphertext. (...)

David Rupp­recht, Ka­tha­ri­na Kohls, Thors­ten Holz, Chris­ti­na Pöp­per

IM­P4GT: IM­Per­so­na­ti­on At­tacks in 4G NeT­works

Net­work and Di­stri­bu­ted Sys­tem Se­cu­ri­ty Sym­po­si­um (NDSS), San Diego, Ca­li­for­nia, USA, Fe­bru­ary 2020

In this work, we introduce a novel cross-layer attack that exploits the existing vulnerability on layer two and extends it with an attack mechanism on layer three. More precisely, we take advantage of the default IP stack behavior of operating systems and show that combining it with the layer-two vulnerability allows an active attacker to impersonate a user towards the network and vice versa; we name these attacks IMP4GT. (...)

Vla­dis­lav Mla­de­nov, Chris­ti­an Main­ka, Kars­ten Meyer zu Sel­hau­sen, Mar­tin Gro­the, Jörg Schwenk

1 Trillion Dollar refund - how to spoof PDF signatures

26th ACM Con­fe­rence on Com­pu­ter and Com­mu­ni­ca­ti­ons Se­cu­ri­ty, 2019

In this paper, we present the first comprehensive security evaluation on digital signatures in PDFs. We introduce three novel attack classes which bypass the cryptographic protection of digitally signed PDF files allowing an attacker to spoof the content of a signed PDF. We analyzed 22 different PDF viewers and found 21 of them to be vulnerable. (...)

Tim Bla­zyt­ko, Cor­ne­li­us Ascher­mann, Mo­ritz Schlö­gel, Ali Ab­ba­si, Ser­gej Schu­mi­lo, Simon Wör­ner, Thors­ten Holz

GRI­MOIRE: Syn­the­si­zing Struc­tu­re while Fuz­zing

USE­NIX Se­cu­ri­ty Sym­po­si­um, Santa Clara, CA, USA, Au­gust 2019

In this paper, we present the design and implementation of GRIMOIRE, a fully automated coverage-guided fuzzer which works without any form of human interaction or pre-configuration; yet, it is still able to efficiently test programs that expect highly structured inputs. (...)

Jens Mül­ler, Mar­cus Brink­mann, Da­mi­an Pod­debni­ak, Hanno Böck, Se­bas­ti­an Schin­zel, Juraj So­mo­rovs­ky, Jörg Schwenk

“John­ny, you are fired!” – Spoo­fing Open­PGP and S/MIME Si­gna­tu­res in Emails

28th USE­NIX Se­cu­ri­ty Sym­po­si­um (USE­NIX Se­cu­ri­ty '19)

In this work we show practical forgery attacks against various implementations of OpenPGP and S/MIME email signature verification in five attack classes: (1) We analyze edge cases in S/MIME’s container format. (2) We exploit in-band signaling in the GnuPG API, the most widely used OpenPGP implementation. (3) We apply MIME wrapping attacks that abuse the email clients’ handling of partially signed messages. (...)

Manu Drijvers, Kasra Edalatnejad, Bryan Ford, Eike Kiltz, Julian Loss, Gregory Neven and Igors Stepanovs

On the Security of Two-Round Multi-Signatures

In 40th IEEE Symposium on Security and Privacy: May 20 2019 to May 22 2019  San Fransisco, CA, US; 2019; pp 780–797.

In this work, we point out serious security issues in all currently known two-round multi-signature schemes (without pairings). First, we prove that none of the schemes can be proved secure without radically departing from currently known techniques. Namely, we show that if the one-more discrete-logarithm problem is hard, then no algebraic reduction exists that proves any of these schemes secure under the discrete-logarithm or one-more discrete-logarithm problem. (...)

Thorben Moos, Amir Moradi, Tobias Schneider, François-Xavier Standaert

Glitch-Resistant Masking Revisited.

IACR Transactions on Cryptographic Hardware and Embedded Systems, 2019(2), 256-292. Best Paper Award.

(...) In this paper, we argue that the lack of proofs for TIs, DOM, UMA and GLM makes the interpretation of their security guarantees difficult as the number of shares increases. For this purpose, we first put forward that the higher-order variants of all these schemes are affected by (local or composability) security flaws in the (robust) probing model, due to insufficient refreshing. (…)

Lea Schönherr, Katharina Kohls, Steffen Zeiler, Thorsten Holz, Dorothea Kolossa

Adversarial Attacks Against Automatic Speech Recognition Systems via Psychoacoustic Hiding.

NDSS ISOC Network and Distributed System Security Symposium 2019.

(...) In this paper, we introduce a new type of adversarial examples based on psychoacoustic hiding. Our attack exploits the characteristics of DNN-based ASR systems, where we extend the original analysis procedure by an additional backpropagation step. (...)

Emre Güler, Cornelius Aschermann, Ali Abbasi, Thorsten Holz

AntiFuzz: Impeding Fuzzing Audits of Binary Executables.

USENIX Security Symposium: conference proceedings ; Santa Clara, CA, USA, August 14-16, 2019; pp 1931–1948.

(...) In this paper, we introduce several techniques to protect a binary executable against an analysis with automated bug finding approaches that are based on fuzzing, symbolic/concolic execution, and taint-assisted fuzzing (commonly known as hybrid fuzzing). More specifically, we perform a systematic analysis of the fundamental assumptions of bug finding tools and develop general countermeasures for each assumption. (...)

Jens Müller, Fabian Ising, Vladislav Mladenov, Christian Mainka, Sebastian Schinzel, Jörg Schwenk

Practical Decryption exFiltration: Breaking PDF Encryption

ACM CCS. ACM Conference on Computer and Communications Security

The Portable Document Format, better known as PDF, is one of the most widely used document formats worldwide, and in order to ensure information confidentiality, this file format supports document encryption. In this paper, we analyze PDF encryption and show two novel techniques for breaking the confidentiality of encrypted documents. (...)

Christine Utz, Martin Degeling, Sascha Fahl, Florian Schaub, Thorsten Holz

(Un)informed Con­sent: Studying GDPR Consent Notices in the Field

ACM CCS. ACM Conference on Computer and Communications Security

Since the ad­op­ti­on of the Ge­ne­ral Data Pro­tec­tion Re­gu­la­ti­on (GDPR) in May 2018 more than 60% of po­pu­lar web­sites in Eu­ro­pe dis­play cook­ie con­sent no­ti­ces to their vi­si­tors. This has quick­ly led to users be­co­ming fa­ti­gued with pri­va­cy no­ti­fi­ca­ti­ons and cont­ri­bu­ted to the rise of both brow­ser ex­ten­si­ons that block these ban­ners and de­man­ds for a so­lu­ti­on that bund­les con­sent across mul­ti­ple web­sites or in the brow­ser. (...)

Eduard Hauck, Eike Kiltz, Julian Loss

A Modular Treatment of Blind Signatures from Identification Schemes

EUROCRYPT. Annual International Conference on the Theory and Applications of Cryptographic Techniques

We propose a modular security treatment of blind signatures derived from linear identification schemes in the random oracle model. To this end, we present a general framework that captures several well known schemes from the literature and allows to prove their security. Our modular security reduction introduces a new security notion for identification schemes called One-More-Man In the Middle Security which we show equivalent to the classical One-More-Unforgeability notion for blind signatures. (...)

Michael Rodler; Wenting Li; Ghassan Karame; Lucas Davi

Sereum: Protecting Existing Smart Contracts Against Re-Entrancy Attacks

NDSS. Usenix Network and Distributed System Security Symposium

Recently, a number of existing blockchain systems have witnessed major bugs and vulnerabilities within smart contracts. Although the literature features a number of proposals for securing smart contracts, these proposals mostly focus on proving the correctness or absence of a certain type of vulnerability within a contract, but cannot protect deployed (legacy) contracts from being exploited. (...)

Daniel J. Bernstein, Andreas Hülsing

Decisional second-preimage resistance: When does SPR imply PRE?

ASIACRYPT. International Conference on the Theory and Application of Cryptology and Information Security

There is a well-known gap between second preimage resistance and preimage resistance for length-preserving hash functions. This paper introduces a simple concept that fills this gap. One consequence of this concept is that tight reductions can remove interactivity for multi-target length-preserving preimage problems, such as the problems that appear in analyzing hash-based signature systems. (...)

Yonglin Hao; Gregor Leander; Willi Meier; Yosuke Todo; Qingju Wang

Modeling for Three-Subset Division Property without Unknown Subset --Improved Cube Attacks against Trivium and Grain-128AEAD

EUROCRYPT. Annual International Conference on the Theory and Applications of Cryptographic Techniques

A division property is a generic tool to search for integral distinguishers, and automatic tools such as MILP or SAT/SMT allow us to evaluate the propagation efficiently. In the application to stream ciphers, it enables us to estimate the security of cube attacks theoretically, and it leads to the best key-recovery attacks against well-known stream ciphers. (...)

Daniel J. Bernstein, Andreas Hülsing, Stefan Kölbl,  Ruben Niederhagen, Joost Rijneveld, Peter Schwabe

The SPHINCS+ signature framework.

ACM CCS. ACM Conference on Computer and Communications Security

We introduce SPHINCS+, a stateless hash-based signature framework. SPHINCS+ has significant advantages over the state of the art in terms of speed, signature size, and security, and is among the nine remaining signature schemes in the second round of the NIST PQC standardization project. One of our main contributions in this context is a new few-time signature scheme that we call FORS. (...)

Andre Esser, Alexander  May

Low Weight Discrete Logarithms and Subset Sum in 2^0.65n with Polynomial Memory

EUROCRYPT. Annual International Conference on the Theory and Applications of Cryptographic Techniques

We propose two heuristic polynomial memory collision finding algorithms for the low Hamming weight discrete logarithm problem in any abelian group G. The first one is a direct adaptation of the BeckerCoron-Joux (BCJ) algorithm for subset sum to the discrete logarithm setting. (...)

Tobias Cloosters, Michael Rodler, Lucas Davi

TeeRex: Discovery and Exploitation of Memory Corruption Vulnerabilities in SGX Enclaves

USENIX-Security. Usenix Security Symposium.

Intel’s Software Guard Extensions (SGX) introduced new instructions to switch the processor to enclave mode which protects it from introspection. While the enclave mode strongly protects the memory and the state of the processor, it cannot withstand memory corruption errors inside the enclave code. (...)

Teemu Rytilahti, Thorsten Holz

On Using Application-Layer Middlebox Protocols for Peeking Behind NAT Gateways

NDSS. Usenix Network and Distributed System Security Symposium

Typical port scanning approaches do not achieve a full coverage of all devices connected to the Internet as not all devices are directly reachable via a public (IPv4) address: due to IP address space exhaustion, firewalls, and many other reasons, an end-to-end connectivity is not achieved in today’s Internet anymore. Especially Network Address Translation (NAT) is widely deployed in practice and it has the side effect of “hiding” devices from being scanned. (...)

Tobias Urban, Dennis Tatang, Martin Degeling, Thorsten Holz, Norbert Pohlmann

Measuring the Impact of the GDPR on Data Sharing in Ad Network

ACM CCS. ACM Conference on Computer and Communications Security

The European General Data Protection Regulation (GDPR), which went into effect in May 2018, brought new rules for the processing of personal data that affect many business models, including online advertising. The regulation’s definition of personal data applies to every company that collects data from European Internet users. (...)

Christian Dresen, Fabian Ising, Damian Poddebniak, Tobias Kappert, Thorsten Holz, Sebastian Schinzel

CORSICA: Cross-origin Web Service Identification

ACM CCS. ACM Conference on Computer and Communications Security

Vulnerabilities in private networks are difficult to detect for attackers outside of the network. While there are known methods for port scanning internal hosts that work by luring unwitting internal users to an external web page that hosts malicious JavaScript code, no such method for detailed and precise service identification is known. (...)

Florian Quinkert, Martin Degeling, Jim Blythe, Thorsten Holz

Be the Phisher - Understanding Users'
Perception of Malicious Domains

ACM CCS. ACM Conference on Computer and Communications Security

Attackers use various domain squatting techniques to convince users that their services are legitimate. Previous work has shown that methods like typosquatting, where single characters are removed or duplicated, can successfully deceive users. In this paper, we present a study that evaluates how well participants distinguish malicious from benign domains before and after they learned and applied domain squatting techniques themselves. (...)

Ram Sundara Raman, Prerana Shenoy, Katharina Kohls, Roya Ensafi

Censored Planet: An Internet-wide, Longitudinal Censorship Observatory

ACM CCS. ACM Conference on Computer and Communications Security

Remote censorship measurement techniques offer capabilities for monitoring Internet reachability around the world. However, operating these techniques continuously is labor-intensive and requires specialized knowledge and synchronization, leading to limited adoption. In this paper, we introduce Censored Planet, an online censorship measurement platform that collects and analyzes measurements from ongoing deployments of four remote measurement techniques (Augur, Satellite/Iris, Quack, and Hyperquack). (...)

Michael Rodler, Wenting Li, Ghassan Karame, Lucas Davi

EVMPatch: Timely and Automated Patching of Ethereum Smart Contracts

USENIX-Security. Usenix Security Symposium

Recent attacks exploiting errors in smart contract code had devastating consequences thereby questioning the benefits of this technology. It is currently highly challenging to fix errors and deploy a patched contract in time. Instant patching is especially important since smart contracts are always online due to the distributed nature of blockchain systems. They also manage considerable amounts of assets, which are at risk and often beyond recovery after an attack. (...)

David Knichel, Pascal Sasdrich, Amir Moradi

SILVER - Statistical Independence and Leakage Verification

ASIACRYPT. International Conference on the Theory and Application of Cryptology and Information Security

Implementing cryptographic functions securely in the presence of physical adversaries is still a challenge although a lion’s share of research in the physical security domain has been put in development of countermeasures. Among several protection schemes, masking has absorbed the most attention of research in both academic and industrial communities, due to its theoretical foundation allowing to provide proofs or model the achieved security level. (...)

Thilo Krachenfels, Fatemeh Ganji, Amir Moradi, Shahin Tajik, Jean-Pierre Seifert

When Real-World Snapshots Question Theory – Revisiting the t-Probing Security Model

S&P. IEEE Symposium on Security and Privacy

Due to its sound theoretical basis and practical efficiency, masking has become the most prominent countermeasure to protect cryptographic implementations against physical sidechannel attacks (SCAs). The core idea of masking is to randomly split every sensitive intermediate variable during computation into at least t+1 shares, where t denotes the maximum number of shares that are allowed to be observed by an adversary without learning any sensitive information. (...)

Marten Oltrogge, Nicolas Huaman, Sabrina Amft, Yasemin Acar, Michael Backes, Sascha Fahl

Why Eve and Mallory Still Love Android: Revisiting TLS (In)Security in Android Applications

USENIX-Security. Usenix Security Symposium.

Android applications have a long history of being vulnerable to man-in-the-middle attacks due to insecure custom TLS certificate validation implementations. To resolve this, Google deployed the Network Security Configuration (NSC), a configuration-based approach to increase custom certificate validation logic security, and implemented safeguards in Google Play to block insecure applications. (...)

Charles Weir, Ben Hermann, Sascha Fahl

From Needs to Actions to Secure Apps? The Effect of Requirements and Developer Practices on App Security

USENIX-Security. Usenix Security Symposium.

Increasingly mobile device users are being hurt by security or privacy issues with the apps they use. App developers can help prevent this; inexpensive security assurance techniques to do so are now well established, but do developers use them? And if they do so, is that reflected in more secure apps? (...)

Peter Leo Gorski, Yasemin Acar, Luigi Lo Iacono, Sascha Fahl

Listen to Developers! A Participatory Design Study on Security Warnings for Cryptographic APIs

CHI. International Conference on Human Factors in Computing Systems

The positive effect of security information communicated to developers through API warnings has been established. However, current prototypical designs are based on security warnings for end-users. To improve security feedback for developers, we conducted a participatory design study with 25 professional software developers in focus groups. (...)

Robert Merget, Marcus Brinkmann, Nimrod Aviram,  Juraj Somorovsky, Johannes Mittmann, Jörg Schwenk

Raccoon Attack: Finding and Exploiting Most-Significant-Bit-Oracles in TLS-DH(E)

USENIX-Security. Usenix Security Symposium.

Diffie-Hellman key exchange (DHKE) is a widely adopted method for exchanging cryptographic key material in realworld protocols like TLS-DH(E). Past attacks on TLS-DH(E) focused on weak parameter choices or missing parameter validation. The confidentiality of the computed DH share, the premaster secret, was never questioned; DHKE is used as a generic method to avoid the security pitfalls of TLS-RSA. (...)

Jörg Schwenk, Marcus Brinkmann, Damian Poddebniak, Jens Müller, Juraj Somorovsky, Sebastian Schinzel

Mitigation of Attacks on Email End-to-End Encryption

ACM CCS. ACM Conference on Computer and Communications Security

OpenPGP and S/MIME are two major standards for securing email communication introduced in the early 1990s. Three recent classes of attacks exploit weak cipher modes (EFAIL Malleability Gadgets, or EFAIL-MG), the flexibility of the MIME email structure (EFAIL Direct Exfiltration, or EFAIL-DE), and the Reply action of the email client (REPLY attacks). (...)

Jens Müller, Dominik Noss, Christian Mainka, Vladislav Mladenov, and Jörg Schwenk

Processing Dangerous Paths – On Security and Privacy of the Portable Document Format

NDSS. Usenix Network and Distributed System Security Symposium

PDF is the de-facto standard for document exchange. It is common to open PDF files from potentially untrusted sources such as email attachments or downloaded from the Internet. In this work, we perform an in-depth analysis of the capabilities of malicious PDF documents. Instead of focusing on implementation bugs, we abuse legitimate features of the PDF standard itself by systematically identifying dangerous paths in the PDF file structure. (...)

Christian Mainka, Vladislav Mladenov, Simon Rohlmann

Shadow Attacks: Hiding and Replacing Content in Signed PDFs

NDSS. Usenix Network and Distributed System Security Symposium