Measuring Performances of a White-Box Approach in the IoT Context

The internet of things (IoT) refers to all the smart objects that are connected to other objects, devices or servers and that are able to collect and share data, in order to "learn" and improve their functionalities. Smart objects suffer from lack of memory and computational power, since they are usually lightweight. Moreover, their security is weakened by the fact that smart objects can be placed in unprotected environments, where adversaries are able to play with the symmetric-key algorithm used and the device on which the cryptographic operations are executed. In this paper, we focus on a family of white-box symmetric ciphers substitution-permutation network (SPN)box, extending and improving our previous paper on the topic presented at WIDECOM2019. We highlight the importance of white-box cryptography in the IoT context, but also the need to have a fast black-box implementation (server-side) of the cipher. We show that, modifying an internal layer of SPNbox, we are able to increase the key length and to improve the performance of the implementation. We measure these improvements (a) on 32/64-bit architectures and (b) in the IoT context by encrypting/decrypting 10,000 payloads of lightweight messaging protocol Message Queuing Telemetry Transport (MQTT)

Hybrid WBC: Secure and Efficient White-Box Encryption Schemes

White-box cryptography aims at providing security against an adversary that has access to the encryption process. Numerous white-box encryption schemes were proposed since the introduction of white-box cryptography by Chow et al. in 2002. However, most of them are slow, and thus, can be used in practice only to protect very small amounts of information, such as encryption keys. In this paper we present a new threat model for white-box cryptography which corresponds to the practical abilities of the adversary in a wide range of applications. Furthermore, we study design criteria for white-box primitives that are important from the industry point of view. Finally, we propose a class of new primitives that combine a white-box algorithm with a standard block cipher to obtain white-box protection for encrypting long messages, with high security and reasonable performance

On the Linear Transformation in White-box Cryptography

Linear transformations are applied to the white-box cryptographic implementation for the diffusion effect to prevent key-dependent intermediate values from being analyzed. However, it has been shown that there still exists a correlation before and after the linear transformation, and thus this is not enough to protect the key against statistical analysis. So far, the Hamming weight of rows in the invertible matrix has been considered the main cause of the key leakage from the linear transformation. In this study, we present an in-depth analysis of the distribution of intermediate values and the characteristics of block invertible binary matrices. Our mathematical analysis and experimental results show that the balanced distribution of the key-dependent intermediate value is the main cause of the key leakage

White-Box Cryptography in the Gray Box - A Hardware Implementation and its Side Channels

Implementations of white-box cryptography aim to protect a secret key in a white-box environment in which an adversary has full control over the execution process and the entire environment. Its fundamental principle is the map of the cryptographic architecture, including the secret key, to a number of encoded tables that shall resist the inspection and decomposition of an attacker. In a gray-box scenario, however, the property of hiding required implementation details from the attacker could be used as a promising mitigation strategy against side-channel attacks (SCA). In this work, we present a first white-box implementation of AES on reconfigurable hardware for which we evaluate this approach assuming a gray-box attacker. We show that - unfortunately - such an implementation does not provide sufficient protection against an SCA attacker. We continue our evaluations by a thorough analysis of the source of the observed leakage, and present additional results which can be used to build stronger white-box designs

Efficient Oblivious Transfer Protocols based on White-Box Cryptography

Oblivious transfer protocol is an important cryptographic primitive having numerous applications and particularly playing an essential role in secure multiparty computation protocols. On the other hand existing oblivious transfer protocols are based on computationally expensive public-key operations which remains the main obstacle for employing such protocols in practical applications. In this paper a novel approach for designing oblivious transfer protocols is introduced based on the idea of replacing public-key operations by white-box cryptography techniques. As a result oblivious transfer protocols based on white-box cryptography run several times faster and require less communication bandwidth compared with the existing protocols

A White-Box Speck Implementation using Self-Equivalence Encodings (Full Version)

In 2002, Chow et al. initiated the formal study of white-box cryptography and introduced the CEJO framework. Since then, various white-box designs based on their framework have been proposed, all of them broken. Ranea and Preneel proposed a different method in 2020, called self-equivalence encodings and analyzed its security for AES. In this paper, we apply this method to generate the first academic white-box Speck implementations using self-equivalence encodings. Although we focus on Speck in this work, our design could easily be adapted to protect other add-rotate-xor (ARX) ciphers. Then, we analyze the security of our implementation against key-recovery attacks. We propose an algebraic attack to fully recover the master key and external encodings from a white-box Speck implementation, with limited effort required. While this result shows that the linear and affine self-equivalences of self-equivalence encodings are insecure, we hope that this negative result will spur additional research in higher-degree self-equivalence encodings for white-box cryptography. Finally, we created an open-source Python project implementing our design, publicly available at https://github.com/jvdsn/white-box-speck. We give an overview of five strategies to generate output code, which can be used to improve the performance of the white-box implementation. We compare these strategies and determine how to generate the most performant white-box Speck code. Furthermore, this project could be employed to test and compare the efficiency of attacks on white-box implementations using self-equivalence encodings

Improvement on a Masked White-box Cryptographic Implementation

White-box cryptography is a software technique to protect secret keys of cryptographic algorithms from attackers who have access to memory. By adapting techniques of differential power analysis to computation traces consisting of runtime information, Differential Computation Analysis (DCA) has recovered the secret keys from white-box cryptographic implementations. In order to thwart DCA, a masked white-box implementation has been suggested. However, each byte of the round output was not masked and just permuted by byte encodings. This is the main reason behind the success of DCA variants on the masked white-box implementation. In this paper, we improve the masked white-box cryptographic implementation in such a way to protect against DCA variants by obfuscating the round output with random masks. Specifically, we implement a white-box AES implementation applying masking techniques to the key-dependent intermediate value and the several outer-round outputs. Our analysis and experimental results show that the proposed method can protect against DCA variants including DCA with a 2-byte key guess, collision and bucketing attacks. This work requires approximately 3.7 times the table size and 0.7 times the number of lookups compared to the previous masked WB-AES implementation

Security Assessment of White-Box Design Submissions of the CHES 2017 CTF Challenge

In 2017, the first CHES Capture the Flag Challenge was organized in an effort to promote good design candidates for white-box cryptography. In particular, the challenge assessed the security of the designs with regard to key extraction attacks. A total of 94 candidate programs were submitted, and all of them were broken eventually. Even though most candidates were broken within a few hours, some candidates remained robust against key extraction attacks for several days, and even weeks. In this paper, we perform a qualitative analysis on all candidates submitted to the CHES 2017 Capture the Flag Challenge. We test the robustness of each challenge against different types of attacks, such as automated attacks, extensions thereof and reverse engineering attacks. We are able to classify each challenge depending on their robustness against these attacks, highlighting how challenges vulnerable to automated attacks can be broken in a very short amount of time, while more robust challenges demand for big reverse engineering efforts and therefore for more time from the adversaries. Besides classifying the robustness of each challenge, we also give data regarding their size and efficiency and explain how some of the more robust challenges could actually provide acceptable levels of security for some real-life applications

Attacks and Countermeasures for White-box Designs

In traditional symmetric cryptography, the adversary has access only to the inputs and outputs of a cryptographic primitive. In the white-box model the adversary is given full access to the implementation. He can use both static and dynamic analysis as well as fault analysis in order to break the cryptosystem, e.g. to extract the embedded secret key. Implementations secure in such model have many applications in industry. However, creating such implementations turns out to be a very challenging if not an impossible task. Recently, Bos et al. proposed a generic attack on white-box primitives called differential computation analysis (DCA). This attack was applied to many white-box implementations both from academia and industry. The attack comes from the area of side-channel analysis and the most common method protecting against such attacks is masking, which in turn is a form of secret sharing. In this paper we present multiple generic attacks against masked white-box implementations. We use the term “masking” in a very broad sense. As a result, we deduce new constraints that any secure white-box implementation must satisfy. Based on the new constraints, we develop a general method for protecting white-box implementations. We split the protection into two independent components: value hiding and structure hiding. Value hiding must pro- vide protection against passive DCA-style attacks that rely on analysis of computation traces. Structure hiding must provide protection against circuit analysis attacks. In this paper we focus on developing the value hiding component. It includes protection against the DCA attack by Bos et al. and protection against a new attack called algebraic attack. We present a provably secure first-order protection against the new al- gebraic attack. The protection is based on small gadgets implementing secure masked XOR and AND operations. Furthermore, we give a proof of compositional security allowing to freely combine secure gadgets. We derive concrete security bounds for circuits built using our construction

Attacks and Countermeasures for White-box Designs

In traditional symmetric cryptography, the adversary has access only to the inputs and outputs of a cryptographic primitive. In the white-box model the adversary is given full access to the implementation. He can use both static and dynamic analysis as well as fault analysis in order to break the cryptosystem, e.g. to extract the embedded secret key. Implementations secure in such model have many applications in industry. However, creating such implementations turns out to be a very challenging if not an impossible task. Recently, Bos et al. proposed a generic attack on white-box primitives called differential computation analysis (DCA). This attack was applied to many white-box implementations both from academia and industry. The attack comes from the area of side-channel analysis and the most common method protecting against such attacks is masking, which in turn is a form of secret sharing. In this paper we present multiple generic attacks against masked white-box implementations. We use the term “masking” in a very broad sense. As a result, we deduce new constraints that any secure white-box implementation must satisfy. Based on the new constraints, we develop a general method for protecting white-box implementations. We split the protection into two independent components: value hiding and structure hiding. Value hiding must pro- vide protection against passive DCA-style attacks that rely on analysis of computation traces. Structure hiding must provide protection against circuit analysis attacks. In this paper we focus on developing the value hiding component. It includes protection against the DCA attack by Bos et al. and protection against a new attack called algebraic attack. We present a provably secure first-order protection against the new al- gebraic attack. The protection is based on small gadgets implementing secure masked XOR and AND operations. Furthermore, we give a proof of compositional security allowing to freely combine secure gadgets. We derive concrete security bounds for circuits built using our construction