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

Two Attacks on a White-Box AES Implementation

International audienceWhite-box cryptography aims to protect the secret key of a cipher in an environment in which an adversary has full access to the implementation of the cipher and its execution environment. In 2002, Chow, Eisen, Johnson and van Oorschot proposed a white-box implementation of AES. In 2004, Billet, Gilbert and Ech-Chatbi presented an efficient attack (referred to as the BGE attack) on this implementation, extracts extracting its embedded AES key with a work factor of 2^30 . In 2012, Tolhuizen presented an improvement of the most time-consuming phase of the BGE attack. The present paper includes three contributions. First we describe several improvements of the BGE attack. We show that the overall work factor of the BGE attack is reduced to 2^22 when all improvements are implemented. This paper also presents a new attack on the initial white-box implementation of Chow et al. This attack exploits collisions occurring on internal variables of the implementation and it achieves a work factor of 2^22 . Eventually, we address the white-box AES implementation presented by Karroumi in 2010 which aims to withstand the BGE attack. We show that the implementations of Karroumi and Chow et al. are the same, making them both vulnerable to the same attacks

Software-Based Protection against Changeware

We call changeware software that surreptitiously modifies resources of software applications, e.g., configuration files. Changeware is developed by malicious entities which gain profit if their changeware is executed by large numbers of end-users of the targeted software. Browser hijacking mal-ware is one popular example that aims at changing web-browser settings such as the default search engine or the home page. Changeware tends to provoke end-user dissat-isfaction with the target application, e.g. due to repeated failure of persisting the desired configuration. We describe a solution to counter changeware, to be employed by ven-dors of software targeted by changeware. It combines several protection mechanisms: white-box cryptography to hide a cryptographic key, software diversity to counter automated key retrieval attacks, and run-time process memory integrity checking to avoid illegitimate calls of the developed API

Conversion from Arithmetic to Boolean Masking with Logarithmic Complexity

A general technique to protect a cryptographic algorithm against side-channel attacks consists in masking all intermediate variables with a random value. For cryptographic algorithms combining Boolean operations with arithmetic operations, one must then perform conversions between Boolean masking and arithmetic masking. At CHES 2001, Goubin described a very elegant algorithm for converting from Boolean masking to arithmetic masking, with only a constant number of operations. Goubin also described an algorithm for converting from arithmetic to Boolean masking, but with O(k) operations where k is the addition bit size. In this paper we describe an improved algorithm with time complexity O(log k) only. Our new algorithm is based on the Kogge-Stone carry look-ahead adder, which computes the carry signal in O(log k) instead of O(k) for the classical ripple carry adder. We also describe an algorithm for performing arithmetic addition modulo 2^k directly on Boolean shares, with the same complexity O(log k) instead of O(k). We prove the security of our new algorithm against first-order attacks. Our algorithm performs well in practice, as for k=64 we obtain a 23% improvement compared to Goubin’s algorithm

Bricklayer Attack: A Side-Channel Analysis on the ChaCha Quarter Round

International audienc

White-Box Cryptography: A Time-Security Trade-Off for the SPNbox Family

White-box cryptography aims to ensure the security of cryptographic algorithms in an untrusted environment where the adversary has full access to their implementations. Typical applications are DRM, Pay Tv boxes, and smartphones. A number of white-box implementations for standard cryptographic algorithms\u2014e.g., AES and DES\u2014have been published in the literature. Unfortunately, such implementations are subjected to algebraic attacks, side channel attacks, etc. and thus researchers developed new ciphers\u2014e.g., SPACE and the SPNbox family\u2014with a dedicated design approach for white-box implementations. In this chapter, we focus on the SPNbox family. Our aim is to modify the small internal block cipher used in SPNbox in order to increase the number of bits of the key used in each round. This approach provides us the possibility to reduce the number of rounds of about 25%, making the algorithm faster than the previous one

On the ineffectiveness of internal encodings - Revisiting the DCA attack on white-box cryptography

\u3cp\u3eThe goal of white-box cryptography is to implement cryptographic algorithms securely in software in the presence of an adversary that has complete access to the software’s program code and execution environment. In particular, white-box cryptography needs to protect the embedded secret key from being extracted. Bos et al. (CHES 2016) introduced differential computational analysis (DCA), the first automated attack on white-box cryptography. The DCA attack performs a statistical analysis on execution traces. These traces contain information such as memory addresses or register values, that is collected via binary instrumentation tooling during the encryption process. The white-box implementations that were attacked by Bos et al., as well as white-box implementations that have been described in the literature, protect the embedded key by using internal encodings techniques introduced by Chow et al. (SAC 2002). Thereby, a combination of linear and non-liner nibble encodings is used to protect the secret key. In this paper we analyse the use of such internal encodings and prove rigorously that they are too weak to protect against DCA. We prove that the use of non-linear nibble encodings does not hide key dependent correlations, such that a DCA attack succeeds with high probability.\u3c/p\u3

White-Box Security Notions for Symmetric Encryption Schemes

International audienc

Higher-Order DCA against Standard Side-Channel Countermeasures

At CHES 2016, Bos et al. introduced differential computational analysis (DCA) as an attack on white-box software implementations of block ciphers. This attack builds on the same principles as DPA in the classical side-channel context, but uses computational traces consisting of plain values computed by the implementation during execution. It was shown to be able to recover the key of many existing AES white-box implementations. The DCA adversary is passive, and so does not exploit the full power of the white-box setting, implying that many white-box schemes are insecure even in a weaker setting than the one they were designed for. It is therefore important to develop implementations which are resistant to this attack. We investigate the approach of applying standard side-channel countermeasures such as masking and shuffling. Under some necessary conditions on the underlying randomness generation, we show that these countermeasures provide resistance to standard (first-order) DCA. Furthermore, we introduce higher-order DCA, along with an enhanced multivariate version, and analyze the security of the countermeasures against these attacks. We derive analytic expressions for the complexity of the attacks – backed up through extensive attack experiments – enabling a designer to quantify the security level of a masked and shuffled implementation in the (higher-order) DCA setting

Doubly half-injective PRGs for incompressible white-box cryptography

\u3cp\u3eWhite-box cryptography was originally introduced in the setting of digital rights management with the goal of preventing a user from illegally re-distributing their software decryption program. In recent years, mobile payment has become a popular new application for white-box cryptography. Here, white-box cryptography is used to increase the robustness against external adversaries (i.e., not the user) who aim to misuse/attack the cryptographic functionalities of the payment application. A necessary requirement for secure white-box cryptography is that an adversary cannot extract the embedded secret key from the implementation. However, a white-box implementation needs to fulfill further security properties in order to provide useful protection of an application. In this paper we focus on the popular property incompressibility that is a mitigation technique against code-lifting attacks. We provide an incompressible white-box encryption scheme based on the standard-assumption of one-way permutations whereas previous work used either public-key type assumptions or non-standard symmetric-type assumptions.\u3c/p\u3