White-box Cryptography Research Articles

On the Security Goals of White-Box Cryptography

On the Security Goals of White-Box Cryptography

Cryptanalysis of the obfuscated round boundary technique for whitebox cryptography

Cryptanalysis of the obfuscated round boundary technique for whitebox cryptography

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 was suggested. It was a customized masking technique that randomizes all the values in the lookup tables with different masks. However, the round output was only permuted by byte encodings, not protected by masking. 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 cryptography in such a way to protect against DCA variants by obfuscating the round output with random masks. Specifically, we introduce a white-box AES (WB-AES) implementation applying the masking technique to the key-dependent intermediate value and the several outer-round outputs computed by partial bits of the key. Our analysis and experimental results show that the proposed WB-AES 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.

On the Linear Transformation in White-Box Cryptography

A linear transformation is 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.

A White-box Implementation of SEED

White-box cryptography is an implementation technique in order to protect secret keys of cryptographic algorithms in the white-box attack model, which is the setting that an adversary has full access to the implementation of the cryptographic algorithm and full control over their execution. This concept was introduced in 2002 by Chow et al., and since then, there have been many proposals for secure implementations. While there have been many approaches to construct a secure white-box implementation for the ciphers with SPN structures, there was no notable result about the white-box implementation for the block ciphers with Feistel structure after white-box DES implementation was broken. In this paper, we propose a secure white-box implementation for a block cipher SEED with Feistel structure, which can prevent the previous known attacks for white-box implementations. Our proposal is simple and practical: it is performed by only 3,376 table lookups during each execution and the total size of tables is 762.5 KB.

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).

Several Methods for Constructing White-box Solutions

White-box cryptography is an important countermeasure for providing software security in untrusted environments. While almost all public white-box solutions have been broken, the methods for constructing such solutions are worth learning. In this paper, we introduce several classic methods for constructing white-box solutions. The methods are divided into two categories: those that make the white-box solutions functionally equivalent to existing ciphers, and those that do not. In each category, we explain each method using steps and figures. Our introduction covers almost all the general methods for constructing white-box solutions and aims at presenting a full overview of white-box designs.

Self-Spectre, Write-Execute and the Hidden State

Abstract The recent Meltdown and Spectre vulnerabilities have highlighted a very present and real threat in the on-chip memory cache units which can ultimately provide a hidden state, albeit only readable via memory timing instructions [Kocher, P.—Genkin, D.— Gruss, D.— Haas, W.—Hamburg, M.—Lipp, M.–Mangard, S.—Prescher, T.—Schwarz, M.—Yarom, Y.: Spectre attacks: Exploiting speculative execution, CoRR, abs/1801.01203, 2018]. Yet the exploits, although having some complexity and slowness, are demonstrably reliable on nearly all processors produced for the last two decades. Moving out from looking at this strictly as a means of reading protected memory, as the large microprocessor companies move to close this security vulnerability, an interesting question arises. Could the inherent design of the processor give the ability to hide arbitrary calculations in this speculative and parallel side channel? Without even using protected memory and exploiting the vulnerability, as has been the focus, there could very well be a whole class of techniques which exploit the side-channel. It could be done in a way which would be largely un-preventable behavior as the technology would start to become self-defeating or require a more complicated and expensive on-chip cache memory system to properly post-speculatively clean itself. And the ability to train the branch predictor to incorrectly speculatively behave is almost certain given hardware limitations, andthusprovidesexactly this pathway. A novel approach looks at just how much computation can be done speculatively with a result store via indirect reads and available through the memory cache. A multi-threaded approach can allow a multi-stage computation pipeline where each computation is passed to a read-out thread and then to the next computation thread [Swanson, S.—McDowell, L. K.—Swift, M. M.—Eggers, S. J.–Levy H. M.: An evaluation of speculative instruction execution on simultaneous multithreaded processors, ACM Trans. Comput. Syst. 21 (2003), 314–340]. Through channels like this, an application can surreptitiously make arbitrary calculations, or even leak data without any standard tracing tools being capable of monitoring the subtle changes. Like a variation of the famous physics Heisenberg uncertainty principle, even a tool capable of reading the cache states would not only be incredibly inefficient, but thereby tamper with and modify the state. Tools like in-circuit emulators, or specially designed cache emulators would be needed to unmask the speculative reads, and it is further difficult to visualize with a linear time-line. Specifically, the AES and RSA algorithms will be studied with respect to these ideas, looking at success rates for various calculation batches with speculative execution, while having a summary view to see the rather severe performance penalties for using such methods. Either approaches could provide for strong white-box cryptography when considering a binary, non-source code form. In terms of white-box methods, both could be significantly challenging to locate or deduce the inner workings of the code. Further, both methods can easily surreptitiously leak or hide data within shared memory in a seemingly innocuous manner.

SDSRS: A Novel White-Box Cryptography Scheme for Securing Embedded Devices in IIoT

In this article, with the rapid development of industrial Internet of Things, a large number of embedded devices, such as sensors and tag readers, have been widely deployed for gathering and sending data. These devices are commonly unreliable and vulnerable to many threats, because they are located in unattended areas which are vulnerable to device capture attacks. Such environments can be regarded as white-box attack contexts, in which the adversary has total visibility and full control of the implementations. White-box cryptography (WBC) aims to protect implementations of symmetric encryption algorithms in white-box attack contexts. Unfortunately, existing WBC schemes are vulnerable to various attacks, and most of them are insufficiently secure in strict white-box attack contexts. Based on the investigation of existing designs and the corresponding cryptanalysis, we propose a novel design approach for securing WBC schemes, which is named state-dependent selectable random substitutions (SDSRS). It uses SDSRSs to defeat various related white-box cryptanalytic approaches. With special considerations for IIoT systems, such as high performance for supporting real-time applications and small block size for fitting industrial protocols, a concrete WBC scheme designed with the proposed approach has been provided. Our theoretical analysis shows that the proposed scheme is secure. Additionally, experimental results indicate that the scheme performs well in practice, and it is significantly efficient in time and energy consumptions compared with existing secure white-box cryptographic schemes.

SOFTWARE SECURITY OVERVIEW

The article analyzes the main threats and problems of software protection. Methods for protecting information, their advantages and disadvantages are considered, and the possibility of using existing tools to protect software is studied. The possibility of improving and using a number of software protection methods against active fraud attacks was brought. Type of attacks exists and why protection is necessary was specified. Furthermore, we discussed several states of the art protection techniques which can be used in software to protect against analysis and tampering attacks. Analyzed such methods: Client-Server Solutions, Code Encryption, Code Diversity, Code Obfuscation, White-Box Cryptography, Tamper Resistant Software, Software Guards, Oblivious Hashing. Although we considered all these possible techniques separately, it is possible to combine these techniques into one solution.

How to reveal the secrets of an obscure white-box implementation

White-box cryptography (WBC) protects key extraction from software implementations of cryptographic primitives. Many academic works have been done achieving partial results toward WBC, but a complete solution has not been found yet by the cryptography community. As a result, the industry can only on proprietary and non-publicly scrutinized white-box implementations. It is therefore of interest to investigate the obtainable resistance of an AES implementation to thwart a white-box adversary in this paradigm. To this purpose, the ECRYPT CSA project has organized the WhibOx contest as the catch the flag challenge of CHES 2017. Researchers and engineers were invited to participate either as designers by submitting the source code of an AES-128 white-box implementation with a freely chosen key, or as breakers by trying to extract the hard-coded keys in the submissions. The participants were not expected to disclose their identities or the underlying designing/attacking techniques. In the end, 94 submitted challenges were all broken, and only 13 of them held more than one day. The strongest (in terms of surviving time) implementation survived for 28 days (which is more than twice as much as the second one). It was only broken by the authors of the present paper with reverse engineering and algebraic analysis. In this paper, we give a detailed description of the different steps of our cryptanalysis. We then generalize it to an attack methodology to break further obscure white-box implementations. In particular, we formalize and generalize the linear decoding analysis that we use to extract the key from the encoded intermediate variables of the target challenge.

Analysis and Improvement of Differential Computation Attacks against Internally-Encoded White-Box Implementations

White-box cryptography is the last security barrier for a cryptographic software implementation deployed in an untrusted environment. The principle of internal encodings is a commonly used white-box technique to protect block cipher implementations. It consists in representing an implementation as a network of look-up tables which are then encoded using randomly generated bijections (the internal encodings). When this approach is implemented based on nibble (i.e. 4-bit wide) encodings, the protected implementation has been shown to be vulnerable to differential computation analysis (DCA). The latter is essentially an adaptation of differential power analysis techniques to computation traces consisting of runtime information, e.g., memory accesses, of the target software. In order to thwart DCA, it has then been suggested to use wider encodings, and in particular byte encodings, at least to protect the outer rounds of the block cipher which are the prime targets of DCA.In this work, we provide an in-depth analysis of when and why DCA works. We pinpoint the properties of the target variables and the encodings that make the attack (in)feasible. In particular, we show that DCA can break encodings wider than 4-bit, such as byte encodings. Additionally, we propose new DCA-like attacks inspired from side-channel analysis techniques. Specifically, we describe a collision attack particularly effective against the internal encoding countermeasure. We also investigate mutual information analysis (MIA) which naturally applies in this context. Compared to the original DCA, these attacks are also passive and they require very limited knowledge of the attacked implementation, but they achieve significant improvements in terms of trace complexity. All the analyses of our work are experimentally backed up with various attack simulation results. We also verified the practicability of our analyses and attack techniques against a publicly available white-box AES implementation protected with byte encodings –which DCA has failed to break before– and against a “masked” white-box AES implementation –which intends to resist DCA.

Protect white‐box AES to resist table composition attacks

White-box cryptography protects cryptographic software in a white-box attack context (WBAC), where the dynamic execution of the cryptographic software is under full control of an adversary. Protecting AES in the white-box setting attracted many scientists and engineers, and several solutions emerged. However, almost all these solutions have been badly broken by various efficient white-box attacks, which target compositions of key-embedding lookup tables. In 2014, Luo, Lai, and You proposed a new WBAC-oriented AES implementation, and claimed that their implementation is secure against both Billet et al. 's attack and De Mulder et al. 's attack. In this study, based on the existing table-composition-targeting cryptanalysis techniques, the authors show that the secret key of the Luo-Lai-You (LLY) implementation can be recovered with a time complexity of about 2 44 . Furthermore, the authors propose a new white-box AES implementation based on table lookups, which is shown to be resistant against the existing table-composition-targeting white-box attacks. The authors, key-embedding tables are obfuscated with large affine mappings, which cannot be cancelled out by table compositions of the existing cryptanalysis techniques. Although their implementation requires twice as much memory as the LLY WBAES to store the tables, its speed is about 63 times of the latter.

Towards practical white-box lightweight block cipher implementations for IoTs

According to the Kerckhoffs’s principle, the security of a system should be only depended on the security of its secret key. To build the trusted computing base, Secure Element (SE) and Trusted Execution Environment (TEE) have been proposed for secure computing and authentication. But users still need to believe that SE and TEE-supported hardware will not be evil or intruded. In order to totally remove the dependence of extra hardware, white-box cryptography was introduced by Chow et al. (2002) which gives a software solution for AES implementations in an extremely hostile environment. After Chow et al.’s seminal paper, many white-box implementations were proposed on different block ciphers. In IoTs applications, SE and TEE might have the practical issues if the implementation costs are constrained. In this paper, we first discuss the practical issues that relate to white-box block cipher implementations from lightweight block ciphers. Furthermore, we give the white-box implementations of KLEIN, Present and LBlock as the typical candidates that represent the Substitution-Permutation Network (SPN) and Feistel structures. Finally the performance and the costs are compared with the white-box AES implementation. The comparison shows that white-box implementations are not only related to block and key lengths, but also the structure of the cipher and its white-box implementation methodology strongly affect the implementation costs.

Secure mobile device structure for trust IoT

In the IoT environment, all devices are connected to each other, and mobile device is considered as key device. But hacking into mobile devices is increasing rapidly with the increase in mobile device users. As the market share of Android OS increases, hacking of mobile devices has focused on Android devices. Although there are many security solutions for mobile devices, they are fragmentary for mobile threats; that is, they are solutions for only several threats rather than comprehensive solutions. There is hence a limit to protecting user’s and company’s data stored or used on mobile devices from various types of hacking. To address this, we propose a mobile device protection technology based on domain isolation. Virtualization technology has emerged to increase CPU utilization in server-class PCs and to run various OSs in one system. As these virtualization technologies become lightweight, they are beginning to be applied to embedded devices. In this paper, we applied this lightweight embedded virtualization technology to mobile devices to divide mobile devices into two areas. Therefore, users can have hidden area from hacker attack in addition to Android OS area which can use same as existing mobile device. There is a hardware-based mobile security solution using an secure element, but this has to be reflected in the manufacturing process of the mobile device. However, since the domain separation technology using the virtualization, proposed in this paper, is a software solution, it has an advantage that it can be applied to a device that is already in use. In addition, to protect the hidden area, application authentication/authorization and user authentication technology were applied. And we use white-box cryptography to get root of trust of the key which is used for secure storage and data encryption/decryption. We believe this is a fundamental solution for protecting the mobile device users from hacking. We implemented and tested various mobile applications operating on a mobile device that incorporates our proposed structure based on domain isolation. There is some performance degradation caused by the domain separation, but it is negligible. According to https://www.wired.com/insights/2012/11/mobile-supercomputers/ , the chips for mobile phones have evolved and mobile phones will soon become supercomputers. In this case, the addition of virtualization to the mobile device will have less impact on the computing power of the mobile device, and data protection stored in mobile devices and secure execution environment of security programs will become more important issues. Therefore, our TeeMo structure is a necessary technology to protect mobile device users.

White-box Implementation to Advantage DRM

Digital Rights Management (DRM) is a popular approach for secure content distribution. Typically, DRM encrypts the content before delivers it. Most DRM applications use secure algorithms to protect content. However, executing these algorithms in an insecure environment may allow adversaries to compromise system and obtain the key. To withstand such attack, algorithm implementation is modified in such a way to make the implementation unintelligible, namely obfuscation approach. White-box cryptography (WBC) is an obfuscation technique intended to protect secret keys from being disclosed in a software implementation using a fully transparent methodology. This mechanism is appropriate for DRM applications and able to enhance security for content provider. However, DRM is required to provide a balanced protection for content provider and users. We construct a protocol on implementing WBC to improve DRM system; The system does not only provide security for content provider, but also preserves privacy for users.

White-box Implementation to Advantage DRM

<p class='IJASEITAbtract'>Digital Rights Management (DRM) is a popular approach for secure content distribution. Typically, DRM encrypts the content before delivers it. Most DRM applications use secure algorithms to protect content. However, executing these algorithms in an insecure environment may allow adversaries to compromise system and obtain the key. To withstand such attack, algorithm implementation is modified in such a way to make the implementation unintelligible, namely obfuscation approach. White-box cryptography (WBC) is an obfuscation technique intended to protect secret keys from being disclosed in a software implementation using a fully transparent methodology. This mechanism is appropriate for DRM applications and able to enhance security for content provider. However, DRM is required to provide a balanced protection for content provider and users. We construct a protocol on implementing WBC to improve DRM system; The system does not only provide security for content provider, but also preserves privacy for users.

A white-box AES-like implementation based on key-dependent substitution-linear transformations

It is becoming increasingly common to deploy cryptographic algorithms within software applications which are executed in untrusted environments owned and controlled by a possibly malicious party. White-box cryptography aims to protect the secret key in such an environment. Chow et al. developed a white-box AES implementation in 2002 by hiding secret keys into lookup tables. Afterwards, some improvements were proposed. However, all the published schemes have been shown to be insecure. AES was originally designed without consideration of execution in a white-box attack context. Because of the fixed confusion and diffusion operations, it is easy to break AES’s white-box version. In this paper, we propose an AES-like cipher by replacing AES’s S-boxes and MixColumn matrices with key-dependent components while keeping their good cryptographic properties. We show that the white-box implementation of our AES-like cipher can resist current known attacks.

Analysis of Software Countermeasures for Whitebox Encryption

Whitebox cryptography aims to ensure the security of cryptographic algorithms in the whitebox model where the adversary has full access to the execution environment. To attain security in this setting is a challenging problem: Indeed, all published whitebox implementations of standard symmetric-key algorithms such as AES to date have been practically broken. However, as far as we know, no whitebox implementation in real-world products has suffered from a key recovery attack. This is due to the fact that commercial products deploy additional software protection mechanisms on top of the whitebox implementation. This makes practical attacks much less feasible in real-world applications. There are numerous software protection mechanisms which protect against standard whitebox attacks. One such technique is control flow obfuscation which randomizes the order of table lookups for each execution of the whitebox encryption module. Another technique is randomizing the locations of the various Look up tables (LUTs) in the memory address space. In this paper we investigate the effectiveness of these countermeasures against two attack paradigms. The first known as Differential Computational Analysis (DCA) attack was developed by Bos, Hubain, Michiels and Teuwen in CHES 2016. The attack passively collects software execution traces for several plaintext encryptions and uses the collected data to perform an analysis similar to the well known differential power attacks (DPA) to recover the secret key. Since the software execution traces contain time demarcated physical addresses of memory locations being read/written into, they essentially leak the values of the inputs to the various LUTs accessed during the whitebox encryption operation, which as it turns out leaks sufficient information to perform the power attack. We found that if in addition to control flow obfuscation, one were to randomize the locations of the LUTs in the memory, then it is very difficult to perform the DCA on the resultant system using such table inputs and extract the secret key in reasonable time. As an alternative, we investigate the version of the DCA attack which uses the outputs of the tables instead of the inputs to mount the power analysis attack. This modified DCA is able to extract the secret key from the flow obfuscated and location randomized versions of several whitebox binaries available in crypto literature. We develop another attack called the Zero Difference Enumeration (ZDE) attack. The attack records software traces for several pairs of strategically selected plaintexts and performs a simple statistical test on the effective difference of the traces to extract the secret key. We show that ZDE is able to recover the keys of whitebox systems. Finally we propose a new countermeasure for protecting whitebox binaries based on insertion of random delays which aims to make both the ZDE and DCA attackspractically difficult by adding random noise in the information leaked to the attacker.

Analysis of Software Countermeasures for Whitebox Encryption

Whitebox cryptography aims to ensure the security of cryptographic algorithms in the whitebox model where the adversary has full access to the execution environment. To attain security in this setting is a challenging problem: Indeed, all published whitebox implementations of standard symmetric-key algorithms such as AES to date have been practically broken. However, as far as we know, no whitebox implementation in real-world products has suffered from a key recovery attack. This is due to the fact that commercial products deploy additional software protection mechanisms on top of the whitebox implementation. This makes practical attacks much less feasible in real-world applications. There are numerous software protection mechanisms which protect against standard whitebox attacks. One such technique is control flow obfuscation which randomizes the order of table lookups for each execution of the whitebox encryption module. Another technique is randomizing the locations of the various Look up tables (LUTs) in the memory address space. In this paper we investigate the effectiveness of these countermeasures against two attack paradigms. The first known as Differential Computational Analysis (DCA) attack was developed by Bos, Hubain, Michiels and Teuwen in CHES 2016. The attack passively collects software execution traces for several plaintext encryptions and uses the collected data to perform an analysis similar to the well known differential power attacks (DPA) to recover the secret key. Since the software execution traces contain time demarcated physical addresses of memory locations being read/written into, they essentially leak the values of the inputs to the various LUTs accessed during the whitebox encryption operation, which as it turns out leaks sufficient information to perform the power attack. We found that if in addition to control flow obfuscation, one were to randomize the locations of the LUTs in the memory, then it is very difficult to perform the DCA on the resultant system using such table inputs and extract the secret key in reasonable time. As an alternative, we investigate the version of the DCA attack which uses the outputs of the tables instead of the inputs to mount the power analysis attack. This modified DCA is able to extract the secret key from the flow obfuscated and location randomized versions of several whitebox binaries available in crypto literature. We develop another attack called the Zero Difference Enumeration (ZDE) attack. The attack records software traces for several pairs of strategically selected plaintexts and performs a simple statistical test on the effective difference of the traces to extract the secret key. We show that ZDE is able to recover the keys of whitebox systems. Finally we propose a new countermeasure for protecting whitebox binaries based on insertion of random delays which aims to make both the ZDE and DCA attackspractically difficult by adding random noise in the information leaked to the attacker.