Search

The recent development of 3D printing technology has brought concerns about its potential misuse, such as in copyright infringement, and crimes. Although there have been many studies on blind 3D mesh watermarking for the copyright protection of digital objects, methods applicable to 3D printed objects are rare. In this paper, we propose a novel blind watermarking algorithm for 3D printed objects with applications for copyright protection, traitor tracing, object identification, and crime investigation. Our method allows us to embed a few bits of data into a 3D-printed object, and retrieve it by 3D scanning without requiring any information about the original mesh. The payload is embedded on the object's surface by slightly modifying the distribution of surface norms, that is, the distance between the surface, and the center of gravity. It is robust to resampling and can work with any 3D printer, and scanner technology. In addition, our method increases the capacity, and resistance by subdividing the mesh into a set of bins, and spreading the data over the entire surface to negate the effect of local printing artifacts. The method's novelties include extending the vertex norm histogram to a continuous surface, and the use of 3D moments to synchronize a watermark signal in a 3D-printing context. In the experiments, our method was evaluated using a public dataset against center, orientation, minimum, and maximum norm misalignments; a printing simulation; and actual print/scan experiments using a standard 3D printer, and scanner.

The wide adoption of cloud greatly facilitates the sharing of explosively generated media content today, yet deprives content providers’ direct control over the outsourced media content. Thus, it is pivotal to build an encrypted cloud media center where only authorized access is allowed. Enforcing access control alone, however, cannot fully protect content providers’ interests, as authorized users may later become traitors that illegally redistribute media content to the public. Such realistic threat should have been seriously treated yet is largely overlooked in the literature. In this paper, we initiate the first study on secure media sharing with fair traitor tracing in the encrypted cloud media center, through a new marriage of proxy re-encryption (for secure media sharing) and fair watermarking (for fair traitor tracing). Our key insight is to fully leverage the homomorphic properties residing in proxy re-encryption to embrace operations in fair watermarking. Two protocols are proposed for different application scenarios. We also provide complexity analysis for performance, showing that our work can also be treated as secure outsourcing of fair watermarking, and thus kills two birds with one stone. We thoroughly analyze the security strengths and conduct extensive experiments to validate the effectiveness of our design.

Parent-identifying set systems and separable codes are useful combinatorial structures which were introduced, respectively, for traitor tracing in broadcast encryption and collusion-resistant fingerprints for copyright protection. Determining the maximum size of such structures is the main research objective. New upper bounds are presented in this paper. Specifically, for parent-identifying set systems, we determine the order of magnitude of $$I_2(4,v)$$ and prove an exact bound when $$w\le \lfloor \frac{t^2}{4}\rfloor +t$$ . For q-ary separable codes, we give a new upper bound by estimating the distance distribution of such codes, improving the existing upper bound when q is relatively small.

Traitor tracing scheme is a paradigm to classify the users who illegal use of their decryption keys in cryptosystems. In the ciphertext-policy attribute-based cryptosystem, the decryption key usually contains the users’ attributes, while the real identities are hidden. The decryption key with hidden identities enables malicious users to intentionally leak decryption keys or embed the decryption keys in the decryption device to gain illegal profits with a little risk of being discovered. To mitigate this problem, the concept of blackbox traceability in the ciphertext-policy attribute-based scheme was proposed to identify the malicious user via observing the I/O streams of the decryption device. However, current solutions with blackbox traceability are impractical since either the composite-order group or the linear complexity of system users is required. In this article, we proposed a secure ciphertext-policy attribute-based set encryption scheme with the short decryption key. The proposed scheme bases on the prime-order group to improve computational performances and aggregates multiple attributes into a constant-size attribute set to reduce the costs of communication overheads. By applying our proposed scheme with fingerprint codes, we then give an instantiation of the ciphertext-policy attribute-based scheme with blackbox traceability. Our scheme is provably secure under various q-type assumptions.

Fine-grained searching is an important feature in multi-user cloud environment and a combination of attribute-based encryption (ABE) and searchable encryption (SE) is used to facilitate it. This combination provides a powerful tool where multiple data owners can share their data with multiple data users in an independent and differential manner. In this article, the authors have used key-policy design framework of attribute-based encryption to construct the multi-keyword search scheme where access rights assigned to a data user are associated with his/her secret key. This leads to a situation where a data user can abuse his secret key to distribute it illegally to the unauthorized users to perform search over the shared data which is not intended for him/her. Therefore, to track such kind of key abusers the authors have embedded an extra functionality of tracing the traitors. For this purpose, each user is assigned a unique identity in the form of binary string where each bit represents an attribute related to his identity. In addition to the normal attributes, the access structure of a user also possesses identity-related attributes which are hidden from the user along with some normal attributes. Hence, the proposed scheme supports partial anonymity. Further, in the event of user revocation the proposed scheme efficiently handles the system update process by delegating the computationally intensive tasks to the cloud server. Finally, the proposed scheme is proved secure under Decisional Bilinear Diffie-Hellman (DBDH) assumption and decision linear assumption in the selective security model.

In order to solve the problem that the importance of the user’s attribute is seldom considered in the most of the existing attribute-based encryption schemes with traitor tracing, we designed a traceable and weighted attribute-based encryption scheme. In our constructed scheme, the private key of the user consisting of user’s identity information is applied to trace traitors. In addition, the idea of weighted attribute is introduced, and the attributes set is transformed into the segmentation set of weighted attributes through the attributes set segmentation algorithm. Via employing a linear secret sharing scheme, the constructed scheme offers fine-grained and nimble access control mechanism. Under the assumption of q-BDHE in the standard model, we prove that the designed scheme is able to reach security against chosen-plaintext attack. By comparing with other relevant schemes, it has significant improvement in the costs of communication and computation, and it is more suitable for the application of the mobile terminal in cloud computing.

The use of digital watermarking to secure the content of database systems is a new research direction in information security. Until now, the majority of the work has been based on image, video and audio. However, because of the growing use of relational database systems, database watermarking has become a research subject. Which addresses the legal issue of database system copyright protection. In this paper, we have focused on the review of four relational database watermarking techniques proposed by researchers [R. Agarwal & Jerry Kiernan, ZHU Qin, Brijesh B. Mehta, A. Al-Haj and Ali Hamadou]. The security of relational databases has been a great concern since the expanded use of these data over the Internet. Digital watermarking for relational databases emerged as a candidate solution to provide copyright protection, tamper detection, traitor tracing and maintaining integrity of relational data.

Forensic watermarking is often used to enable the tracing of digital pirates that leak copyright-protected videos. However, existing watermarking methods have a limited robustness and may be vulnerable to targeted attacks. Our previous work proposed a fallback detection method that uses secondary watermarks rather than the primary watermarks embedded by existing methods. However, the previously proposed fallback method is slow and requires access to all watermarked videos. This paper proposes to make the fallback watermark detection method faster using perceptual hashes instead of uncompressed secondary watermark signals. These perceptual hashes can be calculated prior to detection, such that the actual detection process is sped up with a factor of approximately 26,000 to 92,000. In this way, the proposed method tackles the main criticism about practical usability of the slow fallback method. The fast detection comes at the cost of a modest decrease in robustness, although the fast fallback detection method can still outperform the existing primary watermark method. In conclusion, the proposed method enables fast and more robust detection of watermarks that were embedded by existing watermarking methods.

Traitor tracing aims to identify the source of leaked decryption keys. Since the “traitor” can try to hide their key within obfuscated code in order to evade tracing, the tracing algorithm should work for general, potentially obfuscated, decoder programs. In the setting of such general decoder programs, prior work uses black box tracing: the tracing algorithm ignores the implementation of the decoder, and instead traces just by making queries to the decoder and observing the outputs.

This thesis considers a number of challenging aspects in multi-user cryptosystems such as traitor tracing, broadcast encryption, trace & revoke, and functional encryption. While a broadcast encryption scheme ensures the confidentiality of digital content against unauthorized users in the system, traitor tracing is an important tool to prevent authorized users from sharing decryption keys outside because if so, the tracer, with the help of the traitor tracing algorithm, will identify which user has disclosed information. In the first part, we focus on privacy in broadcast encryption schemes. We propose an anonymous broadcast encryption scheme in the bounded model (AnoBEB) whose security is based on the k-LWE assumption, which is a variant of the learning with errors (LWE) assumption. Our construction enjoys optimal efficiency (as efficient as LWE encryption) in the case where the number of users is bounded. In the second part, we integrate the proposed AnoBEB system with a robust identifiable parent property code (IPP) into a traceable scheme. Moreover, we achieve a very strong functionality scheme, also covering revocation and thus yielding the first trace & revoke scheme from a traceability code. Our construction becomes the most efficient trace & revoke scheme for standard black-box tracing in the bounded collusion model. The third part deals with traitor tracing algorithms for functional encryption. We introduce a new primitive, which is called {em traceable functional encryption}. We then formalize the notion of security and provide a concrete construction for {em traceable inner product functional encryption} (traceable IPFE). The proposed construction relies on pairings. It enjoys a high efficiency and achieves black-box confirmation. Finally, we recall the notion of {em revocable functional encryption}. We provide several pairing-based constructions for inner product functional encryption with short ciphertexts or decryption keys. We will then extend this notion to the {em fine-grained revocable functional encryption} and propose a candidate construction for fine-grained revocable inner product functional encryption., Cette thèse considère des aspects principaux dans les cryptosystèmes multi-utilisateurs tels que la diffusion de données chiffrées, la révocation, le traçage des traîtres et le chiffrement fonctionnel. Alors qu'un schéma de diffusion de données chiffrées garantit la confidentialité du contenu numérique contre les utilisateurs non autorisés du système, le traçage des traîtres est un outil important pour empêcher les utilisateurs autorisés de partager les clés de déchiffrement à l'extérieur.Dans la première partie, nous revisitons la privacy dans les schémas de diffusion de données chiffrées. Nous proposons un schéma anonyme (AnoBEB) dont la sécurité est basée sur l'hypothèse k-LWE, qui est une variante de l'hypothèse d'apprentissage avec erreurs (LWE). Notre construction bénéficie d'une efficacité optimale (aussi efficace que le chiffrement LWE) dans le cas où le nombre d'utilisateurs est borné. Dans la deuxième partie, nous intégrons le système AnoBEB proposé avec un code traçable IPP robuste dans un schéma de traçage de traîtres. De plus, nous obtenons également une propriété de révocation et produisons ainsi le premier schéma de trace & revoke à partir d'un code traçable. Notre construction devient le schéma de trace & revoke le plus efficace pour le traçage en boîte noire dans le modèle de collusion bornée. La troisième partie traite des algorithmes de traçage des traîtres pour le chiffrement fonctionnel. Nous introduisons dans un premier temps une nouvelle primitive, appelée traceable functional encryption (TFE). Nous formalisons ensuite la notion de sécurité et fournissons une construction concrète du TFE dans le cas du produit scalaire ( traceable IPFE). La construction proposée repose sur des couplages sur des courbes elliptiques, est très efficace et obtient le niveau de traçabilité dit de black-box confirmation. Enfin, nous rappelons la notion de revocable functional encryption. Nous fournissons plusieurs constructions basées sur les couplages pour le chiffrement fonctionnel dans le cas du produit scalaire avec des textes chiffrés courts ou des clés de déchiffrement courts. Nous étendrons ensuite cette notion au fine-grained revocable functional encryption et proposerons une construction candidate pour fine-grained revocable inner product functional encryption.

Securing multimedia content and preventing it from being maliciously manipulated has developed at a rapid pace, and researchers have been studying the traitor tracing as an appropriate solution. This approach consists in retrieving back the actors who contributed to the construction of an illegal release of a multimedia product. It includes two major steps which are the fingerprinting step and the tracing one. The fingerprinting step relies on the watermarking technique whereas the efficiency of the tracing scheme depends on several requirements: the robustness of the watermarking technique, the type of the media content, and even the computational complexity. In this paper, we propose a new collusion-secure fingerprinting scheme for 3D videos. It has essentially a twofold purpose: at a first step, we propose to embed the watermark in the video copy by applying a standard Least Significant Bit (LSB) substitution to all the frames of both the 2D video and the depth map components in order to ensure simultaneously and independently the protection of these two parts. In the second step, we apply the tracing process whose target is the identification of eventual colluders by extracting the hidden identifier from the suspicious video and analyse it. Experimental assessments show that the proposed scheme provides interesting results in terms of speed and tracing accuracy constraints.

Aggregate signature schemes enable us to aggregate multiple signatures into a single short signature. One of its typical applications is sensor networks, where a large number of users and devices measure their environments, create signatures to ensure the integrity of the measurements, and transmit their signed data. However, if an invalid signature is mixed into aggregation, the aggregate signature becomes invalid, thus if an aggregate signature is invalid, it is necessary to identify the invalid signature. Furthermore, we need to deal with a situation where an invalid sensor generates invalid signatures probabilistically. In this paper, we introduce a model of aggregate signature schemes with interactive tracing functionality that captures such a situation, and define its functional and security requirements and propose aggregate signature schemes that can identify all rogue sensors. More concretely, based on the idea of Dynamic Traitor Tracing, we can trace rogue sensors dynamically and incrementally, and eventually identify all rogue sensors of generating invalid signatures even if the rogue sensors adaptively collude. In addition, the efficiency of our proposed method is also sufficiently practical.

Cryptography is an active field of theoretical research. It is also a place where many unproven,but time-tested practical ideas exist. This work exposits a few strands that connectthese two sides of the Cryptographic coin.The two main results presented are,1. The first traitor tracing scheme based on prime order bilinear groups. While primeorder bilinear groups are practical, existing schemes for traitor tracing were basedon the more structurally rich, but much less practical composite order bilinear groups.Our work brings the rich structure of composite order bilinear groups and the efficiencyof prime order groups together.2. A formal model for CAPTCHAs which captures the intuition that any automatonmust request human help to solve CAPTCHA problems. We use this model to obtainpositive results in the eld of concurrent security. This is the first result that bringsCAPTCHA, a widely adopted practical security tool, into main stream cryptographyto achieve tasks that are known to be theoretically impossible in the plain model.

Attribute-based encryption received widespread attention as soon as it proposes. However, due to its specific characteristics, the attribute-based access control method is not flexible enough in actual operation. In addition, since access authorities are determined according to users' attributes, users sharing the same attributes are difficult to distinguish. Once a malicious user makes illicit gains by their decryption authorities, it is difficult to trace specific users. This paper follows the practical demand to propose a more flexible key-policy attribute-based encryption scheme with black-box traceability. The scheme has a constant number of constant parameters which can be utilized to construct attribute-related parameters flexibly, and the method of traitor tracing in broadcast encryption is introduced to achieve effective malicious user tracing. In addition, the security and feasibility can be proved by the security proofs and performance evaluation in this paper.

Cloud-based deep learning (DL) solutions have been widely used in applications ranging from image recognition to speech recognition. Meanwhile, as commercial software and services, such solutions have raised the need for intellectual property rights protection of the underlying DL models. Watermarking is the mainstream of existing solutions to address this concern, by primarily embedding pre-defined secrets in a model's training process. However, existing efforts almost exclusively focus on detecting whether a target model is pirated, without considering traitor tracing. In this paper, we present SecureMark_DL, which enables a model owner to embed a unique fingerprint for every customer within parameters of a DL model, extract and verify the fingerprint from a pirated model, and hence trace the rogue customer who illegally distributed his model for profits. We demonstrate that SecureMark_DL is robust against various attacks including fingerprints collusion and network transformation (e.g., model compression and model fine-tuning). Extensive experiments conducted on MNIST and CIFAR10 datasets, as well as various types of deep neural network show the superiority of SecureMark_DL in terms of training accuracy and robustness against various types of attacks.

E-healthcare cloud remarkably facilitates patients to outsource their electronic health record (EHR) to achieve large-scale information sharing in real-time for improving the efficiency of diagnosis and treatment. Unfortunately, compared with other outsourced data, EHR contains more personal privacy, which makes it more preferred by the adversaries. Besides, in the e-healthcare cloud, there may exist malicious users who deliberately disclose their access privileges to obtain financial benefits. In this paper, we propose a fine-grained EHR sharing scheme in e-healthcare cloud with hidden policy and traceability. Specifically, we present a new black-box traitor tracing scheme based on partial policy hiding attribute-based encryption and it performs fine-grained access control on the encrypted EHR, which not only prevents privacy leakage from access policy but also effectively track malicious users who leak decryption privileges to construct a black-box. Our scheme is proved to be fully secure under the standard model. Performance analysis shows that the scheme can achieve the design goals in terms of storage and computation overhead. In the meantime, it is more efficient than the existing schemes under the composite order group.

Today mobile devices are an integral part of our lives with the development of applications. In addition to smart phones, which are increasingly powerful, other devices such as connected objects may have to handle data that must remain secret. For example, the authentication of a connected object in a network requires the existence of a ``secret" held by the object. In the case of mobile applications, the emergence of payment applications allowing contactless payment from the telephone or banking applications poses serious security challenges. The need to secure applications is therefore essential both for users wishing to access a service without risking their goods and for service providers who have a financial interest in it. Thus, cryptography is used to protect these various mobile applications. In this context, we wish to meet this need with both a software and hardware approach to secure cryptography on open and exposed platforms. The aim of this thesis is to verify the security of software implementations of cryptographic algorithms in the white-box model and to propose techniques to reinforce this security in a mobile environment. The white-box model or white-box attacks context is opposed to the traditional black-box model and refers to a context in which an attacker controls an execution environment and has access to software implementations of cryptographic algorithms. Once a secret key is revealed, the security of the encryption scheme is no longer valid. In this context, the last line of defense is the implementation itself: the secret key is hidden in the code so that it cannot be distinguished or extracted. Many studies have been conducted on White-Box Cryptography and have led to proposals for white-box implementations of standardized algorithms such as the DES (Data Encryption Standard) or the AES (Advanced Encryption Standard). These algorithms are of particular interest due to their wide deployment. Unfortunately these proposals have revealed vulnerabilities and do not guarantee the confidentiality of the secret key. In this thesis, we are first interested in the reasons why not all proposed implementations allow to ``hide'' the secret key sufficiently. We will make a detailed study of the techniques used as well as the possible attacks. Secondly, we propose new techniques to counter these attacks and study the cost of these techniques in terms of code size and performance. Another approach in White-Box Cryptography is to design algorithms that can be proved to be resistant to key extraction. This new approach involves proposing security notions adapted to the white-box model. In particular, the main problem is to ensure that the implementation of the cryptographic algorithm cannot be copied and executed in another environment. This attack called "code lifting" (code copying) is equivalent to extracting the secret key. One solution proposed in the literature is to increase the size of the code in order to increase the space complexity of the attack. We propose a solution to this problem by defining an encryption scheme that can be implemented in a white-box and that uses a physical device called Physically Unclonable Function (PUF). A PUF refers to a physical device with unique and unclonable characteristics that can be used to identify it. Thus, a PUF can be seen as the fingerprint (in the biometric sense) of a device. The PUF will be used in our scheme as a means of identifying the execution environment of a cryptographic algorithm and will generate a key specific to a given device.; Aujourd'hui les équipements mobiles font partie intégrante de nos vies avec le développement des applications. En plus des téléphones intelligents, d'autres équipements comme les objets connectés peuvent avoir à manipuler des données qui doivent rester secrètes. Par exemple, l'authentification d'un objet connecté dans un réseau nécessite l'existence d'un "secret" détenu par l'objet. Dans le cas des applications mobiles, l'apparition des applications de paiement permettant un paiement sans contact à partir du téléphone ou encore les applications bancaires pose de sérieux enjeux de sécurité. Le besoin de sécurisation des applications est ainsi primordial à la fois pour un utilisateur désireux d'accéder à un service sans risquer ses biens mais aussi pour les fournisseurs de services qui y ont un intérêt financier. Ainsi, la cryptographie est utilisée pour protéger ces diverses applications mobiles. Dans ce contexte, on souhaite répondre à ce besoin avec une approche à la fois logicielle et matérielle pour sécuriser la cryptographie sur des plateformes ouvertes et exposées. Le but de cette thèse est de vérifier la sécurité des implémentations logicielles d’algorithmes cryptographiques dans le modèle boîte blanche et de proposer des techniques permettant de renforcer cette sécurité dans un environnement mobile. Le modèle boîte blanche s’oppose au modèle boîte noire traditionnel et décrit un contexte dans lequel un attaquant contrôle l'environnement d’exécution et a accès aux implémentations logicielles. Une fois qu'une clé secrète est révélée, la sécurité du schéma de chiffrement n’est plus valable. Dans ce contexte, la dernière ligne de défense est l’implémentation elle-même : la clé secrète est cachée dans le code de manière à ce qu’elle ne puisse être ni identifiée, ni extraite. De nombreuses études ont été menées sur la cryptographie en boîte blanche et ont abouti à des propositions d’implémentations d’algorithmes standardisés tels que le DES (Data Encryption Standard) ou l’AES (Advanced Encryption Standard). Ces algorithmes intéressent particulièrement du fait de leur large déploiement. Malheureusement ces propositions ont révélé des vulnérabilités et ne garantissent pas la confidentialité de la clé secrète. Dans cette thèse, nous nous intéressons premièrement aux raisons pour lesquelles toutes les propositions d’implémentations ne permettent pas de "cacher" suffisamment la clé secrète. Nous ferons une étude détaillée des techniques utilisées ainsi que des attaques possibles. Deuxièmement, nous proposons des techniques nouvelles permettant de contrecarrer ces attaques et étudions le coût de ces techniques en termes de taille et de performance de code. Une autre approche en cryptographie en boîte blanche est de concevoir des algorithmes dont on peut prouver la résistance à l’extraction de clé. Cette nouvelle approche implique de proposer des notions de sécurité adaptées au modèle boîte blanche. En particulier, le problème principal est de garantir que l’implémentation ne puisse être copiée et exécutée dans un autre environnement. Cette attaque appelée "code lifting" (copie de code) est équivalent à extraire la clé secrète. Une solution proposée dans la littérature est d’augmenter la taille du code afin d’augmenter la complexité en espace de l’attaque. Nous proposons une solution à ce problème en définissant un schéma de chiffrement que l’on peut implémenter en boîte blanche et qui utilise un dispositif physique appelé Physically Unclonable Function (PUF). Une PUF désigne un dispositif physique présentant des caractéristiques uniques et inclonables permettant de l’identifier. Ainsi, une PUF peut être vue comme l’empreinte (au sens biométrique) d’un appareil. Ce dispositif sera utilisé dans notre schéma comme moyen d’identifier l’environnement d’exécution d’un algorithme cryptographique et permettra de générer une clé spécifique à un appareil donné.

Today mobile devices are an integral part of our lives with the development of applications. In addition to smart phones, which are increasingly powerful, other devices such as connected objects may have to handle data that must remain secret. For example, the authentication of a connected object in a network requires the existence of a ``secret" held by the object. In the case of mobile applications, the emergence of payment applications allowing contactless payment from the telephone or banking applications poses serious security challenges. The need to secure applications is therefore essential both for users wishing to access a service without risking their goods and for service providers who have a financial interest in it. Thus, cryptography is used to protect these various mobile applications. In this context, we wish to meet this need with both a software and hardware approach to secure cryptography on open and exposed platforms. The aim of this thesis is to verify the security of software implementations of cryptographic algorithms in the white-box model and to propose techniques to reinforce this security in a mobile environment. The white-box model or white-box attacks context is opposed to the traditional black-box model and refers to a context in which an attacker controls an execution environment and has access to software implementations of cryptographic algorithms. Once a secret key is revealed, the security of the encryption scheme is no longer valid. In this context, the last line of defense is the implementation itself: the secret key is hidden in the code so that it cannot be distinguished or extracted. Many studies have been conducted on White-Box Cryptography and have led to proposals for white-box implementations of standardized algorithms such as the DES (Data Encryption Standard) or the AES (Advanced Encryption Standard). These algorithms are of particular interest due to their wide deployment. Unfortunately these proposals have revealed vulnerabilities and do not guarantee the confidentiality of the secret key. In this thesis, we are first interested in the reasons why not all proposed implementations allow to ``hide'' the secret key sufficiently. We will make a detailed study of the techniques used as well as the possible attacks. Secondly, we propose new techniques to counter these attacks and study the cost of these techniques in terms of code size and performance. Another approach in White-Box Cryptography is to design algorithms that can be proved to be resistant to key extraction. This new approach involves proposing security notions adapted to the white-box model. In particular, the main problem is to ensure that the implementation of the cryptographic algorithm cannot be copied and executed in another environment. This attack called "code lifting" (code copying) is equivalent to extracting the secret key. One solution proposed in the literature is to increase the size of the code in order to increase the space complexity of the attack. We propose a solution to this problem by defining an encryption scheme that can be implemented in a white-box and that uses a physical device called Physically Unclonable Function (PUF). A PUF refers to a physical device with unique and unclonable characteristics that can be used to identify it. Thus, a PUF can be seen as the fingerprint (in the biometric sense) of a device. The PUF will be used in our scheme as a means of identifying the execution environment of a cryptographic algorithm and will generate a key specific to a given device.; Aujourd'hui les équipements mobiles font partie intégrante de nos vies avec le développement des applications. En plus des téléphones intelligents, d'autres équipements comme les objets connectés peuvent avoir à manipuler des données qui doivent rester secrètes. Par exemple, l'authentification d'un objet connecté dans un réseau nécessite l'existence d'un "secret" détenu par l'objet. Dans le cas des applications mobiles, l'apparition des applications de paiement permettant un paiement sans contact à partir du téléphone ou encore les applications bancaires pose de sérieux enjeux de sécurité. Le besoin de sécurisation des applications est ainsi primordial à la fois pour un utilisateur désireux d'accéder à un service sans risquer ses biens mais aussi pour les fournisseurs de services qui y ont un intérêt financier. Ainsi, la cryptographie est utilisée pour protéger ces diverses applications mobiles. Dans ce contexte, on souhaite répondre à ce besoin avec une approche à la fois logicielle et matérielle pour sécuriser la cryptographie sur des plateformes ouvertes et exposées. Le but de cette thèse est de vérifier la sécurité des implémentations logicielles d’algorithmes cryptographiques dans le modèle boîte blanche et de proposer des techniques permettant de renforcer cette sécurité dans un environnement mobile. Le modèle boîte blanche s’oppose au modèle boîte noire traditionnel et décrit un contexte dans lequel un attaquant contrôle l'environnement d’exécution et a accès aux implémentations logicielles. Une fois qu'une clé secrète est révélée, la sécurité du schéma de chiffrement n’est plus valable. Dans ce contexte, la dernière ligne de défense est l’implémentation elle-même : la clé secrète est cachée dans le code de manière à ce qu’elle ne puisse être ni identifiée, ni extraite. De nombreuses études ont été menées sur la cryptographie en boîte blanche et ont abouti à des propositions d’implémentations d’algorithmes standardisés tels que le DES (Data Encryption Standard) ou l’AES (Advanced Encryption Standard). Ces algorithmes intéressent particulièrement du fait de leur large déploiement. Malheureusement ces propositions ont révélé des vulnérabilités et ne garantissent pas la confidentialité de la clé secrète. Dans cette thèse, nous nous intéressons premièrement aux raisons pour lesquelles toutes les propositions d’implémentations ne permettent pas de "cacher" suffisamment la clé secrète. Nous ferons une étude détaillée des techniques utilisées ainsi que des attaques possibles. Deuxièmement, nous proposons des techniques nouvelles permettant de contrecarrer ces attaques et étudions le coût de ces techniques en termes de taille et de performance de code. Une autre approche en cryptographie en boîte blanche est de concevoir des algorithmes dont on peut prouver la résistance à l’extraction de clé. Cette nouvelle approche implique de proposer des notions de sécurité adaptées au modèle boîte blanche. En particulier, le problème principal est de garantir que l’implémentation ne puisse être copiée et exécutée dans un autre environnement. Cette attaque appelée "code lifting" (copie de code) est équivalent à extraire la clé secrète. Une solution proposée dans la littérature est d’augmenter la taille du code afin d’augmenter la complexité en espace de l’attaque. Nous proposons une solution à ce problème en définissant un schéma de chiffrement que l’on peut implémenter en boîte blanche et qui utilise un dispositif physique appelé Physically Unclonable Function (PUF). Une PUF désigne un dispositif physique présentant des caractéristiques uniques et inclonables permettant de l’identifier. Ainsi, une PUF peut être vue comme l’empreinte (au sens biométrique) d’un appareil. Ce dispositif sera utilisé dans notre schéma comme moyen d’identifier l’environnement d’exécution d’un algorithme cryptographique et permettra de générer une clé spécifique à un appareil donné.

Recently, many enterprises have moved their data into the cloud by using file syncing and sharing (FSS) services, which have been deployed for mobile users. However, Bring-Your-Own-Device (BYOD) solutions for increasingly deployed mobile devices have also in fact raised a new challenge for how to prevent users from abusing the FSS service. In this paper, we address this issue by using a new system model involving anomaly detection, tracing, and revocation approaches. The presented solution applies a new threshold public key based cryptosystem, called partially-ordered hierarchical encryption (PHE), which implements a partial-order key hierarchy and it is similar to role hierarchy widely used in RBAC. PHE provides two main security mechanisms, i.e., traitor tracing and key revocation, which can greatly improve the efficiency compared to previous approaches. The security and performance analysis shows that PHE is a provably secure threshold encryption and provides following salient management and performance benefits: it can promise to efficiently trace all possible traitor coalitions and support public revocation not only for the users but for the specified groups.

This article first describes a paper by Ling, Phan, and Stehle at the CRYPTO 2014 which presented the first encryption scheme for traitor tracing from lattice, and the scheme is almost as efficient as the learning with errors (LWE) encryption. However, their scheme is not constructed on an efficient trapdoor, that is, the trapdoor generation and preimage sampling algorithms are rather complex and not suitable for practice. This article is considered to use the MP12 trapdoor to construct an improved traitor tracing scheme. First, by using batch execution method, this article proposes an improved extracting algorithm for the user's key. Then, this article combines that with multi-bit encryption system to construct an efficient one-to-many encryption scheme. Furthermore, it is presented that a novel projective sampling family has very small hidden constants. Finally, a comparative analysis shows that the parameters of the scheme such as lattice dimension, trapdoor size, and ciphertext expansion rate, etc., all decrease in some degree, and the computational cost is reduced.

Ciphertext-policy attribute-based encryption (CP-ABE) has been proposed to enable fine-grained access control on encrypted data for cloud storage service. In the context of CP-ABE, since the decryption privilege is shared by multiple users who have the same attributes, it is difficult to identify the original key owner when given an exposed key. This leaves the malicious cloud users a chance to leak their access credentials to outsourced data in clouds for profits without the risk of being caught, which severely damages data security. To address this problem, we add the property of traceability to the conventional CP-ABE. To catch people leaking their access credentials to outsourced data in clouds for profits effectively, in this paper, we first propose two kinds of non-interactive commitments for traitor tracing. Then we present a fully secure traceable CP-ABE system for cloud storage service from the proposed commitment. Our proposed commitments for traitor tracing may be of independent interest, as they are both pairing-friendly and homomorphic. We also provide extensive experimental results to confirm the feasibility and efficiency of the proposed solution.