Analysis of Key Wrapping APIs:Generic Policies, Computational Security

International audienceWe present an analysis of key wrapping APIs with generic policies. We prove that certain minimal conditions on policies are sufficient for keys to be indistinguishable from random in any execution of an API. Our result captures a large class of API policies, including both the hierarchies on keys that are common in the scientific literature and the non-linear dependencies on keys used in PKCS#11. Indeed, we use our result to propose a secure refinement of PKCS#11, assuming that the attributes of keys are transmitted as authenticated associated data when wrapping and that there is an enforced separation between keys used for wrapping and keys used for other cryptographic purposes. We use the Computationally Complete Symbolic Attacker developed by Bana and Comon. This model enables us to obtain computational guarantees using a simple proof with a high degree of modularity

A Provably Secure PKCS#11 Configuration Without Authenticated Attributes

Cryptographic APIs like PKCS#11 are interfaces to trusted hardware where keys are stored; the secret keys should never leave the trusted hardware in plaintext. In PKCS#11 it is possible to give keys conflicting roles, leading to a number of key-recovery attacks. To prevent these attacks, one can authenticate the attributes of keys when wrapping, but this is not standard in PKCS#11. Alternatively, one can configure PKCS#11 to place additional restrictions on the commands permitted by the API. Bortolozzo et al. proposed a configuration of PKCS#11, called the Secure Templates Patch (STP), supporting symmetric encryption and key wrapping. However, the security guarantees for STP given by Bortolozzo et al. are with respect to a weak attacker model. STP has been implemented as a set of filtering rules in Caml Crush, a software filter for PKCS#11 that rejects certain API calls. The filtering rules in Caml Crush extend STP by allowing users to compute and verify MACs and so the previous analysis of STP does not apply to this configuration. We give a rigorous analysis of STP, including the extension used in Caml Crush. Our contribution is as follows: (i) We show that the extension of STP used in Caml Crush is insecure. (ii) We propose a strong, computational security model for configurations of PKCS#11 where the adversary can adaptively corrupt keys and prove that STP is secure in this model. (iii) We prove the security of an extension of STP that adds support for public-key encryption and digital signatures

CamlCrush: A PKCS\#11 Filtering Proxy

PKCS\#11 is a very popular cryptographic API: it is the standard used by many Hardware Security Modules, smartcards and software cryptographic tokens. Several attacks have been uncovered against PKCS\#11 at different levels: intrinsic logical flaws, cryptographic vulnerabilities or severe compliance issues. Since affected hardware remains widespread in computer infrastructures, we propose a user-centric and pragmatic approach for secure usage of vulnerable devices. We introduce \textit{Caml Crush}, a PKCS\#11 filtering proxy. Our solution allows to dynamically protect PKCS\#11 cryptographic tokens from state of the art attacks. This is the first approach that is immediately applicable to commercially available products. We provide a fully functional open source implementation with an extensible filter engine effectively shielding critical resources. This yields additional advantages to using \textit{Caml Crush} that go beyond classical PKCS\#11 weakness mitigations

A Secure Key Management Interface with Asymmetric Cryptography

Cryptographic devices such as Hardware Security Modules are only as secure as their application programme interfaces (APIs) that offer cryptographic functionality to the outside world. Design flaws and implementation errors in security APIs have been shown to cause vulnerabilities that may leak secrets such as keys and PINs. Ideally, we would like to design such interfaces in such a way that we can formally prove security properties, even in the presence of some corrupted keys. In this work, we take such a design for a provably secure interface for symmetric key management, due to Cortier and Steel, and extend it to asymmetric cryptography, giving new security definitions and associated proofs. Asymmetric cryptography forces us to consider confidentiality and integrity properties separately and provide support for classical operations of public key infrastructure (e.g. certification of public keys). As far as we are aware this is the first such provably secure interface to support asymmetric key operations for key management: Cachin and Chandran's secure token interface supports asymmetric key operations only for encrypting and signing data, not for managing keys.Les systèmes cryptographiques tels que les modules matériels de sécurité ne peuvent apporter un niveau de sécurité que dans la mesure où leur interface de programmation (API) qui offre les services de cryptographie à l'extérieur de module atteint ce même niveau de sécurité. Il a été constaté que des défauts de conception ou des erreur d'implémentation dans les APIs de sécurité sont à l'origine de vulnérabilités pouvant entrainer la fuite de secrets comme des clefs ou des PINs. Idéalement, nous voudrions concevoir de telles interfaces de manière à pouvoir prouver formellement des propriétés de sécurité, même si certaines clefs sont corrompues. Dans cet article, nous partons d'une telle API, due à Cortier et Steel, conçue de manière disposer d'une preuve de sécurité pour la gestion de clefs symétriques, et nous l'adaptons à la cryptographie asymétrique en donnant une nouvelle définition de sécurité avec les preuves associées. Afin de prendre en compte la cryptographie asymétrique, nous sommes amenés à gérer de manière différentiée les propriétés de confidentialité et d'intégrité et à ajouter les fonctionalités classiques d'une infrastructure de gestion de clefs publiques (i.e. la certification des clefs publiques). Á notre connaissance, il s'agit de la première preuve d'interface prouvée permettant l'usage de primitives asymétriques pour la gestion de clefs : l'interface de Cachin et Chandra prévoit l'usage de primitives asymétriques uniquement pour le chiffrement et la signature de données, et non pas pour la gestion des clefs

Analysis of the IBM CCA Security API Protocols in Maude-NPA

Standards for cryptographic protocols have long been attractive candidates for formal verification. It is important that such standards be correct, and cryptographic protocols are tricky to design and subject to non-intuitive attacks even when the underlying cryptosystems are secure. Thus a number of general-purpose cryptographic protocol analysis tools have been developed and applied to protocol standards. However, there is one class of standards, security application programming interfaces (security APIs), to which few of these tools have been applied. Instead, most work has concentrated on developing special-purpose tools and algorithms for specific classes of security APIs. However, there can be much advantage gained from having general-purpose tools that could be applied to a wide class of problems, including security APIs. One particular class of APIs that has proven difficult to analyze using general-purpose tools is that involving exclusive-or. In this paper we analyze the IBM 4758 Common Cryptographic Architecture (CCA) protocol using an advanced automated protocol verification tool with full exclusive-or capabilities, the Maude-NPA tool. This is the first time that API protocols have been satisfactorily specified and analyzed in the Maude-NPA, and the first time XOR-based APIs have been specified and analyzed using a general-purpose unbounded session cryptographic protocol verification tool that provides direct support for AC theories. We describe our results and indicate what further research needs to be done to make such protocol analysis generally effective.Antonio González-Burgueño, Sonia Santiago and Santiago Escobar have been partially supported by the EU (FEDER) and the Spanish MINECO under grants TIN 2010-21062-C02-02 and TIN 2013-45732-C4-1-P, and by Generalitat Valenciana PROMETEO2011/052. José Meseguer has been partially supported by NSF Grant CNS 13-10109.González Burgueño, A.; Santiago Pinazo, S.; Escobar Román, S.; Meadows, C.; Meseguer, J. (2014). Analysis of the IBM CCA Security API Protocols in Maude-NPA. En Security Standardisation Research. Springer International Publishing. 111-130. https://doi.org/10.1007/978-3-319-14054-4_8S111130Abadi, M., Blanchet, B., Fournet, C.: Just fast keying in the pi calculus. ACM Trans. Inf. Syst. Secur. 10(3) (2007)Blanchet, B.: An Efficient Cryptographic Protocol Verifier Based on Prolog Rules. In: 14th IEEE Computer Security Foundations Workshop (CSFW 2014), Cape Breton, Nova Scotia, Canada, June 2001, pp. 82–96. IEEE Computer Society (2014)Bond, M.: Attacks on cryptoprocessor transaction sets. In: Koç, Ç.K., Naccache, D., Paar, C. (eds.) CHES 2001. LNCS, vol. 2162, pp. 220–234. Springer, Heidelberg (2001)Butler, F., Cervesato, I., Jaggard, A.D., Scedrov, A.: A formal analysis of some properties of kerberos 5 using msr. In: CSFW, pp. 175–1790. IEEE Computer Society (2002)Cachin, C., Chandran, N.: A secure cryptographic token interface. In: Proceedings of the 22nd IEEE Computer Security Foundations Symposium, CSF 2009, Port Jefferson, New York, USA, July 8-10, pp. 141–153 (2009)Chevalier, Y., Küsters, R., Rusinowitch, M., Turuani, M.: An NP decision procedure for protocol insecurity with XOR. In: 18th Annual IEEE Symposium on Logic in Computer Science, LICS 2003 (2003)Comon-Lundh, H., Shmatikov, V.: Intruder deductions, constraint solving and insecurity decision in presence of exclusive-or. In: 18th Annual IEEE Symposium on Logic in Computer Science (LICS 2003), pp. 271–280 (2003)Comon-Lundh, H., Cortier, V.: New decidability results for fragments of first-order logic and application to cryptographic protocols. In: Nieuwenhuis, R. (ed.) RTA 2003. LNCS, vol. 2706, pp. 148–164. Springer, Heidelberg (2003)Cortier, V., Keighren, G., Steel, G.: Automatic analysis of the aecurity of XOR-based key management schemes. In: Grumberg, O., Huth, M. (eds.) TACAS 2007. LNCS, vol. 4424, pp. 538–552. Springer, Heidelberg (2007)Cortier, V., Steel, G.: A generic security API for symmetric key management on cryptographic devices. In: Backes, M., Ning, P. (eds.) ESORICS 2009. LNCS, vol. 5789, pp. 605–620. Springer, Heidelberg (2009)Erbatur, S., et al.: Effective Symbolic Protocol Analysis via Equational Irreducibility Conditions. In: Foresti, S., Yung, M., Martinelli, F. (eds.) ESORICS 2012. LNCS, vol. 7459, pp. 73–90. Springer, Heidelberg (2012)Escobar, S., Meadows, C., Meseguer, J.: Maude-NPA: Cryptographic Protocol Analysis Modulo Equational Properties. In: Aldini, A., Barthe, G., Gorrieri, R. (eds.) FOSAD 2007/2008/2009. LNCS, vol. 5705, pp. 1–50. Springer, Heidelberg (2007)Escobar, S., Meadows, C., Meseguer, J., Santiago, S.: Sequential Protocol Composition in Maude-NPA. In: Gritzalis, D., Preneel, B., Theoharidou, M. (eds.) ESORICS 2010. LNCS, vol. 6345, pp. 303–318. Springer, Heidelberg (2010)Thayer Fabrega, F.J., Herzog, J., Guttman, J.: Strand Spaces: What Makes a Security Protocol Correct? Journal of Computer Security 7, 191–230 (1999)González-Burgueño, A.: Protocol Analysis Modulo Exclusive-Or Theories: A Case study in Maude-NPA. Master’s thesis, Universitat Politècnica de València (March 2014), https://angonbur.webs.upv.es/Previous_work/Master_Thesis.pdfIBM. Comment on Mike’s Bond paper A Chosen Key Difference Attack on Control Vectors (2001), http://www.cl.cam.ac.uk/~mkb23/research/CVDif-Response.pdfIBM. CCA basic services reference and guide: CCA basic services reference and guide for the IBM 4758 PCI and IBM 4764 (2001), http://www-03.ibm.com/security/cryptocards/pdfs/bs327.pdf.2008Keighren, G.: Model Checking IBM’s Common Cryptographic Architecture API. 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Proving Cryptographic C Programs Secure with General-Purpose Verification Tools

Security protocols, such as TLS or Kerberos, and security devices such as the Trusted Platform Module (TPM), Hardware Security Modules (HSMs) or PKCS#11 tokens, are central to many computer interactions. Yet, such security critical components are still often found vulnerable to attack after their deployment, either because the specification is insecure, or because of implementation errors. Techniques exist to construct machine-checked proofs of security properties for abstract specifications. However, this may leave the final executable code, often written in lower level languages such as C, vulnerable both to logical errors, and low-level flaws. Recent work on verifying security properties of C code is often based on soundly extracting, from C programs, protocol models on which security properties can be proved. However, in such methods, any change in the C code, however trivial, may require one to perform a new and complex security proof. Our goal is therefore to develop or identify a framework in which security properties of cryptographic systems can be formally proved, and that can also be used to soundly verify, using existing general-purpose tools, that a C program shares the same security properties. We argue that the current state of general-purpose verification tools for the C language, as well as for functional languages, is sufficient to achieve this goal, and illustrate our argument by developing two verification frameworks around the VCC verifier. In the symbolic model, we illustrate our method by proving authentication and weak secrecy for implementations of several network security protocols. In the computational model, we illustrate our method by proving authentication and strong secrecy properties for an exemplary key management API, inspired by the TPM

Gestão segura de múltiplas instâncias de uma mesma chave de assinatura em autoridades certificadoras

Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-Graduação em Ciência da Computação, Florianópolis, 2011Chaves criptográficas são hoje parte fundamental na proteção de dados e informações que trafegam por canais inseguros de forma análoga às chaves físicas na proteção de patrimônios, pessoas, entre outros valores. Uma chave, seja física ou lógica, impede ou dificulta o acesso não autorizado a um bem valioso, por intermédio de um segredo ou combinação de difícil previsão ou composição. Nesses materiais, o procedimento de replicação é de suma importância para garantir que, mesmo que uma das cópias de determinada chave torne-se indisponível, seja por perda, roubo ou excesso de demanda, o acesso às informações por ela protegidas não seja interrompido. Entretanto, mesmo em hardwares dedicados exclusivamente à gestão do ciclo de vida de chaves, é comum que a segurança seja por vezes preterida em nome da garantia de disponibilidade. Isso se dá em virtude dos modelos de gestão existentes, que unicamente levam em consideração a existência de uma instância da chave ou que trata as diferentes instancias separadamente. O presente trabalho propõe dois novos modelos de gestão voltados a chaves assimétricas de autoridades certificadoras, que levem em consideração as múltiplas cópias possíveis de uma mesma chave criptográfica, de forma que seu custodiante ou grupo de custodiantes jamais percam o controle sobre nenhuma de suas instâncias. Com isso, busca-se possibilitar a rastreabilidade das cópias, agregando as propriedades alta disponibilidadee e tolerância a faltas à gestão de chaves, sem contudo comprometer sua segurança. Com os modelos propostos, foi possível identificar univocamente cada nova instância de uma mesma chave privada, através de rastros que liguem a chave pai à sua filha. Com isso, a disponibilidade foi beneficiada, sem contudo prejudicar o controle sobre a utilização das múltiplas instâncias, por parte dos custodiantes.Cryptographic keys consist on an essential component to provide data security over the electronic environment. Associated with an algorithm, they are responsible for protecting transactions, information and other electronic assets providing authenticity, confidentiality and integrity. To assure the availability of the protected assets, however, the keys must be strictly controled. One of the aspects in key lifecycle management is the secure replication of keys, in order to avoid the loss of so valuable resources, in case of unavailability of the key. This work shows that even in hardwares dedicated to securely manage keys lifecycle, namely HSM, security is sometimes underestimated in name of the availability. This work proposes two new models for keymanagement, allowing the replication of key material, without compromise the control over the managed keys. The main goal of the methods is to keep a track among all derivates of the original key, balancing availability assurances with the control of the multiple instances by the key owners

Restricting information flow in security APIs via typing

Security APIs are designed to enable the storage and processing of confidential data without that data becoming known to individuals who are not permitted to obtain it, and are central to the operation of Automated Teller Machines (ATM) networks, Electronic Point of Sale (EPOS) terminals, set-top boxes for subscription-based TV, pre-payment utility meters, and electronic ticketing for an increasing number of public transport systems (e.g., Oyster in London). However, since the early 2000s, it has become clear that many of the security APIs in widespread use contain subtle flaws which allow malicious individuals to subvert the security restrictions and obtain confidential data that should be protected. In this thesis, we attempt to address this problem by presenting a type system in which specific security properties are guaranteed to be enforced by security APIs that are well-typed. Since type-checking is a form of static analysis, it does not suffer from the scalability issues associated with approaches that simulate interactions between a security API and one or more malicious individuals. We also show how our type system can be used to model an existing security API and provide the same guarantees of security that the API authors proved it upholds. This result follows directly from producing a well-typed implementation of the API, and demonstrates how our type system provides security guarantees without requiring additional API-specific proofs

A secure cryptographic token interface

Cryptographic keys must be protected from exposure. In real-world applications, they are often guarded by cryptographic tokens that employ sophisticated hardware-security measures. Several logical attacks on the key management operations of cryptographic tokens have been reported in the past, which allowed to expose keys merely by exploiting the token API in unexpected ways. This paper proposes a novel, provably secure, cryptographic token interface that supports multiple users, implements symmetric cryptosystems and public-key schemes, and provides operations for key generation, encryption, authentication, and key wrapping. The token interface allows only the most important operations found in real-world token APIs; while flexible to be of practical use, it is restricted enough so that it does not expose any key to a user without sufficient privileges. An emulation of the security policy in the industry-standard PKCS #11 interface is demonstrated.