Encontrados 8 documentos, a visualizar página 1 de 1
Delegatable homomorphic encryption with applications to secure outsourcing of c...
Barbosa, Manuel Bernardo; Farshim, P.In this work we propose a new cryptographic primitive called Delegatable Homomorphic Encryption (DHE). This allows a Trusted Authority to control/delegate the capability to evaluate circuits over encrypted data to untrusted workers/evaluators by issuing tokens. This primitive can be both seen as a public-key counterpart to Verifiable Computation, where input generation and output verification are performed by d...
Relations among notions of complete non-malleability : indistinguishability cha...
Barbosa, Manuel Bernardo; Farshim, P.We study relations among various notions of complete non-malleability, where an adversary can tamper with both ciphertexts and public-keys, and ciphertext indistinguishability. We follow the pattern of relations previously established for standard non-malleability. To this end, we propose a more convenient and conceptually simpler indistinguishability-based security model to analyse completely non-malleable sch...
Strong knowledge extractors for public-key encryption schemes
Barbosa, Manuel Bernardo; Farshim, P.Completely non-malleable encryption schemes resist attacks which allow an adversary to tamper with both ciphertexts and public keys. In this paper we introduce two extractor-based properties that allow us to gain insight into the design of such schemes and to go beyond known feasibility results in this area. We formalise strong plaintext awareness and secret key awareness and prove their suitability in realisin...
Security analysis of standard authentication and key agreement protocols utilis...
Barbosa, Manuel Bernardo; Farshim, P.We propose a generic modelling technique that can be used to extend existing frameworks for theoretical security analysis in order to capture the use of timestamps. We apply this technique to two of the most popular models adopted in literature (Bellare-Rogaway and Canetti-Krawczyk). We analyse previous results obtained using these models in light of the proposed extensions, and demonstrate their application to...
Certificateless sIgncryption
Barbosa, Manuel Bernardo; Farshim, P.Certificateless cryptography inherits a solution to the certificate management problem in public-key encryption from identity-based techniques, whilst removing the secret key escrow functionality inherent to the identity-based setting. Signcryption schemes achieve confidentiality and authentication simultaneously by combining public-key encryption and digital signatures, offering better overall performance and ...
Randomness reuse : extensions and improvements
Barbosa, Manuel Bernardo; Farshim, P.We extend the generic framework of reproducibility for reuse of randomness in multi-recipient encryption schemes as proposed by Bel- lare et al. (PKC 2003). A new notion of weak reproducibility captures not only encryption schemes which are (fully) reproducible under the criteria given in the previous work, but also a class of efficient schemes which can only be used in the single message setting. In parti...
Secure cryptographic workflow in the standard model
Barbosa, Manuel Bernardo; Farshim, P.Following the work of Al-Riyami et al. we define the notion of key encapsulation mechanism supporting cryptographic workflow (WF-KEM) and prove a KEM-DEM composition theorem which extends the notion of hybrid encryption to cryptographic workflow. We then generically construct a WF-KEM from an identity-based encryption (IBE) scheme and a secret sharing scheme. Chosen ciphertext security is achieved using one-tim...
Efficient identity-based key encapsulation to multiple parties
Barbosa, Manuel Bernardo; Farshim, P.We introduce the concept of identity based key encapsulation to multiple parties (mID-KEM), and define a security model for it. This concept is the identity based analogue of public key KEM to multiple parties. We also analyse possible mID-KEM constructions, and propose an efficient scheme based on bilinear pairings. We prove our scheme secure in the random oracle model under the Gap Bilinear Diffie-Hellman ass...
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