Privacy enhancing cryptographic mechanisms with public verifiability

Technology is linking the slightest of our actions to the virtual world. In such connected environments, cryptography aims at building schemes with provable security in order to mathematically protect the users' security in electronic exchanges. Relying on the existence of pairings in bilinear groups wherein the discrete logarithm problem is hard, this thesis puts forth mechanisms to efficiently enhance the privacy in three of the most fundamental cryptographic primitives, namely, digital signatures, encryption schemes and zero-knowledge proofs. Furthermore, these mechanisms support public verifiability so as to force the honesty of all participants in the standard model. We first focus on group signatures, a primitive proposed some 20 years ago, for which we propose the first efficient revocation mechanisms, overcoming the main obstacle to the deployment of this primitive in practical applications. We then focus on P-homomorphic signatures that make it possible to modify a signed message in a controlled way. In particular, we propose new mechanisms providing structure-preserving linearly homomorphic signatures, from which we build the first constant-size non-malleable commitments compatible with standard proof systems, as well as a generalization of this construction into a generic transformation. Finally we further investigate the unexpected applications of this kind of malleable signatures to non-malleable cryptography. This leads us to new proof systems for linear languages which in turn provide the most efficient publicly verifiable CCA-secure threshold encryption to date, and other new extensions.