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In the implicit certification model, the process of verifying the validity of the signer's public key is combined with the verification of the signature itself. When compared to traditional, explicit certificates, the main advantage of the implicit approach lies in the shorter public key validation data. This property is particularly important in resource-constrained scenarios where public key validation is performed very often, which is common in vehicular communications (V2X) that employ pseudonym certificates. In this article, we show an alternative Schnorr-based implicit certification procedure that can improve the efficiency of a popular V2X-oriented Vehicular Public Key Infrastructure (VPKI), the Security Credential Management System (SCMS). As an additional contribution, we show that SCMS's underlying certificate provisioning procedure, based on butterfly keys, is vulnerable to existential forgery attacks under certain conditions. We then discuss how this issue can be fixed in an effective and efficient manner. [ABSTRACT FROM AUTHOR]

Supersingular isogeny-based cryptography is one of the more recent families of post-quantum proposals. An interesting feature is the comparatively low bandwidth occupation in key agreement protocols, which stems from the possibility of key compression. However, compression and decompression introduce a significant overhead to the overall processing cost despite recent progress. In this paper we address the main processing bottlenecks involved in key compression and decompression, and suggest substantial improvements for each of them. Some of our techniques may have an independent interest for other, more conventional areas of elliptic curve cryptography as well. [ABSTRACT FROM AUTHOR]

Public key cryptography is an extremely active research area. New protocols, primitives and attacks are often proposed. Some public key cryptographic primitives tend to be extremely prolific in terms of flexibility, efficiency and security. One of the most flexible cryptographic class of primitives is the lattice-based cryptography. Among the main challenges of this class is to reduce the key and ciphertext sizes. This challenge has been many times addressed by adopting a structured matrix for represent the lattices. The most common types of structured matrix are the circulant and negacyclic matrices. In this paper, we propose a new parameterization for building compact lattices, in the form of the so-called discrete Rojo algebras. This parameterization may be as compact as the circulant and negacyclic matrix rings found in the literature, but with the advantage of having a completely different nature. Thereby, contributing with the biodiversity of primitives, avoid patents, or certain possible attacks for the literature parameters. [ABSTRACT FROM PUBLISHER]

We propose a new, efficient nondeterministic decoding algorithm for square-free Goppa codes over \BBFp for any prime p. If the code in question has degree t and the average distance to the closest codeword is at least (4/p)t+1, the proposed decoder can uniquely correct up to (2/p)t errors with high probability. The correction capability is higher if the distribution of error magnitudes is not uniform, approaching or reaching t errors when any particular error value occurs much more often than others or exclusively. This makes the method interesting for (semantically secure) cryptosystems based on the decoding problem for permuted and punctured Goppa codes. [ABSTRACT FROM AUTHOR]

The Alred construction is a lightweight strategy for constructing message authentication algorithms from an underlying iterated block cipher. Even though this construction's original analyses show that it is secure against some attacks, the absence of formal security proofs in a strong security model still brings uncertainty on its robustness. In this paper, aiming to give a better understanding of the security level provided by different authentication algorithms based on this design strategy, we formally analyze two Alred variants—the Marvin message authentication code and the LetterSoup authenticated-encryption scheme,—bounding their security as a function of the attacker's resources and of the underlying cipher's characteristics. [ABSTRACT FROM AUTHOR]