Ricardo Felipe Custódio

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Farnel is a voting system proposed in 2001 in which each voter signs a ballot. It uses two ballot boxes to avoid the association between a voter and a vote. In this paper we first point out a flaw in the ThreeBallot system proposed by Rivest that seems to have gone unnoticed so far: it reveals statistical information about who is winning the election. Then,(More)
Hardware Security Modules (HSMs) are an useful tool to deploy public key infrastructure (PKI) and its applications. This paper presents necessary procedures and protocols to perform backup and audit in such devices when deployed in PKIs. These protocols were evaluated in an implementation of a real HSM, enabling it to perform secure backups and to provide(More)
The private keys used in a PKI are its most important asset. Protect these keys from unauthorised use or disclosure is essential to secure a PKI. Relying parties need assurances that the private key used to sign their certificates is controlled and managed following pre-defined statement policy. Hardware Security Modules (HSM) offer physical and logical(More)
Trusted time sources are required to insert time stamps in electronic documents. A signed and time stamped electronic document is equivalent to a traditional paper document and is legally recognized. Clock synchronization protocols of the sort provided by Network Time Protocol (NTP) do not satisfy all requirements to assure that a time source is(More)
—Ceremonies are a useful tool to establish trust in scenarios where protocols operate. They describe a greater range of issues not taken into account by protocol designers. We take an already-designed protocol and ceremony for a key management protocol operating in a Public-Key Infrastructure environment and test it using a formal method. The ceremonies(More)
We propose a new Public Key Infrastructure model for long-term signatures. It is based on X.509 and the real world of handwritten signatures. In the model, notaries certify that a signer's certificate is trustworthy to verify a particular signature at a specific time. An end user issues his own X.509 certificate, whose validity period is meaningless and(More)
Secure archiving of authenticated and sensitive documents is becoming a necessity due to the dematerialization of paper based documents and processes. Huhnlein et al. combined the Open Archival Information System (OAIS) Reference Model, Evidence Record Syntax (ERS) with Secret Sharing and proposed the Comprehensive Reference Architecture for Trustworthy(More)
IEEE 802.15.4/Zigbee is one of the most widespread Wireless Sensor Network technologies. It may work either in beacon-enabled mode or in beaconless mode. When operating in beacon-enabled mode, it divides the superframe in sixteen equally-sized time slots, where the request for slot allocation is achieved through a CSMA/CA approach. This allocation method(More)
The concept of a ceremony as an extension of network and security protocols was introduced by Ellison. There are no currently available methods or tools to check correctness of the properties in such ceremonies. The potential application for security ceremonies are vast and fill gaps left by strong assumptions in security protocols. Assumptions include the(More)