1,721,022 research outputs found
Algebrallisia menetelmiä kryptografiseen avaintenvaihtoon
No full textAbstractCryptographic key exchange is an integral part of modern cryptography. Such schemes allow two parties to derive a common secret key over a public channel without a priori shared information. One of the most successful key agreement schemes is the one suggested by Diffie and Hellman in their seminal work on public key cryptography. In this thesis, we give an algebraic generalization of the Diffie-Hellman scheme called AGDH utilizing its implicit algebraic properties. The generalization is based on the problem of computing homomorphic images from an algebra to another. Appropriately, we call this problem the homomorphic image problem (HIP). We also devise an authenticated key exchange protocol that is secure in the Canetti-Krawczyk model assuming the infeasibility of the decision HIP (DHIP).For the secure instantiation of the scheme, we consider symmetric encryption schemes that are homomorphic over an algebraic operation. We derive a condition for the encryption scheme to be homomorphic key agreement capable. We show that whenever this condition is satisfied, the induced DHIP is computationally infeasible based on the security of the encryption scheme. To show that there are such schemes, we give a description of one such that the infeasibility of the DHIP follows from a weaker version of the McEliece generator matrix pseudorandomness assumption and the learning parity with noise (LPN) problem.We also study algebraic methods for generating suitable structures for the devised scheme. Since the platform structure requires a large set of homomorphisms, we consider classes of algebras for which this is the case. In particular, we concentrate on a class of algebras satisfying the left distributivity (LD) property. We formulate a non-associative generalization of the conjugacy search problem (CSP) called partial CSP (PCSP) for left conjugacy closed left quasigroups. We show that the feasibility of the HIP on LD left quasigroups depends on the PCSP. Application of this problem leads to a non-associative variant of the Anshel-Anshel-Goldfeld key agreement scheme. We also formulate different versions of the PCSP and show several relative hardness results related to them. Finally, we study more closely the PCSP for a class of conjugacy closed loops of order p2, where p is a prime. We show that the hardness of the PCSP depends on the number of generators for the conjugator and on that of conjugacy equation pairs. Based on the weakest variant of the PCSP, we devise a symmetric blind decryption scheme on these loops and show that it satisfies perfect secrecy against passive adversaries.TiivistelmäKryptografiset avaintenvaihtomenetelmät ovat eräs modernin kryptografian tärkeimmistä osista. Näiden menetelmien avulla pystytään sopimaan ilman aiempaa tiedonvaihtoa yhteisestä salaisesta avaimesta käyttämällä julkista kanavaa. Diffie-Hellman -avaintenvaihto on yksi parhaiten tunnetuista ja eniten käytetyistä menetelmistä. Tässä työssä tarkastellaan kyseisen menetelmän yleistämistä perustuen sen algebrallisiin ominaisuuksiin. Johdettu yleistys perustuu vaikeuteen löytää annetun alkion homomorfinen kuva, jota työssä kutsutaan homomorfisen kuvan ongelmaksi (HIP). Lisäksi suunnitellaan autentikoitu avaintenvaihtoprotokolla, joka on turvallinen Canetti-Krawczyk -mallissa olettaen että homomorfisen kuvan ongelman päätösversio (DHIP) on laskennallisesti vaikea.Menetelmän turvallista toteuttamista varten tarkastellaan symmetrisen avaimen salausmenetelmiä, jotka ovat homomorfisia joidenkin algebrallisten operaatioiden yli. Työssä johdetaan symmetrisen avaimen salainten ominaisuus, kyvykkyys homomorfiseen avaintenvaihtoon, joka takaa että aikaansaatu DHIP on laskennallisesti vaikea. Lisäksi rakennetaan symmetrinen menetelmä, joka toteuttaa kyseisen ehdon. Menetelmän turvallisuus perustuu tavallista heikompaan oletukseen McEliece-generaattorimatriisin pseudosatunnaisuudesta sekä pariteetin oppimisongelman häiriölliseen versioon (LPN).Työssä tarkastellaan lisäksi menetelmiä soveltuvien algebrallisten rakenteiden generointiin. Koska menetelmä vaatii suuren joukon homomorfismeja, tarkastellaan rakenteita, joille tämä ehto pätee. Erityisesti keskitytään ns. vasemmalta distributiivisiin (LD) rakenteisiin. Työssä määritellään epäassosiatiivinen yleistys konjugointiongelman hakuversiolle (CSP) konjugoinnin suhteen suljettuille vasemmille kvasiryhmille. Tätä yleistystä kutsutaan osittaiseksi CSP:ksi (PCSP). Työssä osoitetaan, että vasemmalta distributiivisissa vasemmissa kvasiryhmissä homomorfisen kuvan ongelman vaikeus liittyy läheisesti PCSP:hen. Lisäksi tätä ongelmaa sovelletaan määrittämään epäassosiatiivinen variantti Anshel-Anshel-Goldfeld -avaintenvaihtomenetelmästä. Lisäksi tarkastellaan PCSP:n erilaisia versioita ja niiden suhteellista laskennallista kompleksisuutta. PCSP:tä tarkastellaan tarkemmin konjugoinnin suhteen suljetuissa luupeissa, joiden kertaluku on p2, missä p on alkuluku. Työssä osoitetaan, että PCSP:n vaikeus riippuu konjugoijan generaattoreiden sekä konjugaatioyhtälöiden lukumäärästä. Käyttämällä hyväksi näitä tuloksia ja erityisesti PCSP:n helpointa versiota, laaditaan symmetrisen avaimen salausmenetelmä, joka tukee ns. sokeaa salauksenpurkua. Lisäksi osoitetaan, että menetelmä takaa täydellisen salassapidon passiivisia hyökkäyksiä vastaan.Academic dissertation to be presented with the assent of the Doctoral Training Committee of Technology and Natural Sciences of the University of Oulu for public defence in Auditorium IT116, Linnanmaa, on 13 March 2015, at 12 noonAbstract
Cryptographic key exchange is an integral part of modern cryptography. Such schemes allow two parties to derive a common secret key over a public channel without a priori shared information. One of the most successful key agreement schemes is the one suggested by Diffie and Hellman in their seminal work on public key cryptography. In this thesis, we give an algebraic generalization of the Diffie-Hellman scheme called AGDH utilizing its implicit algebraic properties. The generalization is based on the problem of computing homomorphic images from an algebra to another. Appropriately, we call this problem the homomorphic image problem (HIP). We also devise an authenticated key exchange protocol that is secure in the Canetti-Krawczyk model assuming the infeasibility of the decision HIP (DHIP).
For the secure instantiation of the scheme, we consider symmetric encryption schemes that are homomorphic over an algebraic operation. We derive a condition for the encryption scheme to be homomorphic key agreement capable. We show that whenever this condition is satisfied, the induced DHIP is computationally infeasible based on the security of the encryption scheme. To show that there are such schemes, we give a description of one such that the infeasibility of the DHIP follows from a weaker version of the McEliece generator matrix pseudorandomness assumption and the learning parity with noise (LPN) problem.
We also study algebraic methods for generating suitable structures for the devised scheme. Since the platform structure requires a large set of homomorphisms, we consider classes of algebras for which this is the case. In particular, we concentrate on a class of algebras satisfying the left distributivity (LD) property. We formulate a non-associative generalization of the conjugacy search problem (CSP) called partial CSP (PCSP) for left conjugacy closed left quasigroups. We show that the feasibility of the HIP on LD left quasigroups depends on the PCSP. Application of this problem leads to a non-associative variant of the Anshel-Anshel-Goldfeld key agreement scheme. We also formulate different versions of the PCSP and show several relative hardness results related to them. Finally, we study more closely the PCSP for a class of conjugacy closed loops of order p2, where p is a prime. We show that the hardness of the PCSP depends on the number of generators for the conjugator and on that of conjugacy equation pairs. Based on the weakest variant of the PCSP, we devise a symmetric blind decryption scheme on these loops and show that it satisfies perfect secrecy against passive adversaries.Tiivistelmä
Kryptografiset avaintenvaihtomenetelmät ovat eräs modernin kryptografian tärkeimmistä osista. Näiden menetelmien avulla pystytään sopimaan ilman aiempaa tiedonvaihtoa yhteisestä salaisesta avaimesta käyttämällä julkista kanavaa. Diffie-Hellman -avaintenvaihto on yksi parhaiten tunnetuista ja eniten käytetyistä menetelmistä. Tässä työssä tarkastellaan kyseisen menetelmän yleistämistä perustuen sen algebrallisiin ominaisuuksiin. Johdettu yleistys perustuu vaikeuteen löytää annetun alkion homomorfinen kuva, jota työssä kutsutaan homomorfisen kuvan ongelmaksi (HIP). Lisäksi suunnitellaan autentikoitu avaintenvaihtoprotokolla, joka on turvallinen Canetti-Krawczyk -mallissa olettaen että homomorfisen kuvan ongelman päätösversio (DHIP) on laskennallisesti vaikea.
Menetelmän turvallista toteuttamista varten tarkastellaan symmetrisen avaimen salausmenetelmiä, jotka ovat homomorfisia joidenkin algebrallisten operaatioiden yli. Työssä johdetaan symmetrisen avaimen salainten ominaisuus, kyvykkyys homomorfiseen avaintenvaihtoon, joka takaa että aikaansaatu DHIP on laskennallisesti vaikea. Lisäksi rakennetaan symmetrinen menetelmä, joka toteuttaa kyseisen ehdon. Menetelmän turvallisuus perustuu tavallista heikompaan oletukseen McEliece-generaattorimatriisin pseudosatunnaisuudesta sekä pariteetin oppimisongelman häiriölliseen versioon (LPN).
Työssä tarkastellaan lisäksi menetelmiä soveltuvien algebrallisten rakenteiden generointiin. Koska menetelmä vaatii suuren joukon homomorfismeja, tarkastellaan rakenteita, joille tämä ehto pätee. Erityisesti keskitytään ns. vasemmalta distributiivisiin (LD) rakenteisiin. Työssä määritellään epäassosiatiivinen yleistys konjugointiongelman hakuversiolle (CSP) konjugoinnin suhteen suljettuille vasemmille kvasiryhmille. Tätä yleistystä kutsutaan osittaiseksi CSP:ksi (PCSP). Työssä osoitetaan, että vasemmalta distributiivisissa vasemmissa kvasiryhmissä homomorfisen kuvan ongelman vaikeus liittyy läheisesti PCSP:hen. Lisäksi tätä ongelmaa sovelletaan määrittämään epäassosiatiivinen variantti Anshel-Anshel-Goldfeld -avaintenvaihtomenetelmästä. Lisäksi tarkastellaan PCSP:n erilaisia versioita ja niiden suhteellista laskennallista kompleksisuutta. PCSP:tä tarkastellaan tarkemmin konjugoinnin suhteen suljetuissa luupeissa, joiden kertaluku on p2, missä p on alkuluku. Työssä osoitetaan, että PCSP:n vaikeus riippuu konjugoijan generaattoreiden sekä konjugaatioyhtälöiden lukumäärästä. Käyttämällä hyväksi näitä tuloksia ja erityisesti PCSP:n helpointa versiota, laaditaan symmetrisen avaimen salausmenetelmä, joka tukee ns. sokeaa salauksenpurkua. Lisäksi osoitetaan, että menetelmä takaa täydellisen salassapidon passiivisia hyökkäyksiä vastaan
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Algebraic generalization of Diffie–Hellman key exchange
Get PDFAbstractThe Diffie–Hellman key exchange scheme is one of the earliest and most widely used public-key primitives. Its underlying algebraic structure is a cyclic group and its security is based on the discrete logarithm problem (DLP). The DLP can be solved in polynomial time for any cyclic group in the quantum computation model. Therefore, new key exchange schemes have been sought to prepare for the time when quantum computing becomes a reality. Algebraically, these schemes need to provide some sort of commutativity to enable Alice and Bob to derive a common key on a public channel while keeping it computationally difficult for the adversary to deduce the derived key. We suggest an algebraically generalized Diffie–Hellman scheme (AGDH) that, in general, enables the application of any algebra as the platform for key exchange. We formulate the underlying computational problems in the framework of average-case complexity and show that the scheme is secure if the problem of computing images under an unknown homomorphism is infeasible. We also show that a symmetric encryption scheme possessing homomorphic properties over some algebraic operation can be turned into a public-key primitive with the AGDH, provided that the operation is complex enough. In addition, we present a brief survey on the algebraic properties of existing key exchange schemes and identify the source of commutativity and the family of underlying algebraic structures for each scheme.</jats:p
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Post-quantum Cryptography in 6G
Get PDFAbstractThe quantum computing paradigm is fundamentally different from the classical one. There are computational problems we are not able to solve on a contemporary computer, but which we can efficiently solve on a quantum one. One of these problems is the discrete logarithm problem (DLP) which is the basis of modern asymmetric cryptography. Once large-scale quantum computing becomes a reality, these cryptographic primitives need to be replaced with quantum-secure ones. While we are still in the early stages of quantum computing, steps have been taken to prepare for the shift to cryptography that is secure in the post-quantum world. According to the current knowledge, contemporary symmetric cryptography remains secure for the most part even after the advent of quantum computing. Asymmetric primitives based on integer factorization and the DLP need to be replaced. In this chapter, we take a look at the post-quantum secure alternatives for key establishment, public-key encryption and digital signatures. We also discuss their properties and the effect on the performance of the future 6G networks.Abstract
The quantum computing paradigm is fundamentally different from the classical one. There are computational problems we are not able to solve on a contemporary computer, but which we can efficiently solve on a quantum one. One of these problems is the discrete logarithm problem (DLP) which is the basis of modern asymmetric cryptography. Once large-scale quantum computing becomes a reality, these cryptographic primitives need to be replaced with quantum-secure ones. While we are still in the early stages of quantum computing, steps have been taken to prepare for the shift to cryptography that is secure in the post-quantum world. According to the current knowledge, contemporary symmetric cryptography remains secure for the most part even after the advent of quantum computing. Asymmetric primitives based on integer factorization and the DLP need to be replaced. In this chapter, we take a look at the post-quantum secure alternatives for key establishment, public-key encryption and digital signatures. We also discuss their properties and the effect on the performance of the future 6G networks
- …
