365 research outputs found
Challenging RSA cryptosystem implementations
No full textIn questo lavoro di tesi abbiamo studiato le proprietà di sicurezza delle implementazioni del cifrario RSA. Nella prima parte, analizziamo i metodi per la generazioni di chiavi RSA di diverse librerie crittografiche. Mostriamo, in particolare, un'applicazione pratica basata su ‘bias’ nelle chiavi RSA che permette di misurare la popolarità delle varie librerie crittografiche e sviluppiamo un metodo di fattorizzazione che rompe un algoritmo proprietario di generazione di chiavi. Nella seconda parte, esaminiamo diversi problemi implementativi del protocollo TLS, come ad esempio i 'padding oracle' di RSA, nel contesto, più ampio, dell'ecosistema Web. Il nostro lavoro mostra come RSA, nonostante la sua apparente semplicità, richieda grande cautela per essere implementato correttamente. Diversamente da RSA, la crittografia basata su curve ellittiche (ECC) utilizza sequenze casuali come chiavi e non richiede padding, risultando, tra le altre cose, più resistente a errori di configurazione. La nostra raccomandazione, quindi, è che gli sviluppatori seguano l’esempio di TLS versione 1.3, in cui è cessato l’utilizzo di RSA in favore di ECC.The aim of our research was to study security properties of real-world deployments of the RSA cryptosystem. First we analyze RSA key generation methods in cryptographic libraries. We show a practical application of biases in RSA keys for measuring popularity of cryptographic libraries and we develop a factorization method that breaks a proprietary key generation algorithm. Later we examine published implementation issues in the TLS protocol, such as RSA padding oracles, in the wider context of the Web ecosystem. Our work helps to demonstrate how RSA, a seemingly simple and intuitive cryptosystem, requires a lot of knowledge to be implemented correctly. Unlike RSA, elliptic curve cryptography (ECC) algorithms do not require padding, and parameters can be chosen such that random strings serve as keys. It is more resistant to bad user configurations and provides many other benefits. We conclude that practitioners should follow the example of TLS version 1.3 and stop using RSA in favor of ECC
Measuring Popularity of Cryptographic Libraries in Internet-Wide Scans
No full textWe measure the popularity of cryptographic libraries in large datasets of RSA public keys. We do so by improving a recently proposed method based on biases introduced by alternative implementations of prime selection in different cryptographic libraries. We extend the previous work by applying statistical inference to approximate a share of libraries matching an observed distribution of RSA keys in an inspected dataset (e.g., Internet-wide scan of TLS handshakes). The sensitivity of our method is sufficient to detect transient events such as a periodic insertion of keys from a specific library into Certificate Transparency logs and inconsistencies in archived datasets.
We apply the method on keys from multiple Internet-wide scans collected in years 2010 through 2017, on Certificate Transparency logs and on separate datasets for PGP keys and SSH keys. The results quantify a strong dominance of OpenSSL with more than 84% TLS keys for Alexa 1M domains, steadily increasing since the first measurement. OpenSSL is even more popular for GitHub client-side SSH keys, with a share larger than 96%. Surprisingly, new certificates inserted in Certificate Transparency logs on certain days contain more than 20% keys most likely originating from Java libraries, while TLS scans contain less than 5% of such keys.
Since the ground truth is not known, we compared our measurements with other estimates and simulated different scenarios to evaluate the accuracy of our method. To our best knowledge, this is the first accurate measurement of the popularity of cryptographic libraries not based on proxy information like web server fingerprinting, but directly on the number of observed unique keys
The Return of Coppersmith's Attack: Practical Factorization of Widely Used RSA Moduli
No full textWe report on our discovery of an algorithmic flaw in the construction of primes for RSA key generation in a widely-used library of a major manufacturer of cryptographic hardware. The primes generated by the library suffer from a significant loss of entropy. We propose a practical factorization method for various key lengths including 1024 and 2048 bits. Our method requires no additional information except for the value of the public modulus and does not depend on a weak or a faulty random number generator. We devised an extension of Coppersmith's factorization attack utilizing an alternative form of the primes in question. The library in question is found in NIST FIPS 140-2 and CC EAL 5+ certified devices used for a wide range of real-world applications, including identity cards, passports, Trusted Platform Modules, PGP and tokens for authentication or software signing. As the relevant library code was introduced in 2012 at the latest (and probably earlier), the impacted devices are now widespread. Tens of thousands of such keys were directly identified, many with significant impacts, especially for electronic identity documents, software signing, Trusted Computing and PGP. We estimate the number of affected devices to be in the order of at least tens of millions.
The worst cases for the factorization of 1024 and 2048-bit keys are less than 3 CPU-months and 100 CPU-years on single core of common recent CPUs, respectively, while the expected time is half of that of the worst case. The attack can be parallelized on multiple CPUs. Worse still, all susceptible keys contain a strong fingerprint that is verifiable in microseconds on an ordinary laptop -- meaning that all vulnerable keys can be quickly identified, even in very large datasets
Laser pulse wavelength conversion by nonlinear optics
No full textNazcv prace; Pouzili nelinearni optiky pro /menu vlnove delky laserovych pulsu Autor: Helena Reichlova Katedra: Katedra chemicke opliky a fyxiky Vedouei bakalafske prace: RNDr. Petr Nemec, Ph.D. e-mail vedouciho: nemeefolkarlov.mff.cuni.cz Abstrakt: Vzajemna interakce mezi svetlem a pcvnou latkou silne zavisi na vykonu pfenasenem svetlem. Jc-li tcnto vykon maly, meni pevna latka u prochazejiciho svetla pouze jeho intenzitu nebo polarizacni stav. V/roste-li vsak tento vykon nad urcitou mez, zaetnaji platit /akony nelinearni optiky. Jednim z aplikticne vclicc zajimavych jcvu, ktcre se zacnou projevovat pfi vysokych svetclnych vykonech, je zmena vlnove delky proehazejiciho svetla. V ramci teto bakalafske prace je studovana mo/nost menit vlnovou delku silnych laserovych pulsu generaci fcmtosekundoveho kontinua s cilem dosahnout laditelnosti svetla v co nejsirsim spektralnim oboru. Klicova slova: nelinearni optika, ultrakratkc laserove pulsy, generace iemtosekundoveho kontinua Title: Laser pulse wavelength conversion by nonlinear optics Author: Helena Reichlova Department: Department of Chemical Physics and Optics Supervisor: RNDr. Petr NC'inec, Ph.D. Supervisor's e-mail address: nemec(Wkarlov.inff.cuni.cz Abstract: An interaction between light and a solid strongly depends on the power, which is carried by the..
Laser pulse wavelength conversion by nonlinear optics
No full textNazcv prace; Pouzili nelinearni optiky pro /menu vlnove delky laserovych pulsu Autor: Helena Reichlova Katedra: Katedra chemicke opliky a fyxiky Vedouei bakalafske prace: RNDr. Petr Nemec, Ph.D. e-mail vedouciho: nemeefolkarlov.mff.cuni.cz Abstrakt: Vzajemna interakce mezi svetlem a pcvnou latkou silne zavisi na vykonu pfenasenem svetlem. Jc-li tcnto vykon maly, meni pevna latka u prochazejiciho svetla pouze jeho intenzitu nebo polarizacni stav. V/roste-li vsak tento vykon nad urcitou mez, zaetnaji platit /akony nelinearni optiky. Jednim z aplikticne vclicc zajimavych jcvu, ktcre se zacnou projevovat pfi vysokych svetclnych vykonech, je zmena vlnove delky proehazejiciho svetla. V ramci teto bakalafske prace je studovana mo/nost menit vlnovou delku silnych laserovych pulsu generaci fcmtosekundoveho kontinua s cilem dosahnout laditelnosti svetla v co nejsirsim spektralnim oboru. Klicova slova: nelinearni optika, ultrakratkc laserove pulsy, generace iemtosekundoveho kontinua Title: Laser pulse wavelength conversion by nonlinear optics Author: Helena Reichlova Department: Department of Chemical Physics and Optics Supervisor: RNDr. Petr NC'inec, Ph.D. Supervisor's e-mail address: nemec(Wkarlov.inff.cuni.cz Abstract: An interaction between light and a solid strongly depends on the power, which is carried by the..
PRINTMAKING AND COLLAGE
No full textDiplomska naloga je osredotočena na kolažiranje različnih medijev v grafiki. Del vsebine zajema predstavitev grafičnih tehnik globokega tiska, ki jih je avtorica osvojila v grafičnem studiu Edinburgh Printmakers. Predstavljeni so tudi različni mediji, kot so kolaž, fotografija, risba in grafika, v medsebojnem odnosu.
V drugem delu je izvedena primerjava posameznih del slovenske grafičarke Zore Stančič z deli avtorice tega diplomskega dela. Vsako izmed del je razloženo z vidika izpričanih kolažnih lastnosti, uporabe posameznega medija in likovnega problema. Avtorica se je odločila za primerjavo svojih del in del Zore Stančič z vidika kolažne tehnike, in to zaradi njunega neprestanega raziskovanja in kombiniranja drugih medijev v grafiko. Preučila je tipične značilnosti kolaža in možnosti, ki nam jih ta tehnika ponuja. Raziskovala je odnos med kolažem in grafiko ter drugimi mediji in grafiko v Zorinih in svojih delih ter predstavila, v katerih njunih delih se prepozna princip kolaža, in ga razložila. Na osnovi obravnavanih grafik je skušala odkriti tako tendence te tehnike kot načine izvedbe. Preko tega je razvidno, da so tendence kolaža prisotne v vseh predstavljenih delih in da je kolažiranje različnih medijev mogoče in lahko tudi zelo kvalitetno. Pridobivanje informacij o temi je potekalo z deskriptivno, zgodovinsko in komparativno metodo. Uporabljeni so bili primarni in sekundarni viri ter viri s spletnih strani avtorjev in projektov. Namen diplomskega dela je preučiti možnosti kolažiranja različnih medijev v grafiki in raziskati vzrok za tovrstno kolažiranje. Hkrati pa medsebojno primerjati njune grafike in njihov nastanek.The bachelor’s degree thesis focuses on combining different media in the field of printmaking. The first part consists of a presentation of intaglio graphic techniques, which the author learned at the Edinburgh Printmakers graphics studio. Different media are presented, such as collage, photography, drawing, and prints, as well as the relationship between them. In the second part, the author carries out a comparison of individual works by the Slovene graphic artist Zora Stančič with works created by the author of the thesis. Each work is explained from the perspective of its evident collage properties, use of individual media, and artistic problem. The author decided to compare her own works with those of Zora Stančič from the perspective of the employment of the collage technique since both artists are devoted to constantly researching and combining printmaking with other media. She analyzed typical characteristics of the collage technique and the possibilities this technique offers. She analyzed both Zora Stančič’s and her own works from the perspective of the relationship between collage and printmaking, and between printmaking and other media. She pointed out the works in which the collage principle can be identified, which then she further explained. By examining individual works the author attempted to uncover the tendencies of printmaking, as well as different means of its employment. In doing so it became evident that some collage tendencies are present in all the presented works and that combining different media is not only possible, but can also lead to high quality results. The information on the topic presented was obtained by means of descriptive, historical, and comparative methods. The author used primary and secondary sources, as well as the web sites of artists, and projects. The purpose of the thesis was to analyze the possibilities of employing a collage of different media in the printmaking, to research the reasons for doing such, and to compare the graphic works of the two artists and their origins
The importance of reading for the integrated development of adolescents
No full textDiplomsko delo se ukvarja z branjem učencev v osnovni šoli. Avtorica želi pokazati, na kakšen način lahko spodbujamo otroke, da bodo lažje in z večjim veseljem brali. V prvem delu naloge predstavi pojme, ki so pri analizi tega problema potrebni (vrste branja, vrste besedil, bralne stopnje, bralne sposobnosti) in predstavi učni načrt. Pomembno je tudi četrto poglavje, v katerem podrobneje predstavi pouk književnosti, predstavi potrebne kompetence učitelja in vlogo staršev. V drugem delu je izvedena analiza vprašanj, ki so zapisana ob besedilih v berilih. Ugotavlja, na kakšen način spodbujajo mladega bralca in ali so vprašanja primerna za določeno starost učencev. Na podlagi analize potrdi, da je učni načrt primeren in da so izbrana berila primerno zastavljena, da je mladi bralec dobro usmerjen h kvalitetnemu branju.This thesis deals with pupils’ reading abilities in primary schools. The author wants to present the way in which we can motivate children to read more easily and with more enthusiasm. In the first part of the paper she presents several key notions (different ways of reading, types of texts, reading levels, reading ability), which are vital for the analysis of the problem and also describes the curriculum at schools. The fourth chapter is important as well, because it shows us what literature classes at schools look like and it talks about required skills of the teachers and the role of the parents. The second part of the thesis presents an analysis of the questions, which we can find next to the texts in reading-books. The author tries to determine how these questions motivate and stimulate a young reader and whether they are suitable for their age. The results of the analysis confirm that the questions and the curriculum are appropriate for the young reader and that they direct the children towards quality reading
The Million-Key Question -- Investigating the Origins of RSA Public Keys
No full textCan bits of an RSA public key leak information about design and implementation choices such as the prime generation algorithm? We analysed over 60 million freshly generated key pairs from 22 open- and closedsource libraries and from 16 different smartcards, revealing significant leakage. The bias introduced by different choices is sufficiently large to classify a probable library or smartcard with high accuracy based only on the values of public keys. Such a classification can be used to decrease the anonymity set of users of anonymous mailers or operators of linked Tor hidden services, to quickly detect keys from the same vulnerable library or to verify a claim of use of secure hardware by a remote party. The classification of the key origins of more than 10 million RSA-based IPv4 TLS keys and 1.4 million PGP keys also provides an independent estimation of the libraries that are most commonly used to generate the keys found on the Internet.
Our broad inspection provides a sanity check and deep insight regarding which of the recommendations for RSA key pair generation are followed in practice, including closed-source libraries and smartcards
Optical spectroscopy of ferromagnetic semiconductors
No full textNazev prace: Optickd spektroskopie feromagnelickych polovodicu Autor: Jifi Parizek Katedra (ustav): Katedra chemickefyziky a opt iky Vedouci bakalafske prace: RNDr. Petr Nemec, Ph.D. e-mail vedoucfho: [email protected] Abstrakt: Feromagneticke polovodice jsou novym druhem magnetickych maleridlu s velkym aplikacnim potencidlem. Neddvno bylo pozorovdno, ze magnelicke vlastnosti feromagnetickych materidlu mohou hyt ovldddny vysoce energetickymi optickymi pulsy. Tohoto jevu muze byt vyuzito pri zdkladnim vyzkumu magnetickych malerialu a casern tez pro rychle premagnetovani v budoucich spintronickych zarizenich. V teio hakaldrske prdci shrmijeme publikovane vysledky o zfedenych polovodicich (DMS) s diirazem kladenym nafotoindukovatwn precesi magnetizace v (Ga.Mn)As. Ddlejsme popsali nielodu ultrarychle htserove spektroskopie - casove rozlisenou Kerrovu rotaci, kterd je velice efeklivni metodou pro stiidovdni feromagnetickych materialu. V expert mentdlni ctisti teto pracejsme se zamefili na testovdni neddvno po.staveneho drzdku kryostatu, ktery umoznuje presne polohovdni vzorku v magnetickem poll vytvorenem elektromagnetem. Na zdver jsme proved!i teslovaci mereni feromagnetickeho polovodice (Ga,Mn)As. Oscilacni cast signdlu Kerrovy rotace by/a pfisouzena svellem indukovane precesi magnetizace v (Ga,Mn)As...
Optical spectroscopy of ferromagnetic semiconductors
No full textNazev prace: Optickd spektroskopie feromagnelickych polovodicu Autor: Jifi Parizek Katedra (ustav): Katedra chemickefyziky a opt iky Vedouci bakalafske prace: RNDr. Petr Nemec, Ph.D. e-mail vedoucfho: [email protected] Abstrakt: Feromagneticke polovodice jsou novym druhem magnetickych maleridlu s velkym aplikacnim potencidlem. Neddvno bylo pozorovdno, ze magnelicke vlastnosti feromagnetickych materidlu mohou hyt ovldddny vysoce energetickymi optickymi pulsy. Tohoto jevu muze byt vyuzito pri zdkladnim vyzkumu magnetickych malerialu a casern tez pro rychle premagnetovani v budoucich spintronickych zarizenich. V teio hakaldrske prdci shrmijeme publikovane vysledky o zfedenych polovodicich (DMS) s diirazem kladenym nafotoindukovatwn precesi magnetizace v (Ga.Mn)As. Ddlejsme popsali nielodu ultrarychle htserove spektroskopie - casove rozlisenou Kerrovu rotaci, kterd je velice efeklivni metodou pro stiidovdni feromagnetickych materialu. V expert mentdlni ctisti teto pracejsme se zamefili na testovdni neddvno po.staveneho drzdku kryostatu, ktery umoznuje presne polohovdni vzorku v magnetickem poll vytvorenem elektromagnetem. Na zdver jsme proved!i teslovaci mereni feromagnetickeho polovodice (Ga,Mn)As. Oscilacni cast signdlu Kerrovy rotace by/a pfisouzena svellem indukovane precesi magnetizace v (Ga,Mn)As...
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