This diploma thesis focuses on the proposal to implement changes of identity management into a particular company. In the theoretical part are the basic concepts and a detailed description of the identity management. There is also described an analysis of the current state of information security in the company, risk analysis and selection of measures to minimize the risks found. At the end of this thesis are proposed changes, their procedure and timetable for implementation of selected measures.

This diploma thesis deals with the issue of security risks and threats of social networks. The work includes basic information about the most popular online social networks such as Facebook, Twitter and Instagram. The work analyzes the development and use of the above mentioned networks. In addition, there are the risks and dangers of communicating on social networks and recommendations for safe use.

This Thesis deals with analysis of the possiblity of password breakthrough for common compression formats and password extraction from self-extraction archives used for malicious software. Structure of compression programs, ciphers and connection between cipher and archives is described. Common and specialized attacks on archives and ciphers are described. Structure of self-extracting archives and password location is used to create extractor of passwords in self-extracting archives.

The method an individual uses to handle their passwords is an important measure to be able to protect their sensitive information from data intrusion. The amount of passwords a person uses is increasing rapidly, this leads to the individual having problems with remembering all of them. Using a password manager that stores all passwords, as well as creating unique strong passwords for different websites is a common solution for this problem.  This study aims to deepen the understanding of the individual's password management. Apple’s own password manager iCloud Keychain has been used as the platform of study. This study aims to seek answers on how secure the common user feels towards iCloud Keychain, as well as user experience point of views. How user friendly is the program and what challenges do users experience?  The study is primarily based on a questionnaire, which forms the basis for in-depth interviews with both a selected focus group as well as an expert interview.  The results show divided opinions about the level of security the users feel towards iCloud Keychain, and where connections can be seen based on users previous knowledge in the field. The conclusion includes that iCloud Keychain is quite a strong candidate on the market for password management but it has some issues when it comes to the overall user experience. Areas for development to create an even stronger candidate include amongst others, opening for use on a wider number of platforms, that is; unlocking the program from Apple's ecosystem. / Individens hantering av sina lösenord är en viktig åtgärd för att kunna skydda sin känsliga information från dataintrång. I dagsläget använder människor sig av ett större antal lösenord, vilket gör det svårare att komma ihåg dem. Att använda sig av en lösenordshanterare som samlar alla lösenord, samt även skapar unika lösenord för varje hemsida gör det säkrare för individen.  I denna studie fördjupas förståelsen för individens hantering av lösenord och dess användning av just Apples egna lösenordshanteringsprogram iCloud Nyckelring. Frågor kring användarens känsla av säkerhet gentemot programmet undersöks. Även användarvänligheten och utmaningar med användandet är några av huvudsakerna som undersöks.  Studien bygger framförallt på en enkät, som lägger grunden till en fördjupad intervju med en fokusgrupp samt en expertintervju.  Resultaten påvisar delade meningar kring säkerheten med iCloud Nyckelring, där samband kan dras utifrån om användaren har tidigare kunskap inom området eller inte. Slutsatsen inkluderar att iCloud Nyckelring är en ganska stark kandidat på marknaden för lösenordshantering, men den har vissa problem när det kommer till den övergripande användarupplevelsen. Utvecklingsområden för att skapa en ännu starkare kandidat är till exempel att öppna för användning på ett större antal plattformar, det vill säga; låsa upp programmet från Apples ekosystem.

With the rapid development of the IoT (Internet of Things) and the integration of connected devices into our households, IoT security is becoming more important. This technology allows the user to accomplish tasks and store information in a more effective way. Due to this large development, various solutions are being established to make sure that only an authorised user gains access to these functions. Among these solutions, passwords have become the most prominent one today. Since passwords allow a user to protect sensitive data and authorise access to their devices, they have become the target of various cyberattacks. Different password policies have therefore been established to strengthen passwords and prevent unauthorised access. In response to this emerging problem, the study conducted in this report has evaluated authentication systems in four categories of smart home devices to assess if they meet security regulations according to best practices. A compilation of the password requirements in these devices has been made and they have been categorized in terms of password security from very weak to very strong. Multiple instances of weak policies were discovered in all of the examined categories and important password features are missing in a majority of them. / Med den hastiga utvecklingen av sakernas internet (IoT) och integrationen av anslutna enheter till hushållet blir IoT säkerhet alltmer viktigt. Denna teknologi tillåter användare att åstadkomma uppgifter och lagra information på ett mer effektivt sätt. På grund av denna stora utveckling har många lösningar skapats för att säkerställa att endast en auktoriserad användare erhålls tillgång. Bland dessa lösningar är lösenord den mest förekommande idag. Eftersom att lösenord tillåter användaren att skydda känslig information och auktorisera tillgång till deras enheter har dem blivit en lockande måltavla för diverse cyberattacker. Ett flertal lösenordspolicys har därför etablerats för att förstärka lösenord och förhindra obehörig tillgång. Som svar på detta framväxande problem, har undersökningen som utförts i denna rapport utvärderat autentiseringssystem i fyra kategorier av smarta hem enheter med mål att bedöma ifall de uppfyller säkerhetsföreskrifter i enighet med bästa praxis. En lista med lösenordskrav i enheterna har skapats och dessa enheter har blivit kategoriserade enligt lösenordssäkerhet från väldigt svag till väldigt stark. Flera olika instanser av svaga policys har upptäckts i alla undersökta kategorier och viktiga lösenordsfunktioner saknas i en majoritet av grupperna.

We study the problem of secure key establishment. We critically examine the security models of Bellare and Rogaway (1993) and Canetti and Krawczyk (2001) in the computational complexity approach, as these models are central in the understanding of the provable security paradigm. We show that the partnership definition used in the three-party key distribution (3PKD) protocol of Bellare and Rogaway (1995) is flawed, which invalidates the proof for the 3PKD protocol. We present an improved protocol with a new proof of security. We identify several variants of the key sharing requirement (i.e., two entities who have completed matching sessions, partners, are required to accept the same session key). We then present a brief discussion about the key sharing requirement. We identify several variants of the Bellare and Rogaway (1993) model. We present a comparative study of the relative strengths of security notions between the several variants of the Bellare-Rogaway model and the Canetti-Krawczyk model. In our comparative study, we reveal a drawback in the Bellare, Pointcheval, and Rogaway (2000) model with the protocol of Abdalla and Pointcheval (2005) as a case study. We prove a revised protocol of Boyd (1996) secure in the Bellare-Rogaway model. We then extend the model in order to allow more realistic adversary capabilities by incorporating the notion of resetting the long-term compromised key of some entity. This allows us to detect a known weakness of the protocol that cannot be captured in the original model. We also present an alternative protocol that is efficient in both messages and rounds. We prove the protocol secure in the extended model. We point out previously unknown flaws in several published protocols and a message authenticator of Bellare, Canetti, and Krawczyk (1998) by refuting claimed proofs of security. We also point out corresponding flaws in their existing proofs. We propose fixes to these protocols and their proofs. In some cases, we present new protocols with full proofs of security. We examine the role of session key construction in key establishment protocols, and demonstrate that a small change to the way that session keys are constructed can have significant benefits. Protocols that were proven secure in a restricted Bellare-Rogaway model can then be proven secure in the full model. We present a brief discussion on ways to construct session keys in key establishment protocols and also prove the protocol of Chen and Kudla (2003) secure in a less restrictive Bellare-Rogaway model. To complement the computational complexity approach, we provide a formal specification and machine analysis of the Bellare-Pointcheval-Rogaway model using an automated model checker, Simple Homomorphism Verification Tool (SHVT). We demonstrate that structural flaws in protocols can be revealed using our framework. We reveal previously unknown flaws in the unpublished preproceedings version of the protocol due to Jakobsson and Pointcheval (2001) and several published protocols with only heuristic security arguments. We conclude this thesis with a listing of some open problems that were encountered in the study.

本文深入探討許多基於公開金鑰密碼和通行碼的密文運算方案。首先第一個主題是「公開金鑰密碼」，從其基本架構和安全定義開始，透過文獻探討逐步地討論公開金鑰密碼學的各項特性、以及討論公開金鑰密碼中兩個常見的密文運算：同態加密系統和可交換性加密系統。同態運算是針對同一把公鑰加密的不同密文間的運算：兩個以同一把公鑰加密的密文可以在不解密的前提下進行運算，進而成為另一個合法密文。這個密文運算的結果等同於兩個明文做運算後再以該公鑰加密。可交換性加密系統是一個容許重複的加密系統：已用甲方公鑰加密的密文可以再度用乙方公鑰再加密，進而之成一個多收件者的密文。第一個主題圍繞著這兩個密文運算的技巧討論相關的加密方案。接下來第二個研究的的主題是「基於公開金鑰密碼之密文相等性驗證」，「密文相等性驗證」是密文運算中一個基礎但重要的功能，經授權的測試者可以在不解密密文的前提下，驗證兩個加密後的訊息是否相等。此外，除了相等或不相等之外，測試者無法得知密文中的其他訊息。「基於公開金鑰密碼之密文相等性驗證」相當於在「公開金鑰密碼」的基礎上，再加上「授權」和「密文相等性驗證」的功能。其中「授權」的範圍和「授權」的設計，直接影響到該方案的實用性及安全性，本文提出三個關於「授權」的主題：「單一密文授權」、「相容性授權」和「語意安全授權」。第三個研究主題是「 可搜尋式加密系統」， 常被應用於以下情境：使用者一個檔案及數個「關鍵字」進行加密，然後儲存在雲端伺服器上。當使用者想要對加密檔案進行關鍵字搜尋時，他可以自訂幾個想搜尋的「關鍵字」並對雲端伺服器發出搜尋要求。在收到搜尋要求後，雖然關鍵字都是加密儲存，仍可利用「可搜尋式加密」技巧將符合關鍵字搜尋的檔案傳回給收件者。整個過程中檔案和關鍵字都被加密保護，伺服器無法得知其儲存及搜尋內容。本文提出兩個「 可搜尋式加密系統」，分別是「子集合式多關鍵字可搜尋式加密系統」和「基於通行碼的可搜尋式加密系統」 。 / This dissertation addresses the research about ciphertext computation skills over public key encryption and password-authenticated cryptosystems. The first topic is related to the public key encryption, the framework and security notions for public key encryption are revised; and two common ciphertext-computable public key encryptions including homomorphic encryption and commutative encryption are following discussed. The homomorphic encryption denotes computations over ciphertexts encrypted using the same public key. The homomorphic operation over ciphertexts may be equal to the encryption of a new message computed between two original messages. In terms of commutative encryption, it stands for a repeated encryption system that Alice’s ciphertext can be duplicated encrypted using Bob’s public key. A dual-receiver ciphertext will appear after the commutative encryption. Following, based on the public key encryption, the second topic focuses on the public key encryption with equality test schemes, the basic and fundamental ciphertext computation. Briefly, the user-authorized testers are able to verify the equivalence between messages hidden in ciphertexts after they acquire trapdoors from ciphertext receivers; and the ciphertexts were never decrypted in the whole equality testing process. The scope and architecture of the authorization directly influence the application and security for equality test schemes. Three authorizations including “cipher-bound authorization”, “compatible authorization” and “semantic secure authorization” will be proposed. The third topic is keyword search. It works in the following scenario: a user outsources encrypted files and encrypted keywords on a cloud file storage system; then, when needed, the user is able to request a search query to the file server, which is corresponding to some encrypted keywords. Although files and keywords are encrypted, the server is still able to verify the match-up and return related files to the user. Two researches about keyword search are proposed: the subset multi-keyword search based on public key encryption, and the password-authenticated keyword search.

Elliptic curves were first proposed as a basis for public key cryptography in the mid 1980's. They provide public key cryptosystems based on the difficulty of the elliptic curve discrete logarithm problem (ECDLP) , which is so called because of its similarity to the discrete logarithm problem (DLP) over the integers modulo a large prime. One benefit of elliptic curve cryptosystems (ECCs) is that they can use a much shorter key length than other public key cryptosystems to provide an equivalent level of security. For example, 160 bit ECCs are believed to provide about the same level of security as 1024 bit RSA. Also, the level of security provided by an ECC increases faster with key size than for integer based discrete logarithm (dl) or RSA cryptosystems. ECCs can also provide a faster implementation than RSA or dl systems, and use less bandwidth and power. These issues can be crucial in lightweight applications such as smart cards. In the last few years, ECCs have been included or proposed for inclusion in internationally recognized standards. Thus elliptic curve cryptography is set to become an integral part of lightweight applications in the immediate future. This thesis presents an analysis of several important issues for ECCs on lightweight devices. It begins with an introduction to elliptic curves and the algorithms required to implement an ECC. It then gives an analysis of the speed, code size and memory usage of various possible implementation options. Enough details are presented to enable an implementer to choose for implementation those algorithms which give the greatest speed whilst conforming to the code size and ram restrictions of a particular lightweight device. Recommendations are made for new functions to be included on coprocessors for lightweight devices to support ECC implementations Another issue of concern for implementers is the side-channel attacks that have recently been proposed. They obtain information about the cryptosystem by measuring side-channel information such as power consumption and processing time and the information is then used to break implementations that have not incorporated appropriate defences. A new method of defence to protect an implementation from the simple power analysis (spa) method of attack is presented in this thesis. It requires 44% fewer additions and 11% more doublings than the commonly recommended defence of performing a point addition in every loop of the binary scalar multiplication algorithm. The algorithm forms a contribution to the current range of possible spa defences which has a good speed but low memory usage. Another topic of paramount importance to ECCs for lightweight applications is whether the security of fixed curves is equivalent to that of random curves. Because of the inability of lightweight devices to generate secure random curves, fixed curves are used in such devices. These curves provide the additional advantage of requiring less bandwidth, code size and processing time. However, it is intuitively obvious that a large precomputation to aid in the breaking of the elliptic curve discrete logarithm problem (ECDLP) can be made for a fixed curve which would be unavailable for a random curve. Therefore, it would appear that fixed curves are less secure than random curves, but quantifying the loss of security is much more difficult. The thesis performs an examination of fixed curve security taking this observation into account, and includes a definition of equivalent security and an analysis of a variation of Pollard's rho method where computations from solutions of previous ECDLPs can be used to solve subsequent ECDLPs on the same curve. A lower bound on the expected time to solve such ECDLPs using this method is presented, as well as an approximation of the expected time remaining to solve an ECDLP when a given size of precomputation is available. It is concluded that adding a total of 11 bits to the size of a fixed curve provides an equivalent level of security compared to random curves. The final part of the thesis deals with proofs of security of key exchange protocols in the Canetti-Krawczyk proof model. This model has been used since it offers the advantage of a modular proof with reusable components. Firstly a password-based authentication mechanism and its security proof are discussed, followed by an analysis of the use of the authentication mechanism in key exchange protocols. The Canetti-Krawczyk model is then used to examine secure tripartite (three party) key exchange protocols. Tripartite key exchange protocols are particularly suited to ECCs because of the availability of bilinear mappings on elliptic curves, which allow more efficient tripartite key exchange protocols.