Reducing the Dependence of Trust-Management Systems on PKI
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生活因减法更精彩关于依赖的英语作文The Art of Subtraction: Embracing Dependence in a Distracted World.In an era characterized by incessant notifications, endless streams of information, and an overwhelming array of choices, the concept of minimalism has emerged as a beacon of clarity and purpose. At its core lies the philosophy of reducing our material possessions and distractions to enhance our focus, improve our well-being, and ultimately live more fulfilling lives. While the benefits of decluttering our physical environment are well-documented, a lesser-explored aspect of minimalism is its transformative power in the realm of our relationships.One of the most counterintuitive yet profound lessons that minimalism teaches us is the importance of embracing dependence. In a society that values self-sufficiency and independence above all else, the notion of relying on others can seem like a weakness. However, it is preciselythrough our interdependence that we unlock our true potential.When we shed the illusion of self-reliance, we open ourselves up to a wealth of support, wisdom, and compassion that would otherwise remain inaccessible. We learn to trust that we are not alone in our struggles and that there are people who care about our well-being. This sense of connectedness fosters a deep sense of belonging and reduces the feelings of isolation and loneliness that are so prevalent in modern society.Moreover, dependence allows us to tap into the collective knowledge and experience of others. No one person can possess all the answers or solve all the problems life throws our way. By seeking guidance and support from those who have been in our shoes, we can learn from their mistakes, gain new perspectives, and make wiser decisions. This is not a sign of weakness; it is a testament to our humility and our willingness to grow.Of course, dependence does not imply blindly followingthe advice of others or becoming subservient to their will. Rather, it is about discerning who we can trust, seeking counsel from those who have our best interests at heart, and ultimately making our own informed choices. It is about recognizing that we are all interconnected and that our actions have an impact on others.In the realm of relationships, embracing dependence can transform our interactions from transactional exchangesinto meaningful connections. True friendship is not about keeping score or relying on others for personal gain. It is about offering support, empathy, and a listening ear when they are needed most. By allowing ourselves to depend on our loved ones, we strengthen our bonds and create aculture of reciprocity where both parties feel valued and respected.Furthermore, recognizing our dependence on others fosters a sense of gratitude. When we realize that our happiness and well-being are not solely dependent on our own efforts, we develop a deep appreciation for those who contribute to our lives in countless ways. This gratitudeextends beyond our immediate circle to include the broader community and the natural world that sustains us.In a world that often prioritizes individuality andself-promotion, embracing dependence is a radical act of humility and compassion. It is a recognition that we areall interdependent beings, and that by supporting each other, we can create a more just, equitable, and fulfilling society for all.As we navigate the complexities of modern life, it is essential to remember that we are not meant to do it alone. By embracing dependence, we unlock a hidden reservoir of strength, wisdom, and connection. Let us shed the burden of self-reliance and cultivate a mindset that values interdependence, empathy, and the transformative power of human relationships.For in the art of subtraction, it is not what we remove that matters most, but what we choose to keep: theessential elements that make life truly meaningful and fulfilling.。
biobutanol英语解释-回复Bio-butanol is a type of alcohol that is derived from renewable resources such as agricultural waste, corn, or sugarcane. It is recognized as a sustainable alternative to traditional petroleum-based fuels and has gained attention in recent years due to its potential to reduce greenhouse gas emissions and contribute to a more sustainable energy future. In this article, we will explore the concept of bio-butanol in more detail, discussing its production process, benefits, and challenges.The production of bio-butanol involves a biological fermentation process similar to the production of ethanol. However, unlike ethanol, bio-butanol can be created through a more complex fermentation process that utilizes bacteria rather than yeast. This process is known as acetone-butanol-ethanol (ABE) fermentation.The ABE fermentation process begins with the selected bacterial strain being added to a fermenter, along with a substrate such as glucose or starch. The bacteria then consume the sugars and convert them into butyric acid, acetic acid, and acetone. These organic acids are produced as metabolic byproducts of the bacteria.During the next stage of the ABE fermentation process, the bacteria undergo a switch in metabolism, utilizing the acetone and butyric acid to produce bio-butanol. This metabolic switch occurs in response to changes in nutrient availability. The bio-butanol produced is then separated and purified from the fermentation broth, resulting in a high-purity fuel source.One of the key benefits of bio-butanol is its superior fuel properties compared to ethanol. It has a higher energy content per liter, which means that vehicles can achieve better mileage when running on bio-butanol. Additionally, bio-butanol has a lower vapor pressure, reducing the risk of vapor lock in fuel systems. This is a significant advantage, especially in hot climates.Moreover, bio-butanol can be blended with gasoline at higher levels than ethanol. This higher blending capacity contributes to reducing the dependence on fossil fuels and decreasing greenhouse gas emissions. Bio-butanol, when used as a fuel, emits fewer pollutants such as carbon monoxide and particulate matter, making it a cleaner and greener alternative to traditional gasoline.In addition to its fuel properties, bio-butanol production also offers economic and environmental advantages. The feedstock forbio-butanol can be sourced from various renewable resources, including agricultural waste and biomass, reducing the reliance on food crops. This not only helps in addressing food security concerns but also reduces the competition for land and resources between the food and energy sectors.Furthermore, the production of bio-butanol can result in the generation of valuable co-products. For example, the fermentation process can yield acetone, which has various industrial applications, including the production of solvents and plastics. This adds value to the bio-butanol production process and increases overall economic viability.However, despite these advantages, there are still challenges that need to be addressed for the widespread adoption of bio-butanol. The scale-up and commercialization of the bio-butanol production process present technical and economic challenges. The ABE fermentation process requires specialized equipment and careful optimization to achieve efficient and cost-effective production.Moreover, the use of bio-butanol as a fuel requires modifications in existing vehicle engines and fuel infrastructure due to its different properties compared to traditional gasoline. These modifications can pose additional costs and logistical challenges that may hinder the adoption of bio-butanol.In conclusion, bio-butanol represents a promising alternative to traditional petroleum-based fuels. Its production from renewable resources, higher energy content, and lower emissions make it an attractive option for a sustainable energy future. However, further research and development are needed to overcome technical and economic challenges and ensure the widespread adoption ofbio-butanol as a viable fuel source. With continued advancements in technology and support from policymakers and the industry, bio-butanol has the potential to contribute significantly to reducing greenhouse gas emissions and promoting a greener and more sustainable transportation sector.。
1、解酒护肝型氨康源氨基酸固体饮料,以人体必需氨基酸为基础的科学配方,通过现代科技手段,充分的保证了氨基酸的多样性、必需性、高营养性,同时也解决了在饮料中的稳定性,并且可充分发挥氨基酸在溶液中易吸收性,是一种全新低热量高营养性护肝解酒饮料。
饮料中含有肝脏所需要的解救氨基酸,同时也含有人体肝脏细胞的功能性营养元素,对肝细胞是很好的保护作用,同时解决饮酒后对小脑和纹状体的损害,减少身体对酒精的依赖性,有减轻酒精中毒的作用,调节机体对酒精的刺激,促进酒后机体的恢复,减少酒后的疲乏、胃肠紊乱、记忆力下降等等的酒后症状,同时减轻因为酒精中毒引起的手震颤等等现象。
1. The solid drink of anti-inebriation and liver protective type employs the scientific formula based on the human essential amino acids, through modern scientific methods; it is fully guaranteed the variety, essentiality, and high nutrition. Meanwhile, it keeps stability of the amino acids in the solution, and fully takes the advantages of their solubility inside the solution. It is an all new low calories, high nutrition drink of anti-inebriation and liver protection.The drink contains amino acids of salvation pathway that are needed in the liver. There are also functional nutritious elements of human liver in the drink. At the same time, the drink solves the damage problems of alcohol to the cerebellum and corpus striatum. It decreases the dependence of the body to alcohol. It has the effects on alleviating the alcohol intoxication, body adjusting to the alcohol stimuli, improving the body recovery after alcohol, reducing the post-alcohol symptoms of fatigue, gastro-intestinal disorders, and memory decrease, etc. It can also ease the hand tremors caused by alcohol intoxication, etc2、氨康源氨基酸饮料,以人体必需氨基酸为基础的科学配方,通过现代科技手段,充分的保证了氨基酸的多样性、必需性、高营养性,同时也解决了在饮料中的稳定性,并且可充分发挥氨基酸在溶液中易吸收性,是一种全新低热量高营养性抗疲劳饮料。
Innovation is the driving force of social progress and the key to national development.In the new era,intelligent innovation has become an important force in promoting social development.Intelligent innovation refers to the use of advanced technologies such as artificial intelligence,big data,and the Internet of Things to drive the transformation and upgrading of traditional industries,thereby enhancing production efficiency and product quality.Firstly,intelligent innovation can improve production efficiency.With the application of intelligent technologies,production processes can be automated and intelligentized, reducing the dependence on human labor and improving production efficiency.For example,in the manufacturing industry,intelligent robots can replace manual labor to complete repetitive and heavy work,improving production efficiency and reducing production costs.Secondly,intelligent innovation can enhance product quality.Through the use of intelligent technologies,products can be designed and manufactured more accurately, improving product quality and meeting consumer needs.For instance,in the medical industry,intelligent diagnostic systems can assist doctors in making more accurate diagnoses,improving the accuracy and safety of medical treatment.Moreover,intelligent innovation can promote the development of emerging industries. With the support of intelligent technologies,new industries such as the Internet of Things, big data,and artificial intelligence can be developed,driving the transformation and upgrading of traditional industries and fostering economic growth.For example,the application of the Internet of Things technology can realize intelligent control of home appliances,making home life more convenient and comfortable.In conclusion,intelligent innovation is an important force in the new era for promoting social development.It can improve production efficiency,enhance product quality,and promote the development of emerging industries.We should actively promote intelligent innovation to drive social progress and national development.。
1.晚宴后我们正往家走,突然发生了事故。
(head)We were heading home after the party when the accident happened.2.他答应来参加晚会的,但是整个晚上他都没有出现。
(show up)He had promised to come to the party, but he didn't show up the whole night.3.我们现在最好不要打扰他们,让他们自己解决问题。
(leave..alone)We'd better leave them alone and let them sole their own problems.4.如果你言行不一,人们很快会发现你不是个可以信任的人。
(match)If you actions do not match your words, people will soon find you are a person that cannot be trusted.5.我知道你不喜欢来参加晚宴,但还是努力遵守惯例(custom),对主人彬彬有礼吧(effort)I know you didn't like to come to the dinner party, but please make an effort to follow the custom and be polite to the host. 6.如果我们能按时赶到机场,那将是个奇迹。
(miracle)It'll be a miracle if we get to the airport in time.7.他宁愿不让别人知道他的过去。
(keep..to oneself)He would rather keep his past to himself.8.机长(captain)宣布飞机就要着陆了。
China's Green Development Philosophy: A Pathway to Sustainable FutureIn recent years, China has emerged as a global leaderin the pursuit of green development, an approach that harmonizes economic growth with environmental sustainability. This理念, deeply rooted in the country's cultural and historical context, aims to balance the needs of the present without compromising the ability of future generations to meet their own needs.The green development philosophy in China is guided by several key principles. Firstly, it emphasizes the importance of ecological conservation and restoration. This involves efforts to protect and restore natural ecosystems, enhance biodiversity, and mitigate the impact of human activities on the environment. For instance, China has implemented ambitious reforestation programs and eco-compensation mechanisms to encourage sustainable land use. Secondly, the green development philosophy promotes a circular economy, which aims to maximize resourceefficiency and minimize waste. This involves the reuse, recycling, and recovery of materials throughout theirlifecycle, reducing the dependence on virgin resources and minimizing environmental pollution. China has madesignificant progress in this regard, with policies that encourage recycling, waste reduction, and the developmentof green technologies.Thirdly, the green development philosophy emphasizesthe integration of economic, social, and environmental considerations in decision-making. This holistic approach ensures that policies and projects not only promote economic growth but also contribute to social well-beingand environmental protection. For instance, China has prioritized green infrastructure investments, such as renewable energy projects and public transportation systems, that benefit both the economy and the environment.The implementation of China's green development philosophy has yielded impressive results. The country has made significant progress in reducing air and water pollution, improving energy efficiency, and expanding the use of renewable energy. These efforts have not only benefited China but have also contributed to global efforts to address climate change and environmental degradation.However, the journey towards green development is ongoing, and China faces numerous challenges. Balancing the needs of rapid economic growth with environmentalprotection remains a significant challenge. Additionally, achieving widespread social acceptance and participation in green development efforts is essential for sustainable progress.In conclusion, China's green development philosophy provides a visionary roadmap for achieving sustainable development. By prioritizing ecological conservation, promoting a circular economy, and integrating economic, social, and environmental considerations, China is leading the way towards a more sustainable future. While challenges remain, the country's commitment to green developmentoffers hope for a better world.**中国绿色发展理念:通往可持续未来的道路**近年来,中国作为全球绿色发展的领军者,展现了一种将经济增长与环境可持续性相结合的独特理念。
(注意:若有主观题目,请按照题目,离线完成,完成后纸质上交学习中心,记录成绩。
在线只需提交客观题答案。
)本次作业是本门课程本学期的第2次作业,注释如下:大学英语III 第2单元作业题一、单项选择题(只有一个选项正确,共40道小题)1. – Thank you so much for the book you sent me.– _________________(A) No, Thank you.(B) I’m glad you like it.(C) Please, don’t say so.(D) No, it’s not so good.正确答案:B解答参考:[第二单元]B 此题考查有关“感谢与应答”的习惯用语。
对别人赠送的礼物,不论轻重,都要表示感谢,这是礼貌。
应答时,中国人往往采取一种谦逊的态度;而英美人却以迎合的态度来表达自己的心情。
所以,I’m glad you like it. 是正确答案。
2. – It’s been a wonderful evening. Thank you very much.– __________________(A) My pleasure.(B) I’m glad to hear that.(C) No, thanks.(D) It’s ok.正确答案:A解答参考:[第二单元]A 此题第一说话人说“晚会很棒,非常感谢。
”,通常在这种情况下,听话人应该礼貌地表示感谢,可用My pleasure, 意为“你这么说,我很荣幸。
”而It do esn’t matter. 通常用于应答别人的道歉,表示“没关系”;It’s ok. 不符合英语习惯;No, thanks. 又与句意不符。
3. –Thanks for the lovely party and the delicious food.– _________________(A) No, thanks.(B) Never mind.(C) All right.(D) Don’t mention it.正确答案:D解答参考:[第二单元]D 同上题,考查对感谢的应答。
雅思阅读机经V2010110
一、考试时间:2015年1月10日(周六)
二、考试概述:
本次考试为2015年的第一篇,如去年第一场一样,不仅难度偏低,而且有两篇文章在去年出现过,且当时的回忆即非常详尽,答案和文章都很全面。
第一篇Bondi Beach,讲悉尼的一个海滩,是2011年8月20日和2012年10月20日的旧题。
澳洲的话题在雅思剑桥真题集中特别多,且2014年最后一场也考到了澳洲的古人,鉴于本篇文章与奥运会有关,所以剑六第一套第一篇Australia’s Sporting Success澳大利亚的体育成功是很好的参考素材。
第二篇Economic Effect ofClimate,讲气候与国家经济的关系,这一篇是2014年1月25日,即春节前最后一次考试的考题,同时也是2006年7月22日的考题。
在经典机经中,《欧洲最热的一年》《意大利与疟疾》等文章都是很好的参考。
第三篇verbal and non-verbal behaviors语言与非语言行为,是新题,不过剑四第三套第三篇Obtaining Linguistic Data 语料的获得与本篇文字非常接近。
三、文章简介
Passage 1:Bondi Beach,悉尼著名的Bondi海滩。
Passage 2:Economic Effect ofClimate,气候与国家经济的关系。
Passage 3:verbal and non-verbal behaviors,语言与非语言行为。
四、篇章分析:。
减少上网依赖英语作文高中Reducing Dependence on the Internet。
With the rapid development of the Internet, people's dependence on it has increased significantly. The Internet has become an indispensable tool for communication, entertainment, and information acquisition. However, excessive dependence on the Internet can lead to a range of negative consequences, such as addiction, social isolation, and decreased productivity. Therefore, it is important to find ways to reduce our dependence on the Internet.Firstly, we can limit our time spent on the Internet. This can be achieved by setting a specific time limit for using the Internet each day and sticking to it. For example, we can allocate only one or two hours per day for browsing the web, checking social media, and watching videos. This can help us avoid getting sucked into the endless stream of online content and free up more time for other activities.Secondly, we can engage in offline activities that we enjoy. This can include reading books, playing sports, drawing, or spending time with friends and family. By doing things that we love, we can reduce our reliance on the Internet for entertainment and relaxation. Moreover, engaging in offline activities can help us improve our physical and mental health, as well as our social skills.Thirdly, we can cultivate a habit of critical thinking and information evaluation. With the vast amount of information available on the Internet, it is important to be able to distinguish between reliable and unreliable sources of information. By developing critical thinking skills, we can become more discerning consumers of online content and avoid being misled by fake news, rumors, and propaganda.Finally, we can seek professional help if we are struggling with Internet addiction. Internet addiction is a serious problem that can have negative effects on our mental and physical health, as well as our relationships and work. If we find ourselves unable to control ourInternet use, we should seek the help of a therapist or counselor who specializes in addiction treatment.In conclusion, reducing our dependence on the Internetis an important step towards achieving a healthy and balanced lifestyle. By limiting our time spent online, engaging in offline activities, developing criticalthinking skills, and seeking professional help if necessary, we can break free from the grip of the Internet and enjoy a more fulfilling life.。
The Double Reduction policy,officially known as the Opinions on Further Reducing the Burden of Homework and OffCampus Training for Students in Compulsory Education,was introduced by the Chinese government in2021to address the heavy academic pressure faced by students.This policy aims to alleviate the excessive workload and reduce the reliance on afterschool tutoring services,which have become increasingly prevalent in recent years.The policy has several key components:1.Reduction of Homework:Schools are instructed to minimize the amount of homework assigned to students,ensuring that it is manageable and does not encroach on their leisure time or rest.2.Curbing AfterSchool Tutoring:The policy seeks to regulate the tutoring industry by imposing restrictions on the hours of operation,the curriculum covered,and the qualifications of tutors.This is to prevent the overdependence on supplementary education and to ensure that learning primarily takes place within the school system.3.Enhancing School Education:There is an emphasis on improving the quality of education within schools to meet the diverse needs of students.This includes the enrichment of curricula,the professional development of teachers,and the implementation of innovative teaching methods.4.Promoting Balanced Development:The policy encourages a more holistic approach to education,focusing not only on academic achievement but also on the physical and mental wellbeing of students.5.Parental Involvement:Parents are urged to play a more active role in their childrens education,supporting them emotionally and providing a conducive environment for learning at home.6.Regulatory Measures:The government has taken steps to enforce the policy,including inspections of schools and tutoring institutions to ensure compliance.The impact of the Double Reduction policy has been significant.It has sparked discussions about the purpose of education and the role of exams in determining a students future.It has also led to a reevaluation of the tutoring industry,which has seen a boom in recent years due to the intense competition for academic success.However,the policy has also faced criticism and challenges.Some argue that it may notaddress the root causes of academic pressure,such as the highstakes nature of entrance exams and societal expectations.Others worry about the potential for a black market in tutoring services to emerge,as parents and students seek to maintain an edge in the competitive educational landscape.In conclusion,the Double Reduction policy represents a bold step by the Chinese government to reform the education system and promote a healthier,more balanced approach to learning.Its success will depend on the effective implementation of these measures and the willingness of all stakeholdersstudents,parents,educators,and policymakersto embrace change and work towards a common goal of educational equity and excellence.。
环境英语作文好句带翻译当我们谈论环境保护时,我们需要意识到这是一项全球性的任务,需要全球性的努力。
以下是一些关于环境保护的好句,带有中文翻译:1. "Environmental degradation has reached an alarming level, necessitating immediate action from governments, industries, and individuals alike." 。
环境退化已经达到令人担忧的程度,需要政府、工业界和个人立即采取行动。
2. "It is imperative that we adopt sustainable practices in our daily lives to mitigate the adverseeffects of climate change." 。
我们必须在日常生活中采取可持续的做法,以减轻气候变化的不良影响。
3. "The preservation of biodiversity is crucial for thehealth of ecosystems and the well-being of future generations." 。
生物多样性的保护对生态系统的健康和未来世代的幸福至关重要。
4. "Rapid urbanization and industrialization have led to unprecedented levels of pollution, posing a grave threat to our planet's ecosystems." 。
快速的城市化和工业化导致了前所未有的污染水平,对我们星球的生态系统构成了严重威胁。
5. "Implementing stringent environmental regulations is essential to hold industries accountable for their ecological footprint." 。
绿色可持续发展英文作文英文回答:Green sustainable development is a crucial topic in today's world. It refers to the practice of using resources in a way that meets the needs of the present generation without compromising the ability of future generations to meet their own needs. It involves finding a balance between economic growth, social development, and environmental protection.One of the key aspects of green sustainable development is the promotion of renewable energy sources. This includes solar power, wind power, hydroelectric power, and geothermal energy. By utilizing these sources, we can reduce our dependence on fossil fuels and decrease carbon emissions, which contribute to climate change. For example, countries like Germany and Denmark have made significant progress in transitioning to renewable energy, with wind turbines and solar panels becoming a common sight in theirlandscapes.Another important element is sustainable agriculture. This involves using farming practices that minimize the use of chemical fertilizers and pesticides, protect soil health, and conserve water resources. Organic farming is a great example of sustainable agriculture, as it avoids the use of synthetic chemicals and promotes biodiversity. Additionally, sustainable agriculture also focuses on reducing food waste and promoting local food production, which can help reduce carbon emissions from transportation.Furthermore, green sustainable development alsoinvolves promoting sustainable transportation. Thisincludes encouraging the use of public transportation, walking, and cycling, as well as the development ofelectric vehicles. By reducing the reliance on private cars and promoting alternative modes of transportation, we can reduce air pollution and congestion in cities. For instance, cities like Amsterdam and Copenhagen have implemented extensive cycling infrastructure, making cycling a popular and efficient mode of transportation.In addition to these examples, green sustainable development also encompasses waste management, water conservation, and the conservation of natural resources. It requires a shift in mindset and a collective effort from individuals, businesses, and governments. By adopting sustainable practices in our daily lives, such as recycling, reducing water usage, and supporting eco-friendly products, we can contribute to a greener and more sustainable future.中文回答:绿色可持续发展是当今世界上一个至关重要的话题。
可再生能源消纳英语Renewable Energy Integration.Renewable energy integration is a crucial aspect of sustainable development, aiming to incorporate renewable energy sources into the existing energy infrastructurewhile maintaining the reliability and stability of the grid. This process is becoming increasingly important due to the global push towards decarbonization and reducing greenhouse gas emissions. In this article, we will delve into the concept of renewable energy integration, its importance, challenges, and strategies to address these challenges.Renewable energy integration involves the integrationof renewable energy sources such as solar, wind, hydroelectric, and biomass into the existing power grid. These sources are renewable because they are naturally replenished and do not deplete over time. By harnessing these renewable resources, we can reduce our dependence on fossil fuels, which are finite and emit harmful greenhousegases.The integration of renewable energy sources into the grid is challenging due to their intermittent nature. Unlike fossil fuel-based power plants, which can generate power on demand, renewable energy sources are dependent on natural conditions such as sunlight and wind speed. This intermittency can lead to fluctuations in power generation, which can affect the stability and reliability of the grid.To address these challenges, various strategies and technologies have been developed. One such strategy is energy storage, which allows for the storage of excess energy generated during peak hours and its release during low generation hours. This helps to balance out the intermittency of renewable energy sources and ensures a stable supply of power to the grid.Another strategy is the development of smart grids, which use advanced technologies such as sensors, meters, and communication systems to monitor and manage the flow of power in the grid. Smart grids can detect and respond tochanges in power generation and demand in real-time, ensuring the stability and reliability of the grid.Renewable energy integration is also facilitated by policy measures such as feed-in tariffs and renewable portfolio standards. Feed-in tariffs provide financial incentives to renewable energy developers, making it more economically viable to invest in renewable energy projects. Renewable portfolio standards, on the other hand, require utilities to generate a certain percentage of their power from renewable sources, ensuring a minimum level of renewable energy integration in the grid.In addition to these strategies and policies, there are also technological advancements being made to improve the efficiency and reliability of renewable energy sources. For example, solar photovoltaic (PV) technology has become more efficient and cost-effective over the years, making it a more viable option for renewable energy integration. Wind turbines are also being developed with larger rotor diameters and improved turbine controls to increase their power generation capacity and reduce their operationalcosts.Renewable energy integration is not only important for environmental reasons but also for economic and social reasons. By reducing our dependence on fossil fuels, we can mitigate the negative impacts of climate change and protect our planet for future generations. Additionally, renewable energy sources create jobs and economic opportunities in the renewable energy industry, supporting sustainable development and economic growth.In conclusion, renewable energy integration is acrucial aspect of sustainable development, aiming to incorporate renewable energy sources into the existing energy infrastructure while maintaining the reliability and stability of the grid. It involves various strategies and technologies to address the intermittency of renewable energy sources and ensure a stable supply of power to the grid. With the global push towards decarbonization and reducing greenhouse gas emissions, renewable energy integration will play a key role in achieving these objectives.。
过度依赖父母的危害英语作文Dangers of Excessive Parental DependenceGrowing up, many individuals become overly reliant on their parents, leading to a range of potential issues that can have long-lasting consequences. This phenomenon, known as excessive parental dependence, can manifest in various ways and can significantly impact an individual's personal growth, independence, and overall well-being. In this essay, we will explore the dangers associated with this phenomenon and the importance of fostering a balanced and healthy relationship with one's parents.One of the primary dangers of excessive parental dependence is the stunted personal growth and development of the individual. When individuals rely too heavily on their parents for decision-making, problem-solving, and everyday tasks, they often fail to develop the necessary skills and confidence to navigate life independently. This can lead to a lack of self-reliance, decision-making abilities, and problem-solving skills, making it challenging for the individual to transition into adulthood and cope with the demands of independent living.Furthermore, excessive parental dependence can hinder an individual's ability to form meaningful relationships outside of the family unit. Individuals who are overly reliant on their parents may struggle to establish their own social networks, romantic relationships, and professional connections. This can lead to a sense of isolation and a lack of personal fulfillment, as the individual's social and emotional needs are primarily met within the confines of the family.Another significant danger of excessive parental dependence is the impact it can have on the individual's emotional and psychological well-being. Individuals who are overly dependent on their parents may struggle with feelings of anxiety, low self-esteem, and a lack of personal agency. This can lead to a heightened sense of vulnerability and an inability to cope with the challenges and stresses of everyday life.Moreover, excessive parental dependence can also have negative consequences for the parents themselves. Parents who are overburdened with the responsibility of constantly supporting their adult children may experience increased levels of stress, exhaustion, and resentment. This can strain the parent-child relationship and lead to a breakdown in communication and trust.In addition to the personal and interpersonal consequences,excessive parental dependence can also have broader societal implications. Individuals who are unable to function independently may struggle to contribute to the workforce, participate in civic duties, and engage in the broader community. This can have a ripple effect on the overall social and economic fabric of a society.To address the dangers of excessive parental dependence, it is crucial for individuals to actively work towards developing their own sense of independence and self-reliance. This can involve setting clear boundaries with parents, learning to make decisions independently, and actively seeking out opportunities for personal growth and development. Additionally, parents can play a pivotal role in fostering independence by gradually reducing the level of support they provide and encouraging their children to take on more responsibility.In conclusion, the dangers of excessive parental dependence are multifaceted and can have far-reaching consequences on an individual's personal, emotional, and social well-being. By recognizing the importance of independence and self-reliance, individuals can take proactive steps to break free from the cycle of excessive dependence and develop the skills and confidence necessary to navigate the complexities of adulthood. Ultimately, striking a balance between parental support and personal autonomy is essential for a fulfilling and well-rounded life.。
英语作文高铁对生活的影响English:The high-speed railway (HSR) has greatly influenced our lives in many ways. Firstly, it has significantly shortened the travel time between cities, making it more convenient for people to travel long distances. Secondly, it has promoted economic development in regions connected by HSR, as it has improved transportation efficiency and reduced logistics costs, making it easier for businesses to transport goods and communicate with other regions. Thirdly, HSR has environmental benefits, as it produces less carbon emissions compared to other modes of transportation, thus helping to reduce air pollution and greenhouse gas emissions.Furthermore, HSR has improved the overall transportation system, as it has attracted a wide range of customers who prefer the comfortable and speedy journey that HSR offers. This has dramatically increased passenger capacity and reduced traffic congestion on roads and highways. It has also reduced the dependence on short-haul air travel, as HSR provides an alternativetransportation method that is more environmentally friendly and convenient.In addition, the development of HSR has contributed to increased tourism and cultural exchange between different regions and countries. HSR has made it easier for people to travel to different destinations, and this, in turn, has created economic opportunities for the tourism industry. Moreover, it has facilitated cultural communication and understanding among people from different regions, and has enabled people to experience and appreciate each other's cultures.In conclusion, the high-speed railway has had a profound impact on people's lives, by promoting economic development, reducing travel time and transportation costs, improving the environment, increasing transportation efficiency and capacity, reducing traffic congestion, and enhancing cultural exchange.中文翻译:高速铁路在许多方面都对我们的生活产生了很大影响。
电子货币取代纸币英语作文简单The rise of electronic currency has been a significant development in the financial landscape, challenging the traditional dominance of paper money. As technology continues to advance, the concept of electronic currency has gained traction, offering a more efficient and secure means of conducting transactions. This essay will explore the potential benefits and drawbacks of electronic currency replacing paper money, examining the implications for individuals, businesses, and the broader economic landscape.One of the primary advantages of electronic currency is its convenience and accessibility. With the widespread adoption of smartphones and digital wallets, individuals can now make purchases and transfer funds with the tap of a button. This eliminates the need to carry physical cash, reducing the risk of loss or theft. Moreover, electronic transactions can be processed instantly, providing a seamless experience for consumers and businesses alike.Another key benefit of electronic currency is its potential to enhance financial inclusion. In many parts of the world, a significant portion ofthe population remains unbanked or underserved by traditional financial institutions. Electronic currency, enabled by mobile technology, can provide these individuals with access to financial services, empowering them to participate in the formal economy and improve their overall financial well-being.Furthermore, electronic currency offers greater transparency and traceability. Every transaction is recorded on a digital ledger, making it easier to track and monitor financial activities. This can help in the fight against financial crimes such as money laundering and tax evasion, as the digital trail provides a more robust audit trail for regulatory authorities.In addition, electronic currency has the potential to reduce transaction costs for businesses. The elimination of physical cash handling and the associated security measures can lead to significant cost savings for merchants and financial institutions. These savings can then be passed on to consumers, potentially leading to lower prices and increased economic efficiency.However, the transition to a fully electronic currency system also presents several challenges. One of the primary concerns is the issue of privacy and data security. The digital nature of electronic currency means that personal and financial information is stored and transmitted electronically, making it vulnerable to cyber threats suchas hacking and data breaches. Ensuring the robust protection of sensitive data is crucial to maintaining public trust in the financial system.Another potential drawback is the reliance on technological infrastructure. The smooth functioning of an electronic currency system is contingent on the availability and reliability of the underlying technology, such as internet connectivity, mobile networks, and power supply. In the event of system failures or disruptions, the ability to conduct financial transactions could be severely impaired, leading to potential economic disruptions.Moreover, the adoption of electronic currency may exacerbate the digital divide, as individuals without access to digital devices or the necessary technological literacy may be excluded from the benefits of the digital financial ecosystem. Addressing this digital divide and ensuring equitable access to electronic currency is crucial to promoting financial inclusion and social equity.Finally, the transition to electronic currency may also have broader macroeconomic implications. Central banks and governments may face challenges in implementing monetary policies and maintaining control over the money supply, as the decentralized nature of some electronic currencies can limit their ability to regulate the financial system effectively.In conclusion, the rise of electronic currency presents both opportunities and challenges. While the potential benefits of convenience, financial inclusion, and cost savings are compelling, the concerns regarding privacy, data security, technological dependence, and the potential for digital exclusion must be addressed. As the adoption of electronic currency continues to grow, policymakers, financial institutions, and the public will need to work collaboratively to navigate this evolving landscape and ensure a smooth and equitable transition towards a digital financial ecosystem. Ultimately, the success of electronic currency in replacing paper money will depend on its ability to strike a balance between innovation and the preservation of financial stability and inclusivity.。
符合规定英文Compliant: Following the RulesTo ensure a fair, safe, and productive environment, it is important for individuals and organizations to comply with rules and regulations. Compliance not only promotes transparency and accountability but also protects the welfare and rights of all stakeholders. In this essay, we will discuss the importance of compliance and its benefits to society.One of the primary reasons why compliance is crucial is because it maintains trust and integrity. When individuals and organizations adhere to the established rules and regulations, it shows their commitment to ethical practices. This creates a sense of trust and credibility among stakeholders, including customers, investors, employees, and the general public. Moreover, compliance helps prevent unethical behavior, such as fraud, corruption, and discrimination, which can damage a company's reputation and lead to legal consequences.Compliance also fosters fairness and equality within organizations and society as a whole. By following rules and regulations, organizations ensure equal opportunities for all employees and avoid any form of discrimination. This promotes diversity, inclusivity, and social justice, ultimately contributing to a harmonious workplace and a more equitable society. Additionally, compliance with labor laws, health and safety regulations, and environmental standards guarantees the well-being and protection of employees, consumers, and the environment.Furthermore, compliance plays a vital role in risk management. Laws and regulations are put in place to mitigate risks and prevent potential harm. By complying with these regulations, organizations can identify, assess, and manage risks effectively. This can help reduce the occurrence of accidents, lawsuits, and other liabilities, thereby safeguarding the interests of both organizations and individuals. Compliance also promotes ethical decision-making and corporate governance, reducing the likelihood of misconduct and financial scandals.In addition, compliance promotes innovation and competitiveness. Many regulations aim to create a level playing field and foster healthy competition among businesses. By complying with such regulations, organizations can differentiate themselves from non-compliant competitors and gain a competitive advantage. Compliance also encourages organizations to adopt best practices, improve operational efficiency, and enhance their overall performance. This not only benefits organizations but also leads to better products and services for consumers.Lastly, compliance ensures the protection of personal data and privacy. With the increasing dependence on technology and the internet, the risk of data breaches and privacy violations has become a major concern. Compliance with data protection laws, such as the General Data Protection Regulation (GDPR), helps safeguard individuals' personal information and ensures its lawful and transparent use. This promotes trust between organizations and customers, enabling businesses to thrive in the digital age.In conclusion, compliance with rules and regulations is essentialfor maintaining trust, fairness, and integrity in society. It protects the rights and welfare of individuals, promotes ethical practices, and mitigates risks. Apart from these benefits, compliance fosters innovation, competitiveness, and the protection of personal data. Therefore, it is imperative for individuals and organizations to prioritize compliance in order to create a just and prosperous society.。
Reducing the Dependence of Trust-Management Systems on PKIHao Wang,Somesh Jha,Thomas RepsComputer Science DepartmentUniversity of Wisconsin{hbwang,jha,reps}@Stefan SchwoonInstitut f¨u r Formale Methoden der InformatikUniversit¨a t Stuttgart schwoosn@fmi.uni-stuttgart.deStuart StubblebineStubblebine Research Labs stuart@Technical ReportUW-CS-TR-1527AbstractTrust-management systems address the authorization problem in distributed systems by defining a formal language for expressing authorization and access-control policies,and relying on an algorithmto determine when a specific request can be granted.For authorization in distributed systems,trust-management systems offer several advantages over other approaches,such as support for delegationand making authorization decisions in a decentralized manner.This paper focuses on a popular trust-management system SPKI/SDSI.Although SPKI/SDSI is an attractive system for authorization in dis-tributed systems,it has seen limited deployment.One of the major hurdles in deploying SPKI/SDSI isthat it is PKI-based,i.e.,every principal is required to have a public-private key pair.We present anapproach that combines SPKI/SDSI with a widely-deployed authentication system,Kerberos,to reducereliance of SPKI/SDSI on PKI.In our approach,only sites need public-private key pairs.We believethat reducing the reliance of SPKI/SDSI on PKI will facilitate its wider deployment.We also haveimplemented a prototype of our technique.1IntroductionSystems with shared resources use access-control mechanisms for protection.There are three fundamental problems in access control:authentication,authorization,and enforcement.Authentication deals with veri-fying the identity of a principal.Authorization addresses the following problem:should a request r by a spe-cific principal A be allowed?Enforcement addresses the problem of implementing the authorization during an execution.In a centralized system,authorization is based on the closed-world assumption,i.e.,all of the parties are known or their identity can be established using an authentication system.In a distributed system, the closed-world assumption is not valid.Trust-management systems[2]solve the authorization problem in distributed systems by defining a formal language for expressing authorization and access-control policies, and relying on an algorithm to determine when a specific request is allowable.Hence,trust-management1systems decouple specification of the security policy from enforcement.Therefore,in the context of au-thorization in distributed systems,trust-management systems offer several advantages,such as support for delegation,no(conceptual)requirement for a central authority,and the ability to make authorization deci-sions in a truly distributed fashion.A survey of trust-management systems,along with a formal framework for understanding them,is presented in[25].Two prominent trust-management systems are Keynote[1]and SPKI/SDSI[8].In this paper,we focus on the trust-management system SPKI/SDSI;however,the basic ideas introduced in this paper are applicable to other trust-management systems.In SPKI/SDSI,name certificates define the names available in an issuer’s local name space;authorization certificates grant authorizations,or delegate the ability to grant authorizations.SPKI/SDSI has been investigated by several researchers.Authorization decisions in SPKI/SDSI are based on certificate chains,which are proofs that a client’s public key is one of the keys that has been authorized to access a given resource—either directly or transitively,via one or more name-definition or authorization-delegation steps.Despite its many advantages,SPKI/SDSI has seen limited deployment.The two major hurdles in deploying SPKI/SDSI are:•The need for a distributed certificate-chain discovery algorithm.•The need for every principal to have a public-private key pair.Thefirst hurdle has been partially addressed by work on distributed certificate-chain discovery algorithms for trust-management systems.1In this paper we focus on the second hurdle.The goal of this paper is to reduce the dependence of SPKI/SDSI on public-key infrastructure(PKI).Reducing the reliance of SPKI/SDSI on PKI will hopefully lead to its wider deployment.Our main approach is to leverage an existing widely deployed authentication system,namely,Ker-beros[20].Specifically,we demonstrate that using SPKI/SDSI in conjunction with Kerberos reduces the reliance on PKI by requiring only one public-private key pair per site,whereas“vanilla”SPKI/SDSI requires each principal to have a public-private key pair.Our approach maintains all the advantages of SPKI/SDSI, such as support for delegation and the ability to make authorization decisions in a distributed fashion.In our approach,there are two levels of certificates;each level resembles vanilla SPKI/SDSI.We call these K-SPKI/SDSI(for SPKI/SDSI with Kerberos),and E-SPKI/SDSI(for extended SPKI/SDSI).Users work at the K-SPKI/SDSI level;E-SPKI/SDSI is the implementation level.The distinction between these levels is dis-cussed further in Section3.1.In our solution,we allow authenticated Kerberos users to issue K-SPKI/SDSI certificates,and therefore eliminate the requirement that every user possess a public/private key pair.Our K-SPKI/SDSI server accepts certificates from authenticated Kerberos users and generates corresponding E-SPKI/SDSI certificates on behalf of the users.These certificates are used by the K-SPKI/SDSI server for answering authorization queries(by invoking certificate-chain discovery at the E-SPKI/SDSI level).By providing a solution that is built on top of Kerberos,an authentication system that is widely deployed in various organizations,ranging from research institutes to corporations,we hope that our approach will be easier to adopt.The contributions of this paper are as follows:•We show how to reduce the dependence of SPKI/SDSI on PKI by leveraging Kerberos.•This insight behind the work is that when a user authenticates using Kerberos,they acquire a session key that serves as evidence of who they are.This property is uses as a substitute for the signing actions that vanilla SPKI/SDSI requires,which provides the ability to participate in a SPKI/SDSI-like scheme without the requirement to have a public-private key pair.•We have created a prototype that implements the technique.Our measurements show that performance depends on how K-SPKI/SDSI certificates are distributed among sites.Background on SPKI/SDSI is given in Section2.Our method for combining SPKI/SDSI and Kerberos is described in Section3.Some applications of our system are discussed in Section4.Section5discusses deployment and performance issues of our prototype.Section6discusses related work.2Background on SPKI/SDSIIn SPKI/SDSI,all principals are represented by their public keys,i.e.,the principal is its public key.A principal can be an individual,process,host,or any other entity.K denotes the set of public keys.Specific keys are denoted by K,K A,K B,K′,etc.An identifier is a word over some alphabetΣ.The set of identifiers is denoted by A.Identifiers will be written in typewriter font,e.g.,A and Bob.A term is a key followed by zero or more identifiers.Terms are either keys,local names,or extended names.A local name is of the form K A,where K∈K and A∈A.For example,K Bob is a local name.Local names are important in SPKI/SDSI because they create a decentralized name space.The local name space of K is the set of local names of the form K A.An extended name is of the form Kσ,where K∈K andσis a sequence of identifiers of length greater than one.For example,K UW CS faculty is an extended name.2.1CertificatesSPKI/SDSI has two types of certificates,or“certs”:Name Certificates(or name certs):A name cert provides a definition of a local name in the issuer’s local name space.Only key K may issue or sign a cert that defines a name in its local name space.A name cert C is a signed four-tuple(K,A,S,V).The issuer K is a public key and the certificate is signed by K.A is an identifier.The subject S is a term.Intuitively,S gives additional meaning for the local name K A.V is the validity specification of the certifiually,V takes the form of an interval[t1,t2],i.e.,the cert is valid from time t1to t2inclusive.Authorization Certificates(or auth certs):An auth cert grants or delegates a specific authorization from an issuer to a subject.Specifically,an auth cert c is afive-tuple(K,S,D,T,V).The issuer K is a public key, which is also used to sign the cert.The subject S is a term.If the delegation bit D is turned on,then a subject receiving this authorization can delegate this authorization to other keys.The authorization specification T specifies the permission being granted;for example,it may specify a permission to read a specificfile,or a permission to login to a particular host.The validity specification V for an auth cert is the same as in the case of a name cert.A labeled rewrite rule is a pair(L−→R,T),where thefirst component is a rewrite rule and the second component T is an authorization specification.For notational convenience,we will write the labeled rewrite rule(L−→R,T)as L T−→R.We will treat certs as labeled rewrite rules:2−→S,where⊤is the authoriza-•A name cert(K,A,S,V)will be written as a labeled rewrite rule K A⊤tion specification such that for all other authorization specifications t,⊤∩t=t,and⊤∪t=⊤.3−→as simply−→,i.e.,a rewrite rule of the form L−→R has an implicit Sometimes we will write⊤label of⊤.•An auth cert(K,S,D,T,V)will be written as K T−→S if the delegation bit D is turned on;otherwise,it will be written as K T−→S .2.2AuthorizationBecause we only use labeled rewrite rules in this paper,we refer to them as rewrite rules or simply rules.A term S appearing in a rule can be viewed as a string over the alphabet K∪A,in which elements of K appear only in the beginning.For uniformity,we also refer to strings of the form S and S as terms.Assume that we are given a labeled rewrite rule L T−→R corresponding to a cert.Consider a term S=LX.In this case,the labeled rewrite rule L T−→R applied to the term S(denoted by(L T−→R)(S))yields the term RX.Therefore,a rule can be viewed as a function from terms to terms that rewrites the left prefix of its argument,for example,(K A Bob−→K B)(K A Bob myFriends)=K B myFriends−→R2),and,in addition,assume that L2is a prefix Consider two rules c1=(L1T−→R1)and c2=(L2T′−→R2X. of R1,i.e.,there exists an X such that R1=L2X.Then the composition c2◦c1is the rule L1T∩T′For example,consider the two rules:c1:K A friends T−→K A Bob myFriends−→K Bc2:K A Bob T′The composition c2◦c1is K A friends T∩T′−→K B myFriends.Two rules c1and c2are called compatible if their composition c2◦c1is well defined.42.3The Authorization Problem in SPKI/SDSIAssume that we are given a set of certs C and that principal K wants access specified by authorization specification T.The authorization question is:“Can K be granted access to the resource specified by T?”A certificate chain ch for C is of a sequence of certificates[c1,c2,···,c k]in C.The label of a cer-tificate chain ch=[c1,···,c k](denoted by L(ch))is the label obtained from c k◦c k−1···◦c1(denoted by compose(ch)).We assume that the authorization specification T is associated with a unique principal K owner[T](the resource to which T refers).Given a set of certificates C,an authorization specification T, and a principal K,a certificate-chain-discovery algorithm looks for afinite set of certificate chains that “prove”that principal K is allowed access specified by T.Formally,certificate-chain discovery attempts tofind afinite set{ch1,···,ch m}of certificate chains such that for all1≤i≤mcompose(ch i)(K owner[T] )∈{K ,K },and T⊆ m i=1L(ch i).Clarke et al.[6]presented an algorithm for certificate-chain discovery in SPKI/SDSI with O(n2K|C|) time complexity,where n K is the number of keys and|C|is the sum of the lengths of the right-hand sides of all rules in C.However,this algorithm only solved a restricted version of certificate-chain discovery:a solution could only consist of a single certificate chain.For instance,consider the following certificate set:c1:(K,K A,0,((dir/etc)read),[t1,t2])c2:(K,K A,0,((dir/etc)write),[t1,t2])Suppose that Alice makes the request(K A,((dir/etc)(*set read write))).In this case,the chain[c1]authorizes Alice to read from directory/etc,and a separate chain[c2]authorizes her to write to/etc.Together,the set{[c1],[c2]}proves that she has both read and write privileges for /etc.However,both of the certificates c1and c2would be removed from the certificate set prior to running the certificate-chain discovery algorithm of Clarke et al.,because read⊇(*set read write)and write⊇(*set read write).Consequently,no proof of authorization for Alice’s request would be found.Schwoon et al.[22]presented algorithms for the full certificate-chain-discovery problem,based on solving reachability problems in weighted pushdown systems(WPDSs).Their formalization allows a proof of authorization to consist of a set of certificate chains.This paper uses the WPDS-based algorithm for certificate-chain-discovery introduced by[22].3SPKI/SDSI and KerberosWe describe the authorization scenario in SPKI/SDSI.In Section3.1we describe how the reliance of SPKI/SDSI on PKI can be reduced by using Kerberos.First,we introduce a small example that will be used throughout this section.Example3.1.Imagine that there are two sites,Bio and CS,which correspond to the biology and the computer science department respectively.Let us say that professor Bob in the biology department wants to provide access to a server V to all his students and students of professor Alice in the computer science department.Assume that there are two sites st1and st2that have SPKI/SDSI servers S st1and S st2,respectively.In the context of our example,sites CS and Bio have SPKI/SDSI servers S CS and S Bio.There are three components to a SPKI/SDSI authorization scenario.Certificate issuance.Each user sends signed auth and name certs to the SPKI/SDSI server at their site. The SPKI/SDSI server verifies the signatures on the certs.If signature verification fails on a cert,it is rejected;otherwise it is stored by the SPKI/SDSI server.In our example,Alice sends to S CS the following name certs,which are signed by Alice:K Alice students−→K XK Alice students−→K YK Alice students−→K ZThe three name certs essentially state that X,Y,and Z are students of Alice.Bob sends to S Bio the following signed auth certs,which are signed by Bob:5K Bob T V−→K Bob studentsK Bob T V−→K Alice studentsThe two auth certs state that students of K Alice and K Bio can access server V(denoted by authorization specification T V),but the students cannot delegate this right.Certificate-chain discovery.Suppose a user U(with public key K U)at site A wants to access a re-source at site B according to authorization specification er U sends a certificate-chain-discovery request for T(denoted by CCDrequest(K U,T))to the SPKI/SDSI server S CS.The SPKI/SDSI serverS CS executes a distributed certificate-chain-discovery algorithm and returns afinite set of certificate chains{ch1,···,ch m}to U.In Example3.1,suppose that user X sends the certificate-chain discovery request CCDrequest(K X,T V)to server S CS.Server S CS executes a distributed certificate-chain discovery algo-rithm and returns the set of chains{ch1},where ch1=[c1,c2](c2and c1are shown below.)c2=K Bob T V−→K Alice studentsc1=K Alice students−→K XRequesting a resource.Assume that user U wants to access a resource according to authorization specifi-cation T.First,U requests that certificate-chain discovery be carried out by sending a request CCDrequest(K U,T) to the SPKI/SDSI server at its site,and obtains back a set of certificate chains SCH={ch1,···,ch m}. User U presents the set of certificate chains SCH to the principal K T(recall that K T is the owner of the resource to which T refers).The principal K T authorizes U iff T⊆ m i=1L(ch i)(this step is usually called compliance checking).The label L(ch i)of a chain ch i is described in Section2.2.In Example3.1,user X wants access to server V according to the authorization specification T V. After making a certificate-chain discovery request,X obtains the set{ch1},where ch1=[c1,c2], compose(ch1)(K Bob )∈{K X ,K X },and T V⊆L(ch1).X presents{ch1}to server V.V checksthat T V⊆L(ch1),which is true,and hence V grants U access.3.1SPKI/SDSI and KerberosNotice that,to use SPKI/SDSI,every user needs to have public/private key pair.In this section,we describean authorization protocol that uses a distributed authentication system,such as Kerberos,but only requiresa public/private key pair per site.Our new authorization system is called K-SPKI/SDSI.We assume that the reader is familiar with Kerberos(for a detailed description of Kerberos see[20]).We make the following assumptions:•Each site is a Kerberos realm.The KDC at site st is denoted by KDC st.•The K-SPKI/SDSI server at each site is Kerberoized.•The KDC and the K-SPKI/SDSI server at a site st share a public/private key pair.The public key of site st is denoted by K st.Next we describe all three components of our authorization scenario in the new context.Certificate issuance.To issue K-SPKI/SDSI certificates,a Kerberos userfirst authenticates with the local KDC using the standard Kerberos authentication protocol and receives a Ticket Granting Ticket(TGT)fromthe ing the TGT,the client requests a Service Granting Ticket(SGT)for accessing the Kerberoized SPKI/SDSI(K-SPKI/SDSI)server.Throughout the rest of the section,assume that the user has obtained6an SGT for the K-SPKI/SDSI server at its ing the SGT,the client issues requests for generating SPKI/SDSI name certs or auth munication on the channel over which the requests are sent is encrypted using the session key K s provided in the SGT.To issue a name cert,a user U at site st sends an encrypted name cert request to the SPKI/SDSI server:[U,A,S,V],E Kswhere U is the name of the user,A is an identifier,S is a subject,and V is a validity specification.As[U,A,S,V]as U A−→S.Upon receiving the encrypted name cert before,we will write the name cert E Ks[U,A,S,V]the local K-SPKI/SDSI server ascertains its validity,and if the name cert is valid,it creates E Ksa new name cert of the form[K st U,A,K st S,V],signs it with its private key,and stores it in the database of certificates.Notice that in the new name cert the public key K st of site st is added before U and S.In our example,Alice sends the following name certs encrypted with the session key K s to the K-SPKI/SDSI server at its site.Alice students−→XAlice students−→YAlice students−→ZThe K-SPKI/SDSI server verifies the encrypted name certs shown above and creates the following E-SPKI/SDSI name certs and signs them.K CS Alice students−→K CS XK CS Alice students−→K CS YK CS Alice students−→K CS Z[U,S,D,T,V]encrypted with the session key from the TGT A user U at site st sends an auth cert E Ksto the K-SPKI/SDSI server.Upon receiving the encrypted auth cert E K[U,S,D,T,V]the K-SPKI/SDSIsserver ascertains its validity,and if the auth cert is valid,it creates a new E-SPKI/SDSI auth cert of the form[K st U,K st S,D,T,V]signs it with its private key,and stores it in the database of certificates.In our example,Bob sends the following auth certs encrypted with the session key from the TGT to the K-SPKI/SDSI server S Bio.−→Bob studentsBob T V−→CS Alice studentsBob T VThe two auth certs state that students of Bob(at the current site)and Alice(at site CS)can access server V (denoted by authorization specification T V),but the students cannot delegate this right.The K-SPKI/SDSI server S Bio verifies the encrypted auth certs shown above,and creates the following E-SPKI/SDSI auth certs,and signs them.−→K Bio Bob studentsK Bio Bob T V−→K Bio CS Alice studentsK Bio Bob T VThe K-SPKI/SDSI servers also adds name certs corresponding to the K-SPKI/SDSI servers of other sites. In our example,S CS signs and adds the name cert K CS Bio−→K Bio,which states that the public key of the site Bio is K Bio.Similarly,S Bio signs and adds the name cert K Bio CS−→K CS.Note:K-SPKI/SDSI servers must support an extended version of SPKI/SDSI:the left-hand sides of ex-tended auth and name certs have three symbols;the left-hand side of an extended auth cert is of the form7KαU or KαU ,where Kαis the public key of siteαand U is a user;the left-hand side of an extended name cert if of the form KαU A,where both U and A are identifiers.However,in SPKI/SDSI the left-hand sides of auth and name certs have just two symbols.Various SPKI/SDSI algorithms must be extended to implement E-SPKI/SDSI;however,this is possible because E-SPKI/SDSI is a special case of left-prefix rewriting,and the primitives generalize to arbitrary left-prefix rewriting systems[4].Requesting a ing the SGT,a user U at site st1sends a request to the local K-SPKI/SDSI server,asking to access the remote server V located in a different site st2.This request is encrypted using the session key K s provided by the SGT.E Ks[st2,V,T]The K-SPKI/SDSI server S st1at site st1initiates a distributed certificate-chain discovery request CCDrequest(K st1U,T)on behalf of U.This process involves K-SPKI/SDSI servers,both local and remote,that contain related E-SPKI/SDSI certificates.If the request CCDrequest(K st1U,T)is successful and returns a set of certificate chains SCH,user U receives the following token from S st1.Token U=E Ks(K1)Ticket UTicket U=E Kst2(K2)E K2[st2,K1,V,T,SCH,T S1,Lifetime1]In Example3.1,user X receives a token with the set of certificate chains SCH={ch1},where ch1is thecertificate chain[c1,c2,c3].Certificates c1,c2,and c3are shown below.c1=K Bio Bob T V−→K Bio CS Alice studentsc2=K Bio CS−→K CSc3=K CS Alice students−→K CS XNotice that compose([c1,c2,c3])(K Bio Bob )∈{K CS X ,K CS X }and T V⊆L([c1,c2,c3]).Upon receiving Token U,user U decrypts E Ks(K1)and retrieves the key K1(recall that K s is the sessionkey in the TGT for the K-SPKI/SDSI server at site st1).User U constructs the following authenticator:Authenticator U=E K1[ID U AD U T S2 Lifetime2]User U sends the following message to the server V at site st2:Ticket U Authenticator UServer V requests its local K-SPKI/SDSI server to verify the message.The K-SPKI/SDSI server at site st2 performs the following steps:•Decrypts the message E Kst2(K2)with its private key,and retrieves the session key K2.•Decrypts the message E K2[st2,K1,V,T,SCH,T S1,Lifetime1]and ascertains its freshness using the time-stamp T S1.Moreover,the server verifies using Lifetime1that the token has not expired.TheK-SPKI/SDSI server also performs the compliance-checking step on the set of certificate chains SCH.•Similarly,the K-SPKI/SDSI server ascertains the validity of the authenticator E K1[ID U AD U T S2 Lifetime2].Notice that the server knows the session key K1from Ticket U.If all the steps given above are successful,then the K-SPKI/SDSI server sends a message to V indicatingthat U should be granted access.83.2Threat AnalysisThe message exchange for requesting a resource described earlier is very similar to the exchange of messages between the client and KDC in Kerberos.In essence,the authenticator Authenticator U states that“anyone who uses K1is U”.Notice that since in the token Token U the session key K1is encrypted with K s, which can only be known by the user U(because K s is in the SGT issued to U).Therefore,assuming the authentication in Kerberos is correct,only U could have known K1.An adversary can still replay the message Ticket U Authenticator U to the server V and masquerade as U.Since the authenticator is intended for use only once,it can have a very short lifetime,and hence the risk of a replay attack is minimal.4ApplicationsOur work is only afirst step towards building a practical distributed authorization system.In this section, we discuss how existing applications can benefit from the K-SPKI/SDSI approach.4.1Authorization for Distributed File SystemsAFS[21]is a popular distributedfile system in active use because it provides users with a consistent name space,regardless of the users’s physical location.Authorization in AFS is an important issue because all AFS users share the same view of the entire AFS.Currently,AFS relies on Kerberos for authentication,and uses Access Control Lists(ACLs),which may contain user names,group names,or both,to control who can access the data inside each AFS directory.The ACL system works well for managing permissions within one site;however,if users from different sites plan to sharefiles,the ACL system becomes less efficient to use and is difficult to maintain.This is because in AFS,authorization is performed locally at each AFS cell.To illustrate this,we use a concrete example to show how AFS ACLs work in a cross-site environment. Then we explain how our approach can simplify cross-site authorization in AFS.Cross-site ACLs in AFS.Let us assume that Professor Bob,from the site Bio,plans to grant access to directory data to students of Professor Alice from the site ing existing AFS,Alice and Bob must follow these steps to accomplish this goal:51.Initial authentication:At site Bio,Bob authenticates with the AFS system(through Kerberos)to obtainan AFS token that is used to access AFS and create ACLs.2.Alice creates a list of her students:At site CS,Alice creates a list of her students,as shown in Figure1(a).63.Bob sets up a group for Alice’s students:Bob creates an AFS group,called Alice@CS:students,for Alice’s students in Bio.He then populates the group with Alice’s students.This is shown in Figure1(b).4.Bob grants access to Alice’s students:Bob grants access to directory data to the group that he createdin the previous step,as shown in Figure1(c).The problem with the above approach is that the group Alice@CS:students,maintained by Bob,is redundant and must be kept in sync with Alice’s own list.As a result,this approach is not efficient and does not scale.Consider the following two scenarios:Alice’s students(CS)studentY...ACL list for datasystem:administrators studentY@cs lAlice@CS:students...rlidwka (b.)Bob’s ACL group(c.)Bob grants accessFigure1:An example of using AFS ACLs for cross-site access control.In(a),Alice maintains a list of her students at site CS.In(b),at site Bio,Bob creates the group Alice@CS:students and adds Alice’s students to the group.In(c),Bob grants access to directory data to the group Alice@CS:students (third entry);the other three ACL entries are managed by AFS.•If Alice adds or removes a student from her list,then Bob must also update his list accordingly.•If three more professors from three different sites plan to grant access permissions to Alice’s students, then each of these professors must also create and maintain a copy of Alice’s student list.AFS Authorization Using K-SPKI/SDSI.In contrast,the K-SPKI/SDSI approach greatly simplifies cross-site authorization.Here are the steps:1.Initial authentication:Alice and Bob authenticate with their KDCs to obtain SGTs for their respectiveK-SPKI/SDSI servers.2.Alice issues name certs:At site CS,using the K-SPKI/SDSI server,Alice issues a name cert for eachone of her students:K CS Alice students−→K CS studentXThis essentially creates a group called K CS Alice students at site CS.3.Bob grants access to Alice’s students:At site Bio,through the K-SPKI/SDSI server,Bob issues oneauth cert granting access to Alice’s students,using the group created at CS:K Bio Bob data rl−−−−−→K Bio CS Alice students Here,because Alice is the only one who manages the list of students,and Bob refers to the symbolic name CS Alice students,Bob no longer needs to create a copy of Alice’s list of students.As a result, this approach is simpler to use and is also more scalable in cross-site environments:•When Alice adds or removes a student from her list,Bob does not need to make any changes on his side.•If three more professors from three different sites want to grant access permissions to Alice’s students, all they need to do is to issue auth certs at their sites,and no duplicate lists of students need to be created.4.2Accessing Kerberos Services through Web ServicesWeb services are traditionally built on top of public-key cryptography,such as SSL.Kerberos services,on the other hand,rely on secret-key cryptography.As a result,it has been a challenge to integrate these two systems so that users can access Kerberos services through web services.In this example,we consider a case where a user,say Alice,wants to access her data through a web service(usually running inside a web10。