Top Tips for Protocol Execution

1 . It's Easier to Get EasierMany teachers make the mistake of starting the school year with a poor discipline plan. Students quickly assess the situation in each class and realize what they will be allowed to get away with. Once you set a precedent of allowing a lot of disruptions, it can be very hard to start better classroom management and discipline techniques. However, it is never tough to get easier as the year goes on. While you don't have to follow the adage, "Never smile until Christmas," it does have its merits.2 . Fairness is KeyStudents have a distinct sense of what is and what is not fair. You must act fairly for all students if you expect to be respected. If you do not treat all students equitably, you will be labelled as unfair students will not be keen to follow your rules. Make sure that if your best student does something wrong, they too get punished for it. More »3 . Deal with Disruptions with as Little Interruption as PossibleWhen you have classroom disruptions, it is imperative that you deal with them immediately and with as little interruption of your class momentum as possible. If students are talking amongst themselves and you are having a classroom discussion, ask one of them a question to try to get them backon track. If you have to stop the flow of your lesson to deal with disruptions, then you are robbing students who want to learn of their precious in-class time.How to Handle Discipline Problems with Effective Classroom Management 4 . Avoid Confrontations in Front of StudentsWhenever there is a confrontation in class there is a winner and a loser. Obviously as the teacher, you need to keep order and discipline in your class. However, it is much better to deal with discipline issues privately than cause a student to 'lose face' in front of their friends. It is not a good idea to make an example out of a disciplinary issue. Even though other students might get the point, you might have lost any chance of actually teaching that student anything in your class. More »5 . Stop Disruptions with a Little HumorSometimes all it takes is for everyone to have a good laugh to get things back on track in a classroom. Many times, however, teachers confuse good humor with sarcasm. While humor can quickly diffuse a situation, sarcasm may harm your relationship with the students involved. Use your best judgment but realize that what some people think as funny others find to be offensive. More »6 . Keep High Expectations in Your ClassExpect that your students will behave, not that they will disrupt. Reinforce this with the way you speak to your students. When you begin the day, tell your students your expectations. For example,you might say, "During this whole group session, I expect you to raise your hands and be recognized before you start speaking. I also expect you to respect each other's opinions and listen to what each person has to say." More »7 . OverplanFree time is something teachers should avoid. By allowing students time just to talk each day, you are setting a precedent about how you view academics and your subject. To avoid this, overplan. Write additional activities into your lesson plans just in case your main lesson run short. When you have too much to cover, you'll never run out of lessons and you will avoid free time. You can also fill up any left over timewith mini-lessons. More »8 . Be ConsistentOne of the worst things you can do as a teacher is to not enforce your rules consistently. If one day you ignore misbehaviors and the next day you jump on someone for the smallest infraction, your students will quickly lose respect for you. Your students have the right to expect you to basically be the same everyday. Moodiness is not allowed. Once your lose your student's respect, you also lose their attention and their desire to please you. More »9 . Make Rules UnderstandableYou need to be selective in your class rules (no one can follow 180 rules consistently). You also need to make them clear. Students should understand what is and what is not acceptable. Further, you should make sure that the consequences for breaking your rules are also clear and known beforehand.10 . Start Fresh EverydayThis tip does not mean that you discount all previous infractions, i.e. if they have three tardies then today means four. However, it does mean that you should start teaching your class each day with the expectation that students will behave. Don't assume that because Julie has disrupted your class everyday for a week, she will disrupt it today. By doing this, you will not be treating Julie any differently and thereby setting her up to disrupt again (like a self-fulfilling prophecy). Read a personal example of this with my best teaching experience.。

易拓管理员手册目录一）Linux基础概念 (2)二）Linux基础操作 (2)1）登入Linux操作系统 (2)2）Linux基础指令 (8)三）相关文件夹/文件介绍 (9)Part2：Oracle部分 (10)一、登入Oracle (10)二、启动Oracle (10)三、关闭Oracle (11)四、查看Oracle表空间使用情况 (11)五、增加Oracle表空间 (12)六、处理表锁 (13)七、备份还原Oracle数据 (13)Part3：GP部分 (15)一、易拓系统架构说明 (15)二、易拓目录结构说明 (16)三、易拓用户说明 (17)四、添加Tiptop ERP用户 (17)五、新建ERP帐套 (19)六、系统备份检查 (22)七、Tiptop GP重要文件介绍 (24)八、环境变量 (24)九、系统慢问题 (25)Part:1 OS部分一）Linux基础概念1)和Windows一样，Linux是一种操作系统，一样有文件、进程、磁盘分区各种概念。

2)不同于Windows，Linux的维护是在命令行界面完成，因此需要掌握一些Linux维护指令。

3)根据28定律，我们只要掌握20%的指令，就可以完成80%的维护操作了。

4)现在开始万里长征第一步：登入Linux，以便进行对Linux的操作。

二）Linux基础操作1）登入Linux操作系统1）推荐下载安装XShell最新版本登入OS，方便日后操作启动XShell 点击New 新建一个到AP操作系统的链接2）点击Connection选项，设定以下栏位的值：Name 连线标识，如：ERP-APHost AP的IP地址3）点击Authentiacation选项，设定以下栏位的值：User Name rootPassword root账户的密码，默认为tiptop4）点击Terminal选项，设定以下栏位的值：Encoding Unicode(UTF-8)5）点击OK，完成连线设置。

jis中nlcp执行标准英文回答：The JIS (Japanese Industrial Standards) NLCP (Network Layer Control Protocol) execution standard is a set of guidelines and requirements for the implementation and operation of network layer control protocols in Japan. These standards are designed to ensure interoperability, reliability, and security in network communications.The JIS NLCP execution standard covers a range of technical specifications and operational procedures for network layer control protocols. This includes requirements for protocol design, message formats, error handling, security mechanisms, and interoperability with other network protocols. The standard also specifies testing and certification procedures to ensure compliance and conformance with the requirements.One key aspect of the JIS NLCP execution standard isits focus on interoperability. The standard defines requirements for how network layer control protocols should interact with other protocols and network devices. This includes specifications for protocol negotiation, message exchange, and error handling to ensure seamless communication between different network elements.In addition to interoperability, the JIS NLCP execution standard also addresses security considerations. Itoutlines requirements for authentication, encryption, and access control mechanisms to protect network communications from unauthorized access and malicious attacks. This helps to ensure the integrity and confidentiality of data transmitted over the network.Furthermore, the JIS NLCP execution standard includes guidelines for performance and reliability. It specifies requirements for message delivery, error detection and correction, and congestion control to ensure efficient and reliable network communications. This helps to optimize the performance of network layer control protocols and enhance the overall quality of service for network users.Overall, the JIS NLCP execution standard plays acrucial role in ensuring the smooth and secure operation of network layer control protocols in Japan. By defining clear requirements and guidelines, the standard helps to promote interoperability, reliability, and security in network communications, ultimately benefiting both users andservice providers.中文回答：JIS（日本工业标准）NLCP（网络层控制协议）执行标准是日本关于网络层控制协议实施和操作的一套指导方针和要求。

英文回答：To guarantee the effective operation of experimental instruments and equipment, it is imperative to establish aprehensive plan for their inspection and deployment. This plan must epass a well-defined schedule for regular maintenanceand inspection of all equipment, aimed at identifying any potential issues before they impede experimental procedures. Furthermore, a meticulous inventory of all instruments and equipment should be upheld to monitor their usage and condition. This practice will facilitate the prompt identificationof any necessary repairs or replacements, thus ensuring the continuous functionality of the instruments when required for experiments.为了保证实验仪器和设备的有效运作，必须制定检查和部署综合计划。

这一计划必须通过一个明确规定的定期保养和检查所有设备的时间表，目的是查明任何可能的问题，以免妨碍试验程序。

应保持对所有仪器和设备的详细清点，以监测其使用情况和状况。

这种做法将有助于迅速查明任何必要的修理或更换，从而确保试验所需仪器的持续功能。

公章代替合同章原因剖析和整改措施Using a company seal instead of a contract seal can have serious consequences. 公章代替合同章可能导致合同无效，给公司带来财务风险和法律纠纷。

It is crucial for businesses to understand the reasons behind this mistake and take appropriate corrective measures. 企业必须深刻了解这一错误背后的原因，并采取适当整改措施。

One of the main reasons for using a company seal instead of a contract seal is lack of awareness or training. 公章代替合同章的主要原因之一是缺乏意识或培训。

Employees may not be properly educated on the proper use of seals and the legal implications of using the wrong seal. 员工可能没有接受关于印章正确使用和错误使用的法律影响的适当教育。

Another reason for this common mistake is convenience. 公章代替合同章的另一个常见原因是便捷性。

Using a company seal may be fasteror easier for employees who are not familiar with the proper procedures for executing contracts. 对于不熟悉执行合同的正确程序的员工来说，使用公司印章可能更快或更容易。

This can lead to laziness or negligence in following the correct protocol for contract execution.这可能导致懒惰或疏忽，没有遵循合同执行的正确协议。

10 Tips for English Learning1. How do you memorize new words?New words should be mastered in several ways. First, pronunciation, if you want to pronounce the word correctly, you'd better listen to it first and practice it again and again by imitation. Second, spelling, if you want to memorize the word how to spell, you'd better learn some knowledge for word building and pronunciation rules. Third, meaning and use, if you want to know the exact meaning and use of the word, you'd better learn it through context and reading. Finally, you should work hard on it.2. How do you improve your reading?First, look at the title of the passage if there is. You can get the general idea of it. Then you pay attention to the first and last sentence of very paragraph of the passage. You can get the main idea of the paragraph. Third, through the context(上下文), you guess the new words that you come across. Finally, note the style and tone in order to the writer's implication in meaning.3. How do you improve your speaking?You can improve your speaking only through practice. Firstly, don't think of too much grammar, when you speak. You try to speak the key words, if you cannot speak the whole sentence, but you must speak the key words clearly and correctly. Secondly, pay attention to the different rhythms (节奏)between English and Chinese. We Chinese tend to stress the words equally, while the English words in the sentence tend to be stressed quite differently. The words with important information are normally stressed. Lastly, try to use your gestures and your facial expressions to go with your verbal communication.4. How do you learn English grammar?The purpose of learning grammar is to help learners to have a better understanding of the language. It is no use remembering grammar rules by rote because there are no rules without exceptions. It is sensible to use English grammar as a tool to help you to understand and master English. You learn grammar only through language phenomena (现象)because it comes from it. So you learn those rules and do some exercises to practise them.5. How do you improve your listening?You can improve your listening only through listening a great deal and there is no shortcut. First, you should have the right pronunciation of the words in your mind so learn to pronounce them correctly. Then, you try to catch the meaning of the sentence but not the separate meanings of the words, that is, do not concentrate on words too much but on the meaning as a whole. Third, pay attention to the liaison, (连读) loss of explosion and assimilation(同化) of the words. Lastly, pay attention to the stressed words and guess the meaning through the intonation.6. How do you start to learn English?First, you must have your purpose of learning English in your mind. Do you want to improve your oral English or written English or for the purpose of tests? Second, what level are you at? Are your English intermediate? Lower or upper? Third, choose the way to learn English according to your time and finance. Do you want to learn English by self-study, English class, English courses on the radio, English learning software or even online courses on the Internet? Finally, you must study hard and insist on learning continuously for a year or two.7. How do you improve your translation?First, learn some basic rules for translation. Then you must have a good master of both English and Chinese. Finally, you must practise, practise and once more practise. You can refer to some bilingual magazines English world for example. You practise translation from Chinese to English and vice versa(反过来). Then you have some comparison with their translation. After some period of practice, you will make great progress. Practise makes perfect.8. How do you tell the differences of English synonyms?There are no synonyms which are exactly the same. You should think of the synonyms in these ways. The style is different. Formal or informal?. The meaning is different. General or specific? It is different in grammar. Different collocations and different sentence patterns.9. How do you learn English verb tense?First, pay attention to the adverbial of time, if there is one, in the sentence. Different adverbials of time indicate the use of different tense. Second, the meaning of predicate verb, Some verbs tend to be used a certain tense. For example, I like music The word like tends to be used in simple present tense. Third, note the context, it will give you hints to use a certain tense. Finally, you'd better do some exercises in order that you have some consciousness(意识) of using English tense.10. How do you buy English dictionary?Nowadays, there are so many different kinds of dictionaries. Find the kind of dictionary that you are looking for. Then you 'd better find out who is the publisher? Is it awell-known publisher? How many copies has it been published? The more, the better. What do you think of the printing quality of the dictionary。

如何去打羽毛球大学生英语作文全文共3篇示例，供读者参考篇1How to Play BadmintonBadminton is a really fun sport that a lot of university students play. It's pretty easy to pick up if you're new to it, but also has a high skill ceiling for those who want to get really good at it. As a student, badminton is great because it doesn't require too much time or money to play recreationally with friends.Getting StartedThe first thing you'll need is some basic equipment - a badminton racket, shuttlecocks (the projectile you hit back and forth), and ideally access to a badminton court. You can get an entry-level racket for around 20-30. Shuttlecocks run about10-15 for a tube of 12.Most university rec centers will have badminton courts you can use for free or a very low cost. You can also look into any local community badminton clubs, which sometimes have open gym times. If you don't have access to a court, you can even play in a driveway or park in a pinch.Once you have your gear, I'd recommend watching some YouTube tutorials on badminton basics - how to grip the racket, ready position, forehand/backhand swings, serving, etc. It's not too complicated but having someone explain the fundamentals really helps when you're first starting out.Playing a GameA standard badminton game is played between two people (singles) or two pairs (doubles) on a rectangular court divided by a high net. Players score points by hitting the shuttlecock over the net and rallying back and forth until one side fails to return it successfully.The scoring system is kind of confusing at first - you have to score with serving to get a point, and only the serving side can score. But you'll pick it up through playing. Games are typically played to 21 points.One of the best things about badminton is that it's social and athletic at the same time. You'll be running back and forth, jumping, lunging, while engaging your mind by anticipating shots and strategizing. It's an amazing cardio workout but feels more like playing than exercising.Having FunDon't take badminton too seriously when you're first learning! The key is just enjoying rallying the birdie back and forth. I remember my first few games, I missed so many shots and felt super uncoordinated. But it was still a blast just being active with friends.As you get better, you can start learning more advanced techniques like smashes, clears, drops, drives, and net shots. Doubles games also add a whole layer of strategy in moving together and communicating with your partner.One thing that makes badminton so enjoyable is how satisfying it feels to nail the sweet spot on your racket and just crush the shuttlecock. There are few better feelings than absolutely demol篇2How to Play BadmintonBadminton is one of the most popular sports on university campuses around the world. It's an incredibly fun game that requires skill, strategy, and athleticism. As a student, badminton is the perfect sport to pick up - it's easy to learn, you can play it almost anywhere, and it provides a great workout. In this essay,I'll share my tips on how to get started playing badminton as a university student.First off, let's go over some of the basic equipment you'll need:Racket - This is the most important piece of equipment. You'll want to get a racket that feels comfortable in your hand and isn't too heavy. Many beginner rackets are made of aluminum and are pretty affordable.Shuttlecocks - These are the projectiles you'll be hitting back and forth. Shuttlecocks made of plastic or nylon with a cork base are pretty standard for recreational play.Non-Marking Shoes - You'll need shoes with non-marking soles so you don't scuff up the court surface. Cross-training shoes work great.That's really all the essential gear you need to get started! Of course, you can get fancier equipment like high-end rackets as you improve.Next up is finding a place to play on campus. Pretty much every university has badminton courts, either outdoor or indoor. The rec center is usually a great place to look. Many schools also have badminton clubs you can join to meet other players.Once you have your gear and a court, it's time to learn the basics of how to actually play the game. The main objective is to hit the shuttlecock over the net and onto the opponent's side of the court in a way that prevents them from returning it before it hits the ground.One of the first shots you'll want to learn is the serve. There are a few different serving techniques, but the most common for beginners is the low serve. For this, you'll want tosstand in the right service court with your racket pointing down. Use an underhand motion to hit the shuttlecock below your waist to send it diagonally to the opponent's service court.After the serve, the next fundamental is the forehand and backhand shots. For the forehand, you'll position your body sideways with your non-racket foot forward and hit the shuttlecock from in front of your body. The backhand is similar, but you'll hit across your body from the other side.As you're starting out, just focus on developing a consistent stroke and getting the shuttlecock back over the net. Onceyou've got the hang of the basic shots, you can start working on things like overhead clears, drop shots, smashes, and other more advanced techniques.One key to improving at badminton is footwork. Since the shuttlecock travels quickly, you'll need to be light on your feet to get into the ideal position to strike it. Spend time practicing quick lateral shuffle steps to move side-to-side andforward/backward lunges.It's also really important to learn proper badminton strategy as you're developing your skills. One of the most fundamental strategies is serving diagonally to move your opponent to the back corners and open up the rest of the court.When receiving a serve, try to return it with a high, deep shot to give yourself time to recover and prepare for the next shot. You'll also want to mix up your shots to keep your opponent off balance - don't just hit the same shot over and over again.If you're playing doubles (with a partner on each side), positioning and communication are crucial. You'll need to coordinate with your partner on who will hit which shots and cover different areas of the court. Calling out "mine!" or "yours!" can prevent collisions and confusion.Besides practicing your strokes and strategy, one of the best things you can do is play games against other people as much as possible. Badminton is one of those sports where you improvemuch faster through actual game experience versus just hitting by yourself.Don't get discouraged if you struggle in the beginning - badminton has a steep learning curve! Be patient, stay positive, and keep drilling those fundamental techniques. Before long, the muscle memory will kick in and you'll start seeing major improvements in your game.Finally, make sure you're following proper badminton etiquette and sportsmanship. Call faults on yourself if you hit the shuttlecock out or it gets caught in your clothes. Don't yell or get angry over bad shots or close calls. Be respectful to your opponents and have fun - that's what recreational badminton is all about!So there you have it - those are my top tips for how to start playing badminton as a university student. It's an amazing sport that will help you get exercise, build hand-eye coordination, and make new friends on campus. Grab a racket, find a court, and start practicing those serves and smashes! Who knows, you may just become the next badminton superstar.篇3How to Play Badminton: A Comprehensive Guide for University StudentsAs a university student, it's essential to find activities that not only provide a break from the rigors of academic life but also contribute to our overall well-being. One such activity that has gained immense popularity on campuses worldwide is badminton. This exhilarating game offers a perfect blend of physical exercise, mental stimulation, and social interaction, making it an ideal choice for students seeking a balanced lifestyle.In this comprehensive guide, I'll share my personal experiences and insights into the world of badminton, covering everything from the basics of the game to advanced strategies and techniques. Whether you're a complete novice or an experienced player looking to hone your skills, this essay will equip you with the knowledge and inspiration to elevate your badminton game to new heights.The Fundamentals: Gear Up and Get ReadyBefore we dive into the intricacies of the game, let's start with the essentials. To play badminton, you'll need a few key pieces of equipment:Badminton Racket: Choose a racket that feels comfortable in your hand and suits your playing style. As a beginner, opt for a lighter racket to ease the strain on your arms and improve control.Shuttlecock: These feathered projectiles come in various speeds and levels of resistance. For starters, use a slower shuttlecock to get a feel for the game.Non-marking Indoor Court Shoes: Proper footwear is crucial for maintaining traction and preventing injuries on the court.Comfortable Athletic Clothing: Opt for lightweight, breathable fabrics that allow for unrestricted movement.Once you've assembled your gear, it's time to familiarize yourself with the court dimensions and scoring system.The Fundamentals: Mastering the BasicsLike any sport, badminton has its own set of rules and techniques that must be mastered. Here are some essential skills every university student should develop:Grip: Experiment with different grip styles (forehand, backhand, etc.) to find the one that feels most natural and provides better control over your shots.Footwork: Proper footwork is the foundation of effective shot execution. Practice moving quickly and efficiently around the court, maintaining a balanced stance throughout.Serves: Learn the different types of serves (high, low, flick, etc.) and practice delivering them with accuracy and consistency.Clears: Clearing the shuttlecock to the back of the opponent's court is a defensive strategy that buys you time and resets the rally.Drops: Mastering the art of dropping the shuttlecock just over the net can catch your opponent off guard and set up offensive opportunities.Smashes: Once you've gained confidence, unleash powerful overhead smashes to dominate the court and score decisive points.Remember, practice makes perfect. Dedicate time to honing these fundamental skills, and you'll soon develop a well-rounded game.Advanced Strategies and TechniquesAs you progress in your badminton journey, you'll encounter more experienced opponents and find yourself in。

Universally Composable Security:A New Paradigm for Cryptographic Protocols(Extended Abstract)Ran CanettiAbstractWe propose a new paradigm for defining security of cryp-tographic protocols,called universally composable secu-rity.The salient property of universally composable defini-tions of security is that they guarantee security even when a secure protocol is composed with an arbitrary set of pro-tocols,or more generally when the protocol is used as a component of an arbitrary system.This is an essential prop-erty for maintaining security of cryptographic protocols in complex and unpredictable environments such as the Inter-net.In particular,universally composable definitions guar-antee security even when an unbounded number of proto-col instances are executed concurrently in an adversarially controlled manner,they guarantee non-malleability with re-spect to arbitrary protocols,and more.We show how to formulate universally composable def-initions of security for practically any cryptographic task. Furthermore,we demonstrate that practically any such def-inition can be realized using known techniques,as long as only a minority of the participants are corrupted.We then proceed to formulate universally composable definitions of a wide array of cryptographic tasks,including authenti-cated and secure communication,key-exchange,public-key encryption,signature,commitment,oblivious transfer,zero knowledge and more.We also make initial steps towards studying the realizability of the proposed definitions in var-ious settings.Keywords:cryptographic protocols,security analysis of protocols,concurrent composition.1IntroductionRigorously demonstrating that a protocol“does its job securely”is an essential component of cryptographic pro-tocol design.This requires coming up with an appropri-ate mathematical model for representing protocols,and then IBM T.J.Watson Research Center.Email:canetti@.formulating,within that model,a definition of security thatcaptures the requirements of the task at hand.Once such a definition is in place,we can show that a protocol“does itsjob securely”by demonstrating that it satisfies the definitionof security in the devised mathematical model.However,coming up with a good mathematical modelfor representing protocols,and even more so formulatingappropriate definitions of security within the devised model, turns out to be a tricky business.The model should be richenough to represent a large variety of realistic adversarial behaviors,and the definition should guarantee that the intu-itive notion of security is captured,for any adversarial be-havior under consideration.This in particular means that security should be maintained when the protocol is used asa component within a larger system.In contrast,cryptographic primitives(or,tasks)were tra-ditionallyfirst defined as stand-alone protocol problems.This allowed for relatively concise and intuitive problem statement,as well as simple analysis of protocols.How-ever,in many cases it turned out that the initial definitionswere insufficient in more complex contexts,and especially when deploying protocols within larger systems or pro-tocol environments.Examples include encryption(wheresemantic security[GM84]was later augmented with sev-eralflavors of security against chosen ciphertext attacks,e.g.[NY90,DDN00,RS91,BDPR98]and adaptive secu-rity[BH92,CFGN96]),commitment(where the original no-tions were augmented with someflavors of non-malleability[DDN00,DIO98,FF00]and equivocability,e.g.,[BCC88, B96]),Zero-Knowledge protocols(where the original no-tions[GMR a89,GO94]were shown not to be closed underparallel and concurrent composition[GK88,F91,DNS98]), Key Exchange[BR93,BCK98,S h99,CK01],ObliviousTransfer[R81,EGL85,GM00],and more.One way to capture the security concerns that arise in some specific protocol environment or in a given applica-tion is to directly represent the given environment or ap-plication within an extended definition of security.(Such an approach was taken,for instance in the cases of concur-rent zero-knowledge and oblivious transfer[DNS98,GM00]as well as non-malleability of protocols[DDN00],where the definitions explicitly model several adversarially coordi-nated instances of the protocol in question.)This approach,however,results in definitions with ever-growing complex-ity,and is inherently limited in scope since it addresses onlyspecific environments and concerns.An alternative approach,taken in this work,is to use def-initions that treat the protocol as stand-alone but guaranteesecure composition.That is,here definitions of security inspect only a single copy of the protocol in vitro.Secu-rity in complex settings(where a protocol instance may runconcurrently with many other protocol instances,on poten-tially related inputs and in an adversarially controlled way)is guaranteed via a general composition theorem.On top of simplifying the process of formulating definitions and ana-lyzing protocols,this approach guarantees security in arbi-trary protocol environments,even unpredictable ones which have not been explicitly stated.In order to make such an approach(and in particular,such a composition theorem)meaningful,wefirst need to have a general framework in which to represent crypto-graphic protocols and the security requirements of crypto-graphic tasks.Indeed,several general definitions of secureprotocols were developed over the years,e.g.[GL90,MR91, B91,BCG93,PW94,C00,HM00,DM00,PSW00,PW00]. Some of these definitions were shown to maintain securityunder natural composition operations.These definitions areobvious candidates for such a general framework.However, the composition operations considered in those works fall short of guaranteeing general secure composition of cryp-tographic protocols,especially in settings where security holds only for computationally bounded adversaries and nu-merous protocols may be running concurrently in an adver-sarially coordinated way.Moreover,many of these works choose to concentrate on the task of secure function evalu-ation which,in spite of its generality,does not capture the requirements of many cryptographic primitives,which are reactive in nature.(Secure function evaluation is the task where a set of parties wish to jointly compute a known func-tion of their secret inputs.)We further elaborate on some of these works and their relation to the present one in Sec-tion1.4.This work proposes a new framework for representingand analyzing cryptographic protocols.Within this frame-work,we propose a general methodology for expressing the security requirements of practically any cryptographic task in a clear,concise and intuitively satisfying way.The salient property of definitions of security generated using this methodology is that they guarantee security even when the given protocol is running in an arbitrary and unknown multi-party environment.In particular,security is preserved under a very general composition operation that captures,as special cases,the standard notions of concurrent composi-tion(with arbitrarily many instances of either the same pro-tocol or other protocols),non-malleability,and more.Wecall this composition operation universal composition,andsay that definitions of security in this framework are univer-sally composable(UC).UC definitions of security tend to be more stringent than other definitions of security.Nonetheless,we show that insettings where parties have access to a set of servers,atmost a minority of which may be corrupted,standard cryp-tographic techniques(e.g.,[BGW88,RB89,CFGN96])canbe used to carry out practically any cryptographic task in auniversally composable way.We also formulate UC defini-tions of a number of well known cryptographic tasks,suchas authenticated and secure communication,key-exchange, public-key encryption,signature,commitment,oblivioustransfer,Zero-Knowledge,secret sharing,and general func-tion evaluation.In some cases,we present initial results regarding the realizability of the definitions.In other casesrealizing the definitions is left open.1.1The proposed frameworkWe briefly sketch the proposed framework and highlight some of its properties.Let usfirst briefly sketch the defini-tional approach of[C00],which is the starting point of thiswork.(The work of[C00]is,in turn,based to a large ex-tent on[B91,MR91,GL90]).This work is geared towardscapturing the task of secure function evaluation in a syn-chronous,ideally authenticated network.The idea is tofirst formulate a model representing the process of protocol exe-cution in real-life.This is called the real-life model.Next, in order to capture the security requirements of a given task,formulate an ideal process for carrying out the task.Thensay that a protocol securely realizes the task at hand if run-ning the protocol in the real-life model amounts to“emulat-ing”the ideal process for that task.The real-life model of computation in[C00]consists of a set of interactive Turing machines(ITMs)representing theparties running the protocol,plus an ITM representing the adversary.The parties and adversary interact on a given setof inputs and each party generates local output.The con-catenation of the local outputs of all parties and adversary is called the global output.The ideal process for evaluat-ing some function is defined similarly,with the impor-tant exception that the parties hand their inputs to an in-corruptible trusted party,which evaluates and hands thecorresponding outputs back to the parties.A protocol se-curely evaluates a function if for any real-life adversary there exists an ideal-process adversary such that,for any input vector,the global output of running with in the real-life model is indistinguishable from the global out-put of the ideal process for with adversary.This def-initional approach is sufficient for capturing“stand-alone”security of protocols.It is also shown to be closed under non-concurrent composition.The present framework preserves the overall structure of that approach.The difference lies in new formulations of the models of computation and the notion of“emulation”. Specifically,we introduce an additional computational en-tity,called the environment machine,to both the real-life model and the the ideal process.The environment machine is an ITM that represents“whatever is external to the cur-rent protocol execution”.This includes other protocol exe-cutions and their adversaries,human users,etc.The envi-ronment provides all the inputs to all parties and reads all their outputs.More importantly,the environment interacts with the adversary freely throughout the computation.That is,between any two atomic operations carried out by the adversary(e.g.,delivery of a message,or corruption of a party)the adversary and the environment may exchange ar-bitrary information.The security requirement is now that executing the protocol in the real-life model should“look the same”as the ideal process from the point of view of the environment.More precisely,a protocol securely realizes a trusted party for some function if for any real-life adver-sary there exists an ideal-process adversary such that no feasible environment can tell with non-negligible proba-bility whether it is interacting with and in the real-life model or with in the ideal process for.In a way,the en-vironment serves as an“interactive distinguisher”between the protocol execution and the ideal process.Note that the same ideal-process adversary is required to work for all environments.Thus,the interaction between and the en-vironment is inherently“black-box”from the point of view of.This requirement is essential for our proof of the com-position theorem.1Another modification to the definition allows capturing not only secure function evaluation but also reactive tasks where new input values become known throughout the com-putation,and may depend on previously generated output values.This is obtained by replacing the“trusted party”in the ideal process for secure function evaluation with a gen-eral algorithmic entity called an ideal functionality.The ideal functionality,which is modeled as another ITM,re-peatedly receives inputs from the parties and provides them with appropriate output values.This way,it is guaranteed that the outputs of the parties in the ideal process have the expected properties with respect to the inputs,even when new inputs are chosen adaptively based on previous outputs.1A very limited variant of the notion of environment appears in[C00]. That variant,aimed at providing non-concurrent composition in the pres-ence of an adaptive adversary,interacts with the parties and the adversary only at few occasions throughout the computation.In particular,the variant there is not known to be sufficient for preserving security under concurrent composition.Yet another difference from[C00]is that here we model networks where the communication is open,unauthenti-cated,and asynchronous(without guaranteed delivery of messages).We also concentrate on the case where the ad-versary is probabilistic polynomial time(PPT).This model-ing seems more suitable for analyzing protocols in realistic settings.Universal Composition.We show that the following prop-erty holds with respect to a protocol that securely realizes some ideal functionality.Let be some arbitrary proto-col(we think of as an“application protocol”)that oper-ates in a model where all parties have ideal access to multi-ple instances of.That is,in this model(which we call the -hybrid model)the parties,the adversary and the environ-ment interact as in the real-life model,and in addition theparties can privately communicate with as many instances of as they wish.It is stressed that the different instances of are running at the same time without any global co-ordination.They are distinguished via special identifiers, generated by the calling protocol.Now,construct the composed protocol from by re-placing each call to a new instance of with an invocation of a fresh copy of.Similarly,a message sent to an ex-isting instance of is replaced with an input value given to the corresponding invocation of,and any output of an invocation of is treated as a message received from the corresponding instance of.(Note that a run of protocol may have an unbounded number of copies of which are running concurrently on related inputs.)The universal composition theorem states that running protocol in the plain real-life model has essentially the same effect as running protocol in the-hybrid model. More precisely,it guarantees that for any real-life adversary there exists an adversary in the-hybrid model such that no environment machine can tell with non-negligible probability whether it is interacting with and parties run-ning in the plain real-life model,or with and parties running in the-hybrid model.In particular,if securely realizes some ideal functionality in the-hybrid model then securely realizes from scratch.Notice that,while other composition theorems address only the case where a single protocol instance is composed with another protocol,here the hybrid model allows for an unbounded number of instances of the composed protocol to run concurrently.It may appear that this more complex formulation of the composition operation is not necessary, since it can be obtained by iteratively composing all in-stances of the protocol,one at a time,with an outside pro-tocol.However,in our computational setting the composi-tion theorem can be safely applied only a constant number of times,otherwise the complexity of the adversary in the hybrid model may become super-polynomial.Conse-quently,this weaker formulation of the composition theo-rem only guarantees secure composition of a constant num-ber of protocol instances running concurrently. Interpreting the composition theorem.Traditionally,com-position theorems are treated as tools for modular design and analysis of complex protocols.(For instance,this is the main motivation in[MR91,C00,DM00,PW00].)That is,given a complex task,first partition the task to several, simpler sub-tasks.Then,design protocols for securely re-alizing the sub-tasks,and in addition design a protocol for realizing the given task in a model where ideal evaluation of the sub-tasks is possible.Finally,use the composition theo-rem to argue that the protocol composed from the already-designed sub-protocols securely realizes the given task.(An example of a context where this interpretation is put to use is the proof of security in[CKOR00].)Note that for this application it suffices to use composition theorems where it is known in advance which protocol instances are running together and how the protocol executions are going to be interleaved.In contrast,here we use the composition theorem as a tool for gaining confidence in the sufficiency of a definition of security in some protocol environment.Indeed,protocols that satisfy a universally composable definition are guar-anteed to maintain their security within any protocol envi-ronment—even environments that are not known a-priori, and even environments where the participants in a proto-col execution are unaware of other instances of the protocol (or other protocols altogether)that may be running concur-rently in the system in an adversarially coordinated manner. This is a strong guarantee.1.2General satisfiability of the definitionsDefinitions of security in the proposed framework tend to be more stringent than other definitions.Moreover,the existing proofs of security of many known protocols do not work in the present framework.Examples include most known Zero-Knowledge protocols,the protocol generator of[GMW87,G98]and more.This is mainly due to the fact that a common proof-technique,namely black-box simula-tion with rewinding of the adversary,does not work in the present framework.(Indeed,here the ideal-process adver-sary has to interact with the environment machine which cannot be“rewound”.)Nonetheless,it can be seen that some known protocols for the general task of secure function evaluation are,in fact, universally composable.For instance,the[BGW88]proto-col(say,with the simplification of[GRR98]),together with encrypting each message using non-committing encryption [CFGN96],is universally composable as long as less than a third of the parties are ing[RB89],any cor-rupted minority is tolerable.The asynchronous setting can be handled using the techniques of[BCG93,BKR94].We use this fact to demonstrate that practically any ideal functionality—even reactive ones and even“two-party functionalities”(i.e.,functionalities where only two par-ties have inputs and outputs)—can be securely realized in the proposed framework.Specifically,our solution assumes that the network contains a set of parties(called“servers”) such that only a minority of these parties can ever be cor-rupted.The servers have no local inputs or outputs;they only assist other parties in realizing the given functionality. All parties share their inputs among the servers,who run the appropriate multiparty function evaluation protocol and send the output values to the appropriate parties.Iterated evaluations(which may involve implementing ideal func-tionalities that maintain internal state between invocations) are handled in standard ways.1.3UC definitions of some specific tasksWe formulate and study universally composable defini-tions of a number of standard cryptographic tasks.In fact, much of the definitional work is already done by the gen-eral framework described above.All that is left to do on the definitional side is to formulate ideal functionalities that capture the security requirements of these tasks.Wefirst address the task of message authentication:the corresponding functionality,AUTH,is invoked with a re-quest by some party,,to transmit a message to another party,.Then AUTH ideally sends to and the adversary,and halts.(Forwarding to the adversarycaptures the fact that secrecy is not provided.)This way,the standard computational model where the communication is ideally authenticated is rephrased as the AUTH-hybrid model.This notion is the natural universally composable extension of the authenticators of[CHH00,BCK98].In particular,the two authenticators presented in[BCK98]se-curely realize AUTH given an authenticated initialization phase.The task of providing secure(i.e.,authenticated and se-cret)transmission of individual messages is addressed next. It is seen that standard semantically secure encryption(or alternatively non-committing encryption for adaptive adver-saries)are sufficient in order to realize the secure communi-cation functionality in the AUTH-hybrid model,if any mes-sage is encrypted using a different public/private key pair.Next we formulate ideal functionalities that capture the tasks of secure sessions and key exchange.Secure sessions is an extension of secure transmission of individual mes-sages to the case where a sequence of messages between a pair of parties are secured together.The main advantage of this functionality over the previous ones is that it allows for more efficient realizations,via key-exchange combined with symmetric cryptography using the generated keys.The key exchange functionality essentially provides parties with“ideally chosen keys.”In particular,protocols that securely realize KE are guaranteed to satisfy the security notion of [CK01].Furthermore,most of the Key-Exchange protocols presented in[CK01]securely realize KE.Next the tasks of public-key encryption and digital sig-natures are addressed.Securely realizing the signature ideal functionality turns out to be essentially equivalent to exis-tential security against chosen message attacks as in Gold-wasser Micali and Rivest[GMR i88].In the case of public-key encryption(where many messages may be encrypted by different parties using the same key),securely realizing the proposed functionality turns out to be closely related(but incomparable)to security against adaptive chosen cipher-text attacks[DDN00,RS91,BDPR98].We then proceed to formulate UC definitions of“clas-sic”two-party primitives such as coin-tossing,commitment, zero-knowledge,and oblivious-transfer.These primitives are treated as two-party protocols in a multi-party setting. As usual,the composition theorem guarantees that secu-rity is maintained under concurrent composition,either with other copies of the same protocol or with other protocols, and within any application protocol.In particular,non-malleability with respect to an arbitrary set of protocols is guaranteed.Unfortunately,these functionalities cannot be securely realized by two-party protocols in the bare model of computation(or even in the AUTH-hybrid model).This result is shown in[CF01]for the cases of commitment and ing similar techniques,we extend this re-sult to the cases of oblivious transfer and zero-knowledge. Nonetheless,as demonstrated in[CF01],the commitment and zero-knowledge functionalities can be securely real-ized by two-party protocols in a hybrid model with ideal access to the coin-tossing functionality.(It is interesting to note that hybrid model with ideal access to the coin-tossing functionality turns out to essentially identical to the popular common random string model of[BFM89].)Finally,we formulate ideal functionalities that capture traditional multi-party tasks such as Verifiable Secret Shar-ing and Secure Function Evaluation in synchronous net-works.In particular,we obtain thefirst definition of pro-tocols for secure function evaluation that is closed under concurrent composition in a setting where all the communi-cation is public.(Two-party Secure Function Evaluation is obtained as a special case.)1.4Related workNumerous definitional works on security of protocols have been carried out over the years.The works of [GL90,MR91,B91,C95]are surveyed in[C00].Here we very briefly review some definitional efforts that are closely related to the present work.Pfitzmann et.al.[PW94,PSW00,PSW00a,PW00,PW01]were thefirst to formally model the security require-ments of general reactive systems.In a series of works that contain many interesting ideas,they model security of re-active systems in an extendedfinite-state machine model of computation that is essentially equivalent to the I/O au-tomata model of[L96].In particular,they introduce the notion of an honest user that‘sees’the functionality(i.e., the inputs and outputs)of a given system,and say that one system“simulates”another if the honest user cannot tell the difference between the two systems.However,they stop short of defining security of protocols for realizing a given task.They also state a composition theorem with respect to their framework;their composition theorem is weaker than the one here in that it deals only with the case where a single protocol execution is carried out concurrently with the call-ing protocol.(In contrast,much of the complexity in pro-tocol composition appears only when the number of com-posed copies is not a-priori bounded.)These works contain also descriptions of ideal systems for public-key encryption and certified mail.Canetti[C00]presents a definition of secure function evaluation in a variety of computational settings,including the case where the communication is public and security is guaranteed only against a computationally bounded adver-sary.Some of the definitions there also use an“environment machine”.however,there both the purpose of the environ-ment and its pattern of interaction with the other participants are different than here.The definitions of[C00]are shown to be closed under a composition theorem similar to the one here,but only in the non-concurrent case where no more than a single protocol execution is running at any point in time.Dodis and Micali[DM00]build on the definition of Mi-cali and Rogaway[MR91]for information-theoretically se-cure function evaluation in synchronous networks,where ideally private communication channels are assumed.In that setting,they prove that their definition of security is closed under a general concurrent composition operation similar to the one in this work.They also formulate an ad-ditional and interesting composition operation(called syn-chronous composition)that provides stronger security guar-antees,and show that their definition is closed under that composition operation in cases where the scheduling of the various invocations of the protocols can be controlled. However,their definition applies only to settings where the communication is ideally private.It is not clear how to ex-tend this definitional approach to realistic settings where the adversary can eavesdrop to the communication between honest parties.The pioneering work of Dolev,Dwork and Naor [DDN00]points out some important security concerns that arise when running cryptographic protocols within a larger system.In particular,they define and construct encryp-tion schemes secure against chosen ciphertext attacks,non-malleable commitment schemes,and more.That work pro-vides motivation for the present one.In particular,making sure that the concerns pointed out in[DDN00]are answered plays a central role in the present framework. Connections with the formal-methods approach to an-alyzing security.A large body of work on analyzing se-curity of protocols using techniques for formal verification of computer programs has been carried out over the years (a very partial list of works includes[DY83,BAN90,M94, KMM94,L96,AG97]).The approach and framework pre-sented here may serve as a“bridge”for connecting that approach with the complexity-based approach pursued inthe cryptographic community,with advantages to both ap-proaches.See more details in our Technical Report[C01]. Organization.Section2defines the notion of securely re-alizing an ideal functionality.Section3presents the compo-sition theorem and very briefly outlines the proof.Section 4states the general satisfiability theorem.Throughout,the presentation is kept high-level and informal for brevity and clarity.Details are available in our Technical Report[C01]. UC definitions of the tasks mentioned in Section1.3also appear there.2The basic frameworkAs sketched in Section1.1,protocols that securely carry out a given task(or,protocol problem)are defined in three steps,as follows.First,the process of executing a protocol in the presence of an adversary and in a given computational environment is formalized.Next,an“ideal process”for car-rying out the task at hand is formalized.In the ideal process the parties do not communicate with each other.Instead they have access to an“ideal functionality”,which is essen-tially an incorruptible“trusted party”that is programmed to capture the desired functionality of the task at hand.A protocol is said to securely realize an ideal functionality if the process of running the protocol amounts to“emulating”the ideal process for that ideal functionality.In the rest of this subsection we overview the model for protocol execu-tion(called the real-life model),the ideal process,and the notion of protocol emulation.We concentrate mainly on the following standard model, aimed at representing current realistic communication net-works(such as the Internet).The network is asynchronous without guaranteed delivery of messages.The communica-tion is public and unauthenticated.That is,the adversary may delete,modify,and generate messages at wish.Par-ties may be broken into(i.e.,become corrupted)throughout the computation,and once corrupted their behavior is arbi-trary(or,Byzantine).Finally,all the involved entities are restricted to probabilistic polynomial time(or,“feasible”)computation.Most other standard models of computation(e.g.,authenticated communication,synchronous message delivery,the common reference string model,or computa-tionally unbounded adversaries)can be captured via appro-priate modifications to the basic model.See more details within.Protocol syntax.Following[GMR a89,G01],a protocol is represented as a system of interactive Turing machines(ITMs),where each ITM represents the program to be runwithin a different party.Specifically,the input and output tapes model inputs and outputs that are received from andgiven to other programs running on the same machine,andthe communication tapes model messages sent to and re-ceived from the network.Adversarial entities are also mod-eled as ITMs.We concentrate on a model where the ad-versaries have an arbitrary additional input,or an“advice”.From a complexity-theoretic point of view,this essentiallyimplies that adversaries are non-uniform ITMs.Protocol execution in the real-life model.We sketch theprocess of executing a given protocol(run by parties)with some adversary and an environment ma-chine with input.All parties have a security parameter and are polynomial in.The execution consists of a sequence of activations,where in each activation a singleparticipant(either,,or some)is activated.The en-vironment is activatedfirst.In each activation it may read the contents of the output tapes of all parties,and may write information on the input tape of either one of the parties or of the adversary.Once the activation of the environment is complete(i,e,once the environment enters a special waiting state),the entity whose input tape was written on is acti-vated next.Once the adversary is activated,it may read its own tapesand in addition the contents of the outgoing communication tapes of all parties.It may either deliver a message to some party by writing this message on the party’s incoming com-munication tape2,or corrupt a party.Upon corrupting a party,the adversary gains access to all the tapes of that party and controls all the party’s future actions.Finally,the ad-versary may write arbitrary information on its output tape. If the adversary delivered a message to some uncorrupted party in an activation then this party is activated once the activation of the adversary is complete.Otherwise the envi-ronment is activated next.Once a party is activated(either due to an input given by the environment or due to a message delivered by the adversary),it follows its code and possibly writes local out-puts on its output tape and outgoing messages on its outgo-ing communication tape.Once the activation of the party is complete the environment is activated.The protocol exe-2In the bare model we do not make any restrictions on the delivered messages.In particular,they need not be related to any of the messages generated by the parties.。

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