Checking Access to Protected Members in the Java Virtual Machine
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Question 143 Secure Authentication for RESTful APIsAn analytics company uses Amazon VPC to run its multi-tier services. The company wants to use RESTful APIs to offer a web analytics service to millions of users. Users must be verified by using an authentication service to access the APIs. which solution will meet these requirements with the MOST operational efficiency? Options• A. Configure an Amazon Cognito user pool for user authentication. Implement Amazon API Gateway REST APIs with a Cognito authorizer.• B. Configure an Amazon Cognito identity pool for user authentication. Implement Amazon API Gateway HTTP APIswith a Cognito authorizer.• C. Configure an AWS Lambda function to handle user authentication. Implement Amazon API Gateway REST APIs with a Lambda authorizer.• D. Configure an IAM user to handle user authentication.Implement Amazon API Gateway HTTP APIs with an IAMauthorizer.Key ServiceCognitoKey PointDesign Secure ArchitecturesNote• A. ✅ Configure an Amazon Cognito user pool for user authentication. Implement Amazon API Gateway REST APIs with a Cognito authorizer. This solution provides secure andefficient user management and integrates well with RESTAPIs.• B. ❌ Configure an Amazon Cognito identity pool for user authentication. Implement Amazon API Gateway HTTP APIswith a Cognito authorizer. Identity pools are better suited forunauthenticated access, while user pools handle authenticated users more effectively.• C. ❌ Configure an AWS Lambda function to handle user authentication. Implement Amazon API Gateway REST APIswith a Lambda authorizer. While this is possible, it introducesadditional complexity compared to using Cognito for usermanagement.• D. ❌ Configure an IAM user to handle user authentication.Implement Amazon API Gateway HTTP APIs with an IAMauthorizer. IAM is not designed for end-user authenticationand would be less efficient for managing millions of users. Question 144 Serverless Authentication and AuthorizationA company wants to restrict access to the content of one of its main web applications and to protect the content by using authorization techniques available on AWS. The company wants to implement a serverless architecture and an authentication solution for fewer than 100 users. he solution needs to integrate with the main web application and serve web content globally. The solution must also scale as the company’s user base grows while providing the lowest login latency possible. which solution will meet these requirements MOST cost-effectively?OptionsA. Use Amazon Cognito for authentication. Use Lambda@Edge forauthorization. Use Amazon CloudFront to serve the webapplication globally.B. Use AWS Directory Service for Microsoft Active Directory forauthentication. Use AWS Lambda for authorization. Use anApplication Load Balancer to serve the web application globally.C. Use Amazon Cognito for authentication. Use AWS Lambda forauthorization. Use Amazon S3 Transfer Acceleration to serve the web application globally.D. Use AWS Directory Service for Microsoft Active Directory for**************************************************** Elastic Beanstalk to serve the web application globally.Key ServiceCognitoKey PointDesign Secure ArchitecturesNote• A. ✅ Use Amazon Cognito for authentication and************************************************** the web application globally providing low latency andscalability. This solution is cost-effective for fewer than 100users and can scale as the user base grows.• B. ❌ Using AWS Directory Service for Microsoft Active Directory for authentication introduces higher costs andcomplexity compared to Amazon Cognito. AWS Lambda forauthorization and an Application Load Balancer to serve theweb application globally do not provide the global servingcapabilities and cost-effectiveness of Amazon CloudFront. • C. ❌ While Amazon Cognito for authentication and AWS Lambda for authorization are suitable, Amazon S3 TransferAcceleration is not designed to serve web applicationsglobally. It is better suited for file transfers and does notprovide the low latency and scalability needed for web content. • D. ❌ Using AWS Directory Service for Microsoft Active Directory for authentication adds unnecessary complexity and higher costs compared to Amazon Cognito. Lambda@Edge for authorization and AWS Elastic Beanstalk to serve the webapplication globally do not offer the global distribution and low latency benefits of Amazon CloudFront.Question 145 Serverless Authentication and AuthorizationA company wants to restrict access to the content of its web application. The company needs to protect the content by using authorization techniques that are available on AWS. The company also wants to implement a serverless architecture for authorization and authentication that as low login latency. he solution must integrate with the web application and serve web content globally. The application currently has a small user base, but the company expects the application’s user base to increase. which solution will meet these requirements?Options•A. Configure Amazon Cognito for authentication. Implement***************************************************** to serve the web application globally.•B. Configure AWS Directory Service for Microsoft Active Directory for authentication. Implement AWS Lambda for authorization. Use an Application Load Balancer to serve the web application globally.•C. Configure Amazon Cognito for authentication. Implement AWS Lambda for authorization. Use Amazon S3 Transfer Acceleration to serve the web application globally.•D. Configure AWS Directory Service for Microsoft Active Directory for authentication. Implement Lambda@Edge for authorization. Use AWS Elastic Beanstalk to serve the web application globally.Key ServiceCognitoKey PointDesign Secure ArchitecturesNote• A. ✅ Configure Amazon Cognito for authentication. Implement *******************************************CloudFront to serve the web application globally. This solution meets the requirement of a serverless architecture with lowlogin latency and global content delivery.• B. ❌ Configure AWS Directory Service for Microsoft Active Directory for authentication. Implement AWS Lambda forauthorization. Use an Application Load Balancer to serve theweb application globally. This option uses Active Directorywhich is not a serverless solution and an Application LoadBalancer does not serve content globally.• C. ❌ Configure Amazon Cognito for authentication. Implement AWS Lambda for authorization. Use Amazon S3 TransferAcceleration to serve the web application globally. While thisoption uses Cognito and Lambda, S3 Transfer Acceleration is designed for object transfers rather than serving webapplications globally.• D. ❌ Configure AWS Directory Service for Microsoft Active Directory for authentication. Implement Lambda@Edge forauthorization. Use AWS Elastic Beanstalk to serve the webapplication globally. This option uses Active Directory which is not a serverless solution and Elastic Beanstalk is not designed for global content delivery.Question 146 Authenticating Users with Amazon Cognito for S3 AccessA company is hosting a web application from an Amazon S3 bucket. The application uses Amazon Cognito as an identity provider to authenticate users and return a JSON Web Token (JWT) that provides access to protected resources that are storedin another S3 bucket. upon deployment of the application, users report errors and are unable to access the protected content. A solutions architect must resolve this issue by providing proper permissions so that users can access the protected content. which solution meets these requirements?”OptionsA. Update the Amazon Cognito identity pool to assume the properIAM role for access to the protected content.B.Update the S3 ACL to allow the application to access theprotected content.C. Redeploy the application to Amazon S3 to prevent eventuallyconsistent reads in the S3 bucket from affecting the ability of users to access the protected content.D. Update the Amazon Cognito pool to use custom attributemappings within the identity pool and grant users the properpermissions to access the protected content.Key ServiceCognitoKey PointDesign Secure ArchitecturesNote• A. ✅ Update the Amazon Cognito identity pool to assume the proper IAM role for access to the protected content. Thisapproach ensures that the JWT issued by Amazon Cognitohas the necessary permissions to access the protected S3bucket.• B. ❌ Update the S3 ACL to allow the application to access the protected content. This does not address the issue becausethe problem is related to user authentication and authorization, not the application’s direct access to the S3 bucket.• C. ❌ Redeploy the application to Amazon S3 to prevent eventually consistent reads in the S3 bucket from affecting the ability of users to access the protected content. This solution does not solve the authentication issue and is unrelated to the problem at hand.• D. ❌ Update the Amazon Cognito pool to use custom attribute mappings within the identity pool and grant users the proper permissions to access the protected content. While this might help customize the attributes, it does not directly address the need to configure an IAM role for accessing the S3 bucket.。
wifi网络安全接入英文WiFi Network Security: Ensuring Safe Access to the InternetIn today's digital age, accessing the internet through WiFi has become a necessity for almost everyone. Whether it's in our homes, offices, or public places, WiFi allows us to connect our devices and access the world wide web seamlessly. However, as convenient as WiFi is, it also poses certain risks to our security and privacy. Therefore, it is essential to take necessary precautions to ensure a safe and secure WiFi network access.One of the primary concerns related to WiFi network security is unauthorized access. Hackers and malicious individuals often attempt to gain access to WiFi networks to snoop on users' activities, steal personal information, or launch cyber attacks. To prevent unauthorized access, it is crucial to set a strong, unique password for the WiFi network. Avoid using easily guessable passwords such as "password" or "123456" and choose a combination of letters, numbers, and special characters.Another important aspect of WiFi network security is encryption. Encryption ensures that the data sent and received over the WiFi network is scrambled and can only be deciphered by authorized devices. Most modern routers support various encryption protocols such as WPA2 (WiFi Protected Access 2) or WPA3, which provide a high level of security. It is recommended to enable encryption on your WiFi network and regularly update the encryption protocol as newer, more secure standards become available.Updating the firmware of your WiFi router is also crucial in maintaining network security. Manufacturers often release firmware updates to fix vulnerabilities and enhance security features. Regularly checking for firmware updates and installing them promptly ensures that your WiFi network is protected against the latest threats.In addition to securing the WiFi network itself, it is also essential to practice safe browsing habits. Be cautious when accessing sensitive information such as banking websites or entering personal details on unsecured websites. Look for the "https:// " in the website's URL, indicating that the connection is encrypted and secure. Using a reliable antivirus software on your devices can further enhance your protection against malware and other online threats.Lastly, being aware of the potential risks and staying informed about the latest security practices is vital in maintaining WiFi network security. Following reputable sources for cybersecurity news and regularly educating yourself about emerging threats can help you stay one step ahead of potential attackers.In conclusion, ensuring the security of your WiFi network is crucial for protecting your privacy and preventing unauthorized access. By setting strong passwords, enabling encryption, updating firmware, practicing safe browsing habits, and staying informed, you can significantly reduce the risks associated with WiFi network access.。
计算机专业外文翻译毕业设计英文翻译作者:XXXThe Delphi Programming LanguageThe Delphi development environment is based on an object-oriented extension of thePascal programming language known as Object Pascal. Most modern programming languagessupport object-oriented programming (OOP). OOP languages are based on three fundamentalconcepts: encapsulation (usually implemented with classes), inheritance, and polymorphism(or late binding).1Classes and ObjectsDelphi is based on OOP concepts, and in particular on the definition of new class types.The use of OOP is partially enforced by the visual development environment, because forevery new form defined at design time, Delphi automatically defines a new class. In addition,every component visually placed on a form is an object of a class type available in or added tothe system library.As in most other modern OOP languages (including Java and C#), in Delphi a class-typevariable doesn't provide the storage for the object, but is only a pointer or reference to theobject in memory. Before you use the object, you must allocate memory for it by creating anew instance or by assigning an existing instance to the variable: varObj1, Obj2: TMyClass;begin // assign a newly created objectObj1 := TMyClass.Create; // assign to an existing objectObj2 := ExistingObject;The call to Create invokes a default constructor available for every class, unless the classredefines it (as described later). To declare a new class data type in Delphi, with some localdata fields and some methods, use the following syntax:typeTDate = classMonth, Day, Year: Integer;procedure SetValue (m, d, y: Integer);function LeapYear: Boolean;第 1 页共 13 页毕业设计英文翻译作者:XXXend;2Creating Components DynamicallyTo emphasize the fact that Delphi components aren't much different from other objects(and also to demonstrate the use of the Self keyword), I've written the CreateComps example.This program has a form with no components and a handler for its OnMouseDown event,which I've chosen because it receives as a parameter the position of the mouse click (unlikethe OnClick event). I need this information to create a button component in that position. Hereis the method's code:procedure TForm1.FormMouseDown (Sender: TObject;Button: TMouseButton; Shift: TShiftState; X, Y: Integer);Var Btn: TButton;beginBtn := TButton.Create (Self);Btn.Parent := Self;Btn.Left := X;Btn.Top := Y;Btn.Width := Btn.Width + 50;Btn.Caption := Format ('Button at %d, %d', [X, Y]);end;The effect of this code is to create buttons at mouse-click positions, as you can see in thefollowing figure. In the code, notice in particular the use of the Self keyword as both theparameter of the Create method (to specify the component's owner) and the value of theParent property.(The output of theexample,which creates Button components at run time第 2 页共 13 页毕业设计英文翻译作者:XXX3EncapsulationThe concept of encapsulation is often indicated by the idea of a "black box." You don'tknow about the internals: You only know how to interface with the black box or use itregardless of its internal structure. The "how to use" portion,called the class interface, allowsother parts of a program to access and use the objects of that class. However, when you usethe objects, most of their code is hidden. You seldom know what internal data the object has,and you usually have no way to access the data directly. Of course, you are supposed to usemethods to access the data, which is shielded from unauthorized access. This is theobject-oriented approach to a classical programming concept known as information hiding.However, in Delphi there is the extra level of hiding, through properties,4PrivateProtectedand PublicFor class-based encapsulation, the Delphi language has three access specifiers: private,protected, and public. A fourth, published, controls run-time type information (RTTI) anddesign-time information, but it gives the same programmatic accessibility as public. Here arethe three classic access specifiers:, The private directive denotes fields and methods of a class thatare not accessible outsidethe unit that declares the class., The protected directive is used to indicate methods and fields with limited visibility. Onlythe current class and its inherited classes can access protected elements. More precisely,only the class, subclasses, and any code in the same unit as the class can access protectedmembers。
狗的生存法则狗是人类最忠诚的朋友,它们陪伴我们度过了许多美好的时光,也给我们带来了无尽的欢乐。
然而,作为一个狗,它们也有自己的生存法则。
在这篇文章中,我们将探讨狗的生存法则,从而更好地理解它们。
首先,狗需要食物和水来维持生命。
这是每个生命体都必须面对的问题。
狗会通过嗅觉寻找食物的来源,它们的嗅觉非常敏锐,能够闻到很远的距离。
当狗找到食物时,会用自己的爪子挖洞,在地里埋藏食物,以备将来需要。
此外,狗还需要定期喝水来保持身体的水分平衡。
所以给狗提供充足的食物和水是很重要的。
其次,狗需要寻找一个安全的避难所。
在野外,狗会在洞穴中寻找安全的避难所。
这样能够保护它们免受天气的影响和其他野生动物的攻击。
而在人类的家中,狗则通常选择舒适的地方作为自己的休息场所。
狗通常会在家里挑选一个角落、床或者沙发来休息,因为这些地方能给它们一种安心的感觉。
狗的生存法则还包括狗与其他狗的相处。
狗是群居动物,它们会与其他狗建立联系和互动。
在野外,狗会以一种特殊的方式进行沟通,比如用尾巴摇动、舔舐等。
这样有助于狗建立彼此的信任感和友谊。
在人类的世界,狗通常是家庭中的宠物,它们会与主人建立深厚的情感联系。
狗会用眼神、摇尾巴、舔舐等方式与主人进行沟通,这是它们表达爱和感激的方式。
狗的生存法则还包括保护自己和主人。
狗是天生的猎犬,它们有天赋的警惕性和保护本能。
狗会保护自己和主人免受伤害,它们会发出警告的声音或者保护姿势来威慑潜在的威胁。
训练有素的守卫犬甚至可以保护整个家庭的安全。
狗的生存法则还包括与环境和其他动物的和谐相处。
狗是社会性动物,它们生活在一个与其他动物和人类共存的世界中。
狗喜欢与其他动物玩耍、奔跑,并且在这个过程中建立友谊。
在家庭中,跟狗的互动能够培养其友善和温顺的品质。
最后,狗的生存法则还包括狗与人类的互动。
狗是人类最忠诚的伴侣之一,它们能够以无条件的爱和忠诚陪伴我们。
狗可以成为人类的朋友、伴侣和家庭的一员。
在人类的世界中,狗依赖人类提供食物、水和安全的环境。
专利名称:Secure protection method for access toprotected resources in a processor发明人:Eric Balard,Alain Chateau申请号:US10618861申请日:20030714公开号:US20040025027A1公开日:20040205专利内容由知识产权出版社提供专利附图:摘要:A computing platform () protects system firmware () using a manufacturer certificate (). The manufacturer certificate binds the system firmware () to the particular computing platform (). A secure run-time platform data checker () and a secure run-timechecker () check the system firmware during operation of the computing platform () to ensure that the system firmware () or information in the manufacturer certificate () has not been altered. Application software files () and data files () are bound to the particular computing device () by a platform certificate (). Access to certain configurations of the device, such as access to a test configuration is initiated by entering a password. The password is encrypted through a hashing process to reduce its size and compared to an access code that has been hashed and stored on the computing platform.申请人:BALARD ERIC,CHATEAU ALAIN更多信息请下载全文后查看。
上网时如何保护个人隐私英语作文With the rapid development of the internet, it has become increasingly important to protect personal privacy when going online. In this digital age, our personal information is constantly being collected, stored, and shared by various online platforms and entities. From social media sites to online shopping platforms, our digital footprints are constantly being tracked and analyzed. Therefore, it is crucial for individuals to take proactive steps to safeguard their personal privacy while browsing the web.One of the first things that individuals can do to protect their privacy online is to carefully read the privacy policies of websites and applications that they use. These policies outline how user data is collected, stored, and used by the platform. By understanding the privacy policies of the websites and applications that they use, individuals can make informed decisions about the type of information that they are comfortable sharing online.Another important step in protecting personal privacy online is to use strong and unique passwords for each online account. Passwords are the first line of defense against hackers and cybercriminals who may try to gain unauthorized access tosensitive information. By creating complex passwords that include a mix of letters, numbers, and special characters, individuals can significantly reduce the risk of their accounts being compromised.Furthermore, individuals should be cautious about the type of personal information that they share online. Social media platforms, in particular, are often used to share personal details such as birthdays, addresses, and phone numbers. While these details may seem harmless on the surface, they can be used by malicious actors to steal identities or commit fraud. Therefore, it is important to think twice before sharing personal information online and to only share information with trusted individuals and platforms.In addition to being mindful of the information that they share online, individuals should also be cautious about the websites that they visit and the links that they click on. Phishing attacks, in which individuals are tricked into providing sensitive information such as passwords or credit card numbers, are a common tactic used by cybercriminals. By only visiting reputable websites and by double-checking the legitimacy of links before clicking on them, individuals can reduce the risk of falling victim to phishing attacks.Moreover, individuals should use privacy settings to control the amount of information that is shared online. Most social media platforms and websites offer privacy settings that allow users to customize who can see their posts and personal information. By adjusting these settings to limit the visibility of personal information to only friends or trusted individuals, individuals can reduce the risk of their information being accessed by unauthorized parties.Lastly, individuals should regularly update their devices and software to ensure that they are protected against the latest security threats. Software updates often contain patches for known vulnerabilities that could be exploited by hackers. By keeping their devices and software up to date, individuals can ensure that they have the latest security measures in place to protect their privacy online.In conclusion, protecting personal privacy online is a critical aspect of navigating the digital landscape. By understanding the privacy policies of websites, using strong passwords, being cautious about the information that is shared online, and utilizing privacy settings, individuals can take proactive steps to safeguard their personal information while browsing the web. Additionally, by being mindful of the websites that they visit andregularly updating their devices and software, individuals can further enhance their online security. By following these tips and best practices, individuals can enjoy a safer and more secure online experience.。
使用社交媒体保护个人信息英语作文全文共3篇示例,供读者参考篇1Social Media and Protecting Your Personal InfoLet's be real, social media is a huge part of our lives as students these days. We're constantly checking Instagram, scrolling through TikTok, or posting updates on Snapchat and Facebook. While social media allows us to stay connected with friends, share our lives, and be entertained, it also opens us up to some serious privacy risks if we're not careful about what we share online.Think about all the personal information you put out there on social media - your name, photos, location data, birthdate, contact information, opinions, and interests. All of that data creates a pretty detailed profile about you that can potentially be accessed by strangers, hackers, advertisers, employers, colleges, and more. And once something is out there on the internet, it's really hard to take it back fully.I've seen firsthand how overlooking privacy settings and oversharing can lead to issues. My friend Jake had his Instagramaccount hacked last year after using a weak password. The hacker got access to his private messages, photos, and personal details. Another friend, Sarah, missed out on a dream internship because the company found some embarrassing posts from when she was younger that gave them the wrong impression about her character.So while social media is awesome for self-expression and staying connected, we really need to be smart about protecting our personal info and online reputation. Here are some of the key privacy tips I try to follow when using social media:Review and tighten privacy settingsThe first step is adjusting the privacy settings for each social media platform to limit what personal information is publicly visible. I have all my accounts set to private so only my friends and followers I approve can see my posts and personal details like location data and birthdate. I also avoid listing my phone number, email, or home address anywhere public.Be cautious about sharing personal detailsI'm really careful about what personal information I choose to share, even with my friends circle. I try not to post about my specific schedule or whereabouts. I also avoid sharing privatefamily details, passwords or financial info that could be misused. When in doubt, I don't post it.Think before postingBefore posting anything on social media, I pause and consider whether it's something I'd want certain people seeing like parents, teachers, colleges, or future employers. We've all seen how people get in trouble for posting offensive, illegal, or just plain dumb stuff online without thinking it through. I keep my posts positive and avoid anything too raunchy, controversial or that could be misconstrued.Use strong passwords and two-factor authenticationUsing a weak or reused password is just asking for your account to get hacked. I make sure to use strong, unique passwords for each of my social accounts and enable two-factor authentication for an added layer of security. Remembering all those passwords can be tough, so I use a password manager to keep track securely.Avoid geotagging postsGeotagging, which attaches your location data to photos and posts, is a feature I always turn off. It's basically like broadcasting where you are to the world, including potentialcreeps and criminals looking for targets. I'd rather my location not be public knowledge.Be cautious about connecting with strangersWhile social media is about connecting, I'm very selective about who I connect with, especially on Facebook and Instagram.I pretty much only accept requests from real-life friends, family, and acquaintances. Connecting with total randos just opens you up to potential scams, harassment, or account hacking.Manage tagging settingsI've set my tagging settings so that I have to manually approve any photos or posts I'm tagged in before they go visible on my profile. That helps me filter out anything embarrassing or inappropriate my friends might tag me in.Use temporary sharing modesApps like Snapchat and Instagram stories offer temporary sharing modes where posts disappear after 24 hours. I tend to use those more than permanent posts, since the content has a shorter lifespan and more limited visibility.Be wary of online quizzes and appsThose "What Disney character are you?" type quizzes and apps may seem harmless, but they often require access to personal data from your social accounts for marketing purposes.I avoid them to limit how much data I give away about my interests and online behavior.Log out and update software regularlyI make sure to log all the way out of social media apps when I'm done using them, rather than just closing them. That way, my accounts can't be easily accessed from my device. I also permit automatic software updates, which helps patch any security vulnerabilities.At the end of the day, we all need to be proactive about managing our social media privacy and personal data online. Sure, being cautious requires some extra effort, but it's worth it to avoid scams, damaged reputations, embarrassment, and violations of your personal privacy. As fun as social media can be, we have to remember that anything we put out in the digital world creates a permanent record that could potentially follow us around.So let's all agree to be a bit more careful and thoughtful about safeguarding personal details and protecting ourselves on social media. Our future selves will thank us when we don't haveregrettable posts resurfacing years down the line. Stay skeptical, stay safe, and keep being smart about your privacy!篇2Social Media and Protecting Your Personal InfoBy A Concerned StudentWe live in an era of oversharing. From constant status updates to documenting every aspect of our lives with photos and videos, social media has become a huge part of how we communicate and connect with others. While this increased connectivity can be great, it also comes with major risks in terms of protecting our personal information and data privacy.As students, we need to be especially cautious. Potential employers, college admissions officers, and even future romantic partners often check social media profiles before making decisions about individuals. One embarrassing photo, risque post, or inappropriate comment could derail academic and career aspirations before they even start. The personal information we share online has never been more permanent and far-reaching.Beyond just reputation management, there are major privacy and security concerns with oversharing on socialplatforms. Identity thieves actively scour sites like Facebook, Twitter, and Instagram looking for details like birthdays, home addresses, phone numbers, travel plans, and other personal data that can be used for nefarious purposes. The more we put out there, the more vulnerable we become to stalkers, hackers, and online predators.So how can we enjoy the benefits of social media while still protecting our privacy and personal information? Here are some key tips all students should follow:Use Maximum Privacy SettingsThe first line of defense is adjusting the privacy settings on each of your social accounts to only share information with those you actually know and trust. Make your profiles private rather than public. Only accept friend/follow requests from real-life contacts. And avoid oversharing personal details, locations, contact info, schedules, etc. with the general public.Think Before You PostWe've all seen friends post embarrassing updates or photos they likely regretted later. Before sharing anything online, pause and think "Is this something I want future employers or others to potentially see?" If not, don't post it! Once it's out there, it'spermanent. It's also critical to avoid giving out personal identifiers like your phone number, email, home address, birthdate, or social security number.Be Cautious About GeotaggingMany social platforms geotag posts to show your exact location when you share updates or photos. This can be convenient, but also reveals your real-time movements and whereabouts to anyone viewing your content. I recommend disabling geotagging to avoid broadcasting where you are to potential criminals, stalkers, or anyone else you'd prefer didn't know.Use Strong Passwords/AuthenticationNo matter how private your accounts, if your login credentials are weak, your profiles and personal data could easily be compromised. Use very strong passwords that are unique for each account and enable two-factor authentication wherever possible. Password manager apps can also help secure and store all your credentials safely.Be Selective About AppsMany apps request permission to access your contacts, photos, social media accounts and other personal data on yourphone or computer. Only allow this access for apps you fully trust from reputable sources. Deny contact/account linking for any shady apps or sources to protect your data and connections.Manage Friend Lists/ConnectionsOn a regular basis, review your friend and connection lists on each social platform. Remove any individuals you don't actually know or no longer want having access to your personal information and posts. The fewer people who can see your content, the more protected your privacy.Search Yourself OnlineAt least twice a year, do a thorough search for your name, photos, email addresses, etc across all major search engines. This allows you to see what personal information about you is publicly accessible and take steps to have it removed if needed. There are even paid monitoring services that can alert you anytime your data is found on new sites.Be Selective About Personal DetailsMany social platforms have fields for personal details like birthdate, home address, phone number, relationship status, biography and more. My advice? Leave as many of these blank as possible or only fill in basic details you're comfortable beingpotentially public. The less personal information you provide upfront, the more protected you'll be.Wait to ShareWith the rise of real-time sharing, there's a growing trend of immediately posting updates and photos while still in the moment. But this can unintentionally broadcast sensitive details like your location, who you're with, what you're doing, etc. An easy privacy solution is to simply wait until you're home or in a secure place before posting about your activities or whereabouts from earlier.Consider Your ConnectionsWhen accepting friends, follows, or connections on social platforms, be very selective, especially with individuals you only know online or in passing. These people may have alternative motives for wanting access to your personal data and life updates beyond just keeping in touch. It's better to be cautious by only linking with those you know and trust in the real world.Privacy and personal security should be top priorities for all of us, but especially for students given how much our current activities and future opportunities could be impacted by oversharing personal data online. While social media hasbecome an integral part of modern communication and connection, we have to be smart and cautious about what we post and share with the world.I urge all of my fellow students to follow the tips outlined above. Be protective of your personal information and data across all your social accounts and activities. A few simple precautions and privacy best practices can go a long way towards keeping your sensitive details secure and maintaining control over your personal brand and reputation, both now and for years to come as you pursue academic and professional ambitions.篇3Protecting Personal Information on Social MediaBy A Concerned StudentSocial media has become an inescapable part of modern life, especially for young people like myself and my peers. Platforms like Facebook, Instagram, Twitter, TikTok and Snapchat allow us to connect with friends, share updates and experiences, access news and information, and explore our interests. However, the pervasiveness of social media also carries significant risks when it comes to protecting our personal information and data privacy.As students, many of us have had social media accounts since our early teens and have documented countless personal experiences, thoughts, images, location data and connections online over the years. The extent of personal data we've shared is staggering when you think about it. And yet, many of my classmates remain blasé about privacy, believing they have nothing to hide or that they're too insignificant for hackers or data brokers to target.This couldn't be further from the truth. Every social media user is vulnerable to surveillance capitalism, the practice of extracting and monetizing our personal data by companies and third parties. Our interests, habits, friend groups, locations, opinions and identities have become marketing commodities. Stolen personal data can also enable identity theft, financial fraud, extortion, discrimination and personal and professional exploitation.Moreover, potential employers, college admissions officers, law enforcement and government agencies may scrutinize our social media presence for any information that could be perceived as a red flag. A single insensitive post during a lapse of judgment in our youth could derail academic and career opportunities for years to come. We could be denied jobs,degrees, loans or security clearances based on our digital footprints.As the eldest daughter in my family, my parents expect me to be a role model for my younger siblings, especially online. It would break their hearts if I wittingly or unwittingly hosted objectionable content that reflects poorly on our family's values and reputation. I feel this sense of duty deeply.For all these reasons, protecting our personal information on social media needs to be a top priority for students. Here are some of the best practices I follow:Stringent privacy settingsThe first line of defense is enabling the strictest privacy settings across all social media platforms to restrict what strangers can see and access. For example, on Facebook I ensure only friends can view my posts, photos, bio information and friend list. On Instagram, I keep my account private. I customize Twitter's settings to protect my tweets, media, location and more. Making personal accounts private may seem like common sense, but many users, including some of my friends, still leave their accounts and posts public by default.Separate personal and professional presencesIncreasingly, career counselors advise students like me to maintain separate personal and professional accounts on sites like LinkedIn for networking and Twitter for showcasing expertise. My personal Instagram is for sharing casual snapshots with friends only, while my LinkedIn and professional Twitter highlight my skills, experience and accomplishments for employers and colleagues. Keeping these identities distinct allows me to represent my best self in the appropriate contexts.Thoughtful content curationEven with stringent privacy settings, we must remain cautious about what we post given how rapidly content can be shared, screenshotted and reposted. Before sharing anything, I pause and ask myself whether it's an accurate representation of who I am and how I wish to be perceived. Does this reflect well on my character, priorities and aspirations? Could this post enable personal attacks or be taken out of context? If so, I refrain from posting or quickly delete the content. My social media presence is carefully curated.FOMO isn't worth itWhile it can be tempting to share exciting travels, parties, inside jokes or edgy commentary for likes and follows, I resist the fear of missing out (FOMO). Those momentary hits of validationaren't worth compromising my privacy and potentially jeopardizing my future. I WANT to miss out on posts that could make me a target down the line. My feeds aim to be a positive but low-risk reflection of my real life.Safe sharing settingsWhen I do choose to share posts or stories publicly, I disable any metadata like location services and tag locations vaguely if at all. I'm also mindful of not inadvertently exposing personal details about myself, friends or family members in any content. Tight sharing settings prevent leaks of data that could enable tracking or surveillance.Lock down accountsIn addition to maximizing privacy settings, I've enabled multi-factor authentication on all accounts, using authentication apps to generate codes in addition to passwords. Longer passphrases uniquely created for each platform are a must. I'm extra cautious about reviewing permissions before granting third-party apps and services access to my social accounts. Locking down login credentials prevents unauthorized account access and data breaches.Be wary of tagsWhen friends tag me in posts, those tagged items could still be visible to a wider audience than intended, even if I've restricted content visibility. I remain vigilant about reviewing tagged posts and proactively untag myself from anything I wouldn't have posted myself. Tagging permissions can also be limited or disabled entirely on most platforms.Periodically audit and pruneEven the most stringent privacy practices can't account for platforms' constantly changing terms of use, data sharing provisions, and privacy policies. As a safeguard, I periodically review all my posts, photos, connections and shared data to prune or delete anything that may be perceived as a liability based on evolving standards and norms. An annual social media audit allows me to course correct and maintain a discreet presence.Explore emerging privacy techBeyond standard privacy settings, I try to stay up to date on new technologies and apps that provide enhanced privacy protections like end-to-end encryption and auto-deletion of messages and ephemeral stories. These emerging tools can further insulate personal information from unauthorized accessand exploitation. I also pay close attention to any data privacy legislation that could enshrine new digital rights and protections.Set a good examplePerhaps most importantly, I aim to be a good role model for my peers and younger friends and family. I openly discuss the importance of personal privacy in the digital age and encourage them to be thoughtful about what they share. My cautious social media habits are part of my personal brand: a reflective individual who understands the weight of our permanent digital footprints.In our oversharing era, actively protecting our privacy and personal information is a form of self-care. It's about respecting our future selves and all the potential versions of ourselves yet to unfold. Restraint and discretion online doesn't make us dull or have anything to hide. Rather, it demonstrates maturity, integrity and an ability to think long-term about the consequences of our actions. Those are admirable traits in a person and prospective employee.My generation will be the first to grapple with the full ramifications of coming of age on social media. Countless classmates have already diminished their prospects with a single ill-considered post from their youth. So many of us have alreadyhad personal moments published to the world without our consent.We can't unmake the permanence of the internet. But those of us who will comprise the workforce of the future must prioritize data privacy today to safeguard our opportunities. Shaping an intentional personal brand online is about curating the footprint we want employers, colleagues and society at large to see and judge us by. It's about protecting our right to define our public selves.Defending personal privacy on social media is how my generation draws a line around our identities in the digital age. It's a profound act of self-respect and self-preservation. For all these reasons, I remain vigilant about protecting my personal information online. When used mindfully, social media can be a powerful complement to our real lives without compromising it.。
关于保护平民的日内瓦公约英文全文The Geneva Conventions: Full Text in English and Its Role in Protecting CiviliansIntroduction:The Geneva Conventions are a set of international treaties and protocols that establish the standards for humanitarian treatment during armed conflicts. These conventions were first adopted in 1864 and have been revised and expanded over the years. The purpose of the Geneva Conventions is to provide protection for all individuals who are not or no longer taking part in the hostilities, including civilians. In this article, we will provide the full text of the Geneva Conventions in English and discuss their significance in safeguarding the rights and well-being of civilians during times of war.Convention I:The first Geneva Convention, formally titled the "Convention for the Amelioration of the Condition of the Wounded and Sick in Armed Forces in the Field," was adopted on August 12, 1949. It lays down the fundamental rules of humanitarian law applicable during armed conflicts. The Convention emphasizes the protection of wounded and sick military personnel and aims to ensure their medical treatment and care without discrimination.Convention II:The second Geneva Convention, known as the "Convention for the Amelioration of the Condition of Wounded, Sick and Shipwrecked Members of Armed Forces at Sea," was also adopted on August 12, 1949. It extends the provisions of the first Convention to those wounded, sick, and shipwrecked at sea during armed conflicts. The Convention states that these individuals should be treated humanely and their medical needs should be addressed.Convention III:The third Geneva Convention, commonly referred to as the "Convention relative to the Treatment of Prisoners of War," was adopted on August 12, 1949. It establishes the protection and rights of prisoners of war captured during international and non-international armed conflicts. The Convention prohibits torture, cruel treatment, and any form of degrading or inhumane treatment against prisoners of war. It also ensures that they are provided with proper medical care and access to religious practices.Convention IV:The fourth Geneva Convention, titled the "Convention relative to the Protection of Civilian Persons in Time of War," was adopted on August 12, 1949. It is the key convention focused on the protection of civilians during times of armed conflict. The Convention prohibits acts of violence, torture, and ill-treatment against civilians. It also prohibits the taking of hostages, collective punishments, and actions that undermine the right to life, liberty, and dignity of individuals. Moreover, it emphasizes the fundamental human rights of civilians, including the right to medical care, access to food and water, and the right to be protected against displacement and deportation.Significance in Protecting Civilians:The Geneva Conventions play a vital role in safeguarding the rights and well-being of civilians during times of armed conflict. These conventions ensure that civilians are treated with humanity and respect, even in the midst of hostilities. By establishing legal frameworks and guidelines, the Geneva Conventions aim to limit the suffering inflicted upon non-combatants.Civilians, as non-combatants, can easily become victims of the chaos and violence that arise during armed conflicts. The Geneva Conventions specifically address the protection of civilians by prohibiting acts of violence, inhumane treatment, and other violations against their dignity and well-being. The conventions explicitly emphasize the importance of respecting the principles of distinction, proportionality, and military necessity, which help prevent harm to innocent civilians.Furthermore, the Geneva Conventions ensure access to essential needs, such as medical care and food, for civilians trapped in conflict zones. By recognizing the right to medical treatment, the conventions guarantee that civilians receive the necessary care, regardless of their nationality, race, or religion. The provision of humanitarian aid to civilian populations is also highlighted, ensuring that essential supplies and relief reach those who are most vulnerable.Conclusion:The full text of the Geneva Conventions in English provides a comprehensive framework to protect civilians during armed conflicts. By upholding the principles of humanity, distinction, and proportionality, the conventions aim to minimize the impact of war on innocent individuals. It is crucial for nations and armed forces to adhere to these conventions, ensuring the safety, well-being, and dignity of civilians in times of war. Only by respecting and implementing the provisions of the Geneva Conventions can we strive towards a more peaceful and humane world.。
access not like语句1. Access is not like it used to be before the security upgrade. (访问不像以前那样,因为进行了安全升级。
)2. I don't like this new system of access, it's too complicated. (我不喜欢这种新的访问系统,太复杂了。
)3. The access to the building is restricted after 6 pm. (晚上6点后进入建筑物的通行受限制。
)4. I cannot access my email account from this computer. (我无法从这台电脑上访问我的电子邮件账户。
)5. Access to the server is limited to authorized personnel only. (只有授权人员才能访问服务器。
)6. I can't access this website from my location due to regional restrictions. (由于地区限制,我无法从我的位置访问此网站。
)7. The company's financial records are protected and cannot be accessed by unauthorized individuals. (公司的财务记录受到保护,未经授权的个人无法访问。
)8. Access to the database requires a username and password for security reasons. (出于安全考虑,访问数据库需要用户名和密码。
)9. I don't have access to that information, it's confidential. (我没有那些信息的权限,它是机密的。
注册流程英语The registration process is a crucial step in many aspects of our lives, from enrolling in educational institutions to accessing various services and resources. Whether you are a student, a professional, or an individual seeking to participate in a specific program or activity, the registration process plays a vital role in ensuring a smooth and efficient experience. In this essay, we will explore the key elements of the registration process and the importance of understanding and navigating it effectively.One of the primary purposes of the registration process is to collect and verify essential information about the individual or entity seeking to participate in a particular activity or service. This information can include personal details such as name, date of birth, contact information, and in some cases, additional documentation like identification cards or proof of residency. This data is typically used to create a unique profile or account for the individual, which serves as a reference point for future interactions and transactions.The registration process also serves to establish the terms andconditions under which the individual or entity will be able to access the desired service or program. This may include the payment of fees, the acceptance of policies and agreements, and the acknowledgment of any rules or regulations that govern the particular activity or service. By completing the registration process, the individual or entity is demonstrating their understanding and acceptance of these requirements, ensuring a clear and mutually agreed-upon framework for the ongoing relationship.One of the key benefits of a well-designed registration process is the ability to streamline and optimize the overall experience for the individual or entity seeking to participate. A user-friendly and efficient registration process can save time, reduce frustration, and enhance the overall satisfaction with the service or program being accessed. This can be particularly important in situations where the individual or entity needs to access the service or program on a regular basis, such as in the case of educational institutions, healthcare providers, or government agencies.In addition to the practical benefits, the registration process also plays a crucial role in ensuring the security and integrity of the service or program being accessed. By collecting and verifying essential information, the registration process helps to prevent unauthorized access, fraud, and other forms of abuse. This is particularly important in sensitive or high-stakes situations, such asfinancial transactions, healthcare services, or national security-related activities.Another important aspect of the registration process is the way in which it is implemented and communicated to the individual or entity seeking to participate. A well-designed and user-friendly registration process should be intuitive, straightforward, and transparent, providing clear instructions and guidance throughout the entire process. This can include the use of online forms, interactive tutorials, or personalized assistance from customer service representatives.Moreover, the registration process should be designed with the needs and preferences of the target audience in mind. This may involve the use of multiple languages, the provision of accessible formats for individuals with disabilities, or the incorporation of cultural and regional considerations. By tailoring the registration process to the specific needs of the target audience, organizations can ensure that the process is inclusive, accessible, and responsive to the diverse needs of the individuals or entities seeking to participate.One of the challenges associated with the registration process is the potential for errors or omissions, which can lead to delays, frustration, or even the denial of access to the desired service or program. To mitigate these risks, it is essential that the registration processincludes robust error-checking mechanisms, clear instructions, and opportunities for the individual or entity to review and correct any information before submitting the registration.Additionally, the registration process should be designed with a strong emphasis on data privacy and security. The collection and storage of sensitive personal information must be handled with the utmost care, in compliance with relevant data protection laws and regulations. This may involve the use of encryption, secure servers, and access controls to ensure that the individual's or entity's information is protected from unauthorized access or misuse.In conclusion, the registration process is a critical component of many aspects of our lives, serving to collect and verify essential information, establish the terms and conditions of participation, and ensure the security and integrity of the service or program being accessed. By designing and implementing a well-crafted registration process, organizations can enhance the overall experience for the individual or entity seeking to participate, while also upholding the necessary standards of security and data privacy. As technology continues to evolve and the demands on individuals and entities grow, the importance of a robust and user-friendly registration process will only continue to increase.。
秘书应保密的英语作文As a secretary, confidentiality is a crucial aspect of my job. It is my responsibility to handle sensitive information with the utmost care and discretion. This includes protecting the privacy of my employer, colleagues, and clients, as well as safeguarding the company's proprietary information.In order to maintain confidentiality, I adhere to strict protocols and procedures. This includes using secure communication channels for sensitive discussions, such as encrypted emails and password-protected documents. I also limit access to confidential information only to those who have a legitimate need to know, and I ensure that any physical copies of sensitive documents are stored securely and disposed of properly when no longer needed.In addition to these measures, I am also mindful of the importance of discretion in my interactions with others. I do not discuss confidential matters in public or with unauthorized individuals, and I am always mindful of my surroundings when handling sensitive information.Furthermore, I understand the importance of maintaining confidentiality in the digital realm. This means being vigilant about potential cybersecurity threats, such as phishing scams or malware, and taking steps to protect the company's digital assets from unauthorized access.Overall, confidentiality is a cornerstone of my role as a secretary, and I take this responsibility very seriously. By following established protocols, exercising discretionin my interactions, and being mindful of cybersecurity best practices, I am able to fulfill my duties in a way that protects the privacy and security of the information entrusted to me.作为一名秘书,保密是我工作中至关重要的一部分。
nginx token认证方式Nginx is a popular web server software known for its high performance, scalability, and flexibility. It also offers various authentication methods, including token-based authentication. Token-based authentication is a secure and efficient way to authenticate users and control access to web resources.In token-based authentication, a token is generated and assigned to a user upon successful login. This token is encrypted and contains specific user information, such as the user's ID or username. The token is then sent with each subsequent request to the server, allowing the server to verify the user's identity and grant access to protected resources.Nginx supports token-based authentication through the ngx_http_auth_request_module module. This module enables the validation of tokens against a backend authentication server or service. Here is a general overview of the process:1. User login: When a user logs in, the authentication server generates a token and sends it back to the client.2. Token inclusion: The client includes the token in the HTTP header of each subsequent request to the Nginx server. For example, the token can be included in the Authorization header as a Bearer token.3. Verification: Nginx receives the request with the token and forwards it to the backend authentication server for verification. The server checks the token's validity and authenticity.4. Access control: Based on the authentication server's response, Nginx allows or denies access to the requested resource. If the token is valid, the user is granted access; otherwise, access is denied.Token-based authentication offers several advantages. Firstly, tokens are stateless, meaning the server doesn't need to store session information for each user, resulting in improved scalability. Secondly, tokens can have an expiration time, ensuring that users must periodically reauthenticate. Additionally, tokens can be easily managed, revoked, or refreshed, enhancing security.It is worth noting that implementing token-based authentication requires more than just Nginx configuration. A backend authentication server or service is needed to generate, validate, and manage tokens. This server can be a custom implementation or utilize existing token-based authentication frameworks.In conclusion, Nginx supports token-based authentication through its ngx_http_auth_request_module module. By implementing token-based authentication, you can enhance security, scalability, and flexibility in your web application, allowing for secure management of user access to protected resources.。
49© Mikael Olsson 2016M. Olsson, PHP 7 Quick Scripting Reference , DOI 10.1007/978-1-4842-1922-5_11 Every class member has an accessibility level that determines where the member is visible. There are three of them available in PHP: p ublic ,p rotected , and p rivate . c lass MyClass{ public $myPublic; // unrestricted accessprotected $myProtected; // enclosing or child classprivate $myPrivate; // enclosing class only} P rivate AccessAll members, regardless of access level, are accessible in the class in which they are declared—the enclosing class. This is the only place where a private member can be accessed.c lass MyClass{ public $myPublic = 'public';protected $myProtected = 'protected';private $myPrivate = 'private';function test(){echo $this->myPublic; // allowedecho $this->myProtected; // allowedecho $this->myPrivate; // allowed}}U nlike properties, methods do not have to have an explicit access level specified. They default to public access unless set to another level.CHAPTER 11 ■ ACCESS LEVELSP rotected AccessA protected member can be accessed from inside the child or the parent classes, as well as from within the enclosing class.c lass MyChild extends MyClass{function test(){echo $this->myPublic; // allowedecho $this->myProtected; // allowedecho $this->myPrivate; // inaccessible}}P ublic AccessP ublic members have unrestricted access. In addition to anywhere a protected member can be accessed, a public member can also be reached through an object variable. $m = new MyClass();e cho $m->myPublic; // allowede cho $m->myProtected; // inaccessiblee cho $m->myPrivate; // inaccessibleV ar KeywordB efore PHP 5, the v ar keyword was used to declare properties. To maintain backward compatibility, this keyword is still usable and gives public access, just like the p ublic modifier.c lass MyVars{var $x, $y; // deprecated property declaration}O bject AccessI n PHP, o bjects of the same class have access to each other’s private and protected members. This behavior is different from many other programming languages where such access is not allowed.50CHAPTER 11 ■ ACCESS LEVELS c lass MyClass{private $myPrivate;function setPrivate($obj, $val) {$obj->myPrivate = $val; // set private property}}$a = new MyClass();$b = new MyClass();$a->setPrivate($b, 10);A ccess Level GuidelineA s a g uideline , when choosing an access level, it is generally best to use the most restrictive level possible. This is because the more places a member can be accessed, the more places it can be accessed incorrectly, which makes the code harder to debug. Using restrictive access levels also makes it easier to modify the class without breaking the code for any other developers using that class.51。
Vol.4,No.8,2005 Checking Access to Protected Members in the Java Virtual MachineAlessandro Coglio,Kestrel Institute,Palo Alto,California,USAThis paper studies in detail how to correctly and efficiently check access to protected members in the Java Virtual Machine.This aspect of type safety is not explained in the official specification and,to the author’s knowledge,has been completely neglected in the research literature.Nonetheless,it is a subtle aspect that is not straightforward to implement correctly,as also evidenced by the presence of a bug in earlier versions of Sun’s Java2SDK.This paper presents example programs that expose the bug, along with a conjectural explanation for it.This paper also presents some corpus measurements of the number of checks that can be performed using various techniques.1INTRODUCTIONJava[5]is normally compiled to a platform-independent bytecode language,which is executed by the Java Virtual Machine(JVM)[7].For security reasons[4],the JVM must ensure type-safe execution(e.g.object references must not be forged from integers),without relying on the type checking performed by Java compilers.This paper studies in detail a narrow but interestingly subtle aspect of ensuring type safety in the JVM:checking access to protected members(fields and methods). Java compilers can easily check access to protected members and constructors1by looking them up in their declaring classes,which must be available in source or bytecode form.Checking access to protected members in the JVM is more difficult because of dynamic class loading.This aspect of type safety in the JVM is not explained in[7]and,to the author’s knowledge,has been completely neglected in the research literature.Section2reviews some relevant features of the JVM.Sections3and4describe the requirements on protected member access and how they can be checked.Section 5reports on the incorrect checking of protected member access by earlier versions of Sun’s Java2SDK,including example programs that expose the bug.Concluding remarks are given in Section6.1In Java,constructors are not members.In the JVM,constructors are realized by instance initialization methods,i.e.methods with the special name<init>,which are members.Cite this article as follows:citationCHECKING ACCESS TO PROTECTED MEMBERS IN THE JAVA VIRTUAL MACHINE 2BACKGROUNDSome of the JVM features described in this section are slightly simplified for brevity and ease of understanding;for instance,we only consider classes and not interfaces. However,the results of the paper do not depend on the simplifications and apply to the unsimplified JVM.For full details on the JVM features described here,see [7,6],as well as[10]for a formal treatment.Class LoadingThe JVM supports dynamic,lazy loading of zy loading improves the response time of a Java applet or application and reduces memory usage:execution starts after loading only a few classes and the other classes are loaded on demand if and when needed.Classes are loaded into the JVM by means of class loaders,which can be user-defined to realize customized loading policies.To load a class,the JVM supplies a (fully qualified)class name C(.kestrel.Specware)to a loader L.L may itself create a class c with name C,e.g.from a binary representation stored in the local file system or fetched through a network connection.Alternatively,L may delegate loading to another loader L by supplying C to L .L may itself create c or delegate loading to yet another loader L ,and so on until some loader L∗eventually creates c.The initiating loader of c is L,thefirst one in the delegation chain,which the JVM supplies C to.The defining loader of c is L∗,the last loader in the delegation chain,which creates c.Initiating and defining loader coincide when no delegation takes place.The JVM prohibits a loader from creating two classes with the same name, but two different loaders may well create two classes with the same name.Classes created by different loaders are always distinct(even though they may have the same binary representation,including name),i.e.each loader has its own name space.Thus,while at compile time a class is uniquely identified by its name,in the JVM a class is uniquely identified by its name plus its defining loader,e.g. edu.kestrel.Specware,L∗ .Accordingly,a(run time)package is uniquely identified by a name plus a loader, e.g. edu.kestrel,L∗ ,which includes edu.kestrel.Specware,L∗ among its classes;as a special case,an unnamed package is uniquely identified by just a loader.All the classes in a package have the same defining loader,which is the loader that,together with the name(unless the package is unnamed),uniquely identifies the package.When a class is loaded,all its superclasses are loaded.So,the JVM satisfies the invariant that the classes present in the machine are closed w.r.t.the superclass relation.56JOURNAL OF OBJECT TECHNOLOGY VOL4,NO.82BACKGROUNDThe JVM maintains a cache of loaded classes in the form of afinite map from names and loaders to classes.When a class c is loaded,the cache is extended with an entry that associates c to its name C and its initiating loader L;if the defining loader is L∗=L,the cache is also extended with an entry that associates c to C and L∗.ResolutionSome bytecode instructions embed symbolic references to classes and members,e.g. to invoke methods.These symbolic references are resolved to actual classes and members before the embedding instructions are executed for thefirst time.A class reference C is a class name.A member reference C.n:d consists of a class reference C,a member name n,and a member descriptor d.Afield descriptor is(a textual representation of)a type,while a method descriptor consists of(a textual representation of)zero or more argument types and a result type(possibly void);a class type occurring in a descriptor is only a class name,without any defining loader because descriptors are generated at compile time when loaders,which are run time entities,are unknown.The JVM resolves a class reference C that occurs in a class X,L by supply-ing C to L,i.e.the defining loader of the class in which the reference occurs;the resulting class c is the result of resolution.More precisely,before supplying C to L for loading,the JVM looks up the loaded class cache.If there is an entry that associates a class c to C and L,c is the result of resolution and no loading takes place.Otherwise,loading takes place as described.This cache look up mechanism ensures that resolving a name C via a loader L(i.e.from a class X,L )consistently yields a unique class,denoted by C L.Both notations C,L and C L[7,6]denote classes.The notation C,L denotes the class with name C and defining loader L;in this notation,L is always the defining loader of the class.The notation C L denotes the class associated to name C and loader L in the loaded class cache;in this notation,L is either the initiating or the defining loader of the class.If C,L is defined,then also C L is defined and it is the case that C,L =C L.A member reference C.n:d is resolved byfirst resolving the class reference C to a class c and then searching for a member with name n and descriptor d declared in c.If such a member m is found,that is the result of resolution.Otherwise,the member is searched in the direct superclass of c,and so on until the member is found in some superclass of c.Bytecode VerificationAfter a class is loaded and before any of its code is executed,its methods go through bytecode verification,one at a time.Bytecode verification is a(forward)dataflow VOL4,NO.8JOURNAL OF OBJECT TECHNOLOGY57CHECKING ACCESS TO PROTECTED MEMBERS IN THE JAVA VIRTUAL MACHINE analysis[9]whose purpose is to statically establish that certain type safety properties will be satisfied when instructions are executed at run time,so that the interpreter or just-in-time compiler can safely omit checks of those properties for better perfor-mance.For example,the bytecode verifier checks that the iadd instruction,which adds two integers together,will always operate on two integers,and not on other data values such asfloating point numbers or object references.As another example, the bytecode verifier checks that the getfield instruction,which retrieves the value stored in afield,will always operate on a reference to an object whose class is the one referenced in thefield reference embedded in the instruction or a subclass of it.As previously explained in the description of resolution,a class reference C oc-curring in a class X,L stands for the class C L.The same holds for a class type C inferred by the bytecode verifier during the dataflow analysis.At the time X,L is verified,C L may or may not have been loaded yet.The bytecode verifier generally avoids resolving(and loading)classes,thus supporting lazy loading.For example,if it infers a type C as the target of a getfield whose embeddedfield reference is C.n:d, C is not resolved because no matter what class C L will be,the referencedfield will be declared in C L or one of its superclasses and so thefield access will be type-safe. However,if the inferred target type is D=C,the bytecode verifier resolves D and C to check that D L is a subclass of C L,written D L<C L.Loading ConstraintsWhen(instructions in)different classes exchange objects,they must agree on the exchanged objects’classes(s plus loaders)and not just class names(agree-ment on names is automatically ensured by resolution).For example,consider a class X,L creating an instance of a class named D and passing it to a method, with argument type D,of a class Y,L .The instance belongs to D L but the method will use it as an instance of D L .So,if L=L ,it must be D L=D L for type safety to be maintained.These constraints are checked when members are resolved.When a class X,L resolves a member C.n:d,if C L= C,L ,for every class name D appearing in the descriptor d the constraint D L=D L must hold.If any of D L and D L has not been loaded yet,the JVM generates“D L=D L ”as a syntactic constraint,adding it to a set of pending constraints that are part of the state of the machine.The loaded class cache and the loading constraints are maintained consistent by re-checking the pending loading constraints every time the loaded class cache is updated.The transitive closure of the pending constraints must be considered,e.g.if D L and D L are loaded but D L is not,the constraints D L=D L and D L =D L are (jointly,though not individually)violated if D L=D L .The need to consider the transitive closure is illustrated by the following example.A class X,L creates an object of class D L and passes it to a method of a class Y,L ;when the method 58JOURNAL OF OBJECT TECHNOLOGY VOL4,NO.83REQUIREMENTS ON PROTECTED MEMBERSpc{m}+s∗oFigure1:Restriction on protected accessis resolved,the constraint D L=D L is generated.The method in Y,L does not access the object(so that D L does not get loaded)but passes it to a method of a class Z,L ;when the method is resolved,the constraint D L =D L is generated. Now Z,L accesses the object as if it had class D L .Thus,it must be D L=D L for type safety to be maintained.It has been proposed in[10,3]to use subtype constraints,next to the equality constraints just described,to support lazier loading during bytecode verification. When a class X,L is verified,instead of resolving D and C to check whether D L<C L,the constraint“D L<C L”is generated.The transitive closure of equality and subtype constraints must be considered.Subtype constraints are not part of[7], but they are presented here because a similar idea will be described for protected members in Section4.3REQUIREMENTS ON PROTECTED MEMBERSIn the JVM,like in Java,every member has an associated access attribute:public, private,protected,or default.The attribute determines the circumstances in which the member can be accessed.Let m be a member declared in a class c that belongs to a package p.If m is public,it can be accessed by(code in)any class.If m is private,it can be accessed only by c.If m has default access,it can be accessed only by any class that belongs to p.If m is protected,things are slightly more complicated.First,m can be accessed by any class belonging to p,as if it had default access.In addition,it can be accessed by any subclass s of c that belongs to a package different from p,with the following restriction:if m is not static,then the class o of the object whose member is being accessed must be s or a subclass of s,written o≤s(if m is static,the restriction does not apply:m can be always accessed by s).The relationship among c,s,o, m,and p is depicted in Figure1,where the double-line arrow labeled by+denotes one or more direct superclasses and the double-line arrow labeled by∗denotes zero or more direct superclasses.VOL4,NO.8JOURNAL OF OBJECT TECHNOLOGY59CHECKING ACCESS TO PROTECTED MEMBERS IN THE JAVA VIRTUAL MACHINE The restriction on protected access(i.e.that o≤s if s<c and s does not belong to p)ensures that a protected member m declared in c is accessible,outside the package p of c,only(on objects whose classes are)inside the part of the class hierarchy rooted at the accessing(sub)class s[1,Sect.3.2][2].In particular,s cannot access m in a part of the class hierarchy rooted at a(sub)class s =s in a different branch.See[1,Sect.3.2][2][5,Sect.6.6.7]for examples.The restriction on protected access prevents almost arbitrary access to protected instance members of objects[12].Suppose that m is a protected instancefield declared in c.Without the restriction,any class x could read the content of the field m of any object of class c,using the following trick:define a subclass s of c (the trick works only if c is notfinal,hence the“almost”adverb above);declare a method in s that takes an object of class c as argument and returns the content of its mfield;and have x call this method.The restriction on protected access prevents this situation,because s can access thefield only if c≤s,which is impossible since s<c.The access rules are described in[7,Sect.5.4.4].The restriction on protected access is described in the specification of the getfield,putfield,invokevirtual,and invokespecial instructions in[7,Chapt.6].The access rules for members in the JVM correspond to the access rules for members and constructors in Java[5,Sect.6.6].The access rules do not include any requirement on the accessibility of c.One might expect,for instance,that if m is public then it can be accessed by a class x not belonging to p only if c is also public.However,c may not be the class directly referenced by x:x may reference a class c that inherits m from c(i.e.m is found in c,starting the search from c ).It is sufficient that c can be accessed by x(i.e.c and x are in the same package or c is public),regardless of whether c can be accessed by x or not.Because of dynamic dispatch,the method actually invoked on an object may differ from the method that the reference resolves to.However,access control checks only apply to the resolved method,not the dynamically invoked one.While Java compilers check that an overriding method does not restrict the access attribute [5,Sect.8.4.6.3],the JVM does not check that:[7]does not explicitly require the check and it is easy to verify that,for instance,SDK1.4does not perform the check. Anyhow,this restriction on overriding methods does not always ensure that access to the resolved method implies access to the overriding method[11]:if both methods are protected and are declared in different packages,then classes in the resolved method’s package that are not subclasses of the overriding method’s declaring class can access the resolved method but not the overriding method.4CHECKING THE REQUIREMENTSMost access rules are checked during resolution.For example,when a getfield is executed for thefirst time,the embeddedfield reference is resolved and the access 60JOURNAL OF OBJECT TECHNOLOGY VOL4,NO.84CHECKING THE REQUIREMENTSattribute of the resultingfield is checked against the class where getfield occurs:if access is disallowed,an exception is thrown;otherwise,getfield retrieves thefield’s content.The restriction on protected access requires additional checking.Suppose that the getfield occurs in a class s,that thefield reference resolves to a non-static, protectedfield declared in a superclass c of s,and that c and s belong to different packages,as in Figure1.Whether thefield access is allowed depends on the class o of the target object,which may be different each time the getfield is executed.The following subsections describe various strategies to check whether o≤s.While[7] states the requirements on protected member access,it does not explain how they can be checked.Run Time CheckingThe class of an object is always available through a reference to the object,in order to support the semantics of the instanceof and checkcast instructions.In typical implementations of the JVM,the storage for an object includes a reference to the object’s class.The simplest strategy to check the restriction on protected access is to have getfield,putfield,invokevirtual,and invokespecial do it each time they are executed. This run time check is performed only if the referenced member is protected and declared in a superclass of the current class(i.e.the one where the instruction occurs) that belongs to a different package.Thefirst edition of[7]describes,in Chapter9,an optimization for JVM imple-mentations:certain instructions are replaced by quick,internal pseudo-instructions thefirst time they are executed.For instance,thefirst time a getfield is executed, it is replaced by the getfield quick pseudo-instruction:instead of afield reference, getfield quick embeds implementation-dependent information(typically,an offset) that is determined when thefield is resolved and that is used to access the target object’sfield more quickly than going through the(resolved)field reference.A similar rewriting approach could be used in a JVM implementation to more efficiently check protected member access at run time.Thefirst time a getfield is executed and thefield reference is resolved,there are two cases:if the resulting field is not protected or is not declared in a superclass of the current class that belongs to a different package,getfield is replaced by getfield quick;otherwise,it is replaced by getfield quick prot.This new pseudo-instruction embeds the same implementation-dependent information as getfield quick;in addition,its execution includes the run time check that o≤s,where o is the class of the target object and s is the current class.An analogous strategy can be introduced for putfield, invokevirtual,and invokespecial.However,getfield quick prot would not be very quick.Even though the run time check is only performed for protectedfields declared in superclasses belonging to VOL4,NO.8JOURNAL OF OBJECT TECHNOLOGY61CHECKING ACCESS TO PROTECTED MEMBERS IN THE JAVA VIRTUAL MACHINEc {m }C L ∗G G G G G G G G G G G G G G G G s +t t t t t t t t t t J J J J J J J J J JD L ∗∗J J J J J J J J J J J J J J J J J J J J o∗∗t t t t t t t t t t t t t t t t t t t t Figure 2:Relationship among all the involved classesdifferent packages,the overhead could be significant in certain programs.In addition,[7,Sect.5.4.4]states explicitly that the restriction on protected access should be checked as part of bytecode verification.In general,type safety in the JVM could be completely ensured via run time checks,but execution would be painfully slow.The purpose of static checking in the JVM is to increase performance.The following strategies check the restriction on protected access statically.Eager ResolutionWhen analyzing a getfield ,putfield ,invokevirtual ,or invokespecial ,the bytecode veri-fier could resolve the embedded member reference and,if needed,check the restric-tion on protected access using the statically inferred target type.Suppose that the class under verification is s = S ,L ,the embedded member reference is C .n :d ,and the inferred target type is D .If the member reference resolves to a protected member m declared in a class c ≥C L that belongs to a package different from s and such that c >s ,the bytecode verifier checks that D L ≤s .If D =S ,this subtype check can be performed by resolving D or,according to the proposal described at the end of Section 2,by generating the subtype constraint D L <S L ;if D =S ,no resolution or constraint is necessary because S L =s .The check that D L ≤s is in addition to the check that D L ≤C L ,which is always needed,regardless of whether m is protected and of where it is declared.Since at run time the class o of the target object always satisfies o ≤D L ,it is always the case that o ≤s if D L ≤s .The relationship among all these classes is depicted in Figure 2,where the single-line arrows denote resolution (i.e.the target class is the result of resolving the name of the target class from the source class).This static check is less precise than a run time check,because it might always be 62JOURNAL OF OBJECT TECHNOLOGY VOL 4,NO.84CHECKING THE REQUIREMENTSo≤s even if D L≤s does not hold.However,less precision is the inevitable price to pay for better performance.In addition,the static check is as precise as the compile time checking in Java:the type statically inferred at compile time corresponds to the type statically inferred by the bytecode verifier.Besides soundness,the only requirement on bytecode verification is that code generated by Java compilers is accepted;if the restriction on protected access is satisfied in some Java code,it is also satisfied in the bytecode generated from that Java code.The problem with this strategy is that every member reference from getfield, putfield,invokevirtual,and invokespecial is eagerly resolved in order to determine whether the member is protected and declared in a superclass of s that belongs to a different package.The additional check that D L≤s is performed if and only if that is the case.Resolution may involve class loading and thus be a costly operation. Furthermore,eager resolution counters lazy loading.As mentioned in Section1,Java compilers check access to protected members and constructors by looking them up in their declaring classes.This effectively corresponds to the eager resolution strategy just described for the JVM.At compile time all classes are available and no dynamic loading is involved;thus,the strategy is adequate for compilation.Limited ResolutionThere are cases in which the restriction on protected access can be checked by the bytecode verifier without eagerly resolving the referenced member.In addition,in certain cases member resolution is guaranteed to cause no loading.For the remaining cases,the member reference can be resolved as described in the previous subsection. Current Class as Target TypeResolving the class name S from a class s= S,L results in s itself because the loaded class cache associates s to S and L when s is created,i.e.S L=s.If the bytecode verifier infers the class name S as the target of a getfield,putfield, invokevirtual,or invokespecial that occurs in s,there is no need to resolve the embed-ded member reference because s≤s,regardless of whether the member is protected and of where it is declared.In other words,resolution can be soundly avoided if the inferred target type coincides with the name of the class under verification. Necessary Condition for Subtype CheckConsider a getfield,putfield,invokevirtual,or invokespecial occurring in a class s,with embedded member reference C.n:d.Since the member resulting from resolution must have name n and descriptor d,a necessary condition for m to be protected and declared in a superclass of s that belongs to a different package is that some VOL4,NO.8JOURNAL OF OBJECT TECHNOLOGY63CHECKING ACCESS TO PROTECTED MEMBERS IN THE JAVA VIRTUAL MACHINE superclass of s,belonging to a different package,declares a protectedfield with namen and descriptor d.This necessary condition can be checked by inspecting the superclasses of s, without resolving the member reference.Since the classes loaded into the JVM are closed under the superclass relation,inspecting the superclasses of s does not cause any loading.If no superclass of s declares a protected member with name n and descriptor d or every superclass that declares it belongs to the same package as s,it is impossible that the member resulting from resolution will be protected and declared in a superclass of s that belongs to a different package.Thus,the additional subtype check(i.e.that D L≤s)needs not be performed.Resolution not Causing LoadingAs mentioned before,resolving the class name S from a class s= S,L results in s itself without any loading taking place.In addition,resolving the direct superclass name R of s results in the direct superclass R L without any loading taking place, because when s is loaded R L is loaded too.So,if the class name referenced by a getfield,putfield,invokevirtual,or invokespe-cial is S or R,the resolution of the member will cause no loading.This is a property that is satisfied because of the way the JVM is designed;no special action by the bytecode verifier is required.Conditional Subtype ConstraintsInstead of eagerly resolving a member reference and then checking the restriction on protected access if needed,the bytecode verified could generate a conditional subtype constraint.The condition of the constraint expresses that the referenced member is protected and declared in a superclass of the current class that belongs to a different package.For example,consider a member reference C.n:d embedded in a getfield,putfield, invokevirtual,or invokespecial that occurs in a class s= S,L .Suppose that D is the inferred target type of that instruction,with D=S.The bytecode verifier generates the conditional subtype constraint“if ProtCond(C.n:d L,S L)then D L<S L”The condition ProtCond(C.n:d L,S L)holds if and only if the member to which C.n:d resolves via L(i.e.the member with name n and descriptor d found searching from C L)is protected and declared in a superclass of S L that belongs to a different package.Conditional subtype constraints are integrated with the unconditional(equality [7,6]and subtype[10,3])constraints in the JVM.The satisfaction of pending 64JOURNAL OF OBJECT TECHNOLOGY VOL4,NO.84CHECKING THE REQUIREMENTSconstraints is re-checked whenever classes are loaded and members are resolved.It is necessary to consider the transitive closure of all the constraints,conditional and unconditional.Even though conditional subtype constraints avoid premature loading altogether, their generation,maintenance,checking,and integration with the other loading con-straints require additional machinery in the JVM that would not be needed other-wise.Thus,there is a trade-offbetween eager resolution and conditional subtype constraints.Corpus MeasurementsThe3,915classes(and interfaces)in the java and javax packages of SDK1.4require 68,621static checks for protected members.That is the total number of triples (s,C.n:d,D)where s is a class in the java or javax package,C.n:d is a reference embedded in a getfield,putfield,invokevirtual,or invokespecial occurring in s,and D is one of the types inferred at that instruction by the bytecode verifier2.Other counts are possible,e.g.the total number of pairs(i,D)where i is an occurrence of getfield,putfield,invokevirtual,or invokespecial in some class in java or javax and D is one of the types inferred at i;however,what seems important in the data below is the relative percentages,which are probably largely invariant to the exact count used.Of the68,621checks:•30,598(45%)can be checked as explained in Subsection“Current Class as Target Type”because the target class coincides with the current class;•31,571(46%)do not cause any loading because the class referenced in the member reference is the current class or its direct superclass,as described in Subsection“Resolution not Causing Loading”;•all68,621can be checked as explained in Subsection“Necessary Condition for Subtype Check”because the necessary condition for the restriction on protected access does not hold.Of course,there is overlap among these three sets of checks.A reasonable implementation of the bytecode verifier could perform those checks as follows:•30,598of the total68,621(45%)by recognizing that the target class coincides with the current class;2While many bytecode verifiers,including the one in SDK,infer only one type for every instruc-tion(by merging types from converging paths),the measurements reported here were taken with a bytecode verifier that infers multiple types,for increased precision.VOL4,NO.8JOURNAL OF OBJECT TECHNOLOGY65。