Ensuring the cryptographic security of timings is a challenging task due to limitations in the client's browser when it comes to secure computation. Any attempt to encrypt data between the client and server can be undermined by adjusting the actual timing values.

Relying on server-side timing also presents challenges, as failing to consider latency issues can result in users with faster connections gaining an unfair advantage. Moreover, users could manipulate latency during certain phases of the game to disrupt compensation mechanisms.

While implementing measures to prevent user manipulation is possible, relying solely on obscurity for security is not a sustainable approach.

Ultimately, striking a balance between trusting users to some extent (which is generally reasonable) and creating gameplay mechanics that are resistant to timing manipulation may be the most effective strategy.

To ensure accurate timing in an application, it is crucial to start timing on the server when the user receives the puzzle and stop timing when they submit their answer. Even if an application is compiled, it can still be manipulated if the user changes their system clock during the timing process, resulting in inaccurate time reporting.

One way to minimize the impact of slow connections is by loading the puzzle data asynchronously after the initial load of the page and game engine. This helps level the playing field by reducing the amount of data that needs to be transmitted over the network.

While latency compensation may not be feasible due to vulnerability to tampering, the delay caused by network latency is likely negligible compared to the time taken for a human to solve the puzzle. For optimal performance, users are advised to avoid using their internet connection for other tasks while playing and can test their speed/latency for better results.

It's important to note that even with 200ms considered as bad lag (the average human reaction time), the impact of latency on puzzle-solving is minimal unless the task is purely based on visual reaction speed. In such cases, lag could significantly affect results, but for more complex puzzles, the effect of lag is less significant.

Commencing and concluding the timer on the client-side poses a risk of tampering...

Any action taken by the user at the client level is susceptible to being modified, halted, or circumvented..

Implementing encryption/decryption on the client side also raises security concerns as users can manipulate data before it gets encrypted..

Due to financial implications, trusting users becomes a challenge..

The timer must be initiated on the server and terminated on the server as well..

Utilize ajax to start the timer on the server exclusively after receiving the puzzle contents response from the ajax call. Avoid loading the puzzle first and then sending an ajax request as this could be intercepted and delayed while the puzzle is being examined...

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One approach would be to handle the timing functionality on the server side, depending on how your server is set up. You could log the time of the website request (saving it in a database if desired), then calculate the duration of the answer by comparing it to the current time when received. Alternatively, you might consider storing the timing data in the session object instead of the database, though I'm not sure about its reliability there.

In order to ensure accuracy, server-side time must be used in this scenario. Here is a possible approach:

Upon document ready, initiate an AJAX request to communicate with the server. Upon receiving the ping, store the server-side time as a session variable (ensuring it does not already exist). When the quiz is completed, record the server-side time once more and compare it to the session variable to determine the duration. Finally, remove the session variable.

Benefits of this method include:

• Avoiding initiation of timer before quiz display
• Accounting for network delays by waiting for the AJAX response
• Preventing spoofing by confirming no existing session variable before storing

Additionally, you could retain client-side time and incorporate it into the final submission. By comparing it against the server-calculated time, if they align closely, you can trust the client's timing.

Out of all the questions you posed, I'll address just one from your original query:

Will I need to work with a compiled tool like Flash? (Scary.)

Absolutely. Considering your requirements: 1) absolute precision and 2) zero chance of user disruption, employing a compiled binary is inevitable.

However, it doesn't necessarily have to be Flash - my recommendation would be a Java applet if the idea of using Flash gives you chills.

-- Update:

After feedback from ZoFrex, it appears that this solution has some flaws.

-- Previous Solution:

One approach is to send a series of "problems" for the JavaScript code to solve while users are engaging with the puzzle. For example, you can provide a large number N that is the product of two prime numbers (prime1 * prime2). This will require clients to factorize the number using JavaScript, which takes time. By profiling clients and sending appropriately sized prime numbers, you can control the difficulty level.

You could then send around 500 of these prime-based problems for solving in the background. The JavaScript will create a list of solutions, and upon submission, you send back the completed value along with this list. By analyzing the total number of responses received, you can determine how much time was spent on the puzzle.

Cons:

• Requires client profiling to gauge capabilities
• Vulnerable to downgrade attacks
• Complex implementation
• Possibility of interruptions by JavaScript computations
• Risk of bots solving problems faster than JavaScript

Pros:

• Calculations are necessary for form submission
• If implemented properly, can prevent all but advanced attacks

While not foolproof, this method seems reasonable, albeit potentially attackable. Ultimately, deploying a more secure client-side system is advisable. Additionally, Flash is not a secure option due to its vulnerability to decompilation. As evidenced by an IQ test conducted live on television in Australia controlled by a Flash app, won by a computer programmer.

-- Update:

OP, I mentioned in a comment but want to reiterate - consider exploring Hashcash, a concept aimed at demonstrating completion of 'Work' by clients. Even if my suggestion doesn't fit your needs, delving into this area might yield valuable insights.

Solving this dilemma poses a challenge as it is inherently unsolvable, requiring one to navigate through the tradeoffs to achieve the best outcome. Numerous valid points have been raised on the technical front, such as: (a) avoiding futile efforts in compiling to Flash, Windows, Silverlight, JVM, or any other platforms, (b) prioritizing the transmission of the encrypted puzzle payload first and then sending the key separately to address the bottleneck issue, (c) acknowledging that the latency of sending a few hundred bytes even on 56k is insignificant compared to human reaction time.

An aspect that has not been highlighted yet is:

Implementing post-event auditing and user tracking. This approach mirrors how genuine casinos operate. Allegedly, this strategy played a significant role in PayPal's success. Instead of heavily relying on pre-emptive security measures, both institutions closely monitor player activities, utilizing various technologies like statistics and pattern detection to flag suspicious behavior for further investigation. In both scenarios, users are unable to immediately withdraw their funds. They must either cash out their chips or wait for the money to transfer from PayPal's system to their actual bank account. Your system should adopt a similar process—preventing them from accessing their winnings right away, giving you time to potentially seize any illicit earnings. Have legal representation, correct? Similar to casinos and PayPal, identifying a user's real identity (necessary for financial transactions) enables legal actions against malevolent actors or serves as a deterrent. By combining these strategies with the previously mentioned tips, cheating can be effectively eradicated.

If cheating persists, revise your objective to mitigating rather than completely eliminating dishonest practices. Strive for a level of integrity akin to maintaining a 99.99% uptime. While it’s true, as noted by another contributor, that one individual compromising the system jeopardizes all, a robust auditing mechanism prevents consistent cheating. Even if an attacker manages to exploit the system occasionally, being caught after one or two attempts dissuades repeated violations. Consequently, only a minuscule fraction of users would engage in fraudulent behavior, with honest users facing minimal risk due to irregular instances of cheating. Any detected cheat affecting an honest user should prompt exceptional efforts to ensure their satisfaction surpasses the incident’s value, instilling confidence in your security measures. People-oriented challenges often necessitate solutions beyond technology alone; incorporating interpersonal approaches alongside technological innovations enhances efficiency.

Could you please clarify why the server time cannot be utilized? The timestamp of when the response is received will serve as the basis for the score calculation.

Like many have mentioned:

1. Using server time is crucial as client time can be easily manipulated.
2. Relying on server time may disadvantage individuals with slow network connections or those located far away from the server.

The key solution lies in implementing a time synchronization protocol between the client and the server, similar to NTP's methodology. By collaborating, the client and server can calculate network latency delay and adjust timestamps accordingly for each user.

While NTP's algorithms are intricate and refined through years of development, a simpler approach can be adopted. The proposed protocol outlined below seems promising, although thorough testing is recommended.

The client initiates two successive HTTP XMLRPC pings to measure round-trip time. Each ping returns a unique nonce, with the second relying on the first to ensure sequential order. Puzzle timing commences upon sending the second HTTP ping. The server timestamps each request and estimates puzzle display halfway between receiving the first and second requests.

Upon completion of the puzzle, the client repeats the process with two additional pings, following the same protocol. The server tracks the timing of both requests and calculates the time delta. By subtracting half the time delta from when the first ping of the second set arrives, we can determine the approximate puzzle completion time accurately.

Check out this rapid implementation of cryptography in JavaScript.

This tool enables public/private key encryption directly on the client side, making it possible to encrypt Ajax communication between your server and the client browser.

For a detailed explanation and instructions on adapting it to your specific needs, visit .

Have you considered using an iFrame to host the game and its JavaScript on your server, where your server-side implementation is running? By doing so, any ajax requests would originate from the same IP address as your server, solving the issue of identifying the source. While additional security measures would still be necessary, this approach could increase confidence in your client-side requests. It's worth noting that services like windowsLive login rely on similar techniques involving JavaScript and iFrames for security.

In my opinion, there is no perfect solution to this issue. However, I have come up with an alternative approach that can make it more difficult for cheaters, although it may also disadvantage honest users who are just unlucky.

To address this problem, gather a range of roundtrip time measurements from specific devices, locations, and other variables in advance for each user, based on their interactions with your website. You should also collect these measurements for the entire user population. Additionally, consider obtaining timestamps for DNS lookups from the user's ISP resolver, using a random hostname and hosting the authoritative DNS server for that domain.

Once you have gathered this data, conduct all measurements on the server side (i.e., sending the puzzle to the user and receiving the solution) and subtract the network time based on previous observations.

It's important to recognize that factors like server load, client load (such as slow processors), and other variables can impact timing in any solution.

Lastly, ensure that you have XSRF protection on the puzzle submission page to enhance security :)