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MarekKnapek Marek Knápek @programming.dev

Level 33 C++ sourcerer. https://about.me/marek.knapek

Posts 9
Comments 17
It must a pain to make a Rich Textbox
  • You can always take a look how for example Windows 3.11 and earlier did it for their *.rtf file format and their "write.exe" editor / viewer / renderer (if you want to call it that way).

  • What operating system and tools should a beginner use to learn programming?
  • Doesn't depend on programming language but something with visual debugger. You know that stuff when you can see current line of your source code highlighted, press a key to step into, step over and so on. You can see values inside your variables. You can also change your variables mid-run right form the debugger.

    Because you spend 20% of your time writing bugs and the other 80% debugging them. At least make it pleasant experience (no printf-style debugging).

    Back in the day I was using Turbo Pascal, Delphi, Visual Basic, C#, Java, PHP with Zend, Java Script, today I'm using Visual C++.

  • randomascii.wordpress.com 32 MiB Working Sets on a 64 GiB machine

    Memory is a relatively scarce resource on many consumer computers, so a feature to limit how much memory a process uses seems like a good idea, and Microsoft did indeed implement such a feature. Ho…

    32 MiB Working Sets on a 64 GiB machine
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    What is your job interview ritual?
  • Yes, I know this. It took me long time to figure this out. My entire life I focused on technical skills / programming / math / logic. As I deemed them most important for the job. I was like: "Hey, if you cannot program, why do you work as programmer (you stupido)?" Only few years ago I realized that even as programmer (as opposed to sales man) you really need those "meh" soft skills. And that they are really important and I should not call them "meh". I'm very good at solving problems, improving product's performance, memory consumption, discovering and fixings bugs, security vulnerabilities. But I'm very very bad at communicating my skills and communicating with people in general. I'm not able to politely tell people that theirs idea is bad, I just say "that's stupid". And I'm mostly/sometimes right (if I'm not 100% sure, I don't say anything), but the damage caused by the way I say it is often inreversible. That post of mine about the job interview and CV was half joke and half reality. I just freeze/stutter when I'm asked something that is obvious because it is written I my CV. I'm immediately thinking "Did he not received the CV?" or "Did he not read it?" "Why the fuck is he not prepared for the call? Why are we wasting time asking me what should be obvious because I sent it in advance?" I'm more robot than human. Put me in front of problem and forget to tell me that it is impossible to solve ... and I will solve it. But easy small talk ... disaster. Communicating what the problem really was ... disaster. Communicating how I solved it ... disaster. "It was not working before and now it works fine, what the hell do you want from me now?" Yes, I'm very bad in team, in collective. I didn't know the reason why, but since few years ago I know the root of the problem. It's not that everybody around me is stupid and don't know basic stuff (what I consider basic), but me unable to communicate with other humans.

  • What is your job interview ritual?
  • The interview starts ... the interviewer asks me "Tell me about yourself." ... I respond "Did you receive my CV? I put all important details about me ... right there. What questions do you have about my past jobs?" The interviewer encourages me again to tell him about myself, my past projects, etc. ... Me: Awkward silence. ... Me to myself: Dafuq? Should I read the CV from top to bottom OR WHAT?

  • How AES Is Implemented
  • Yes, but (there is always a but) it does not apply if you implement off-line encryption. Meaning no on-line service encrypting / decrypting attacker provided data (such as SSL / TLS / HTTPS). Meaning if you are running the cipher on your own computer with your own keys / plaintexts / ciphertexts. There is nobody to snoop time differences or power usage differences when using different key / different ciphertext. Then I would suggest this is fine. The only one who can attack you is yourself. In fact, I implemented AES from scratch in C89 language, this source code is at the same time compatible with C++14 constexpr evaluation mode. I also implemented the Serpent cipher, Serpent was an AES candidate back then when there were no AES and Rijndael was not AES yet. The code is on my GitHub page.

  • codingnest.com The Little Things: The Missing Performance in std::vector

    `std::vector` is often said to be the default container, because it provides good baseline performance for common operations. Recently, I experimented with a simple API change that can improve the performance of a common usage pattern by 10+ %.

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    The Little Things: The Missing Performance in std::vector
  • std::vector::reserve + std::vector::push_back in loop is sub-optimal, because push_back needs to check for re-allocation, but that never comes.

    std::vector::resize + std::vector::operator[] in loop is also sub-optimal, because resize default-initializes all elements only to be overwritten soon anyway.

    This article's author suggests push_back_unchecked.

    I suggest std::vector::insert with pair of random access iterators with custom dereference operator that does the "transform element" or "generate element" functionality. The standard will have resize_and_overwrite hopefully soon.

    Moar discussion:

    https://codingnest.com/the-little-things-the-missing-performance-in-std-vector/

    https://twitter.com/horenmar_ctu/status/1695823724673466532

    https://twitter.com/horenmar_ctu/status/1695331079165489161

    https://www.reddit.com/r/cpp/comments/162tohr/the_little_things_the_missing_performance_in/

    https://www.reddit.com/r/cpp/comments/162tohr/the_little_things_the_missing_performance_in/jy21hgd/

    https://twitter.com/basit_ayantunde/status/1644895468399337473

    https://twitter.com/MarekKnapek/status/1645272474517422081

    https://www.reddit.com/r/cpp/comments/cno9ep/improving_stdvector/

  • codingnest.com The Little Things: The Missing Performance in std::vector

    `std::vector` is often said to be the default container, because it provides good baseline performance for common operations. Recently, I experimented with a simple API change that can improve the performance of a common usage pattern by 10+ %.

    8
    I Don't Use Exceptions in C++ Anymore
  • Another alternative to C++ exceptions (instead of return code) is to use global (or thread local) variable. This is exactly what errno that C and POSIX are using or GetLastError what Windows is using. Of course, this has its own pros and cons.

  • PostgreSQL Optimizations
  • For this purpose I would search for Linux specific thing - a RAM based storage that receives data writes and even flushes/fsycs and then lazily writes them to HDD/SSD. There would be problem in case of power loss, but the gained performance... Unfortunately, I don't know any such tool.

  • What's New for C++ Developers in Visual Studio 2022 17.7 - C++ Team Blog
  • ABI break when?

    I know some unnamed big customers want ABI stability. But common ... VS2015, VS2017, VS2019 and VS2022 all compatible with each other if used with new enough linker? They all are sharing pre-defined macro _MSC_VER 19xx and VC++ toolset version number 14.xx. That is too much of holding back progress on performance and correctness fronts. Eight years is enough.

    Customers need to learn that they cannot rely on ABI stability of STL provided classes, cos guess what: The Holy Standard doesn't specify any. Toolchain vendors do. This also applies to MFC/ATL/whatnot distributed as part of Visual Studio. Remember the GCC copy-on-write string ABI problem? We already have technology to help migrate between ABI versions: one is called COM, other is pimpl, other is version number as first member of struct or first function parameter. I bet there are many more out there.

  • devblogs.microsoft.com What's New for C++ Developers in Visual Studio 2022 17.7 - C++ Team Blog

    We are happy to announce that Visual Studio 2022 version 17.7 is now generally available! This post summarizes the new features you can find in this release for C++. You can download Visual Studio 2022 from the Visual Studio downloads page or upgrade your existing installation by following...

    What's New for C++ Developers in Visual Studio 2022 17.7 - C++ Team Blog
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    Java
  • Makes sense, how would you represent floor(1e42) or ceil(1e120) as integer? It would not fit into 32bit (unsigned) or 31bit (signed) integer. Not even into 64bit integer.

  • C++ AES-256 encryption at compile-time
  • Think of advanced features of WinRAR not being accessible without valid licence key. Ehm, WinRAR distributes the same binary for both licensed and unlicensed users, unlocking the features with license key or with a crack (equivalent of NOPing the if). What if instead WinRAR distributed different binary for each licensed user, advanced features encrypted by per-user key. Crack or keygen would need to use some particular user's binary with theirs license. Easily trackable. Or crack would need need to be applied once and then distribute the un-encrypted features / code.

  • C++ AES-256 encryption at compile-time
  • Think of password protected access to something, anything. Instead of checking if(password == some_constant){...} or if(hash(password) == precomputed_hash){...} you encrypt that something. The first variant has disadvantage that some_constant is stored inside your binary, thus password visible to anybody. The second variant ... the same, hash of the password is stored inside the binary and could be brute-forced or rainbow-tabled. Both variants have the disadvantage, that there is a run-time check refusing access to some data, but those data are available in the binary anyway. Just open the program in debugger or in hex editor and NOP the if out. With my approach the data is unreadable without the correct password. The app could not be convinced / persuaded to provide the data in any way without the password.

  • C++ AES-256 encryption at compile-time

    github.com GitHub - MarekKnapek/mk_clib: My C stuff.

    My C stuff. Contribute to MarekKnapek/mk_clib development by creating an account on GitHub.

    GitHub - MarekKnapek/mk_clib: My C stuff.

    Do you want to encrypt something and include it into your application? Don't want to use pre-build step? Encrypt it at compile-time! Decrypt it at run-time, assuming end-user knows the key or password. Plain-text is not stored inside your binary file. https://github.com/MarekKnapek/mk_clib#constexpr-aes-256-encryption-and-run-time-decryption

    3

    AES encryption in C from scratch on web.

    Wanna encrypt something? I implemented AES-256 (aka military grade encryption) from scratch in C89, compiled it into WebAssembly and published it on web at https://marekknapek.github.io/crypt/ You need web browser that supports writing files to your disk from JavaScript.

    1
    FYI: Lemmy.world and other instances were hacked. Beehaw.org took itself down to mitigate risks
  • It is trade-off between convenience and security. With my approach stolen cookies are not usable from different computer / IP, the attacker needs additional work, he needs the victim computer to do the harm, his computer cannot do any harm. The downside is the user needs another log-in in case of his external IP changes. How often is it? Switch between mobile/WiFi. Otherwise ... almost never ... maybe 1x per day? I'm not proposing to log-out the user after IP change, I'm proposing to keep multiple sessions (on server) / auth cookies (on client) for each IPv4 or IPv6 prefix (let's say /56).

  • FYI: Lemmy.world and other instances were hacked. Beehaw.org took itself down to mitigate risks
  • And that JavaScript has access to cookies, that’s just a basic part of how web browsers work. Lemmy can’t do anything to prevent that.

    Yes and No. Cookies could be accessed by JS on the client. BUT. When the cookie is sent by the server with additional HttpOnly header, then the cookie cannot be accessed from JS. Look at Lemmy GitHub issue, they discuss exactly this. Lemmy server absolutely has power to prevent this.

    Again, Lemmy can’t do anything about that. Once there’s a vulnerability that allows an attacker to inject arbitrary JS into the site, Lemmy can’t do anything to prevent that JS from making requests.

    I believe they can. But I'm not sure about this one. The server could send a response preventing the web browser to request content from other domains. Banks are using this. There was an attack years ago when attacker created a web page with i-frame in it. The i-frame was full screen to confuse the victim it is actually using the Banks site and not the attacker site. The bank web site was inside the inner i-frame, the code in the outer frame then had access to sensitive data in the inner frame. I believe there are HTTP response headers that instruct the web browser to not allow this. But I'm not sure I remember how exactly this works.

    completely independent backend

    Yes, it would be more costly, but more secure. It is trade-off, which one is more important to you? In case of chat/blog/forum app such as Lemmy I prefer cheap, in case of my Bank website I prefer secure.

  • FYI: Lemmy.world and other instances were hacked. Beehaw.org took itself down to mitigate risks
  • Oh I forgot another line of defense / basic security mitigation. If a server produces an access token (such as JWT or any other old school cookie / session ID), pair it with an IP address. So in case of cookie theft, the attacker cannot use this cookie from his computer (IP address). If the IP changes (mobile / WiFi / ADSL / whatever), the legitimate user should log-in again, now storing two auth cookies. In case of another IP change, no problemo, one of the stored cookies will work. Of course limit validity of the cookie in time (lets, say, keep it valid only for a day or for a week or so).

  • FYI: Lemmy.world and other instances were hacked. Beehaw.org took itself down to mitigate risks
  • So what happened:

    • Someone posted a post.
    • The post contained some instruction to display custom emoji.
    • So far so good.
    • There is a bug in JavaScript (TypeScript) that runs on client's machine (arbitrary code execution?).
    • The attacker leveraged the bug to grab victim's JWT (cookie) when the victim visited the page with that post.
    • The attacker used the grabbed JWTs to log-in as victim (some of them were admins) and do bad stuff on the server.

    Am I right?

    I'm old-school developer/programmer and it seems that web is peace of sheet. Basic security stuff violated:

    • User provided content (post using custom emojis) caused havoc when processing (doesn't matter if on server or on client). This is lack of sanitization of user-provided-data.
    • JavaScript (TypeScript) has access to cookies (and thus JWT). This should be handled by web browser, not JS. In case of log-in, in HTTPS POST request and in case of response of successful log-in, in HTTPS POST response. Then, in case of requesting web page, again, it should be handled in HTTPS GET request. This is lack of using least permissions as possible, JS should not have access to cookies.
    • How the attacker got those JWTs? JavaScript sent them to him? Web browser sent them to him when requesting resources form his server? This is lack of site isolation, one web page should not have access to other domains, requesting data form them or sending data to them.
    • The attacker logged-in as admin and caused havoc. Again, this should not be possible, admins should have normal level of access to the site, exactly the same as normal users do. Then, if they want to administer something, they should log-in using separate username + password into separate log-in form and display completely different web page, not allowing them to do the actions normal users can do. You know, separate UI/applications for users and for admins.

    Am I right? Correct me if I'm wrong.

    Again, web is peace of sheet. This would never happen in desktop/server application. Any of the bullet points above would prevent this from happening. Even if the previous bullet point failed to do its job. Am I too naïve? Maybe.

    Marek.

  • Cryptographic hash functions calculator on-line.

    Hi all, I implemented yet another on-line cryptographic hash functions calculator. It is written in C, compiled into WebAssembly and is running inside your web browser (nothing is sent to the server). The calculator: https://marekknapek.github.io/hash, web page source code: https://github.com/MarekKnapek/MarekKnapek.github.io, C source code: https://github.com/MarekKnapek/mk_clib.

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    Cryptographic hash functions calculator on-line.

    Hi all, I implemented yet another on-line cryptographic hash functions calculator. It is written in C, compiled into WebAssembly and is running inside your web browser (nothing is sent to the server). The calculator: https://marekknapek.github.io/hash, web page source code: https://github.com/MarekKnapek/MarekKnapek.github.io, C source code: https://github.com/MarekKnapek/mk_clib.

    1

    Cryptographic hash functions calculator on-line.

    Hi all, I implemented yet another on-line cryptographic hash functions calculator. It is written in C, compiled into WebAssembly and is running inside your web browser (nothing is sent to the server). The calculator: https://marekknapek.github.io/hash, web page source code: https://github.com/MarekKnapek/MarekKnapek.github.io, C source code: https://github.com/MarekKnapek/mk_clib.

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