A simple attack on DESX in time $2^{120}$
DES-X , computation load and storage
How can one use multi threading in PHP applications Is there a realistic way of implementing a multi-threaded model in PHP whether truly, or just simulating it. Some time back it was suggested that you could force the operating system to load another instance of the PHP executable and handle other simultaneous processes.  The problem with this is that when the PHP code finished executing the PHP instance remains in memory because there is no way to kill it from within PHP.  So if you are simulating several threads you can imagine whats going to happen.  So I am still looking for a way multi-threading can be done or simulated effectively from within PHP. Any ideas? Show that an operation being commutative is a structural property "Unable to locate package" while trying to install packages with APT What is Active Directory Domain Services and how does it work? This is a  about Active Directory Domain Services (AD DS).         I find myself explaining some of what I assume is common knowledge about it almost daily. This question will, hopefully, serve as a canonical question and answer for most basic Active Directory questions. If you feel that you can improve the answer to this question, please edit away. How to evaluate the integral $$\int_{25\pi / 4}^{53\pi / 4}\frac{1}{(1+2^{\sin x})(1+2^{\cos x})}dx\ ?$$ Thought Experiment - Poking a stick across a Black Hole's Event Horizon The classical explanation of a black hole says that if you get to close, you reach a point - the event horizon radius - from which you cannot escape even travelling at the speed of light. Then they normally talk about spaghetti.  But here's a thought experiment. What if I have a BH with event horizon radius R such that the gravitational gradient at the event horizon is far too weak for creating pasta. I build a Ring with radius R+x around the BH. Then I lower a pole of length x+d from my ring towards the BH, so that the tip passes beyond the event horizon.  Now what happens when I try to pull the pole back? How do I set up my studio for shooting large rugs from the ceiling? What is the most efficient way to add rows and columns to a matrix? Why doesn't Cantor's diagonal argument also apply to natural numbers? Let $G$ be a group, where $(ab)^3=a^3b^3$ and $(ab)^5=a^5b^5$. Prove that $G $ is an abelian group. How do I drop root privileges in shell scripts? The "--up" option in OpenVPN is normally used for routing etc. And so it is processed before OpenVPN drops root privileges to run as nobody. However, I am invoking shell scripts that need to run as an unprivileged user.  How do I do that? I have studied , especially polynomial's and tylerl's answers, but I do not understand how to implement. I am working in Centos 6.5, and suid is blocked, both as "chmod u+s" and as "setuid()".  There is an OpenVPN plugin ("openvpn-down-root.so") which enables scripts invoked by the "--down" option to run as root. There could be an equivalent, such as "openvpn-up-user.so", but I have not found it.  Edit0  Per Nikola Kotur's answer, I've installed . Although the chpst command works in terminal, in the up script it fails with "command not found". What works is "sudo chpst" plus setting the proper display and language. Please see  Given that, the up script needs these four lines:  LANG="en_US.UTF-8"; export LANG GDM_LANG="en_US.UTF-8"; export GDM_LANG DISPLAY=:0; export DISPLAY sudo chpst -u user -U user /home/user/unprivileged.sh &amp;   Edit1  Per 0xC0000022L's comment, I find that "sudo -u user" works as well as "sudo chpst -u user -U user":  LANG="en_US.UTF-8"; export LANG GDM_LANG="en_US.UTF-8"; export GDM_LANG DISPLAY=:0; export DISPLAY sudo -u user /home/user/unprivileged.sh &amp;   I'll study man sudoers and update if/when I get sudo alone to work. Where are all islands and discoverable locations? After taking off in Simpleplanes and flying around over the ocean for a while, I've found a lots of tiny islands all over the place, and a few really big ones that unlock new spawn locations once found.  Large islands appear to also have many discoverable 'locations' around them as well, like airports, carriers, or landmarks.  These locations automatically become available as start points once discovered.  Where can I find all of these major islands, and once there, where should I look to unlock all of the locations? In my assignment I have to prove that the following function doesn't have a limit:  $$f(x)=\frac{x}{x-\lfloor{\sin x}\rfloor}$$ when $${x \to 0}$$  In other words, I have to prove that for every $\delta$ such that $0&lt;|x-{x_0}|&lt;\delta,$ $|f(x)-L|&gt;\epsilon$.  In fact, I don't even know how to start. Do I choose my $\delta$? I know that the sin function has certain values that's supposed to help me. How do I use it?  I have to prove this by definition, so I can't use limit arithmetic for example  Thanks. Does there exist a holomorphic function with the following property? Why are my Elytra Wings are not activating? Why do my Elytra Wings only work intermittently?  I do not forget to jump, but when I switch to Survival and then back to Creative, they won't activate whatsoever. Any help is much appreciated. Thanks. How do I hide Thunderbird from the launcher while running? I have a question for you all.  It's possible to "hide" thunderbird from the unity application bar when thunderbird is running?  For my is unhelpfull see thunderbird on the "mail" tray ( near shutdown button) and the unity "running" application.  If i close thunder with the close button, it don't notify me new email. Turning off and on images in figures Is it possible to prevent the contents of a figure from being rendered? I have a large book document, and to speed up compiling while working on a draft, I would like to have some way of ignoring the content of the images, but ensuring that the figure size remains.  In several cases I am using a line like:  \includegraphics[width=\linewidth]{figure.pdf}     so I do not know the actual size of the image. data.table and table unexpected behavior Let $R$ be a commutative ring with 1 then why does $a\in N(R) \Rightarrow 1+a\in U(R)$? Selectively disable iCloud keychain syncing for WiFi passwords I have iCloud Keychain sync enabled, but I want to stop it syncing WiFi passwords.  I have a portable WiFi hotspot which I use for my laptop and iPad, but I don't want my iPhone to connect to it since it has it's own 3G  Because iCloud is syncing the settings, within about 30 seconds of connecting my laptop to the 3G hotspot, my iPhone will connect itself. If I go into wifi settings on the iPhone and manually disconnect, about 30 seconds later my laptop will disconnect too. It seems with iCloud wifi sync on, I can’t connect my laptop to WiFi without my phone also connecting.  The only way to get around it seems to be disabling Keychain sync in iCloud. I’ve tried Googling, but got no real help on how to disable it without turning off Keychain, which is what I’ve done at the moment.  I also don't want to enable 'Ask before joining networks' on my iPhone, since I'll be manually re-connecting it constantly.