As far as I know there are two padding mechanisms, which are PKCS 5 and 7. Which one should be used for CBC?
One runtime platform provides an API that supplies PKCS#5 padding for block cipher modes such as ECB and CBC. These modes have been defined for the triple DES, AES and Blowfish block ciphers. The other platform API only provides PKCS#7 padding.  Are PKCS#5 padding and PKCS#7 padding compatible?
I'm trying to mount my HDD,  /dev/sdb, which is connected via an enclosure but every time I try do so I get an error message   mount: /dev/sdb: can't read superblock   How do I solve this problem and mount my HDD? Best answer versus best solution I've got a bunch of files named with a the pattern 99 - DescriptiveName.txt and I'd like to remove the number from the front so I just have DescriptiveName.txt.  How can I do this? Can I do it from the command line or is there a utility that can do this? How can I show that the sum   $$ \sum_{k = 0}^n 2^k \binom{n}{k}$$  is equal to $3^n$? I have a DVD I was trying to rip, and handbrake froze up when scanning it.  I tried to eject the DVD by dragging and dropping it to the trash, which trashed the icon, but didn't eject the DVD.  I then forced Handbrake to quit, but without an icon on my desktop to select, how can I eject the DVD? For any real number $a \geq 1$ let $f(a)$ denote the real solution of the equation $x(1+\ln x)=a$ then the    question is to find out $$ \lim_{a \to \infty} \frac{f(a)\ln a}{a}$$.  It is clear that if we denote $h(a)$ by $h(a)=a(1+\ln a)$ then $f(a)$ is the inverse function of $h(a)$. Also $f(a)$ is increasing function in its domain. Also the limit persuades using lhospital's but I cannot see how to apply it here. Thanks. Using Ubuntu 11.10, how do I format an external or USB drive? I don't find an option to 'format' when I right click. In the new version, the drives don't come up on the desktop, but instead come on the Launcher. This is a general, community wiki  question to address non-specific "I need a CMS or Wiki that does x, y, and z..." questions.  If your question was closed as a duplicate of this question and you feel that the information provided here does not provide a sufficient answer, please open a discussion on .    I have a list of features that I want for my website's Content Management System (CMS) - where can I find a [free] script that includes all of them? Specifically, define the sub-gaussian norm for a r.v. X as  $$ \|X\|_{\psi_2}=\inf\{t&gt;0:e^{X^2/t^2}\leq 2\}. $$  How do we prove that the centering inequality with $C=1$ does not hold in general? i.e. $$ \|X-\mathbb{E}X\|_{\psi_2}\leq C\|X\|_{\psi_2}.  $$ A counter example would work too. Thanks in advance! How do I set a default host for nginx? I'm trying to figure out how to set a default host for my nginx installation. I found this article in the nginx Wiki:    Unfortunately, this doesn’t work. After restarting I get this:  Restarting nginx: nginx: [emerg] unknown directive "http" in /etc/nginx/sites-enabled/catchall:1 nginx: configuration file /etc/nginx/nginx.conf test failed   After removing the http directive I get this:  Restarting nginx: nginx: [emerg] unknown log format "main" in /etc/nginx/sites-enabled/catchall:7 nginx: configuration file /etc/nginx/nginx.conf test failed   I’m on Ubuntu 10.04.3 where I’m using the official nginx PPA. Version 1.0.9 of nginx is running. I recall a short lived TV show that I think was broadcast on the British TV channel ITV in the late 90s or early 2000s and it was about time travel. It was set in Britain in relatively modern times. The scene that really sticks in my head is when the protagonist goes to use their time travelling machine they go in to a room where the machine is and they close all the windows. The windows have latches on them and by closing the window it creates a circuit. By closing all the latches the circuit is complete and the machine is able to be activated. I don't know if it's much to go on, but it's been really bugging me for ages. Function $f(z)$ such that $|f(z)| > |z|$ for every $z\in\mathbb{C}, 1/f(z)$ SCP through multiple hosts describes how to SSH into a machine that can only be accessed through one or more hosts (that can also be SSH'd into).  Is there an equivalent way of using scp? That is, copy a file to my local machine from the far machine (assuming I have password or key access to all machines along the way)? How to ignore certain files in Git If $A = \tan6^{\circ} \tan42^{\circ},~~B = \cot 66^{\circ} \cot78^{\circ}$ find the relation between $A$ and $B$ My trigonometric problem is:     If $A = \tan6^{\circ} \tan42^{\circ}$ B = cot$66^{\circ} \cot78^{\circ}$ find the relation between $A$ and $B$.    Working :   $$B = \cot 66^{\circ} \cot78^{\circ} = 1- \frac{\tan24^{\circ}+\tan18^{\circ}}{\tan42^{\circ}}$$  $$A= \tan6^{\circ} \tan42^{\circ} = 1- \frac{\tan6^{\circ} +\tan42^{\circ}}{\tan48^{\circ}}$$  but it seems  this is the wrong way of doing this...please suggest. Thanks! If $(1), (log_yx), (log_zy), (-15log_xz)$ are in Arithmetic Progression... If $(1), (log_yx), (log_zy), (-15log_xz)$ are in AP then...   (A)$z^3=x$   (B)$x=y^{-1}$   (C)$z^{-3}=y$   (D)$x=y^{-1}=z^3$   (Multiple answers may be correct)   I tried many approaches, one of them being: $1+log_zy=2log_yx$ $log_zz+log_zy=log_yx^2$ $log_z(yz)=log_yx^2$ But the fact that the bases are different is causing the main problem as I don't know how to proceed further. It would be great if anybody could give me a hint for solving such questions. How to uninstall Windows from a Dual Boot system? How do I grep for all non-ASCII characters? Task manager for Ubuntu Is my ESTA valid for a second trip? I visited the USA in May this year, on an ESTA which I applied for in April. It was approved and I was allowed entry into the country.    I'm re-visiting again this November for two weeks. Am I able to use the same ESTA again or do I need to re-apply for a new one? I know it says it's valid for two years, but is that valid for every use within those two years, or I have to use it within two years, and once I have visited on that visa, it's invalid?