I've been reading papers on variable sized block cipher constructions based on fixed-length block ciphers, and they tend to focus on increasing the block size. They either gloss over or speak too generally about decreasing the block size. (Or I'm just not getting it, which is possible)     While these are certainly helpful, I also need a way to encrypt a size much smaller than the usual block ciphers. For example, a credit card has 16 digits, which can be represented in 54 bits. To encrypt a credit card number to another one would require a 54-bit block cipher. (The 54-bits could be brought even lower if you consider that the first and last digits are not random)  Is there a way to do this in such a way that the security isn't brought below the chance of simply guessing the plaintext?
Suppose I want a strong 20-bit blockcipher.  In other words, I want a function that takes a key (suppose the key is 128 bits), and implements a permutation from 20 bits to 20 bits.  The set of permutations should be close to a randomly-chosen subset of size $2^{128}$ of all $2^{20}!$ permutations on 20 bits.  I don't want you to build a new blockcipher from scratch.  Instead, assume you have a "strong" blockcipher like AES (128-bit blocksize, 128-bit keysize) and use this to build your 20-bit cipher.   Of course, your construction should be practical (i.e., you should be able to run it in both directions with reasonable amounts of time and memory).
Regression without intercept: deriving $\hat{\beta}_1$ in least squares (no matrices) I  as unclear what you're asking after receiving flags on it in the moderator queue.   Once I did that, the text for the question title in the moderator queue changed from:     How to use handler to display images from database without passing ID in querystring?    to     How to use handler to display images from database without passing ID in querystring? [undefined more votes needed]    The text on the main page has stayed consistent with the new 'on hold' verbiage, however.  Here's a screenshot: JavaScript property access: dot notation vs. brackets? Why do single-author community wiki answers (or questions?) link to revisions, rather than to the author's profile? Possible Duplicate:             Looking at  , I noticed something peculiar: Community Wiki posts* with only one author have not one, but two different links to the revisions page.    Is this entirely necessary? When clicking on the author's name in this case, I entirely would expect to be brought to the author's profile, rather than to the (potentially one-item-long) revisions list.   *(maybe only answers? couldn't find any good single-author CW question references) 3-manifold examples of homomorphisms between fundamental groups that are not induced by continuous maps I need to repair my Windows 10 installation. Where can I get a clean ISO (with install.wim, no Install.ESD, so that I can run DISM against the WIM) of the specific Windows 10 build required for this?  In my case, I need the Anniversary update (Build 14393), Creators Update (Build 15063) or Fall Creators Update (Build 16299.15). The question asks us to classify all distributions in $\mathbb{R}^2$, say $u$, such that $$(xy)u(x,y) = (x^2-y^2)u(x,y)= 0.$$ I am genuinely stuck, any help is extremely appreciated. Time Dilation When In Orbit How to determine if string contains specific substring within the first X characters Cannot install Oracle JDK via apt in Ubuntu 16.04 I created a new Ubuntu 16.04.3 VM and am attempting to install JDK 9. Unfortunately, the latest version of the JDK apt installer, 9.0.1-1~webupd8~0, is failing to download the binaries and I suspect that the reason is because   I carried out the typical steps for installation:    add-apt-repository ppa:webupd8team/java apt-get update &amp;&amp; apt-get install oracle-java9-installer   I am then prompted with the following error message:  Downloading Oracle Java 9... --2018-01-16 15:15:07--  http://download.oracle.com/otn-pub/java/jdk/9.0.1+11/jdk-9.0.1_linux-x64_bin.tar.gz Resolving download.oracle.com (download.oracle.com)... 23.200.70.136 Connecting to download.oracle.com (download.oracle.com)|23.200.70.136|:80... connected. HTTP request sent, awaiting response... 302 Moved Temporarily Location: https://edelivery.oracle.com/otn-pub/java/jdk/9.0.1+11/jdk-9.0.1_linux-x64_bin.tar.gz [following] --2018-01-16 15:15:11--  https://edelivery.oracle.com/otn-pub/java/jdk/9.0.1+11/jdk-9.0.1_linux-x64_bin.tar.gz Resolving edelivery.oracle.com (edelivery.oracle.com)... 23.35.226.115, 2600:1404:21:49d::2d3e, 2600:1404:21:493::2d3e Connecting to edelivery.oracle.com (edelivery.oracle.com)|23.35.226.115|:443... connected. HTTP request sent, awaiting response... 302 Moved Temporarily Location: http://download.oracle.com/otn-pub/java/jdk/9.0.1+11/jdk-9.0.1_linux-x64_bin.tar.gz?AuthParam=1516137431_0e89d10b30203a572ea858768475ef74 [following] --2018-01-16 15:15:11--  http://download.oracle.com/otn-pub/java/jdk/9.0.1+11/jdk-9.0.1_linux-x64_bin.tar.gz?AuthParam=1516137431_0e89d10b30203a572ea858768475ef74 Connecting to download.oracle.com (download.oracle.com)|23.200.70.136|:80... connected. HTTP request sent, awaiting response... 404 Not Found 2018-01-16 15:15:11 ERROR 404: Not Found.  download failed Oracle JDK 9 is NOT installed. dpkg: error processing package oracle-java9-installer (--configure):  subprocess installed post-installation script returned error exit status 1 Errors were encountered while processing:  oracle-java9-installer E: Sub-process /usr/bin/dpkg returned an error code (1)   I found , but it does not appear that the  works for JDK 9.0.4+11. I've updated the SHA checksums (), set the major version to 9.0.4, and set the minor version to 11, but I'm still not having success.  What steps need to be carried out to get the JDK apt installer to work until the WebUpd8 team is able to update the PPA? To turn off my system, I can use one of these three commands:  sudo halt   Or:  sudo poweroff   Or:  sudo shutdown -h now   What are the differences between these commands, or are they all just aliases of each other? Is it somehow possible that I can extend the link to something which I produce by using \ref with a label by the word standing before \ref? If I write something like that: For further information, have a look into chapter \ref{chap:abc} and figure \ref{fig:def}  then the only thing being &quot;clickable&quot; are the chapter number and the figure number. Is it somehow possible to make the words &quot;chapter&quot; and &quot;figure&quot; being linked to those objects as well? Express $\sqrt{3}\sin\theta - \cos\theta$ as: $a\cos (\theta + \alpha) $ Find an example of a function sum $\sum_{n=1}^\infty u_n $ that converges   uniformly on $[a,b]$ and converges absolutely pointwise, but   $\sum_{n=1}^\infty |u_n| $ doesn't converge uniformly on $[a,b]$.   This seems pretty straightfoawrd but it's really hard to find an example. The choice of $u_n$ must be very specific. You can actually prove any power series wont work (due to Abel's theorem)  In addition, in order to prove the uniform convergence, $u_n$ must not satisfy Weierstrass' M-Test (because then $\sum |u_n|$ would converge uniformly aswell) What LaTeX markup would one have to write to produce a result similar to the image below?    Please excuse my Paint-and-mouse drawing skills. :-) Can I change directory to a Windows drive in Ubuntu Bash on WSL? I am a super newbie for Ubuntu and basically need Ubuntu for a Python package.  I would like to run a Python file in say e:/username/folder1/folder2/python.py. I tried every method online and the only reply is bash: cd./e: No such file or directory. I am not sure whether it is because of the bash windows or virtualenv.  When I use bash on Ubuntu on Windows, ls, it says VIRTUALENV_DIR. cd, it says /home/username. The cd .. etc changes the directory a little, but not another drive, nor the folder I would like it to find. How to get things off your head in Minecraft Mo' Creatures mod I installed the Mo'Creatures mod into Minecraft, then made a fish bowl. After catching a fish I went to put it on top of a bookshelf in my room, but instead of placing it, the bowl just dropped at my feet. When I tried to pick it up my character put it on his head. Now I'm stuck with a fish bowl on my head and I can't find any mention anywhere of how to get it off. There are a number of other animals from the mod that you can put on your head for some effect, but no mention of how to remove them pretty much anywhere. Do class spells take up spell slots? So I'm fairly new and ended up being the Cleric in my also fairly new group. I haven't played a caster before and the book says that at level 1 I have Bless and Cure Wounds. Do I need to assign these to a spell slot or do I have them inherently (not to be confused with a cantrip; I know I'd have to use a slot to cast them)? Alpha over layers but maintain environment background How do I transfer my Destiny account from Xbox 360 to Xbox One?