In the web application I use 10,000+ iterations for hashing passwords stored in database (random salt and all). Password-related operations are not frequent enough to create a noticeable performance hit. Signing authentication tokens is a different story. This happens on every token renewal which may happen on every request but in practice is configured to happen at least every X seconds. I cannot find any recommendation as to the number of iterations for generating HMAC for encrypted payload such as the token. What are the risks of using a very low number, let's say 10? I use 24 byte salts.
I'm developing a messenger application with encrypted chats.   In the first version of the app I've used PBKDF2 (10000 iterations, SHA1, random salt) to extend a short user password and generate keys to encrypt (AES256) and sign message (HMAC).  In the current version of the app I generate a random 130-bit key and use it instead of a user password. I think that using PBKDF2 with such a key has some overhead.   I see 2 possible ways to improve the current approach:   Keep using PBKDF2 and decrease iterations to 1 or 10. Don't use PBKDF2 and use HKDF instead.   What are the advantages and disadvantages of each approach? Are there any other options?
Delay HTML5 :invalid pseudo-class until the first event Access parent's parent from javascript object Is it possible to have site-specific badges? Is there any preference given based on how far in advance of the deadline a graduate application is submitted? How to use GROUP BY to concatenate strings in SQL Server? I am trying to use a file repository for updating linux/ubuntu on a non-connected machine. The architecture for this machine (uname -a):  x86_64 GNU/Linux   The results of dpkg --printarchitecture are:  amd64   It is a Trusty Tahr amd64 machine, and it specifically says this, for example, in the aptitude sources.list file. Also, the "About this Computer" in ubuntu specifically says the machine is 64-bit. So, I installed the amd64 packages on the machine. However, when I try to do apt-get update, I get errors such as:  W: Failed to fetch file:/var/spool/apt-mirror-trusty/mirror/archive.ubuntu.com/ubuntu/dists/trusty/main/binary-i386/Packages  File not found   So, in other words, even though it is a 64-bit machine, apt is inexplicably trying to read i386 packages. Why is it doing this and how can I make it use the 64-bit packages?  Note that there is nothing in sources.list that specifies i386.  The only uncommented line in the sources.list file is:  deb file:///var/spool/apt-mirror-trusty/mirror/archive.ubuntu.com/ubuntu trusty main restricted universe multiverse What is the integral of 0? I need my pre-installed version of Windows 7 (or any other version of Windows), how could I install Ubuntu without erasing it? Formal Languages - Regular Expression I've been battling the following two questions for more than a day today.  Write a regular expression (comprised of {a, b}) that contain at least two b and do not contain abb. Write a regular expression (comprised of {a, b}) that contain abba and do not contain baa.  For the first part I wrote a basic one to start off with that doesn't handle the must two-b: b* OR a* OR (a+ AND b)* OR a*  I ran a few &quot;truth tables&quot; inputs over it and it seems ok. But the moment I add the requirement, things go haywire. Mostly because when pushing in those &quot;b&quot;s, you can suddenly use the OR to break things up. Same thing on the second one.... Any help would be greatly appreciated! Norah Ubuntu 14.04 multi touch screen support Just installed 14.04. It seems to be converting all my screen touch gestures to mouse gestures. And it only supports one point touch. It is supposed to support ten touch points (tested with windows 8.1).  Am I missing something here? Do I have to install some kind of package? Or is it just not supported?  Test - being able to draw here: How do I pass JavaScript variables to PHP? What is the equation for the tension on the ends of a cable suspended at different heights? I'm looking for an equation to find the tension on the ends of a cable suspended between two poles (one higher than the other) with no load but the cable itself.    I determined that the tension would be different on each end, that the shape of the suspended cable would be a  truncated at one end, and that the following would be the variables necessary in the equation:   cable weight cable length vertical distance between ends horizontal distance between ends   Some links that could be helpful: Can I use B1 visa (Visitor-Business) to travel to the Canada without a business purpose? I got a B1 visa (Visitor-Business) for Canada in 2012 when I traveled to Canada for a business trip from my company. It expires in 2015 and I'd love to visit the Canada again, but for no other purpose than traveling, visiting family.  I want to know, If I can legally travel to Canada with B1 visa without a real business need (assuming I'm honest);  I live in India, and I have B1/B2 from US and used same Visa for Business &amp; Personal visits multiple times. Canonical vs. non-canonical terminal input I am currently in a clan with three members. When we tried to initiate a clan war it said we had insufficient clan requirements. Does anyone know what the full requirements are? Is there a minimum clan member requirement? Any Info on Generalized Binomial and Exponential Series? I was reading Concrete Mathematics by Knuth et al. and on p. 200, it references the generalized binomial series $\mathcal B_t(z)$ and the generalized exponential series $\mathcal E_t(z)$, defined as $$\mathcal B_t(z)=\sum_{k\ge0}(tk)^{\underline{k-1}}\frac{z^k}{k!}\quad\text{and}\quad\mathcal E_t(z)=\sum_{k\ge0}(tk+1)^{k-1}\frac{z^k}{k!},$$ where $x^{\underline k}$ denotes the falling factorial. I was interested in the generalized binomial series because it satisfied the identity $$\frac{\mathcal B_t(z)^r}{1-t+t\mathcal B_t(z)^{-1}}=\sum_{k\ge0}\binom{tk+r}{k}z^k.$$ I've been trying to find a way to compute the sum $\sum_{n\le k\le m}\binom{tk+r}{k}$, so this seemed related. It seems that $\mathcal E_1(z)$ is also somewhat related to the Lambert $W$ function, though I might be wrong. Searching them up online didn't seem to get anywhere, and I just want to find more sources where I can learn about these functions. If anyone can find some resources, I'd appreciate it! Check whether an array is a subset of another Any idea on how to check whether that list is a subset of another?  Specifically, I have  List&lt;double&gt; t1 = new List&lt;double&gt; { 1, 3, 5 }; List&lt;double&gt; t2 = new List&lt;double&gt; { 1, 5 };   How to check that t2 is a subset of t1, using LINQ? Curvature of a curve on a sphere How do I create a key binding that allows me to mount my google drive? I want to mount/unmount my google drive using with a key binding without having to open a terminal. How can I set this up? Word meaning you are describing something as if to a child Looking for a word that describes the feeling of being told something in an overly simplified manner that feels offensive.