HMAC for encrypted authentication token: recommended iteration number 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.
PBKDF vs HKDF for pretty long key 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?
Wired connection not working Ubuntu 12.04 I have some shares that are mounted during login. I used Users &amp; Groups' "Login Items" panel to do this. When I login, all of the shares pop up in their own Finder windows.  How can I keep the Finder windows from popping up at login? I've already tried checking the Hide checkbox. If a run the watch command containing an alias, it will not expand the alias. I have tried both with single quote and double quotes, in fact given the following alias:  # alias ll alias ll='ls -l --color=tty'   The following command will fail  # watch ll sh: ll: command not found   Shouldn't command line expansion work in this case? Why doesn't a commutator cause the rotation to reverse periodically or stop? I understand the field magnets attracting/repelling the armature/coil so that it turns one half-turn and then, because the commutator is turned, its contact with the brushes has switched sides, and the current goes in the opposite direction, reversing the electromagnetic polarity. Then, because the polarity is swapped, it attracts/repels to complete the second half-turn. The thing is, isn't it a bit of a gamble that it will turn in the same direction? Couldn't the it just be pulled/pushed back, more or less undoing the half-turn?  I'm also a bit confused how the rotation doesn't just stop once the commutator is oriented so that the brushes are contacting both sides of the commutator. In other words, there's a brief period just as the commutator switches the current directions where each both the brushes are in contact with both sides of the commutator where the current is neutralized. Shouldn't this stop the motor?    For reference, I'm just talking about a simple DC motor. How to open recovered files in word? My computer restarted while I was asleep because of system updates (need to turn that off), and when I opened up Word the first time after it restarted, it gave me a pane on the left hand side that showed me all the documents I had opened.  I chose one of the documents but I want to open them all, how can I bring that pane back?    Update:  I forgot to mention I'm on Word 2007.  I've found that if you go to      C:\Users*YOURUSER*\AppData\Roaming\Microsoft\Word   you can see the autorecovery files.  Mine are still in there, but I don't want to touch them, I'd rather bring back that pane and do it right just in case they disappear as soon as I double click haha... Please recommend undergraduate-level textbooks on electrodynamics which emphasize practical applications and real life examples. Please describe the book's level and contents and its intended audience in as much detail as possible.   Please provide both applications from everyday life for curious students as well as engineering applications from a physics perspective. Is it "I" or "me" in "Keep Tom and I/me updated"? In this case what is correct?        Keep Tom and I updated.      or         Keep Tom and me updated.      I understand that me is an object pronoun. And therefore I feel the second option is correct.  Especially, because I would say "Keep him updated" and also "Keep me updated". Instead of "Keep he updated" or "Keep I updated". But something about saying "Keep him and me updated" feels wrong.  However I am not sure, because several people have told me that in this case I is the correct option because it is being used in conjunction with a name (Tom) and not a pronoun. Is that correct? this code always returns 0 in PHP 5.2.5 for microseconds:  &lt;?php $dt = new DateTime(); echo $dt-&gt;format("Y-m-d\TH:i:s.u") . "\n"; ?&gt;   Output:  [root@www1 ~]$ php date_test.php 2008-10-03T20:31:26.000000 [root@www1 ~]$ php date_test.php 2008-10-03T20:31:27.000000 [root@www1 ~]$ php date_test.php 2008-10-03T20:31:27.000000 [root@www1 ~]$ php date_test.php 2008-10-03T20:31:28.000000   Any ideas? Given two increasing continuous functions $f,g$ prove that $(b-a) \int^b_a f(x)g(x) dx > \int^b_a f(x) dx \int^b_a g(x) dx$ Given two monotonically increasing continuous functions $f,g$ prove that  $$(b-a) \int^b_a f(x)g(x) dx &gt; \int^b_a f(x) dx \int^b_a g(x) dx,\; b&gt;a$$  what I have tried:  Let $$h(x) = (x-a)\int^x_a f(t)g(t) dt - \int^x_a f(t)dt\int^x_a g(t)dt $$ and trying to figure out that $h'&gt;0$ using MVT to reform $h'(x)$ as   $$h'(x) = (x-a)(-f(x)g(\xi_1) - g(x)f(\xi_2) + f(x)g(x) + f(\xi_3)g(\xi_3))$$ where $\xi_{1,2,3} \in (a,x)$ (That method does not seem to work) Drawing wavy, wiggly lines in QGIS? Is there a QGIS function or plugin to draw wiggly line?   I have used Spline Tool to manually draw some waves, but it is time consuming.  If possible, I would like to draw something like:    Inkscape Function Plotter ( sin(x) curve). Can anyone tell me if there is a way with generics to limit a generic type argument T to only:   Int16 Int32 Int64 UInt16 UInt32 UInt64   I'm aware of the where keyword, but can't find an interface for only these types,  Something like:  static bool IntegerFunction&lt;T&gt;(T value) where T : INumeric Do tag edits count for Archaeologist? Environment.TickCount vs DateTime.Now List of all active modules used in a site Assume $R=(\mathcal{U}_n)_n$ is a sequence of distinct ultrafilters on some set $X$. Since every Hausdorff space has an infinite discrete subspace, there is a subsequence $R=(\mathcal{V}_n)_n$ of $R=(\mathcal{U}_n)_n$ such that $\{\mathcal{V}_n|n \in \mathbb{N} \}$ is a discrete subspace of $\beta X$. In particular, there is a sequence $(A_n)_n$ of sets with $A_n \in \mathcal{V}_m$ if and only if $m =n$. If we let $B_n=A_n - (A_0 \cup...\cup A_{n−1})$, then the sequence $(B_n)_n$ is pairwise disjoint and $B_n \in \mathcal{V}_m$  iff $m=n$. If we let $B =\cup_n B_{2n}$, then $B \in \mathcal{V}_m$ if and only if $m$ is even. In other words, if $B =\{ \mathcal{V} \in βX|B \in \mathcal{V}\}$, then $B$ is a clopen set with $\mathcal{V}_m \in B$ iff $m$ is even. Therefore, we conclude that the sequence $(\mathcal{V}_m)_m$ cannot converge to any point, so the sequence $(\mathcal{U}_n)_n$ cannot converge to any point either.     I would like to know that:      (1) Why "$B_n \in \mathcal{V}_m$  iff $m=n$"? And " $B =\cup_n B_{2n}$, then $B \in \mathcal{V}_m$ if and only if $m$ is even "?      (2)$B$ is a clopen set with $\mathcal{V}_m \in B$ iff $m$ is even Touchpad stopped working 20.04 Let $ \boldsymbol{x} $ be a vector of $n$ numbers in the range $ \left[0, c \right] $, where $ c $ is a positive real number.  What's is the maximum of the variance function of this $ n $ numbers? Maximum in the meaning what spread of the number will maximize the variance? What would be a tighter bound for other assumptions on the spread of the numbers.  The variance of the vector $ \boldsymbol{x} $ is given by:  $$ \operatorname{var} (\boldsymbol{x}) = \frac{1}{n} \sum_{i = 1}^{n} {\left( {x}_{i} - \overline{\mathbf{x}} \right )}^2 $$  Where the mean $\overline{\boldsymbol{x}}$ is given by:  $$ \overline{\boldsymbol{x}} = \frac{1}{n} \sum_{i = 1}^{n} {x}_{i} $$ What's the difference between Invoke() and BeginInvoke() Just wondering what the difference between BeginInvoke() and Invoke() are?   Mainly what each one would be used for.  EDIT: What is the difference between creating a threading object and calling invoke on that and just calling BeginInvoke() on a delegate? or are they the same thing? Options to hide reputation information on Stack Overflow? jQuery Isotope filter to no items?