Understanding birthday attacks on 256 bit hashing and 512 bit hashing
Is 512 bits a more secure hashing than 256 bits?
4 cards are drawn from a pack without replacement. What is the probability of getting all 4 from different suits?  Here's how I tried to solve:  For the first draw, we have 52 cards, and we have to pick one suit. So, probability for this is $\frac{13}{52}$.  For the second draw, only 51 cards are left. The second suit has to be selected, so there are 13 cards from that suit. The probability is $\frac{13}{51}$.  Similarly, the third and fourth draw have probabilities $\frac{13}{50}$ and $\frac{13}{49}$ respectively.  Since the draws are independent, the total probability becomes $$\frac{13}{52} \times \frac{13}{51} \times \frac{13}{50} \times \frac{13}{49}$$  But my book says the answer is $\frac{{13\choose 1} \times {13 \choose 1} \times {13\choose1} \times {13\choose1}}{52 \choose 4}$.  My answer differs by a factor of $4!$. What did I do wrong? Repeat copies of array elements: Run-length decoding in MATLAB "The thing is, is that..." When are stopovers permitted on Japan Railways (JR) trains? Can a Filipino citizen with no Korean visa with a long layover in Seoul take the airport free city tour? I am a Filipino citizen traveling from Saipan to Manila via Seoul, with 13 hours layover.  Do I need a Korean visa to take the airport free city tour? What time zone do SO's servers operate in? What time zone do Stack Overflow's servers operate in?  I noticed that it couldn't be my time zone, or the ones before me (I'm in North American Eastern Time), because I logged into SO earlier today (around 12 pm), then I logged in just a few minutes ago (around 8 pm), then about a minute later I got the Fanatic badge (yay me!). Highest quality website screenshot? I have created a  that i would like to add to my portfolio, but i'm having a hard time getting high quality screenshots of the full site. I tried to save the website as PDF, but that was full of errors, other online services cant recreate the images and so on. I've also just tried to take regular screenshots on the mac at put it all together, but it really lost a lot of quality when i scaled it down.  Any good ideas? :) How to get the current time in Python I'm married have a job with stable income.I have 2 kids. I have applied for UK visit visa about 7 years ago and was refused. I can't remember what exactly was the reason for refusal.  I want to travel for tourism to spend 9 days and my budget is around 1300GBP for the trip. I would be spending part of my annual leave in the UK. I have the following people in UK: Mother, Dad, Sister(she's married), Brother (married), Uncle and Aunt.  I'm travelling alone since my wife is pregnant. I haven't travelled since I was in school then.  I will be on my yearly 21 days annual leave during which I will be spending 9days in UK. I can't think of anything more about my circumstance.  So what should a cover letter look like?  secondly I have just 1 account where my salary is paid in monthly and my savings.I will be submitting the 6 months bank statement for the account.  Additional question:  In the income &amp; expenditure where one is asked to indicate if I have income and savings,should I click Yes or No. And if Yes should state the ending balance as at the time of my application. Object Positions Reset On Blender Load So I am attempting to make a modular environment in Blender, so I'm modeling many pieces in one scene to make sure they all match up properly before separating them out.  However, whenever I restart Blender after saving and closing it, many of my grouped objects (and their subobjects) have positions reset NOT to where I placed them.  For example, take a look at this:   Here you can see that the door pieces are in the "open" state, when I left them closed AND the "column" for the wall on the left has been moved from being flush with the wall (on the side) to being inside it.  It appears to be trying to move all of the objects to 0,0,0 which is what is messing this up. I'm not sure if it's an object hierarchy problem, but here is my hierarchy if anyone has ideas there:  Wall_Normal (parent)   Wall_Normal_Column (child)   Empty Axis Object (parent)   Door_Left (child a) Door_Right (child b)   Is there a reason why object positions (and their relative subobjects) aren't being saved? number length limit in SOQL Where condition When I execute SOQL in Developer Console:  Select Id, Amount From Opportunity Where Amount &gt; 10000000000   An parsing error occurs:  Unknown error parsing query   Is there length limit of number on SOQL Where condition? What is the difference between /sbin/nologin and /bin/false? I have often heard it recommended that a user account should be disabled by setting its shell to /bin/false. But, on my existing Linux systems, I see that a great number of existing accounts (all of them service accounts) have a shell of /sbin/nologin instead.  I see from the man page that /sbin/nologin prints a message to the user saying the account is disabled, and then exits. Presumably /bin/false would not print anything.  I also see that /sbin/nologin is listed in /etc/shells, while /bin/false is not.  The man page says that FTP will disable access for users with a shell not listed in /etc/shells and implies that other programs may do the same. Does that mean that somebody could FTP in with an account that has /sbin/nologin as its shell?  What is the difference here? Which one of these should I use to disable a user account, and in what circumstances? What other effects does a listing in /etc/shells have? Why does the C++ map type argument require an empty constructor when using []? Definition of "pepper" in hash functions Can I dump my non-Retina Images for a iOS7 only app? Negative pressure Should the weight of downvotes be increased? Gravitational waves and time Deleted user's posts showing in 'First Posts' queue On Scifi.SE, a user had their account deleted this morning.  Also this morning, about half a dozen of "their" posts were in the First Posts queue.  The posts were all roughly a month old, and they all had the same disassociated user#.   one of them.  Why'd this person's posts show up in the First Posts queue?  Why do a deleted user's posts ever show up in that queue, when it's purpose is to help the community provide feedback to new users?  A deleted user is no longer a member of the community, and they're not even going to be able to act on any feedback. What's a word for someone who is constantly asking for same thing? Hi I'm looking for a word for someone who is constantly asking for something and keeps wanting updates about it. The closest words I can think of is pushy and, to a lesser extent, annoying. But clearly these words don't directly mean what I intend.