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  • Is there a circular hash function?

    - by Phil H
    Thinking about this question on testing string rotation, I wondered: Is there was such thing as a circular/cyclic hash function? E.g. h(abcdef) = h(bcdefa) = h(cdefab) etc Uses for this include scalable algorithms which can check n strings against each other to see where some are rotations of others. I suppose the essence of the hash is to extract information which is order-specific but not position-specific. Maybe something that finds a deterministic 'first position', rotates to it and hashes the result? It all seems plausible, but slightly beyond my grasp at the moment; it must be out there already...

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  • ASP.NET Membership Password Hash -- .NET 3.5 to .NET 4 Upgrade Surprise!

    - by David Hoerster
    I'm in the process of evaluating how my team will upgrade our product from .NET 3.5 SP1 to .NET 4. I expected the upgrade to be pretty smooth with very few, if any, upgrade issues. To my delight, the upgrade wizard said that everything upgraded without a problem. I thought I was home free, until I decided to build and run the application. A big problem was staring me in the face -- I couldn't log on. Our product is using a custom ASP.NET Membership Provider, but essentially it's a modified SqlMembershipProvider with some additional properties. And my login was failing during the OnAuthenticate event handler of my ASP.NET Login control, right where it was calling my provider's ValidateUser method. After a little digging, it turns out that the password hash that the membership provider was using to compare against the stored password hash in the membership database tables was different. I compared the password hash from the .NET 4 code line, and it was a different generated hash than my .NET 3.5 code line. (Tip -- when upgrading, always keep a valid debug copy of your app handy in case you have to step through a lot of code.) So it was a strange situation, but at least I knew what the problem was. Now the question was, "Why was it happening?" Turns out that a breaking change in .NET 4 is that the default hash algorithm changed to SHA256. Hey, that's great -- stronger hashing algorithm. But what do I do with all the hashed passwords in my database that were created using SHA1? Well, you can make two quick changes to your app's web.config and everything will be OK. Basically, you need to override the default HashAlgorithmTypeproperty of your membership provider. Here are the two places to do that: 1. At the beginning of your element, add the following element: <system.web> <machineKey validation="SHA1" /> ... </system.web> 2. On your element under , add the following hashAlgorithmType attribute: <system.web> <membership defaultProvider="myMembership" hashAlgorithmType="SHA1"> ... </system.web> After that, you should be good to go! Hope this helps.

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  • Recommend software: File checksum calculator

    - by Johnny W
    Hi, I'm looking for a light, fast hash/checksum calculator (eg. MD5, SHA1, etc.). I've been using HashCalc and it works fine enough, but I was wondering if there was something better. When downloading .ISOs from MS BizSpark, I've found that it's essential to check the SHA1, and I'm sure that other people have found the same... So what's the defacto, light, fast, simple app that does the job? :) Thanks for any recommendations.

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  • Monitoring folder diffs across servers with zabbix

    - by Marcus
    Problem: I want to make sure that a certain folder is equal regarding it's contents across my servers. I do not want an automatic filesync to keep them equal, changing is done manually. My initial thought was to once a day calculate some crc/hash on folder and send to Zabbix, and trigger when values differ. Is there any good tools out there that can calculate crc or similar of a folder? Anyone know of another solution that solves my problem?

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  • AS3 and hashing

    - by gok
    Is it possible to hash flv videos so it is unplayable by itself and the format is unrecognizable by softwares, but i could actually de-hash them and play in my as3 script? This is going to be realized on a CD so I can't use server scripts.

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  • Operations on Python hashes

    - by cdecker
    I've got a rather strange problem. For a Distributed Hash Table I need to be able to do some simple math operations on MD5 hashes. These include a sum (numeric sum represented by the hash) and a modulo operation. Now I'm wondering what the best way to implement these operations is. I'm using hashlib to calculate the hashes, but since the hashes I get are then string, how do I calculate with them?

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  • Numeric operations over SHA-1 generated keys in C#

    - by webdreamer
    I'm trying to implement a Chord distributed hash table. I want to use SHA-1 as the hash function to generate node ids and map values to the DHT. However, I'll need to use numerical operations on the SHA-1 generated key, such as a modulo, for example. I wonder in which type of variable should I put the array of bytes I get, and how can I convert from one to another.

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  • How does Microsoft generate the Event ID for winqual events?

    - by Tim
    I am curious about the IDs that are used to identify items in winqual. I assume it is some sort of hash. Is this published? Hash of the module name, its version and an offset? That seems appropriate but the size is too small to cover the possibilities unless some truncation/lossy algorithm is used. This seems to be generated with the minidump on the client machine.

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  • What's the big deal with brute force on hashes like MD5

    - by Jan Kuboschek
    I just spent some time reading http://stackoverflow.com/questions/2768248/is-md5-really-that-bad (I highly recommend!). In it, it talks about hash collisions. Maybe I'm missing something here, but can't you just encrypt your password using, say, MD5 and then, say, SHA-1 (or any other, doesn't matter.) Wouldn't this increase the processing power required to brute-force the hash and reduce the possibility of collision?

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  • Hashing (hidding) strings in Python

    - by Lucas
    What I need is to hash a string. It doesn't really have to be secure because its just going to be a hidden pharse in the text file (simply it doesn't have to be recognizable for a human-eye). It should not be just a random string because when user will be typing the string I would like to hash it and compare it with already hashed one (in the text file). What would be the best for this purpose? Can it be done with the own class?

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  • Rails - Why is HAML showing the full hash?

    - by Mr. Demetrius Michael
    View: !!! %html %head %title= full_title(yield(:title)) =stylesheet_link_tag "application", media: "all" =javascript_include_tag "application" =csrf_meta_tags =render 'layouts/shim' %body =render 'layouts/header' .container =flash.each do |key, value| %div{class: "alert alert-#{key}"} #{value} Controller def create @user = User.new(params[:user]) if @user.save flash[:success] = "This is Correct" redirect_to @user else flash[:wrong] = "no" render 'new' end end Regardless of the flash (:success or :wrong or otherwise) it always compiles the entire hash as html (below) Output: <!DOCTYPE html> .... <div class='container'> <div class='alert alert-wrong'>no</div> {:wrong=&gt;&quot;no&quot;} </div> </body> </html> I have no idea why {:wrong=&gt;&quot;no&quot;} is being displayed. I've been staring at this terminal for hours. What's interesting is that the hash is being outputted with the container id, but not in the alert class. It feels like an indentation problem, but I went through several permutations with no success.

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  • HREF link that targets nothing, does not want to use hash or void(0)

    - by Mattis
    I have a link that I want to be able to click to trigger a piece of jQuery code. Currently I have <a href="#" id="foo">Link</a> and $('#foo').click(function(){ // Do stuff }); which works well. But, I have always hated using hash in this way. The page flickers and the hash is added to the page url. One alternative is to use <a href="javascript:void(0);" id="foo">Link</a> but I also dislike seeing that piece of code in the browser status bar. It looks tacky. What I'd rather have is an explanatory javascript placeholder that does nothing, like <a href="javascript:zoom();" id="foo">Link</a> which actually works, but throws an ReferenceError in the javascript console since there are no such function. What's the minimum definition of a function that does nothing? Are there any other alternatives? Should I just skip the link and use something like <span id="foo" style="cursor:pointer;cursor:hand;">Link</span> instead?

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  • Prevent hash navigation url

    - by Koningh
    I have the following problem: I'm using a slider (coda) to let people navigate trough some 'pages'. The slider uses hash links to navigate to the next page/slide. If a user is at page one (#page1), there is a link which will lead the user to page 2 (#page2) and so on. At the top of the slider the numbers of the pages appear as a link, but only when the page is visited. So if there are six pages and the user navigates from the first to the second and then the third one, there are only three links at the top of the slider (to page one, two and three). The problem is that a user can navigate to page five (or any page actually) without first visiting the pages previous to page five by just using the hash URL and typing the whole link in their address bar. For example if I would type www.mydomain.com/slider/index.php#page5 the slider automatically navigates to the fifth slide/page of the slider and thereby skipping the first four. I want to allow users to navigate to #page5 only if they have visited the first four (So by clicking trough the slides). This means that if they would go to #page5 directly by typing the URL in the address bar, I would like them to be send to the first page (#page1). Does anyone have any idea on solving this?

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  • Perl help dereferencing a reference to an array of hash references, containing record set data

    - by user1724150
    I'm using the a Amazon Perl module that returns a reference to an array of hash references as $record_sets, containing record set data and I'm having a hard time dereferencing it. I can print the data using data dumper but I need to be able to manipulate the data. Below is the documentation provided for the module Thanks In Advance: #list_resource_record_sets #Lists resource record sets for a hosted zone. #Called in scalar context: $record_sets = $r53->list_resource_record_sets(zone_id => '123ZONEID'); #Returns: A reference to an array of hash references, containing record set data. Example: $record_sets = [ { name => 'example.com.', type => 'MX' ttl => 86400, records => [ '10 mail.example.com' ] }, { name => 'example.com.', type => 'NS', ttl => 172800, records => [ 'ns-001.awsdns-01.net.', 'ns-002.awsdns-02.net.', 'ns-003.awsdns-03.net.', 'ns-004.awsdns-04.net.' ]

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  • Storing large json strings to database + hash

    - by Guy
    I need to store quiete large JSON data strings to the database. I am using gzip to compress the string and therefore BLOB MySQL data type to store it. However, only 5% of all the requests contain unique data and only unique data ought to be stored to the database. My approach is as follows. array_multisort data (array [a, b, c] is virtually the same as [a, c, b]). json_encode data (json_encode is faster than serialize; we need string array representation for the step 3). sha1 data (slower than md5, though less possible the collisions). Check if the hash exists in the database. 5.1 yes – do not insert the data. 5.2. no – gzip the data and store it along the hash. Is there anything about this (apart from storing JSON data to the database in the first place) that sounds fishy or should be done a different way? p.s. We are talking about a database with roughly 1kk unique records being created every month.

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  • hash tables and 2d vectors

    - by Sunil
    I want to push a 2d vector into a hash table row by row and later search for a row (vector) in the hash table and want to be able to find it. I want to do something like #include <iostream> #include <set> #include <vector> using namespace std; int main(){ std::set < vector<int> > myset; vector< vector<int> > v; int k = 0; for ( int i = 0; i < 5; i++ ) { v.push_back ( vector<int>() ); for ( int j = 0; j < 5; j++ ) v[i].push_back ( k++ ); } for ( int i = 0; i < 5; i++ ) { std::copy(v[i].begin(),v[i].end(),std::inserter(myset)); // This is not correct but what is the right way ? // and also here, I want to search for a particular vector if it exists in the table. for ex. the second row of vector v. } return 0; } I'm not sure how to insert and look up a vector in a set. So if nybody could guide me, it will be helpful. Thanks

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  • Is hashing of just "username + password" as safe as salted hashing

    - by randomA
    I want to hash "user + password". EDIT: prehashing "user" would be an improvement, so my question is also for hashing "hash(user) + password". If cross-site same user is a problem then the hashing changed to hashing "hash(serviceName + user) + password" From what I read about salted hash, using "user + password" as input to hash function will help us avoid problem with reverse hash table hacking. The same thing can be said about rainbow table. Any reason why this is not as good as salted hashing?

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  • Cacti is ignoring hash marks in interface aliases

    - by Matt Simmons
    I'm attempting to set up Cacti to monitor a router's interfaces, and I'm having trouble getting the graph templates to show the information that I'd like. Our interface configuration looks like this: interface GigabitEthernet3/6 description WalljackNumber # Server info no ip address no shutdown switchport switchport access vlan 116 switchport mode access ip dhcp snooping trust spanning-tree portfast The "Server Info" string is really just the machine name, and a short relevant description, such as "PolarSprings vmnic2". The important part appears to be that it follows the hashmark. When I run snmpwalk, I get the proper output: IF-MIB::ifAlias.230 = STRING: WalljackNumber # Server info But in Cacti, when I go into the graph templates and set the title to this: |host_description| - Traffic - |query_ifName| (|query_ifAlias|) All that shows up in the graph is: switchname - Traffic - Gi3/6 (WalljackNumber #) Which strikes me as a little weird. What I suppose MAY be happening is that somewhere in the cacti stream, it's interpreting # as being a comment and stripping everything after, but I'm not sure. I was hoping someone could tell me that this was a known documented behavior, or that I could change it in a setting that I wasn't aware of. The alternative answer is to change the delimiter from # to something else, but I've got over a thousand lit switchports on an old college infrastructure, and I'm not sure what else might be relying on them.

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  • linux: accessing thousands of files in hash of directories

    - by 130490868091234
    I would like to know what is the most efficient way of concurrently accessing thousands of files of a similar size in a modern Linux cluster of computers. I am carrying an indexing operation in each of these files, so the 4 index files, about 5-10x smaller than the data file, are produced next to the file to index. Right now I am using a hierarchy of directories from ./00/00/00 to ./99/99/99 and I place 1 file at the end of each directory, like ./00/00/00/file000000.ext to ./00/00/00/file999999.ext. It seems to work better than having thousands of files in the same directory but I would like to know if there is a better way of laying out the files to improve access.

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  • Hashing the state of a complex object in .NET

    - by Jan
    Some background information: I am working on a C#/WPF application, which basically is about creating, editing, saving and loading some data model. The data model contains of a hierarchy of various objects. There is a "root" object of class A, which has a list of objects of class B, which each has a list of objects of class C, etc. Around 30 classes involved in total. Now my problem is that I want to prompt the user with the usual "you have unsaved changes, save?" dialog, if he tries to exit the program. But how do I know if the data in current loaded model is actually changed? There is of course ways to solve this, like e.g. reloading the model from file and compare against the one in memory value by value or make every UI control set a flag indicating the model has been changed. Now instead, I want to create a hash value based on the model state on load and generate a new value when the user tries to exit, and compare those two. Now the question: So inspired of that, I was wondering if there exist some way to generate a hash value from the (value)state of some arbitrary complex object? Preferably in a generic way, e.g. no need to apply attributes to each involved class/field. One idea could be to use some of .NET's serialization functionality (assuming it will work out-of-the-box in this case) and apply a hash function to the content of the resulting file. However, I guess there exist some more suitable approach. Thanks in advance.

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  • How would you implement a hashtable in language x?

    - by mk
    The point of this question is to collect a list of examples of hashtable implementations using arrays in different languages. It would also be nice if someone could throw in a pretty detailed overview of how they work, and what is happening with each example. Edit: Why not just use the built in hash functions in your specific language? Because we should know how hash tables work and be able to implement them. This may not seem like a super important topic, but knowing how one of the most used data structures works seems pretty important to me. If this is to become the wikipedia of programming, then these are some of the types of questions that I will come here for. I'm not looking for a CS book to be written here. I could go pull Intro to Algorithms off the shelf and read up on the chapter on hash tables and get that type of info. More specifically what I am looking for are code examples. Not only for me in particular, but also for others who would maybe one day be searching for similar info and stumble across this page. To be more specific: If you had to implement them, and could not use built-in functions, how would you do it? You don't need to put the code here. Put it in pastebin and just link it.

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  • Generating an identifier for objects so that they can be added to a hashtable I have created

    - by dukenukem
    I have a hashtable base class and I am creating different type of hashtable by deriving from it. I only allow it to accept objects that implement my IHashable interface.For example - class LinearProbingHashTable<T> : HashTableBase<T> where T: IHashable { ... ... ... } interface IHashable { /** * Every IHashable implementation should provide an indentfying value for use in generating a hash key. */ int getIdentifier(); } class Car : IHashable { public String Make { get; set; } public String Model { get; set; } public String Color { get; set; } public int Year { get; set; } public int getIdentifier() { /// ??? } } Can anyone suggest a good method for generating an identifier for the car that can be used by the hash function to place it in the hash table? I am actually really looking for a general purpose solution to generating an id for any given class. I would like to have a base class for all classes, HashableObject, that implements IHashable and its getIdentifier method. So then I could just derive from HashableObject which would automatically provide an identifier for any instances. Which means I wouldn't have to write a different getIdentifier method for every object I add to the hashtable. public class HashableObject : IHashable { public int getIdentifier() { // Looking for code here that would generate an id for any object... } } public class Dog : HashableObject { // Dont need to implement getIdentifier because the parent class does it for me }

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