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Search found 337 results on 14 pages for 'hashing'.

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• Efficient way of detecting a touched object in a game?

  - by Pin

  Imagine a Sims-like 2D game for a touch based mobile phone where one can interact with virtually any object in the scene. How can I efficiently detect which object is being touched by the player? In my short experience, looping through all the visible objects in the scene and checking if they're touched has so far done the job, but when there may be many many moving objects in the screen that sounds kind of inefficient isn't it? Keeping the visible moving objects list can consume time in itself as one may have to loop through all of them each frame. Other solutions I've thought are: Spatial hashing. Divide the screen as a grid and place the visible objects in the corresponding bucket. Detection of the clicked object is fast but there's additional overhead for placing the objects in the correct bucket each frame. Maintaining a quad-tree. Moving objects have to be rearranged all the time, the previous solution looks better. What is usually done in this case?

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• Proper password handling for login

  - by piers

  I have read a lot about PHP login security recently, but many questions on Stack Overflow regarding security are outdated. I understand bcrypt is one of the best ways of hashing passwords today. However, for my site, I believe sha512 will do very well, at least to begin with. (I mean bcrypt is for bigger sites, sites that require high security, right?) I´m also wonder about salting. Is it necessary for every password to have its own unique salt? Should I have one field for the salt and one for the password in my database table? What would be a decent salt today? Should I join the username together with the password and add a random word/letter/special character combination to it? Thanks for your help!

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• Searching for fast skeletal animation algorithm

  - by igf

  Is it theoretically possible to dynamicaly animate scene with 100-150 400 poly characters meshes on high-end GL ES 2.0 mobile devices or i definetley should use prerendered keyframe animation? Scene have only one light source and precalculated shadow maps. View from top like in Warcraft 3. No any other meshes or objects. 2d collision detecting between objects calculated via spatial hashing. It can be any other algorithm besides ragdoll, but it must supply fast and simple skeletal animation for frame with 100+ low poly meshes for each mesh. Any ideas?

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• Handle all authentication logic in database or code?

  - by Snuffleupagus

  We're starting a new(ish) project at work that has been handed off to me. A lot of the database sided stuff has been fleshed out, including some stored procedures. One of the stored procedures, for example, handles creation of a new user. All of the data is validated in the stored procedure (for example, password must be at least 8 characters long, must contain numbers, etc) and other things, such as hashing the password, is done in the database as well. Is it normal/right for everything to be handled in the stored procedure instead of the application itself? It's nice that any application can use the stored procedure and have the same validation, but the application should have a standard framework/API function that solves the same problem. I also feel like it takes away the data from the application and is going to be harder to maintain/add new features to.

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• In Search Data Structure And Algorithm Project Title Based on Topic

  - by Salehin Suhaimi

  As the title says, my lecturer gave me a project that i needed to finish in 3 weeks before final semester exams. So i thought i will start now. The requirement is to "build a simple program that has GUI based on all the chapter that we've learned." But i got stuck on WHAT program should i build. Any idea a program that is related to this chapter i've learned? Any input will help. list, array list, linked list, vectors, stacks, Queues, ADT, Hashing, Binary Search Tree, AVL Tree, That's about all i can remember. Any idea where can i start looking?

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• Convert URI to GUID

  - by David Rutten

  What is a good way to convert a file path (URI) into a System.Guid? I'd like to minimize the possibility of a collision, but I'm happy with a reasonably unique hashing (probably never more than a few dozen/hundred items in the database)

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• 128-Bit Hash Method

  - by Kyle Rozendo

  Hi All, Does anyone know of a hashing method that you can use with .NET, that will output 128 Bytes? I cannot use SHA-2+ generation hashes, as it's not supported on many client machines. Thanks, Kyle

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• How are hash functions like MD5 unique?

  - by Aly

  Im aware that MD5 has had some collisions but this is more of a high level question about hashing functions. If MD5 hashes any arbitrary string into a 32-digit hex value, then according to the Pigeonhole Principle surely this can not be unique as there are more unique arbitrary strings than there are unique 32-digit hex values

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• What's the best library to do a URL hash/history in JQuery?

  - by alex

  I've been looking around JQuery libraries for the URL hash, but found none that were good. There is the "history plugin", but we all know it's buggy and isn't flexible. I am loading my pages inside a div. I'll need a way to do back/forward along with the url hashing. mydomain.com/#home mydomain.com/#aboutus mydomain.com/#register What's the best library that can handle all of this?

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• MD5 hash with salt for keeping password in DB in C#

  - by abatishchev

  Could you please advise me some easy algorithm for hashing user password by MD5, but with salt for increasing reliability. Now I have this one: private static string GenerateHash(string value) { var data = System.Text.Encoding.ASCII.GetBytes(value); data = System.Security.Cryptography.MD5.Create().ComputeHash(data); return Convert.ToBase64String(data); }

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• Are hash collisions with different file sizes just as likely as same file size?

  - by rwmnau

  I'm hashing a large number of files, and to avoid hash collisions, I'm also storing a file's original size - that way, even if there's a hash collision, it's extremely unlikely that the file sizes will also be identical. Is this sound (a hash collision is equally likely to be of any size), or do I need another piece of information (if a collision is more likely to also be the same length as the original). Or, more generally: Is every file just as likely to produce a particular hash, regardless of original file size?

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• Segmenting a double array of labels

  - by Ami

  The Problem: I have a large double array populated with various labels. Each element (cell) in the double array contains a set of labels and some elements in the double array may be empty. I need an algorithm to cluster elements in the double array into discrete segments. A segment is defined as a set of pixels that are adjacent within the double array and one label that all those pixels in the segment have in common. (Diagonal adjacency doesn't count and I'm not clustering empty cells). |-------|-------|------| | Jane | Joe | | | Jack | Jane | | |-------|-------|------| | Jane | Jane | | | | Joe | | |-------|-------|------| | | Jack | Jane | | | Joe | | |-------|-------|------| In the above arrangement of labels distributed over nine elements, the largest cluster is the “Jane” cluster occupying the four upper left cells. What I've Considered: I've considered iterating through every label of every cell in the double array and testing to see if the cell-label combination under inspection can be associated with a preexisting segment. If the element under inspection cannot be associated with a preexisting segment it becomes the first member of a new segment. If the label/cell combination can be associated with a preexisting segment it associates. Of course, to make this method reasonable I'd have to implement an elaborate hashing system. I'd have to keep track of all the cell-label combinations that stand adjacent to preexisting segments and are in the path of the incrementing indices that are iterating through the double array. This hash method would avoid having to iterate through every pixel in every preexisting segment to find an adjacency. Why I Don't Like it: As is, the above algorithm doesn't take into consideration the case where an element in the double array can be associated with two unique segments, one in the horizontal direction and one in the vertical direction. To handle these cases properly, I would need to implement a test for this specific case and then implement a method that will both associate the element under inspection with a segment and then concatenate the two adjacent identical segments. On the whole, this method and the intricate hashing system that it would require feels very inelegant. Additionally, I really only care about finding the large segments in the double array and I'm much more concerned with the speed of this algorithm than with the accuracy of the segmentation, so I'm looking for a better way. I assume there is some stochastic method for doing this that I haven't thought of. Any suggestions?

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• Are has collisions with different file sizes just as likely as same file size?

  - by rwmnau

  I'm hashing a large number of files, and to avoid hash collisions, I'm also storing a file's original size - that way, even if there's a hash collision, it's extrememly unlikely that the file sizes will also be identical. Is this sound (a hash collision is equally likely to be of any size), or do I need another piece of information (if a collision is more likely to also be the same length as the original). Or, more generally: Is every file just as likely to produce a particular hash, regardless of original file size?

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• Searching through large data set

  - by calccrypto

  how would i search through a list with ~5 mil 128bit (or 256, depending on how you look at it) strings quickly and find the duplicates (in python)? i can turn the strings into numbers, but i don't think that's going to help much. since i haven't learned much information theory, is there anything about this in information theory? and since these are hashes already, there's no point in hashing them again

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• Combine hash values in C#

  - by Chris

  I'm creating a generic object collection class and need to implement a Hash function. I can obviously (and easily!) get the hash values for each object but was looking for the 'correct' way to combine them to avoid any issues. Does just adding, xoring or any basic operation harm the quality of the hash or am I going to have to do something like getting the objects as bytes, combining them and then hashing that? Cheers in advance

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• How can I convert a C# list into something that's hashable?

  - by gatoatigrado

  I want something along the lines of Python's tuples (or, for sets, frozensets), which are hashable. I have a List<String> which is most certainly not hashing correctly (i.e. by value).

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• How to Create Own HashMap in Java?

  - by Taranfx

  I know about hashing algorithm and hashCode() to convert "key" into an equivalent integer (using some mathematically random expression) that is then compressed and stored into buckets. But can someone point me to an implementation or at least data structure that should be used as baseline? I haven't found it anywhere on the web.

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• best encryption method

  - by mazhar kaunain baig

  What is the most standard encryption technique used in sql server for asp.net c# enterprise level application? . i am talking with respect to standards like md5 or sh1 etc, hashing

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• Saving private data

  - by rajatgoel

  Hi, Can anybody detail some approach on how to save private data in social websites like facebook, etc. They cant save all the updates and friends list in clear text format because of privacy issues. So how do they actually save it? Hashing all the data with user password so that only a valid session view it is one possibility. But I think there are some problem with this approach and there must be some better solution.

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• How can I hash a string to an int using c++?

  - by zebraman

  I have to write my own hash function. If I wanted to just make the simple hash function that maps each letter in the string to a numerical value (i.e. a=1, b=2, c=3, ...), is there a way I can perform this hash on a string without having to first convert it to a c-string to look at each individual char? Is there a more efficient way of hashing strings?

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• Webservice for uploading data: security considerations

  - by Philip Daubmeier

  Hi everyone! Im not sure about what authentification method I should use for my webservice. I've searched on SO, and found nothing that helped me. Preliminary Im building an application that uploads data from a local database to a server (running my webservice), where all records are merged and stored in a central database. I am currently binary serializing a DataTable, that holds a small fragment of the local database, where all uninteresting stuff is already filtered out. The byte[] (serialized DataTable), together with the userid and a hash of the users password is then uploaded to the webservice via SOAP. The application together with the webservice already work exactly like intended. The Problem The issue I am thinking about is now: What is if someone just sniffs the network traffic, 'steals' the users id and password hash to send his own SOAP message with modified data that corrupts my database? Options The approaches to solving that problem, I already thought of, are: Using ssl + certificates for establishing the connection: I dont really want to use ssl, I would prefer a simpler solution. After all, every information that is transfered to the webservice can be seen on the website later on. What I want to say is: there is no secret/financial/business-critical information, that has to be hidden. I think ssl would be sort of an overkill for that task. Encrypting the byte[]: I think that would be a performance killer, considering that the goal of the excercise was simply to authenticate the user. Hashing the users password together with the data: I kind of like the idea: Creating a checksum from the data, concatenating that checksum with the password-hash and hashing this whole thing again. That would assure the data was sent from this specific user, and the data wasnt modified. The actual question So, what do you think is the best approach in terms of meeting the following requirements? Rather simple solution (As it doesnt have to be super secure; no secret/business-critical information transfered) Easily implementable retrospectively (Dont want to write it all again :) ) Doesnt impact to much on performance What do you think of my prefered solution, the last one in the list above? Is there any alternative solution I didnt mention, that would fit better? You dont have to answer every question in detail. Just push me in the right direction. I very much appreciate every well-grounded opinion. Thanks in advance!

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• Are fragments of hashes collision-resistent?

  - by Mark

  Let me see if someone would mind clearing up this elementary point about md5 and hashing. If you only use the first 4 bytes of an md5 hash, would that mean theoretically only 1 in 255^4 chance of collision. iow is that the intention with it (and other hash algorithms) - that you only have to use a small portion of the returned hash (say the hash is of a file of some size).

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• How to hash a password and store for later verification with another digest

  - by oxygen8

  I am using gsoap's wsseapi plugin and would like to store hashed sha1 passwords rather than plain text. I have spent a rediculous amount of time experimenting with various methods of hashing the plain text password for storage. Can anyone suggest a way to hash a password so it can be later verified against a username token digest sent by the client. I can't seem to get the client password to authenticate against my stored hash

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• Can I override a query in DJango?

  - by stinkypyper

  I know you can override delete and save methods in DJango models, but can you override a select query somehow to intercept and change a parameter slightly. I have a hashed value I want to check for, and would like to keep the hashing internal to the model.

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• Possible Ways to Communicate Between iFrame and Parent Page across domains

  - by SKR

  Please suggest possible techniques to trigger events in parent page from an iFrame. I tried out url Hashing and using window.postMessage techniques but without any success.

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