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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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  • Sorting versus hashing

    - by Paul Siegel
    My problem is as follows. I have an array of n strings with m < n of them distinct. I want to create a one-to-one function which assigns each of the m distinct strings to the numbers 0 ... m-1. For example, if my strings are: Bob, Amy, Bob, Charlie, Amy then the function: Bob -> 0, Amy -> 1, Charlie -> 2 would meet my needs. I have thought of three possible approaches: Sort the list of strings, remove duplicates, and construct the function using a search algorithm. Create a hash table and check each string to see if it is already in the table before inserting it. Sort the list of strings, remove duplicates, and put the resulting list into a hash table. My code will be written in Java, and I will likely use standard Java algorithms: merge sort for sorting, binary search for searching, and whatever the standard Java hash table algorithm is. Question: Assume that after creating the function I will have to evaluate it on each of the n original strings. Which of the three approaches is fastest? Is there a better way? Part of the problem is that I don't really know what's going on "under the hood" in standard hashing algorithms. Any help would be appreciated.

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  • Do encryption algorithms require an internal hashing algorithm?

    - by Rudi
    When I use C# to implement the AES symmetric encryption cipher, I noticed: PasswordDeriveBytes derivedPassword = new PasswordDeriveBytes(password, saltBytesArray, hashAlgorithmName, numPasswordIterations); Why do I need to use a hashing algorithm for AES encryption? Aren't they separate? Or is the hashing algorithm only used to create a secure key? The AES algorithm doesn't use a hashing algorithm internally does it?

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  • extendible hashing

    - by Phenom
    I need to make a program that shows the hash value of a given key, using extendible hashing. In extendible hashing, I know that the buckets split and directories change. So if I make my program, do I have to already know things like if the bucket it hashes to is filled, or do I not have to worry about those things and just compute a hash value based on the key?

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  • Updating password hashing without forcing a new password for existing users

    - by Willem
    You maintain an existing application with an established user base. Over time it is decided that the current password hashing technique is outdated and needs to be upgraded. Furthermore, for UX reasons, you don't want existing users to be forced to update their password. The whole password hashing update needs to happen behind the screen. Assume a 'simplistic' database model for users that contains: ID Email Password How does one go around to solving such a requirement? My current thoughts are: create a new hashing method in the appropriate class update the user table in the database to hold an additional password field Once a user successfully logs in using the outdated password hash, fill the second password field with the updated hash This leaves me with the problem that I cannot reasonable differentiate between users who have and those who have not updated their password hash and thus will be forced to check both. This seems horribly flawed. Furthermore this basically means that the old hashing technique could be forced to stay indefinitely until every single user has updated their password. Only at that moment could I start removing the old hashing check and remove the superfluous database field. I'm mainly looking for some design tips here, since my current 'solution' is dirty, incomplete and what not, but if actual code is required to describe a possible solution, feel free to use any language.

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  • array size for extendible hashing

    - by Phenom
    If I want to use extendible hashing to store a maximum of 100 records, then what is the minimum array size that I need? I am guessing that an array of 100 would be sufficient, but I could be wrong. I also suspect that I can use a smaller array.

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  • Implementing password hashing/salting algorithm from crackstation.net

    - by Mason240
    I am trying to implement a password hashing/salting algorithm from crackstation.net, but I am unsure how implement it. Storing the password upon user registration seems to be as simple as passing the password into create_hash(). $password = create_hash($_POST['Password']; I'm not following how to validate upon user login. validate_password($password, $good_hash) returns either true or false, and takes $password as parameter, so it seems like a no brainer except for the second parameter $good_hash. Where does this param come from? It is my understanding that password is turned into a hash value every time its used, and that the hash value is what is stored and compared. So why would I have both the $password and $good_hash values? Quick overview of the functions: function create_hash($password){ calls pbkdf2() } function validate_password($password, $good_hash){ calls pbkdf2() calls slow_equals() } function slow_equals($a, $b){ } function pbkdf2($algorithm, $password, $salt, $count, $key_length, $raw_output = false){ } Of course a different, better method for this would also be just as helpful. Thank you

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  • MD5 Hashing Given a Key in C#

    - by Jared
    I've been looking for a way to hash a given string in C# that uses a predetermined key. On my adventures through the internet trying to find an example i have seen lots of MD5CryptoServiceProvider examples which seem to use a default key for the machine, but none of them that apply a specific key. I need to have a specific key to encode data as to synchronize it to someone else's server. I hand them a hashed string and an ID number and they use that analyze the data and return a similar set to me. So is there anyway to get md5 to hash via a specific key that would be consistent to both. I would prefer this to be done in C#, but if its not possible with the libraries can you do so with some web languages like php or asp? Edit: Misunderstood the scenario I was thrown into and after a little sitting and thinking about why they would have me use a key it appears they want a key appended to the end of the string and hashed. That way the server can appended the key it has along with the data passed to ensure its a valid accessing computer. Anyways... thanks all ^_^ Edit2: As my comment below says, it was the term 'salting' I was oblivious to. Oh the joys of getting thrown into something new with no directions.

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  • Compile time string hashing

    - by Caspin
    I have read in few different places that using c++0x's new string literals it might be possible to compute a string's hash at compile time. However, no one seems to be ready to come out and say that it will be possible or how it would be done. Is this possible? What would the operator look like? I'm particularly interested use cases like this. void foo( const std::string& value ) { switch( std::hash(value) ) { case "one"_hash: one(); break; case "two"_hash: two(); break; /*many more cases*/ default: other(); break; } } Note: the compile time hash function doesn't have to look exactly as I've written it. I did my best to guess what the final solution would look like, but meta_hash<"string"_meta>::value could also be a viable solution.

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  • Double hashing passwords - client & server

    - by J. Stoever
    Hey, first, let me say, I'm not asking about things like md5(md5(..., there are already topics about it. My question is this: We allow our clients to store their passwords locally. Naturally, we don't want them stored in plan text, so we hmac them locally, before storing and/or sending. Now, this is fine, but if this is all we did, then the server would have the stored hmac, and since the client only needs to send the hmac, not the plain text password, an attacker could use the stored hashes from the server to access anyone's account (in the catastrophic scenario where someone would get such an access to the database, of course). So, our idea was to encode the password on the client once via hmac, send it to the server, and there encode it a second time via hmac and match it against the stored, two times hmac'ed password. This would ensure that: The client can store the password locally without having to store it as plain text The client can send the password without having to worry (too much) about other network parties The server can store the password without having to worry about someone stealing it from the server and using it to log in. Naturally, all the other things (strong passwords, double salt, etc) apply as well, but aren't really relevant to the question. The actual question is: does this sound like a solid security design ? Did we overlook any flaws with doing things this way ? Is there maybe a security pattern for something like this ?

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  • djb2 Hash Function

    - by Jainish
    I am using the djb2 algorithm to generate the hash key for a string which is as follows hash(unsigned char *str) { unsigned long hash = 5381; int c; while (c = *str++) hash = ((hash << 5) + hash) + c; /* hash * 33 + c */ return hash; } Now with every loop there is a multiplication with two big numbers, After some time with the 4th of 5th character of the string there is a overflow as the hash value becomes huge What is the correct way to refactor so that the hash value does not overflow and the hashing also happens correctly

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  • Hashing 3D position into 2D position

    - by notabene
    I am doing volumetric raycasting and curently working on depth jitter. I have 3D position on ray and want to sample 2D noise texture to jitter the depth. Function for converting (or hashing) 3D position to 2D have to produce absolutely different numbers for a little changes (especialy because i am sampling in texture space so sample values differs very very little) and have to be "shader-wise" - so forget about branches, cycles etc. I'm looking forward for yours nice and fast solutions.

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  • Basic memcached question

    - by Aadith
    I have been reading up on distributed hashing. I learnt that consistent hashing is used for distributing the keys among cache machines. I also learnt that, a key is duplicated on mutiple caches to handle failure of cache hosts. But what I have come across on memcached doesn't seem to be in alignment with all this. I read that all cache nodes are independent of each other and that if a cache goes down, requests go to DB. Theres no mention of cache miss on a host resulting in the host directing the request to another host which could either be holding the key or is nearer to the key. Can you please tell me how these two fit together? Is memcached a very preliminary form of distributed hashing which doesnt have much sophistication?

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  • Getting Started with Hashing in SQL Server

    Encryption brings data into a state which cannot be interpreted by anyone who does not have access to the decryption key, password, or certificates. Hashing brings a string of characters of arbitrary size into a usually shorter fixed-length value or key. Here's how to get started using it. Need to compare and sync database schemas?Let SQL Compare do the hard work. ”With the productivity I'll get out of this tool, it's like buying time.” Robert Sondles. Download a free trial.

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  • Data Aggregation of CSV files java

    - by royB
    I have k csv files (5 csv files for example), each file has m fields which produce a key and n values. I need to produce a single csv file with aggregated data. I'm looking for the most efficient solution for this problem, speed mainly. I don't think by the way that we will have memory issues. Also I would like to know if hashing is really a good solution because we will have to use 64 bit hashing solution to reduce the chance for a collision to less than 1% (we are having around 30000000 rows per aggregation). For example file 1: f1,f2,f3,v1,v2,v3,v4 a1,b1,c1,50,60,70,80 a3,b2,c4,60,60,80,90 file 2: f1,f2,f3,v1,v2,v3,v4 a1,b1,c1,30,50,90,40 a3,b2,c4,30,70,50,90 result: f1,f2,f3,v1,v2,v3,v4 a1,b1,c1,80,110,160,120 a3,b2,c4,90,130,130,180 algorithm that we thought until now: hashing (using concurentHashTable) merge sorting the files DB: using mysql or hadoop or redis. The solution needs to be able to handle Huge amount of data (each file more than two million rows) a better example: file 1 country,city,peopleNum england,london,1000000 england,coventry,500000 file 2: country,city,peopleNum england,london,500000 england,coventry,500000 england,manchester,500000 merged file: country,city,peopleNum england,london,1500000 england,coventry,1000000 england,manchester,500000 The key is: country,city. This is just an example, my real key is of size 6 and the data columns are of size 8 - total of 14 columns. We would like that the solution will be the fastest in regard of data processing.

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