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  • When is it safe to use a broken hash function?

    - by The Rook
    It is trivial to use a secure hash function like SHA256 and continuing to use md5 is reckless behavior. However, there are some complexities to hash function vulnerabilities that I would like to better understand. Collisions have been generated for md4 and md5. According to NIST md5() is not a secure hash function. It only takes 2^39th operations to generate a collision and should never be used for passwords. However SHA1 is vulnerable to a similar collision attack in which a collision can be found in 2^69 operations, where as brute force is 2^80th. No one has generated a sha1 collision and NIST still lists sha1 as a secure message digest function. So when is it safe to use a broken hash function? Even though a function is broken it can still be "big enough". According to Schneier a hash function vulnerable to a collsion attack can still be used as an HMAC. I believe this is because the security of an HMAC is Dependant on its secret key and a collision cannot be found until this key is obtained. Once you have the key used in a HMAC its already broken, so its a moot point. What hash function vulnerabilities would undermine the security of an HMAC? Lets take this property a bit further. Does it then become safe to use a very weak message digest like md4 for passwords if a salt is perpended to the password? Keep in mind the md4 and md5 attacks are prefixing attacks, and if a salt is perpended then an attacker cannot control the prefix of the message. If the salt is truly a secret, and isn't known to the attacker, then does it matter if its a appended to the end of the password? Is it safe to assume that an attacker cannot generate a collision until the entire message has been obtained? Do you know of other cases where a broken hash function can be used in a security context without introducing a vulnerability? (Please post supporting evidence because it is awesome!)

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  • Cant install software

    - by user53209
    So I just installed the ubuntu 11.10 .. And when i goto software center and try to download any software(use source).. all i get is a window saying that "Failed to download repository information" , "check your internet connection" and W:Failed to fetch bzip2:/var/lib/apt/lists/partial/archive.ubuntu.com_ubuntu_dists_oneiric_restricted_binary-i386_Packages Hash Sum mismatch , W:Failed to fetch bzip2:/var/lib/apt/lists/partial/archive.ubuntu.com_ubuntu_dists_oneiric_universe_binary-i386_Packages Hash Sum mismatch , W:Failed to fetch bzip2:/var/lib/apt/lists/partial/archive.ubuntu.com_ubuntu_dists_oneiric_multiverse_binary-i386_Packages Hash Sum mismatch , W:Failed to fetch htt p ://archive.ubuntu.com/ubuntu/dists/oneiric/main/i18n/Index No Hash entry in Release file /var/lib/apt/lists/partial/archive.ubuntu.com_ubuntu_dists_oneiric_main_i18n_Index , W:Failed to fetch http ://archive.ubuntu.com/ubuntu/dists/oneiric/multiverse/i18n/Index No Hash entry in Release file /var/lib/apt/lists/partial/archive.ubuntu.com_ubuntu_dists_oneiric_multiverse_i18n_Index , W:Failed to fetch htt ://archive.ubuntu.com/ubuntu/dists/oneiric/restricted/i18n/Index No Hash entry in Release file /var/lib/apt/lists/partial/archive.ubuntu.com_ubuntu_dists_oneiric_restricted_i18n_Index , W:Failed to fetch ht tp://archive.ubuntu.com/ubuntu/dists/oneiric/universe/i18n/Index No Hash entry in Release file /var/lib/apt/lists/partial/archive.ubuntu.com_ubuntu_dists_oneiric_universe_i18n_Index , W:Failed to fetch bzip2:/var/lib/apt/lists/partial/archive.ubuntu.com_ubuntu_dists_oneiric-updates_main_source_Sources Hash Sum mismatch , W:Failed to fetch bzip2:/var/lib/apt/lists/partial/archive.ubuntu.com_ubuntu_dists_oneiric-updates_restricted_binary-i386_Packages Hash Sum mismatch , W:Failed to fetch bzip2:/var/lib/apt/lists/partial/archive.ubuntu.com_ubuntu_dists_oneiric-updates_universe_binary-i386_Packages Hash Sum mismatch , W:Failed to fetch bzip2:/var/lib/apt/lists/partial/archive.ubuntu.com_ubuntu_dists_oneiric-updates_multiverse_binary-i386_Packages Hash Sum mismatch , W:Failed to fetch h tp://archive.ubuntu.com/ubuntu/dists/oneiric-updates/main/i18n/Index No Hash entry in Release file /var/lib/apt/lists/partial/archive.ubuntu.com_ubuntu_dists_oneiric-updates_main_i18n_Index , W:Failed to fetch h ttp://archive.ubuntu.com/ubuntu/dists/oneiric-updates/multiverse/i18n/Index No Hash entry in Release file /var/lib/apt/lists/partial/archive.ubuntu.com_ubuntu_dists_oneiric-updates_multiverse_i18n_Index , W:Failed to fetch ht tp://archive.ubuntu.com/ubuntu/dists/oneiric-updates/restricted/i18n/Index No Hash entry in Release file /var/lib/apt/lists/partial/archive.ubuntu.com_ubuntu_dists_oneiric-updates_restricted_i18n_Index , W:Failed to fetch htt p://archive.ubuntu.com/ubuntu/dists/oneiric-updates/universe/i18n/Index No Hash entry in Release file /var/lib/apt/lists/partial/archive.ubuntu.com_ubuntu_dists_oneiric-updates_universe_i18n_Index , W:Failed to fetch bzip2:/var/lib/apt/lists/partial/archive.ubuntu.com_ubuntu_dists_oneiric-backports_main_source_Sources Hash Sum mismatch , W:Failed to fetch bzip2:/var/lib/apt/lists/partial/archive.ubuntu.com_ubuntu_dists_oneiric-backports_restricted_binary-i386_Packages Hash Sum mismatch , W:Failed to fetch bzip2:/var/lib/apt/lists/partial/archive.ubuntu.com_ubuntu_dists_oneiric-backports_universe_binary-i386_Packages Hash Sum mismatch , W:Failed to fetch bzip2:/var/lib/apt/lists/partial/archive.ubuntu.com_ubuntu_dists_oneiric-backports_multiverse_binary-i386_Packages Hash Sum mismatch , W:Failed to fetch h ttp://archive.ubuntu.com/ubuntu/dists/oneiric-backports/main/i18n/Index No Hash entry in Release file /var/lib/apt/lists/partial/archive.ubuntu.com_ubuntu_dists_oneiric-backports_main_i18n_Index , W:Failed to fetch h ttp://archive.ubuntu.com/ubuntu/dists/oneiric-backports/multiverse/i18n/Index No Hash entry in Release file /var/lib/apt/lists/partial/archive.ubuntu.com_ubuntu_dists_oneiric-backports_multiverse_i18n_Index , W:Failed to fetch ht tp://archive.ubuntu.com/ubuntu/dists/oneiric-backports/restricted/i18n/Index No Hash entry in Release file /var/lib/apt/lists/partial/archive.ubuntu.com_ubuntu_dists_oneiric-backports_restricted_i18n_Index , W:Failed to fetch ht tp://archive.ubuntu.com/ubuntu/dists/oneiric-backports/universe/i18n/Index No Hash entry in Release file /var/lib/apt/lists/partial/archive.ubuntu.com_ubuntu_dists_oneiric-backports_universe_i18n_Index , W:Failed to fetch bzip2:/var/lib/apt/lists/partial/archive.ubuntu.com_ubuntu_dists_oneiric-security_main_source_Sources Hash Sum mismatch , E:Some index files failed to download. They have been ignored, or old ones used instead." Neglect the http typos, its to evade the 2 hyperlink.. I tried making a file in the apt.conf.d folder also, and added proxy entries, also set the system proxy.. and also the "network proxy", but nothing works.. And now I cant install any software!! Help needed

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  • Does Oracle re-hash the driving table for each join on the same table columns?

    - by thecoop
    Say you've got the following query on 9i: SELECT /*+ USE_HASH(t2 t3) */ * FROM table1 t1 -- this has lots of rows LEFT JOIN table2 t2 ON t1.col1 = t2.col1 AND t1.col2 = t2.col2 LEFT JOIN table3 t3 ON t1.col1 = t3.col1 AND t1.col2 = t3.col2 Due to 9i not having RIGHT OUTER HASH JOIN, it needs to hash table1 for both joins. Does it re-hash table1 between joining t2 and t3 (even though it's using the same join columns), or does it keep the same hash information for both joins?

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  • Converting a md5 hash byte array to a string

    - by Blankman
    How can I convert the hashed result, which a byte array, to a string? byte[] bytePassword = Encoding.UTF8.GetBytes(password); using (MD5 md5 = MD5.Create()) { byte[] byteHashedPassword = md5.ComputeHash(bytePassword); } So I need to convert byteHashedPassword to a string

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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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  • Generate fixed length hash in python for url parameter

    - by LeRoy
    I am working in python on appengine. I am trying to create what is equivalent to the "v" value in the youtube url's (http://www.youtube.com/watch?v=XhMN0wlITLk) for retrieving specific entities. The datastore auto generates a key but it is way too long (34 digits). I have experimented with hashlib to build my own, but again I get a long string. I would like to keep it to under 11 digits (I am not dealing with a huge number of entities) and letters and numbers are acceptable. It seems like there should be a pretty standard solution. I am probably just missing it.

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  • How do I find hash value of a 3D vector ?

    - by brainydexter
    I am trying to perform broad-phase collision detection with a fixed-grid size approach. Thus, for each entity's position: (x,y,z) (each of type float), I need to find which cell does the entity lie in. I then intend to store all the cells in a hash-table and then iterate through to report (if any) collisions. So, here is what I am doing: Grid-cell's position: (int type) (Gx, Gy, Gz) = (x / M, y / M, z / M) where M is the size of the grid. Once, I have a cell, I'd like to add it to a hash-table with its key being a unique hash based on (Gx, Gy, Gz) and the value being the cell itself. Now, I cannot think of a good hash function and I need some help with that. Can someone please suggest me a good hash function? Thanks

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  • Passing hash as values in hidden_field_tag

    - by funkymunky
    I am trying to pass some filters in my params through a form like so: hidden_field_tag "filters", params[:filters] For some reason the params get changed in the next page. For example, if params[:filters] used to be... "filters"={"name_like_any"=["apple"]} [1] ...it gets changed to... "filters"="{\"name_like_any\"=[\"apple\"]}" [2] note the extra quotations and backslashes in [2] when compared to [1]. Any ideas? I'm attempting to use this with searchlogic for some filtering, but I need it to persist when I change change objects in forms. I would prefer not to have to store it in session.

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  • Hash Table: Should I increase the element count on collisions?

    - by Nazgulled
    Hi, Right now my hash tables count the number of every element inserted into the hash table. I use this count, with the total hash table size, to calculate the load factor and when it reaches like 70%, I rehash it. I was thinking that maybe I should only count the inserted elements with fills an empty slot instead of all of them. Cause the collision method I'm using is separate chaining. The factor load keeps increasing but if there can be a few collisions leaving lots of empty slots on the hash table. You are probably thinking that if I have that many collisions, maybe I'm not using the best hashing method. But that's not the point, I'm using one of the know hashing algorithms out there, I tested 3 of them on my sample data and selected the one who produced less collisions. My question still remains. Should I keep counting every element inserted, or just the ones that fill an empty slot in the Hash Table?

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  • Better way to fill a Ruby hash?

    - by sardaukar
    Is there a better way to do this? (it looks clunky) form_params = {} form_params['tid'] = tid form_params['qid'] = qid form_params['pri'] = pri form_params['sec'] = sec form_params['to_u'] = to_u form_params['to_d'] = to_d form_params['from'] = from form_params['wl'] = wl

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  • Using hash to check if page with $_POST values was refreshed

    - by Dieseltime
    When posting a form to the same PHP page, what is the correct method to find if the page was accidentally refreshed instead of submitted again? Here's what I'm using right now: $tmp = implode('',$_POST); $myHash = md5($tmp); if(isset($_SESSION["myHash"]) && $_SESSION["myHash"] == $myHash) { header("Location: index.php"); // page refreshed, send user somewhere else die(); } else { $_SESSION["myHash"] = $myHash; } // continue processing... Is there anything wrong with this solution?

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  • C# hash password create salt question

    - by 5YrsLaterDBA
    If I create salt by using something like this: public class User { private const int Hash_Salt_Length = 8; private byte[] saltBytes = new byte[Hash_Salt_Length]; public User() { RNGCryptoServiceProvider rng = new RNGCryptoServiceProvider(); rng.GetNonZeroBytes(saltBytes); } .... } The saltBytes bytes array will be different for each session (restart the application). How can I check password to allow user login our application?

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  • RoR: Output Hash, getting correct parameters?

    - by andrewliu
    I have output something like this: #<Hashie::Mash created_time="1366008641" from=#<Hashie::Mash full_name="Cor Valen" id="22340" username="_corin"> id="4344344286" text="Look Who It Is, My Brother, My Favorite Deputy"> This was an output if I did this: <%= media.caption %> I wanted to get the text part, and I did this: <%= media.caption.text %> gets me error: undefined method `text' for nil:NilClass <%= media.caption[:text] %> gets me error: undefined method `[]' for nil:NilClass I don't get it? Thanks

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  • How to hash and check for equality of objects with circular references

    - by mfya
    I have a cyclic graph-like structure that is represented by Node objects. A Node is either a scalar value (leaf) or a list of n=1 Nodes (inner node). Because of the possible circular references, I cannot simply use a recursive HashCode() function, that combines the HashCode() of all child nodes: It would end up in an infinite recursion. While the HashCode() part seems at least to be doable by flagging and ignoring already visited nodes, I'm having some troubles to think of a working and efficient algorithm for Equals(). To my surprise I did not find any useful information about this, but I'm sure many smart people have thought about good ways to solve these problems...right? Example (python): A = [ 1, 2, None ]; A[2] = A B = [ 1, 2, None ]; B[2] = B A is equal to B, because it represents exactly the same graph. BTW. This question is not targeted to any specific language, but implementing hashCode() and equals() for the described Node object in Java would be a good practical example.

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  • Ruby Hash.merge with specified keys only

    - by ba
    I'm pretty sure I saw on a Rails related site something along the lines of: def my_function(*opts) opts.require_keys(:first, :second, :third) end And if one of the keys in require_keys weren't specified, or if there were keys that weren't specified, an exception was raised. I've been looking through ActiveSupport and I guess I might be looking for something like the inverse of except. I like to try and use as much of the framework as possible compared to writing my own code, that's the reason I'm asking when I know how to make the same functionality on my own. :) At the moment I'm doing it through the normal merge routine and making sure that I have what I need with some IFs.

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  • Data Structure / Hash Function to link Sets of Ints to Value

    - by Gaminic
    Given n integer id's, I wish to link all possible sets of up to k id's to a constant value. What I'm looking for is a way to translate sets (e.g. {1, 5}, {1, 3, 5} and {1, 2, 3, 4, 5, 6, 7}) to unique values. Guarantees: n < 100 and k < 10 (again: set sizes will range in [1, k]). The order of id's doesn't matter: {1, 5} == {5, 1}. All combinations are possible, but some may be excluded. All sets and values are constant and made only once. No deletes or inserts, no value updates. Once generated, the only operations taking place will be look-ups. Look-ups will be frequent and one-directional (given set, look up value). There is no need to sort (or otherwise organize) the values. Additionally, it would be nice (but not obligatory) if "neighboring" sets (drop one id, add one id, swap one id, etc) are easy to reach, as well as "all sets that include at least this set". Any ideas?

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  • How can I make hash key lookup case-insensitive?

    - by mseery
    Evidently hash keys are compared in a case-sensitive manner. $ perl -e '%hash = ( FOO => 1 ); printf "%s\n", ( exists $hash{foo} ) ? "Yes" : "No";' No $ perl -e '%hash = ( FOO => 1 ); printf "%s\n", ( exists $hash{FOO} ) ? "Yes" : "No";' Yes Is there a setting to change that for the current script? Thanks.

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  • Ruby 1.9 regex as a hash key

    - by Liutauras
    I am trying this example myhash = {/(\d+)/ => "hello"} with ruby 1.9.2p136 (2010-12-25) [i386-mingw32]. It doesn't work as expected (edit: as it turned out it shouldn't work as I was expecting): irb(main):004:0> myhash = {/(\d+)/ => "hello"} => {/(\d+)/=>"Hello"} irb(main):005:0> myhash[2222] => nil irb(main):006:0> myhash["2222"] => nil In Rubular which is on ruby1.8.7 the regex works. What am I missing?

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  • .Net Hash Codes no longer persistent?

    - by RobV
    I have an API where various types have custom hash codes. These hash codes are based on getting the hash of a string representation of the object in question. Various salting techniques are used so that as far as possible Hash Codes do not collide and that Objects of different types with equivalent string representations have different Hash Codes. Obviously since the Hash Codes are based on strings there are some collisions (infinite strings vs the limited range of 32 bit integers). I use hashes based on string representations since I need the hashes to persist over sessions and particularly for use in database storage of objects. Suddenly today my code has started generating different hash codes for Objects which is breaking all kinds of things. It was working earlier today and I haven't touched any of the code involved in Hash Code generation. I'm aware that the .Net documentation allows for implementation of hash codes between .Net framework versions to change (and between 32 and 64 bit versions) but I haven't changed the framework version and there has been no framework updates recently as far as I can remember Any ideas because this seems really weird? Edit Hash Codes are generated like follows: //Compute Hash Code this._hashcode = (this._nodetype + this.ToString() + PlainLiteralHashCodeSalt).GetHashCode();

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  • Comparing lists of field-hashes with equivalent AR-objects.

    - by Tim Snowhite
    I have a list of hashes, as such: incoming_links = [ {:title => 'blah1', :url => "http://blah.com/post/1"}, {:title => 'blah2', :url => "http://blah.com/post/2"}, {:title => 'blah3', :url => "http://blah.com/post/3"}] And an ActiveRecord model which has fields in the database with some matching rows, say: Link.all => [<Link#2 @title='blah2' @url='...post/2'>, <Link#3 @title='blah3' @url='...post/3'>, <Link#4 @title='blah4' @url='...post/4'>] I'd like to do set operations on Link.all with incoming_links so that I can figure out that <Link#4 ...> is not in the set of incoming_links, and {:title => 'blah1', :url =>'http://blah.com/post/1'} is not in the Link.all set, like so: #pseudocode #incoming_links = as above links = Link.all expired_links = links - incoming_links missing_links = incoming_links - links expired_links.destroy missing_links.each{|link| Link.create(link)} One route I've tried: I'd rather not rewrite Array#- and such, and I'm okay with converting incoming_links to a set of unsaved Link objects; so I've tried overwriting hash eql? and so on in Link so that it ignored the id equality that AR::Base provides by default. But this is the only place this sort of equality should be considered in the application - in other places the Link#id default identity is required. Is there some way I could subclass Link and apply the hash, eql?, etc overwriting there? The other route I've tried is to pull out the attributes hash for each Link and doing a .slice('id',...etc) to prune the hashes down. But this requires writing seperate methods for keeping track of the Link objects while doing set operations on the hashes, or writing seperate Collection classes to wrap the incoming_links hash-list and Link-list which seems a bit overkill. What is the best way to design this interaction? Extra credit for cleanliness.

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  • Title of the page in search results and title of google's cached version are different. Why?

    - by Azmorf
    Check this: http://www.google.com/search?q=site:gunlawsbystate.com+kansas+gun+laws The title of the first result is "Kansas Gun Laws - Gun Laws By State". Although, on the page google has cached the title is different: <title>Kansas Gun Laws - Kansas Gun Law - Reciprocity Guide</title> Google shows the title that has been on the site 2-3 months ago. Google bot has visited the website a lot of times since that, and as you see it even cached it (the latest version is of 15th Sept), however for some reason it doesn't change the title to the new one in the search results. We use hash-bang URL structure on this website. It completely meets google's requirements for AJAX websites (_escaped_fragment_ stuff). The issue I explained is happening with almost all hash-bang pages that got indexed. Questions: Why does it keep old page title in the search results? Can it be connected to the fact that I'm using hash-bang URLs? There are lots of pages on the site that have the same issue, all of them have hash-bang URLs. Another thing I noticed is that Google's "Preview" feature doesn't work for any hash-bang URLs on the site. Did I do anything wrong? It has got cached versions of the pages, why wouldn't it generate a preview? Thanks (and sorry for my English) PS. Here's a weird thing I also noticed: this search query https://www.google.com/search?q=Kansas+Gun+Laws+-+Reciprocity+Guide shows the correct title for the same page as in the example above. Why does google show different titles for the same page when you run different queries?

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