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  • Hash Code for a group of three fields

    - by Gauranga
    I have three fields namely Number1 Number2 Time I am trying to write a function in java that returns a unique hash value (long needs to be the return type of hash) for the above fields. This hash would then be used to store database rows corresponding to the above mentioned fields in a HashSet. I am new to writing a hash code function, can someone please review what I have. Any help would be appreciated. public class HashCode { private long Number1; private long Number2; String Time; public HashCode(long Number1, long Number2, String Time){ this.Number1 = Number1; this.Number2 = Number2; this.Time = Time; } public long getHashCode() { long hash = 3; hash = 47 * hash + (long) (this.Number1 ^ (this.Number1 >>> 32)); hash = 47 * hash + (long) (this.Number2 ^ (this.Number2 >>> 32)); hash = 47 * hash + (this.Time != null ? this.Time.hashCode() : 0); return hash; } }

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  • Contrary to Python 3.1 Docs, hash(obj) != id(obj). So which is correct?

    - by Don O'Donnell
    The following is from the Python v3.1.2 documentation: From The Python Language Reference Section 3.3.1 Basic Customization: object.__hash__(self) ... User-defined classes have __eq__() and __hash__() methods by default; with them, all objects compare unequal (except with themselves) and x.__hash__() returns id(x). From The Glossary: hashable ... Objects which are instances of user-defined classes are hashable by default; they all compare unequal, and their hash value is their id(). This is true up through version 2.6.5: Python 2.6.5 (r265:79096, Mar 19 2010 21:48:26) ... ... >>> class C(object): pass ... >>> c = C() >>> id(c) 11335856 >>> hash(c) 11335856 But in version 3.1.2: Python 3.1.2 (r312:79149, Mar 21 2010, 00:41:52) ... ... >>> class C: pass ... >>> c = C() >>> id(c) 11893680 >>> hash(c) 743355 So which is it? Should I report a documentation bug or a program bug? And if it's a documentation bug, and the default hash() value for a user class instance is no longer the same as the id() value, then it would be interesting to know what it is or how it is calculated, and why it was changed in version 3.

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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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  • CMS is Perfect Solution for Small Business Owners

    A website can be built easily with content management system because it has the ability to add Pages in simple format like text format and they are automatically translated into perfect to near perfe... [Author: Alan Smith - Web Design and Development - March 21, 2010]

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  • VIA M'SERV: the Perfect Little Linux Box?

    <b>Linux Planet:</B> "Take a small box. Add a 64-bit CPU, two SATA hard drives, a Compact Flash slot, dual Gigabit Ethernet, and quiet operation, and what do you have? The VIA M'SERV mini-server. Could this be the perfect Linux box?"

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  • Perfect SEO Keywords

    Having good keywords for your search engine optimisation are a great way to help you improve the search engine rankings for your website and get more traffic coming in. There are a few ways that you can try to find the perfect keywords for your site...

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  • Task of SEO Consultant is Building the Perfect Web Page

    Current trend in the market is using the services of reputed and reliable SEO consultant for the purpose of search engine optimization and website promotion. Use of the consultant is basically aimed at developing perfect web page for the client. Certain primary areas are also there that should be taken care of.

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  • The Perfect Link Building

    We've all heard that building links is the most important factor in getting high search positions, but how do you get that perfect link. This article will show you how to obtain the best links possible.

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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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  • 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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  • How can I keep a hash sorted?

    - by srk
    use strict; use warnings; my @aoh =( { 3 => 15, 4 => 8, 5 => 9, }, { 3 => 11, 4 => 25, 5 => 6, }, { 3 => 5, 4 => 18, 5 => 5, }, { 0 => 16, 1 => 11, 2 => 7, }, { 0 => 21, 1 => 13, 2 => 31, }, { 0 => 11, 1 => 14, 2 => 31, }, ); #declaring a new array to store the sorted hashes my @new; print "\n-------------expected output------------\n"; foreach my $href (@aoh) { #i want a new array of hashes where the hashes are sorted my %newhash; my @sorted_keys = sort {$href->{$b} <=> $href->{$a} || $b <=> $a} keys %$href; foreach my $key (@sorted_keys) { print "$key => $href->{$key}\n"; $newhash{$key} = $href->{$key}; } print "\n"; push(@new,\%newhash); } print "-----------output i am getting---------------\n"; foreach my $ref(@new) { my @skeys = skeys %$ref; foreach my $key (@skeys) { print "$key => $ref->{$key}\n" } print "\n"; } The output of the program : -------------expected output------------ 3 => 15 5 => 9 4 => 8 4 => 25 3 => 11 5 => 6 4 => 18 5 => 5 3 => 5 0 => 16 1 => 11 2 => 7 2 => 31 0 => 21 1 => 13 2 => 31 1 => 14 0 => 11 -----------output i am getting--------------- 4 => 8 3 => 15 5 => 9 4 => 25 3 => 11 5 => 6 4 => 18 3 => 5 5 => 5 1 => 11 0 => 16 2 => 7 1 => 13 0 => 21 2 => 31 1 => 14 0 => 11 2 => 31 Please tell me what am i doing wrong in storing the hashes into a new array.. how do i achieve what i want.. ? Thanks in advance...

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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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  • 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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  • 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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  • 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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