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• How long can a hash left out in the open be considered safe?

  - by Xeoncross

  If I were to leave a SHA2 family hash out on my website - how long would it be considered safe? How long would I have before I could be sure that someone would find a collision for it and know what was hashed? I know that the amount of time would be based on the computational power of the one seeking to break it. It would also depend on the string length, but I'm curious just how secure hashes are. Since many of us run web-servers we constantly have to be prepared for the day when someone might make it all the way to the database which stores the user hashes. So, move the server security out of the way and then what do you have? This is a slightly theoretical area for many of the people I have talked with, so I would love to actually have some more information about average expectations for cracking.

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• Block call in Ruby on Rails

  - by Mattias

  Hi, I'm trying to clean up my code and get rid of a lot of ugly hashes. In my views I define several actions like this: @actions = { :interest => {'Show interest', link_to(..), :disabled => true}, :follow => {'Follow this case', link_to(..)} ... } As these hashes grow, the maintainability decreases. I want to convert the above format to something like: actions do item :interest, 'Show interest', link_to(..), :disabled => true item :follow, 'Follow', link_to(..) ... end How do I structure my helper methods to allow this? Preferably the 'item'-method should only be available in the 'actions' block and not in the global scope. Thanks!

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• Alternate CD image downloaded last year gives different hash

  - by Oxwivi

  I had downloaded the alternate CD images through torrents some time last year, and now that I need it again I decided to check it's md5 hash. $ md5sum ubuntu-11.10-alternate-i386.iso b502888194367acdec4d79203e7a539c ubuntu-11.10-alternate-i386.iso Now the problem is, the reference hashes it's supposed to match to is completely different: 24da873c870d6a3dbfc17390dda52eb8 ubuntu-11.10-alternate-i386.iso Can I safely conclude the image I downloaded is corrupted? Reference UbuntuHashes - Community Ubuntu Documentation

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• How does a web browser save passwords?

  - by marcus

  How do current web browsers (or mobile mail clients and any software in general) save user passwords? All answers about storing passwords say we should store only hashes, not the password themselves. But I'm having a hard time searching the web trying to find the best techniques to store passwords when we know we will need them in plain text later on — without storing them in plain text, without using a weak encryption (known key) and without asking the user for a master password. Any ideas?

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• Week in Geek: Free Version of Google Apps for Business has been Discontinued

  - by Asian Angel

  This week’s edition of WIG is filled with news link coverage on topics such as Android’s ‘Google Now’ services are headed for Chrome, Microsoft is ready to push Hotmail users to Outlook.com, a 25 GPU setup devours password hashes at up to 348 billion per second, and more. How to Factory Reset Your Android Phone or Tablet When It Won’t Boot Our Geek Trivia App for Windows 8 is Now Available Everywhere How To Boot Your Android Phone or Tablet Into Safe Mode

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• Finding duplicate files?

  - by ub3rst4r

  I am going to be developing a program that detects duplicate files and I was wondering what the best/fastest method would be to do this? I am more interested in what the best hash algorithm would be to do this? For example, I was thinking of having it get the hash of each files contents and then group the hashes that are the same. Also, should there be a limit set for what the maximum file size can be or is there a hash that is suitable for large files?

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• What actions should I not rely on the packaged functionality of my language for?

  - by David Peterman

  While talking with one of my coworkers, he was talking about the issues the language we used had with encryption/decryption and said that a developer should always salt their own hashes. Another example I can think of is the mysql_real_escape_string in PHP that programmers use to sanitize input data. I've heard many times that a developer should sanitize the data themselves. My question is what things should a developer always do on their own, for whatever reason, and not rely on the standard libraries packaged with a language for it?

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• Windows cant repair even with sfc /scannow

  - by GeekyDewd

  Clean install of windows 8, then installed the windows 8.1 update (after all other updates). CBS Log: CBS Log on Google Drive Important pieces of the log: Found: {l:32 b:LrOXAtJDCCTN+z+D1bKj7ogYIrX7sfCCDh+wVBfsrCQ=} Expected: {l:32 b:n520k714Uu3utHa5JGQ6HQYbZphKhlMWq5pEmfnCDuw=} 2014-05-17 21:35:38, Info CSI 00000505 [SR] Cannot repair member file [l:36{18}]"Amd64\CNBJ2530.DPB" of prncacla.inf, Version = 6.3.9600.16384, pA = PROCESSOR_ARCHITECTURE_AMD64 (9), Culture neutral, VersionScope = 1 nonSxS, PublicKeyToken = {l:8 b:31bf3856ad364e35}, Type = [l:24{12}]"driverUpdate", TypeName neutral, PublicKey neutral in the store, hash mismatch 2014-05-17 21:35:40, Info CSI 00000506 Hashes for file member \SystemRoot\WinSxS\amd64_prncacla.inf_31bf3856ad364e35_6.3.9600.16384_none_9590ba64d5b91f79\Amd64\CNBJ2530.DPB do not match actual file [l:36{18}]"Amd64\CNBJ2530.DPB" : Found: {l:32 b:LrOXAtJDCCTN+z+D1bKj7ogYIrX7sfCCDh+wVBfsrCQ=} Expected: {l:32 b:n520k714Uu3utHa5JGQ6HQYbZphKhlMWq5pEmfnCDuw=} 2014-05-17 21:35:40, Info CSI 00000507 [SR] Cannot repair member file [l:36{18}]"Amd64\CNBJ2530.DPB" of prncacla.inf, Version = 6.3.9600.16384, pA = PROCESSOR_ARCHITECTURE_AMD64 (9), Culture neutral, VersionScope = 1 nonSxS, PublicKeyToken = {l:8 b:31bf3856ad364e35}, Type = [l:24{12}]"driverUpdate", TypeName neutral, PublicKey neutral in the store, hash mismatch 2014-05-17 21:35:40, Info CSI 00000508 [SR] This component was referenced by [l:186{93}]"Microsoft-Windows-Printer-Drivers-Package~31bf3856ad364e35~amd64~~6.3.9600.16384.INF_prncacla" 2014-05-17 21:35:43, Info CSI 00000509 [DIRSD OWNER WARNING] Directory [ml:520{260},l:138{69}]"\??\C:\WINDOWS\System32\WindowsPowerShell\v1.0\Modules\NetSecurity\en" is not owned but specifies SDDL in component Networking-MPSSVC-WMI.Resources, pA = PROCESSOR_ARCHITECTURE_AMD64 (9), Culture = [l:10{5}]"en-US", VersionScope = 1 nonSxS, PublicKeyToken = {l:8 b:31bf3856ad364e35}, Type neutral, TypeName neutral, PublicKey neutral And: Found: {l:32 b:LrOXAtJDCCTN+z+D1bKj7ogYIrX7sfCCDh+wVBfsrCQ=} Expected: {l:32 b:n520k714Uu3utHa5JGQ6HQYbZphKhlMWq5pEmfnCDuw=} 2014-05-17 21:42:12, Info CSI 00000888 [SR] Cannot repair member file [l:36{18}]"Amd64\CNBJ2530.DPB" of prncacla.inf, Version = 6.3.9600.16384, pA = PROCESSOR_ARCHITECTURE_AMD64 (9), Culture neutral, VersionScope = 1 nonSxS, PublicKeyToken = {l:8 b:31bf3856ad364e35}, Type = [l:24{12}]"driverUpdate", TypeName neutral, PublicKey neutral in the store, hash mismatch 2014-05-17 21:42:13, Info CSI 00000889 Hashes for file member \SystemRoot\WinSxS\amd64_prncacla.inf_31bf3856ad364e35_6.3.9600.16384_none_9590ba64d5b91f79\Amd64\CNBJ2530.DPB do not match actual file [l:36{18}]"Amd64\CNBJ2530.DPB" : Found: {l:32 b:LrOXAtJDCCTN+z+D1bKj7ogYIrX7sfCCDh+wVBfsrCQ=} Expected: {l:32 b:n520k714Uu3utHa5JGQ6HQYbZphKhlMWq5pEmfnCDuw=} 2014-05-17 21:42:13, Info CSI 0000088a [SR] Cannot repair member file [l:36{18}]"Amd64\CNBJ2530.DPB" of prncacla.inf, Version = 6.3.9600.16384, pA = PROCESSOR_ARCHITECTURE_AMD64 (9), Culture neutral, VersionScope = 1 nonSxS, PublicKeyToken = {l:8 b:31bf3856ad364e35}, Type = [l:24{12}]"driverUpdate", TypeName neutral, PublicKey neutral in the store, hash mismatch 2014-05-17 21:42:13, Info CSI 0000088b [SR] This component was referenced by [l:186{93}]"Microsoft-Windows-Printer-Drivers-Package~31bf3856ad364e35~amd64~~6.3.9600.16384.INF_prncacla" 2014-05-17 21:42:13, Info CSI 0000088c [SR] Repair complete

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• How to edit known_hosts when several hosts share the same IP and DNS name?

  - by Frédéric Grosshans

  I regularly ssh into a computer which is a dual-boot OS X / Linux computer. The two OS instance do not share the same host key, so they can be seen as two host sharing the same IP and DNS. Let's say the IP is 192.168.0.9, and the names are hostname and hostname.domainname As far as I understood, the solution to be able to connect to the two host is to add them both to the ~/.ssh/know_hosts file. However, it is easier said than done, because the file is hashed, and has probably several entries per host (192.168.0.9, hostname, hostname.domainname). As a consequence, I have the following warning Warning: the ECDSA host key for 'hostname' differs from the key for the IP address '192.168.0.9' Is there an easy way to edit the known_hosts file, while keeping the hashes. For example, how can I find the lines corresponding to a given hostame? How can I generate the hashes for some known hosts? The ideal solution would allow me to connect to seamlessly to this computer with ssh, no matter whether I call it 192.168.0.9, hostname or hostname.domainname, nor if it uses its Linux hostkey or its OSX hostkey. However, I still want to receive a warning if there is a real man-in-the middle attack, i.e. if another key than these two is used.

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• Windows Vista freezes

  - by Kakurady

  Windows Vista (32-bit) would randomly freeze on my computer, usually 15-30 minutes after login but can happen just after login. All applications would stop responding and the hard drive will not make any sound, and after a while, the mouse cursor will also stop moving. I dual-boot Ubuntu, and that still works fine. It started with the computer freezing when loading Team Fortress 2. Alt-Tab and Ctrl-Alt-Del have no effect, and the hard drive does not make any sound. I tried to verify the game data using Steam and that freezes the computer too. So I stupidly reinstalled the game. Now the game doesn't freeze when it starts, but instead the whole computer randomly freezes. This computer is a Dell XPS M1530 with a 320GB (298GiB) drive (WDC WD3200BEVT-7) split 5-ways, with Windows and Linux a partition each, one more for Linux swap space, and another two partitions for Dell diagnostic program and factory image and drivers. There was once where the hard drive would make clicking noises all day, and only stopped when I rebooted the computer. Since then, the BIOS diagnostics would fail the drive (for "self-test log contains previous errors") whenever ran. (The on-disk diagnostics cannot be run because I overwrote the MBR with GRUB.) Naturally, I thought the hard drive could be the problem. CHKDSK found one bad sector, but this seems to have no effect. System File Checker found two protected files with wrong hashes, one is some kind of IE manifest, and the other is a tcpmon.ini. Neither of them can be restored because their back up copy also have wrong hashes. Nothing about system failures in the event viewer. What should I do next?

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• Is there any reason this cronjob would fail in cron, but not on the command line?

  - by Treffynnon

  I have written a little one liner that will email me when a list of files changes - I used sha512 to generate a list of hashes and then periodically check that those hashes still match. */5 * * * * /usr/bin/sha512sum --status -c /sha512.sumlist && echo "Success" > /dev/null || echo "Check robots.txt and index.html in /var/www as staging sites are now potentially exposed to the world and the damned googlebot" | /usr/bin/mail -s "Default staging server files have changed" [email protected] It works fine on the command line with: /usr/bin/sha512sum --status -c /sha512.sumlist && echo "Success" > /dev/null || echo "Check robots.txt and index.html in /var/www as staging sites are now potentially exposed to the world and the damned googlebot" | /usr/bin/mail -s "Default staging server files have changed" [email protected] As soon as I run it as a cronjob though it emails every time it runs with the failure message instead of only when the sha512sum check should fail. Is there something silly I have missed in a rush? I forgot to mention that I am running an Ubuntu machine.

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• Expire Files In A Folder: Delete Files After x Days

  - by Brett G

  I'm looking to make a "Drop Folder" in a windows shared drive that is accessible to everyone. I'd like files to be deleted automagically if they sit in the folder for more than X days. However, it seems like all methods I've found to do this, use the last modified date, last access time, or creation date of a file. I'm trying to make this a folder that a user can drop files in to share with somebody. If someone copies or moves files into here, I'd like the clock to start ticking at this point. However, the last modified date and creation date of a file will not be updated unless someone actually modifies the file. The last access time is updated too frequently... it seems that just opening a directory in windows explorer will update the last access time. Anyone know of a solution to this? I'm thinking that cataloging the hash of files on a daily basis and then expiring files based on hashes older than a certain date might be a solution.... but taking hashes of files can be time consuming. Any ideas would be greatly appreciated! Note: I've already looked at quite a lot of answers on here... looked into File Server Resource Monitor, powershell scripts, batch scripts, etc. They still use the last access time, last modified time or creation time... which, as described, do not fit the above needs.

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• Can I retrieve objects from a complex query that limits results to fields from a single table?

  - by Sean Redmond

  I have a model whose rows I always want to sort based on the values in another associated model and I was thinking that the way to implement this would be to use set_dataset in the model. This is causing query results to be returned as hashes rather than objects, though, so none of the methods from the class can be used when iterating over the dataset. I basically have two classes class SortFields < Sequel::Model(:sort_fields) set_primary_key :objectid end class Items < Sequel::Model(:items) set_primary_key :objectid one_to_one :sort_fields, :class => SortFields, :key => :objectid end Some backstory: the data is imported from a legacy system into mysql. The values in sort_fields are calculated from multiple other associated tables (some one-to-many, some many-to-many) according to some complicated rules. The likely solution will be to just add the values in sort_fields to items (I want to keep the imported data separate from the calculated data, but I don't have to). First, though, I just want to understand how far you can go with a dataset and still get objects rather than hashes. If I set the dataset to sort on a field in items like so class Items < Sequel::Model(:items) set_primary_key :objectid one_to_one :sort_fields, :class => SortFields, :key => :objectid set_dataset(order(:sortnumber)) end then the expected clause is added to the generated SQL, e.g.: >> Items.limit(1).sql => "SELECT * FROM `items` ORDER BY `sortnumber` LIMIT 1" and queries still return objects: >> Items.limit(1).first.class => Items If I order it by the associated fields though... class Items < Sequel::Model(:items) set_primary_key :objectid one_to_one :sort_fields, :class => SortFields, :key => :objectid set_dataset( eager_graph(:sort_fields). order(:sort1, :sort2, :sort3) ) end ...I get hashes ?> Items.limit(1).first.class => Hash My first thought was that this happens because all fields from sort_fields are included in the results and maybe if selected only the fields from items I would get Items objects again: class Items < Sequel::Model(:items) set_primary_key :objectid one_to_one :sort_fields, :class => SortFields, :key => :objectid set_dataset( eager_graph(:sort_fields). select(:items.*). order(:sort1, :sort2, :sort3) ) end The generated SQL is what I would expect: >> Items.limit(1).sql => "SELECT `items`.* FROM `items` LEFT OUTER JOIN `sort_fields` ON (`sort_fields`.`objectid` = `items`.`objectid`) ORDER BY `sort1`, `sort2`, `sort3` LIMIT 1" It returns the same rows as the set_dataset(order(:sortnumber)) version but it still doesn't work: >> Items.limit(1).first.class => Hash Before I add the sort fields to the items table so that they can all live happily in the same model, is there a way to tell Sequel to return on object when it wants to return a hash?

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• Installing into the GAC with WiX 3.0

  - by Jeff Yates

  I have a DLL that I would like to install into the Global Assembly Cache so that it can be referenced from multiple locations. I have a File declaration with the Assembly attribute set to ".net" but when the installation tries to install the DLL into the GAC, I get the following error (I have tided it up a bit to make it more readable): MSI (s) (58:38) [19:14:31:031]: Product: MyProductName 1.01 -- Error 1935. An error occurred during the installation of assembly  'Compass,   version="1.0.0.0",   culture="neutral",   publicKeyToken="392B26B760D48103",   processorArchitecture="MSIL"'. Please refer to Help and Support for more information. HRESULT: 0x80131043. assembly interface:       IAssemblyCacheItem, function:             Commit, component: {53AEE63B-F356-4D4F-8D61-EB0640A6E160} I have hunted around to find out what this means and the error relates to FUSION_E_UNEXPECTED_MODULE_FOUND. This link also includes this information: /// When installing multi-file assemblies into the GAC, the hash of each module is /// checked against the hash of that file stored in the manifest. If the /// hash of one of the files in the multi-file assembly does not match what is recorded /// in the manifest, FUSION_E_UNEXPECTED_MODULE_FOUND will be returned. /// The name of the error, and the text description of it, are somewhat confusing. /// The reason this error code is described this way is that the internally, /// Fusion/CLR implements installation of assemblies in the GAC, by installing /// multiple "streams" that are individually committed. /// Each stream has its hash computed, and all the hashes found /// are compared against the hashes in the manifest, at the end of the installation. /// Hence, a file hash mismatch appears as if an "unexpected" module was found. Unfortunately, this doesn't make much sense to me and I don't see how it relates to my assembly, which isn't fancy or complex from my perspective (it's just a regular .NET 3.5 class library and the current installation test is occurring on my development machine, which is a valid target environment for my project - 32-bit Windows XP SP3). Can anyone shed some light on why I might be getting this error and how I might hope to fix it?

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• SHA1 hashing in Delphi XE

  - by Leonardo Herrera

  Hello, I'm in the process of implementing XML digital signatures. I'm starting with little steps, so right now I want to solve the problem of SHA-1 hashing. There are lots of questions about this in SO: Digitially Sign Key with Lockbox Encryption library for Delphi Convert this php digital signing to Delphi Delphi: is there a version of LockBox for Delphi-XE Delphi 2010 Cryptography libraries ...and probably more. However, I'm using Delphi XE. So far, I've tried LockBox 2 (both the Songbeamer and Sourceforge versions), Lock Box 3, DCPCrypto2 and some others (Hashes is an easy to use unit which uses Windows crypto functions) I prepared a small test rig that gives me the following: LockBox2 FAILED: 1 ('abc') Got: '9f04f41a848514162050e3d68c1a7abb441dc2b5' Expected: 'a9993e364706816aba3e25717850c26c9cd0d89d' FAILED: 2 ('abcdbcdecdefdefgefghfghighijhijkijkljklmklmnlmnomnopnopq') Got: '51d7d8769ac72c409c5b0e3f69c60adc9a039014' Expected: '84983e441c3bd26ebaae4aa1f95129e5e54670f1' LockBox3 FAILED: 1 ('abc') Got: '9f04f41a848514162050e3d68c1a7abb441dc2b5' Expected: 'a9993e364706816aba3e25717850c26c9cd0d89d' FAILED: 2 ('abcdbcdecdefdefgefghfghighijhijkijkljklmklmnlmnomnopnopq') Got: '51d7d8769ac72c409c5b0e3f69c60adc9a039014' Expected: '84983e441c3bd26ebaae4aa1f95129e5e54670f1' DCPCrypto2 FAILED: 1 ('abc') Got: '9f04f41a848514162050e3d68c1a7abb441dc2b5' Expected: 'a9993e364706816aba3e25717850c26c9cd0d89d' FAILED: 2 ('abcdbcdecdefdefgefghfghighijhijkijkljklmklmnlmnomnopnopq') Got: '51d7d8769ac72c409c5b0e3f69c60adc9a039014' Expected: '84983e441c3bd26ebaae4aa1f95129e5e54670f1' Hashes Test 1 passes Test 2 passes Have you succeeded in compile the mentioned libraries under Delphi XE and make them give the appropriate values? I'm particularly interested in DCPCrypt2 SelfTest procedure. Edit: I've added this answer with the fixed source code. Thank you all for your help, it is most appreciated.

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• Tinyurl API Example - Am i doing it right :D

  - by Paul Weber

  Hi ... we use super-long Hashes for the Registration of new Users in our Application. The Problem is that these Hashes break in some Email Clients - making the Links unusable. I tried implementing the Tinyurl - API, with a simple Call, but i think it times out sometimes ... sometimes the mail does not reach the user. I updated the Code, but now the URL is never converted. Is Tinyurl really so slow or am i doing something wrong? (I mean hey, 5 Seconds is much in this Times) Can anybody recommend me a more reliable service? All my Fault, forgot a false in the fopen. But i will leave this sample of code here, because i often see this sample, wich i think does not work very reliable: return file_get_contents('http://tinyurl.com/api-create.php?url='.$u); This is the - i think fully working sample. I would like to hear about Improvements. static function gettinyurl( $url ) { $context = stream_context_create( array( 'http' => array( 'timeout' => 5 // 5 Seconds should be enough ) ) ); // get tiny url via api-create.php $fp = fopen( 'http://tinyurl.com/api-create.php?url='.$url, 'r', $context); // open (read) api-create.php with long url as get parameter if( $fp ) { // check if open was ok $tinyurl = fgets( $fp ); // read response if( $tinyurl && !empty($tinyurl) ) // check if response is ok $url = $tinyurl; // set response as url fclose( $fp ); // close connection } // return return $url; // return (tiny) url }

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• When to Store Temporary Values in Hidden Field vs. Session vs. Database?

  - by viatropos

  I am trying to build a simple OpenID login panel similar to how Stack Overflow's works. The goal is: User clicks OpenID/Oauth provider OpenID/Oauth stuff happens, we end up with the result (already made that) Then we want to confirm that the user wants to actually create a new account (vs. associating account with another OpenID account). In StackOverflow, they keep a hidden field on a form that looks like this: <form action="/users/openidconfirm" method="post"> <p>This is an OpenID we haven't seen on Stack Overflow before:</p> <p class="openid-identifier">https://me.yahoo.com/a/some-hash</p> <p>Do you want to associate this OpenID with your Stack Overflow account?</p> <div> <input type="hidden" name="fkey" value="9792ab2zza1q2a4ac414casdfa137eafba7"> <input type="hidden" name="s" value="c1a3q133-11fa-49r0-a7bz-da19849383218"> <input type="submit" value="Associate OpenID"> <input type="button" value="Cancel" onclick="window.location.href = 'http://stackoverflow.com/users/169992/viatropos?s=c1a3q133-11fa-49r0-a7bz-da19849383218'"> </div> </form> Initial question is, what are those hashes fkey and s? Not that I really care what these specific hashes are, but what it seems like is happening is they have processed the openid response and saved it to the DB in a temporary object or something, and from there they generate these keys, because they don't look like Oauth keys to me. Main situation is: after I have processed OpenID/Oauth responses, I don't yet want to create a new user/account until the user submits the "confirm" form. Should I store the keys and tokens temporarily in a "Confirm" form like this? Or is there a better way? It seems that using a temp database object would be a lot of work to manage properly. Thanks for the help. Lance

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• Understanding Symbols In Ruby

  - by Kezzer

  Despite reading this article, I'm still confused as to the representation of the data in memory when it comes to using symbols. If a symbol, two of them contained in different objects, exist in the same memory location, then how is it that they contain different values? I'd have expected the same memory location to contain the same value. As a quote from the link: Unlike strings, symbols of the same name are initialized and exist in memory only once during a session of ruby I just don't understand how it manages to differentiate the values contained in the same memory location. EDIT So let's consider the example: patient1 = { :ruby => "red" } patient2 = { :ruby => "programming" } patient1.each_key {|key| puts key.object_id.to_s} 3918094 patient2.each_key {|key| puts key.object_id.to_s} 3918094 patient1 and patient2 are both hashes, that's fine. :ruby however is a symbol. If we were to output the following: patient1.each_key {|key| puts key.to_s} Then what will be output? "red", or "programming"? FURTHER EDIT I'm still really quite confused. I'm thinking a symbol is a pointer to a value. Let's forget hashes for a second. The questions I have are; can you assign a value to a symbol? Is a symbol just a pointer to a variable with a value in it? If symbols are global, does that mean a symbol always points to one thing?

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• How do I interact with a Perl object that has a hash attribute?

  - by brydgesk

  I have a class with several variables, one of which is a hash (_runs): sub new { my ($class, $name) = @_; my $self = { _name => $name, ... _runs => (), _times => [], ... }; bless ($self, $class); return $self; } Now, all I'm trying to do is create an accessor/mutator, as well as another subroutine that pushes new data into the hash. But I'm having a hell of a time getting all the referencing/dereferencing/$self calls working together. I've about burned my eyes out with "Can't use string ("blah") as a HASH ref etc etc" errors. For the accessor, what is 'best practice' for returning hashes? Which one of these options should I be using (if any)?: return $self->{_runs}; return %{ $self->{_runs} }; return \$self->{_runs}; Further, when I'm using the hash within other subroutines in the class, what syntax do I use to copy it? my @runs = $self->{_runs}; my @runs = %{ $self->{_runs} }; my @runs = $%{ $self->{_runs} }; my @runs = $$self->{_runs}; Same goes for iterating over the keys: foreach my $dt (keys $self->{_runs}) foreach my $dt (keys %{ $self->{_runs} }) And how about actually adding the data? $self->{_runs}{$dt} = $duration; %{ $self->{_runs} }{$dt} = $duration; $$self->{_runs}{$dt} = $duration; You get the point. I've been reading articles about using classes, and articles about referencing and dereferencing, but I can't seem to get my brain to combine the knowledge and use both at the same time. I got my _times array working finally, but mimicking my array syntax over to hashes didn't work.

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• Time complexity to fill hash table (homework)?

  - by Heathcliff

  This is a homework question, but I think there's something missing from it. It asks: Provide a sequence of m keys to fill a hash table implemented with linear probing, such that the time to fill it is minimum. And then Provide another sequence of m keys, but such that the time fill it is maximum. Repeat these two questions if the hash table implements quadratic probing I can only assume that the hash table has size m, both because it's the only number given and because we have been using that letter to address a hash table size before when describing the load factor. But I can't think of any sequence to do the first without knowing the hash function that hashes the sequence into the table. If it is a bad hash function, such that, for instance, it hashes every entry to the same index, then both the minimum and maximum time to fill it will take O(n) time, regardless of what the sequence looks like. And in the average case, where I assume the hash function is OK, how am I suppossed to know how long it will take for that hash function to fill the table? Aren't these questions linked to the hash function stronger than they are to the sequence that is hashed? As for the second question, I can assume that, regardless of the hash function, a sequence of size m with the same key repeated m-times will provide the maximum time, because it will cause linear probing from the second entry on. I think that will take O(n) time. Is that correct? Thanks

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• How do you verify that 2 copies of a VB 6 executable came from the same code base?

  - by Tim Visher

  I have a program under version control that has gone through multiple releases. A situation came up today where someone had somehow managed to point to an old copy of the program and thus was encountering bugs that have since been fixed. I'd like to go back and just delete all the old copies of the program (keeping them around is a company policy that dates from before version control was common and should no longer be necessary) but I need a way of verifying that I can generate the exact same executable that is better than saying "The old one came out of this commit so this one should be the same." My initial thought was to simply MD5 hash the executable, store the hash file in source control, and be done with it but I've come up against a problem which I can't even parse. It seems that every time the executable is generated (method: Open Project. File Make X.exe) it hashes differently. I've noticed that Visual Basic messes with files every time the project is opened in seemingly random ways but I didn't think that would make it into the executable, nor do I have any evidence that that is indeed what's happening. To try to guard against that I tried generating the executable multiple times within the same IDE session and checking the hashes but they continued to be different every time. So that's: Generate Executable Generate MD5 Checksum: md5sum X.exe > X.md5 Verify MD5 for current executable: md5sum -c X.md5 Generate New Executable Verify MD5 for new executable: md5sum -c X.md5 Fail verification because computed checksum doesn't match. I'm not understanding something about either MD5 or the way VB 6 is generating the executable but I'm also not married to the idea of using MD5. If there is a better way to verify that two executables are indeed the same then I'm all ears. Thanks in advance for your help!

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• What hash algorithms are paralellizable? Optimizing the hashing of large files utilizing on mult-co

  - by DanO

  I'm interested in optimizing the hashing of some large files (optimizing wall clock time). The I/O has been optimized well enough already and the I/O device (local SSD) is only tapped at about 25% of capacity, while one of the CPU cores is completely maxed-out. I have more cores available, and in the future will likely have even more cores. So far I've only been able to tap into more cores if I happen to need multiple hashes of the same file, say an MD5 AND a SHA256 at the same time. I can use the same I/O stream to feed two or more hash algorithms, and I get the faster algorithms done for free (as far as wall clock time). As I understand most hash algorithms, each new bit changes the entire result, and it is inherently challenging/impossible to do in parallel. Are any of the mainstream hash algorithms parallelizable? Are there any non-mainstream hashes that are parallelizable (and that have at least a sample implementation available)? As future CPUs will trend toward more cores and a leveling off in clock speed, is there any way to improve the performance of file hashing? (other than liquid nitrogen cooled overclocking?) or is it inherently non-parallelizable?

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• PHP - Find a string in file then show it's line number

  - by xZero

  I have an application which needs to open the file, then find string in it, and print a line number where is string found. For example, file example.txt contains few hashes: APLF2J51 1a79a4d60de6718e8e5b326e338ae533 EEQJE2YX 66b375b08fc869632935c9e6a9c7f8da O87IGF8R c458fb5edb84c54f4dc42804622aa0c5 APLF2J51 B7TSW1ZE 1e9eea56686511e9052e6578b56ae018 EEQJE2YX affb23b07576b88d1e9fea50719fb3b7 So, I want to PHP search for "1e9eea56686511e9052e6578b56ae018" and print out its line number, in this case 4. Please note that there are will not be multiple hashes in file. I found a few codes over Internet, but none seem to work. I tried this one: <?PHP $string = "1e9eea56686511e9052e6578b56ae018"; $data = file_get_contents("example.txt"); $data = explode("\n", $data); for ($line = 0; $line < count($data); $line++) { if (strpos($data[$line], $string) >= 0) { die("String $string found at line number: $line"); } } ?> It just says that string is found at line 0.... Which is not correct.... Final application is much more complex than that... After it founds line number, it should replace string which something else, and save changes to file, then goes further processing.... Thanks in advance :)

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• What hash algorithms are parallelizable? Optimizing the hashing of large files utilizing on multi-co

  - by DanO

  I'm interested in optimizing the hashing of some large files (optimizing wall clock time). The I/O has been optimized well enough already and the I/O device (local SSD) is only tapped at about 25% of capacity, while one of the CPU cores is completely maxed-out. I have more cores available, and in the future will likely have even more cores. So far I've only been able to tap into more cores if I happen to need multiple hashes of the same file, say an MD5 AND a SHA256 at the same time. I can use the same I/O stream to feed two or more hash algorithms, and I get the faster algorithms done for free (as far as wall clock time). As I understand most hash algorithms, each new bit changes the entire result, and it is inherently challenging/impossible to do in parallel. Are any of the mainstream hash algorithms parallelizable? Are there any non-mainstream hashes that are parallelizable (and that have at least a sample implementation available)? As future CPUs will trend toward more cores and a leveling off in clock speed, is there any way to improve the performance of file hashing? (other than liquid nitrogen cooled overclocking?) or is it inherently non-parallelizable?

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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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