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  • Python MD5 Hash Faster Calculation

    - by balgan
    Hi everyone. I will try my best to explain my problem and my line of thought on how I think I can solve it. I use this code for root, dirs, files in os.walk(downloaddir): for infile in files: f = open(os.path.join(root,infile),'rb') filehash = hashlib.md5() while True: data = f.read(10240) if len(data) == 0: break filehash.update(data) print "FILENAME: " , infile print "FILE HASH: " , filehash.hexdigest() and using start = time.time() elapsed = time.time() - start I measure how long it takes to calculate an hash. Pointing my code to a file with 653megs this is the result: root@Mars:/home/tiago# python algorithm-timer.py FILENAME: freebsd.iso FILE HASH: ace0afedfa7c6e0ad12c77b6652b02ab 12.624 root@Mars:/home/tiago# python algorithm-timer.py FILENAME: freebsd.iso FILE HASH: ace0afedfa7c6e0ad12c77b6652b02ab 12.373 root@Mars:/home/tiago# python algorithm-timer.py FILENAME: freebsd.iso FILE HASH: ace0afedfa7c6e0ad12c77b6652b02ab 12.540 Ok now 12 seconds +- on a 653mb file, my problem is I intend to use this code on a program that will run through multiple files, some of them might be 4/5/6Gb and it will take wayy longer to calculate. What am wondering is if there is a faster way for me to calculate the hash of the file? Maybe by doing some multithreading? I used a another script to check the use of the CPU second by second and I see that my code is only using 1 out of my 2 CPUs and only at 25% max, any way I can change this? Thank you all in advance for the given help.

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  • I'm trying to understand hash tables - can someone explain it to me - clearly?

    - by Stevo
    I want to understand the correct use and implementation of hash tables in php (sorry). I read somewhere that an in-experienced programmer created a hash table and then iterated through it. Now, I understand why that is wrong but I haven't quite got the full knowledge to know if my understanding is correct (if you know what I mean). So could someone explain to me how to implement a hash table in php (presumably an associative array) and perhaps more importantly, how to access the values 'with a hash' and what that actually means?

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  • Numeric UIDs/GIDs in ACLs on OS X server (10.6)

    - by Oliver Humpage
    Hi, On one (old OS X 10.4) server I'm tarring up some files which have ACLs. I'm then using ``tar -xp'' to untar the archive onto a new 10.6 server, which doesn't have any users/groups configured on it yet except the default admin (UID 501) (there's a reason for that, don't ask!). Obviously this means an "ls -lne" will list files and ACLs with numeric UIDs and GIDs. Now for the normal file permissions it makes sense: you get UIDs like "1037". And for some ACLs, it also makes sense: you get things like "AAAABBBB-CCCC-DDDD-EEEE-FFFF00000402" for groups (0x402 = GID 1026) and "FFFFEEEE-DDDD-CCCC-BBBB-AAAA000001F5" for users (0x1F5 = UID 501). However, some ACLs have a UIDs like "E51DA674-AE70-41BC-8340-9B06C243A262" or GIDs like "0A3FCD24-0012-46FA-B085-88519E55EF29" and I have absolutely no idea how to translate these IDs back into something that could be matched back to the original IDs (UID 1072 and GID 1047 respectively in this example). Can anyone help me translate these weird long hex strings? (Basically we're moving from local users to an Active Directory setup, so I want to move all files to the new server with permissions intact, then chmod, chgrp and set ACLs such that we translate old IDs to the new AD IDs. Hence needing some way to map between the sets. I don't believe there's an easier way to do this?) Many thanks, Oliver.

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  • SQL Server insert with XML parameter - empty string not converting to null for numeric

    - by Mayo
    I have a stored procedure that takes an XML parameter and inserts the "Entity" nodes as records into a table. This works fine unless one of the numeric fields has a value of empty string in the XML. Then it throws an "error converting data type nvarchar to numeric" error. Is there a way for me to tell SQL to convert empty string to null for those numeric fields in the code below? -- @importData XML <- stored procedure param DECLARE @l_index INT EXECUTE sp_xml_preparedocument @l_index OUTPUT, @importData INSERT INTO dbo.myTable ( [field1] ,[field2] ,[field3] ) SELECT [field1] ,[field2] ,[field3] FROM OPENXML(@l_index, 'Entities/Entity', 1) WITH ( field1 int 'field1' ,field2 varchar(40) 'field2' ,field3 decimal(15, 2) 'field3' ) EXECUTE sp_xml_removedocument @l_index EDIT: And if it helps, sample XML. Error is thrown unless I comment out field3 in the code above or provide a value in field3 below. <?xml version="1.0" encoding="utf-16"?> <Entities> <Entity> <field1>2435</field1> <field2>843257-3242</field2> <field3 /> </Entity> </Entities>

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  • The algorithm used to generate recommendations in Google News?

    - by Siddhant
    Hi everyone. I'm study recommendation engines, and I went through the paper that defines how Google News generates recommendations to users for news items which might be of their interest, based on collaborative filtering. One interesting technique that they mention is Minhashing. I went through what it does, but I'm pretty sure that what I have is a fuzzy idea and there is a strong chance that I'm wrong. The following is what I could make out of it :- Collect a set of all news items. Define a hash function for a user. This hash function returns the index of the first item from the news items which this user viewed, in the list of all news items. Collect, say "n" number of such values, and represent a user with this list of values. Based on the similarity count between these lists, we can calculate the similarity between users as the number of common items. This reduces the number of comparisons a lot. Based on these similarity measures, group users into different clusters. This is just what I think it might be. In Step 2, instead of defining a constant hash function, it might be possible that we vary the hash function in a way that it returns the index of a different element. So one hash function could return the index of the first element from the user's list, another hash function could return the index of the second element from the user's list, and so on. So the nature of the hash function satisfying the minwise independent permutations condition, this does sound like a possible approach. Could anyone please confirm if what I think is correct? Or the minhashing portion of Google News Recommendations, functions in some other way? I'm new to internal implementations of recommendations. Any help is appreciated a lot. Thanks!

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  • Tool to compute SHA256 Tree Hash

    - by Benjamin
    I've started using AWS Glacier, and noticed that it hashes the files using an algorithm called SHA-256 Tree Hash. To my surprise, this algorithm is different from SHA-256, so I can't use the tools I'm used to, to compare hashes and verify file integrity. Do you know a Windows tool, if possible integrated in the context menu, to compute the SHA-256 Tree Hash of a file? I'd also accept a Linux command-line tool, as a second choice :-)

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  • MySQL Hashing Function Implementation

    - by Jonas Stevens
    I know that php has md5(), sha1(), and the hash() functions, but I want to create a hash using the MySQL PASSWORD() function. So far, the only way I can think of is to just query the server, but I want a function (preferably in php or Perl) that will do the same thing without querying MySQL at all. For example: MySQL hash - 464bb2cb3cf18b66 MySQL5 hash - *01D01F5CA7CA8BA771E03F4AC55EC73C11EFA229 Thanks!

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  • hashing password giving different results

    - by geoff
    I am taking over a system that a previous developer wrote. The system has an administrator approve a user account and when they do that the system uses the following method to hash a password and save it to the database. It sends the unhashed password to the user. When the user logs in the system uses the exact same method to hash what the user enters and compares it to the database value. We've run into a couple of times when the database entry doesn't match the user's entry whey they should. So it appears that the method isn't always hashing the value the same. Does anyone know if this method of hashing isn't reliable and how to make it reliable? Thanks. private string HashPassword(string password) { string hashedPassword = string.Empty; // Convert plain text into a byte array. byte[] plainTextBytes = Encoding.UTF8.GetBytes(password); // Allocate array, which will hold plain text and salt. byte[] plainTextWithSaltBytes = new byte[plainTextBytes.Length + SALT.Length]; // Copy plain text bytes into resulting array. for(int i = 0; i < plainTextBytes.Length; i++) plainTextWithSaltBytes[i] = plainTextBytes[i]; // Append salt bytes to the resulting array. for(int i = 0; i < SALT.Length; i++) plainTextWithSaltBytes[plainTextBytes.Length + i] = SALT[i]; // Because we support multiple hashing algorithms, we must define // hash object as a common (abstract) base class. We will specify the // actual hashing algorithm class later during object creation. HashAlgorithm hash = new SHA256Managed(); // Compute hash value of our plain text with appended salt. byte[] hashBytes = hash.ComputeHash(plainTextWithSaltBytes); // Create array which will hold hash and original salt bytes. byte[] hashWithSaltBytes = new byte[hashBytes.Length + SALT.Length]; // Copy hash bytes into resulting array. for(int i = 0; i < hashBytes.Length; i++) hashWithSaltBytes[i] = hashBytes[i]; // Append salt bytes to the result. for(int i = 0; i < SALT.Length; i++) hashWithSaltBytes[hashBytes.Length + i] = SALT[i]; // Convert result into a base64-encoded string. hashedPassword = Convert.ToBase64String(hashWithSaltBytes); return hashedPassword; }

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  • Are fragments of hashes collision-resistent?

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

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  • Optimizing hash lookup & memory performance in Go

    - by Moishe
    As an exercise, I'm implementing HashLife in Go. In brief, HashLife works by memoizing nodes in a quadtree so that once a given node's value in the future has been calculated, it can just be looked up instead of being re-calculated. So eg. if you have a node at the 8x8 level, you remember it by its four children (each at the 2x2 level). So next time you see an 8x8 node, when you calculate the next generation, you first check if you've already seen a node with those same four children. This is extended up through all levels of the quadtree, which gives you some pretty amazing optimizations if eg. you're 10 levels above the leaves. Unsurprisingly, it looks like the perfmance crux of this is the lookup of nodes by child-node values. Currently I have a hashmap of {&upper_left_node,&upper_right_node,&lower_left_node,&lower_right_node} -> node So my lookup function is this: func FindNode(ul, ur, ll, lr *Node) *Node { var node *Node var ok bool nc := NodeChildren{ul, ur, ll, lr} node, ok = NodeMap[nc] if ok { return node } node = &Node{ul, ur, ll, lr, 0, ul.Level + 1, nil} NodeMap[nc] = node return node } What I'm trying to figure out is if the "nc := NodeChildren..." line causes a memory allocation each time the function is called. If it does, can I/should I move the declaration to the global scope and just modify the values each time this function is called? Or is there a more efficient way to do this? Any advice/feedback would be welcome. (even coding style nits; this is literally the first thing I've written in Go so I'd love any feedback)

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  • Version hash to solve Event Sourcing problems

    - by SystematicFrank
    The basic examples I have seen about Event Sourcing do not deal with out of order events, clock offsets in different systems and late events from system partitions. I am wondering if more polished Event Sourcing implementations rely on a version stamp of modified objects? For example, assuming that the system is rendering the entity Client with version id ABCD1234. If the user modifies the entity, the system will create an event with the modified fields AND the version id reference to which version it applies. Later the event responder would detect out of order events and merge them.

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  • Coldfusion Components:- The argument passed to the function is not of type numeric

    - by salim.vali
    Hi I have a simple form form.cfm:- <cfset Registr = createObject("component", "forms.Registr") /> <cfset setFoo = createObject('component','forms.Registr).putNUsr(username,password,rating) /> <form name="regFrm" action="#cgi.script_name#" method="post" onsubmit="submitform();" > <tr><td>Username:</td> <td><input type="text" name=" Username" value="#form. Username#" ></td></tr> <tr><td>Password:</td> <td><input class="" type="password" name="password" value="#form.password#" ></td></tr> <tr><td>Rate:</td> <select name="rating" > <option value="" ></option> <cfloop query="qGetReting"> <option value="#rating_id#" <cfif form. rating eq prof_id>selected</cfif> >#rating#</option> </cfloop> </select> </td> </tr> </form> Now there is this cfc called Registr.cfc in the "forms" folder which has an insert-function called 'putNUsr'the code for 'Registr.cfc' is as follows. <cfcomponent> <cffunction name="putNUsr" returntype="void" displayname="" output="no"> <cfargument name="password" type="string" required="true"> <cfargument name="rating" type="numeric" required="true"> <cfargument name="username" type="string" required="true"> <cfquery datasource="#application.xyz#" name="q_putNUsr"> insert into users (username , password , rating) values( <cfqueryparam value="#arguments. username#" cfsqltype="CF_SQL_VARCHAR" />, <cfqueryparam value="#arguments.password#" cfsqltype="CF_SQL_VARCHAR" />, <cfqueryparam value="#arguments.rating#" cfsqltype="CF_SQL_INTEGER" ) </cfquery> </cffunction> </cfcomponent> I am able to populate the DB with the data if I do not use the form field "rating" which is numeric. Else i am getting the error as follows:- The RATING argument passed to the putNUsr function is not of type numeric. If the component name is specified as a type of this argument, it is possible that either a definition file for the component cannot be found or is not accessible. KINDLY HELP -S Vali

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  • Convert varchar to numeric in Informix

    - by user302705
    Hi All I have problem while converting varchar type to Int type in Informix. Actually I dont know if the value is really varchar or not which I want to convert to INT. Its a sandbox system. As Example: I am trying to run this kind of Select telnumber from numbers n where Cast(n.telnumber AS INT) between 1234 and 9999 I got this error: "Character to numeric conversion error" If I run this query like this: Select telnumber from numbers n where n.telnumber between '1234' and '9999' it brings a resultset but not in the range that I defined. 130987 130710 130723 How can I convert telnumber to a numeric value and use it in "between" 1234 and 9999 range Thanks in advance.

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  • AbsoluteTime with numeric argument behaves strangely.

    - by dreeves
    This is strange: DateList@AbsoluteTime[596523] returns {2078, 7, 2, 2, 42, 9.7849} But DateList@AbsoluteTime[596524] returns {1942, 5, 26, 20, 28, 39.5596} The question: What's going on? Note that AbsoluteTime with a numeric argument is undocumented. (I think I now know what it's doing but figured this is useful to have as a StackOverflow question for future reference; and I'm curious if there's some reason for that magic 596523 number.) PS: I encountered this when writing these utility functions for converting to and from unix time in Mathematica: (* Using Unix time (an integer) instead of Mathematica's AbsoluteTime... *) tm[x___] := AbsoluteTime[x] (* tm is an alias for AbsoluteTime. *) uepoch = tm[{1970}, TimeZone->0]; (* unixtm works analogously to tm. *) unixtm[x___] := Round[tm[x]-uepoch] (* tm & unixtm convert between unix & *) unixtm[x_?NumericQ] := Round[x-uepoch] (* mma epoch time when given numeric *) tm[t_?NumericQ] := t+uepoch (* args. Ie, they're inverses. *)

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  • Numeric literals in sql server 2008

    - by costa
    What is the type that sql server assigns to the numeric literal: 2. , i.e. 2 followed by a dot? I was curious because: select convert(varchar(50), 2.) union all select convert(varchar(50), 2.0) returns: 2 2.0 which made me ask what's the difference between 2. and 2.0 type wise? Sql server seems to assign types to numeric literals depending on the number itself by finding the minimal storage type that can hold the number. A value of 1222333 is stored as int while 1152921504606846975 is stored as big int. thanks

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  • MySQL Unique hash insertion

    - by Jesse
    So, imagine a mysql table with a few simple columns, an auto increment, and a hash (varchar, UNIQUE). Is it possible to give mysql a query that will add a column, and generate a unique hash without multiple queries? Currently, the only way I can think of to achieve this is with a while, which I worry would become more and more processor intensive the more entries were in the db. Here's some pseudo-php, obviously untested, but gets the general idea across: while(!query("INSERT INTO table (hash) VALUES (".generate_hash().");")){ //found conflict, try again. } In the above example, the hash column would be UNIQUE, and so the query would fail. The problem is, say there's 500,000 entries in the db and I'm working off of a base36 hash generator, with 4 characters. The likelyhood of a conflict would be almost 1 in 3, and I definitely can't be running 160,000 queries. In fact, any more than 5 I would consider unacceptable. So, can I do this with pure SQL? I would need to generate a base62, 6 char string (like: "j8Du7X", chars a-z, A-Z, and 0-9), and either update the last_insert_id with it, or even better, generate it during the insert. I can handle basic CRUD with MySQL, but even JOINs are a little outside of my MySQL comfort zone, so excuse my ignorance if this is cake. Any ideas? I'd prefer to use either pure MySQL or PHP & MySQL, but hell, if another language can get this done cleanly, I'd build a script and AJAX it too. Thanks!

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  • Character encoding issues when generating MD5 hash cross-platform

    - by rogueprocess
    This is a general question about character encoding when using MD5 libraries in various languages. My concern is: suppose I generate an MD5 hash using a native Python string object, like this: message = "hello world" m = md5() m.update(message) Then I take a hex version of that MD5 hash using: m.hexdigest() and send the message & MD5 hash via a network, let's say, a JMS message or a HTTP request. Now I get this message in a Java program in the form of a native Java string, along with the checksum. Then I generate an MD5 hash using Java, like this (using the Commons Codec library): String md5 = org.apache.commons.codec.digest.DigestUtils.DigestUtils.md5Hex(s) My feeling is that this is wrong because I have not specified character encodng at either end. So the original hash will be based on the bytes of the Python version of the string; the Java one will be based on the bytes of the Java version of the string , these two byte sequences will often not be the same - is that right? So really I need to specify "UTF-8" or whatever at both ends right? (I am actually getting an intermittent error in my code where the MD5 checksum fails, and I suspect this is the reason - but because it's intermittent, it's difficult to say if changing this fixes it or not. ) Thank you!

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  • How to transform phrases and words into MD5 hash?

    - by brilliant
    Can anyone, please, explain to me how to transform a phrase like "I want to buy some milk" into MD5? I read Wikipedia article on MD5, but the explanation given there is beyond my comprehension: "MD5 processes a variable-length message into a fixed-length output of 128 bits. The input message is broken up into chunks of 512-bit blocks (sixteen 32-bit little endian integers)" "sixteen 32-bit little endian integers" is already hard for me. I checked the article on little endians and didn't understand a bit. However, the examples of some phrases and their MD5 hashes are very nice: MD5("The quick brown fox jumps over the lazy dog") = 9e107d9d372bb6826bd81d3542a419d6 MD5("The quick brown fox jumps over the lazy dog.") = e4d909c290d0fb1ca068ffaddf22cbd0 Can anyone, please, explain to me how this MD5 algorithm works on some very simple example? And also, perhaps you know some software or a code that would transform phrases into their MD5. If yes, please, let me know.

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  • Hash Map Usage and Idea

    - by Anand
    Hi, I have been working in Java for the last 6 months and have been using Hash Maps What is the basic idea of a Hash Map ? I am using it as it easy for me to store so much data with direct key references rather than having to iterate through an arraylist ? Where is the power of Hash Map seen ? What is the scientific idea behind this data structure ?

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  • good __eq__, __lt__, ..., __hash__ methods for image class?

    - by Marten Bauer
    I create the following class: class Image(object): def __init__(self, extension, data, urls=None, user_data=None): self._extension = extension self._data = data self._urls = urls self._user_data = user_data self._hex_digest = hashlib.sha1(self._data).hexDigest() Images should be equal when all values are equal. Therefore I wrote: def __eq__(self, other): if isinstance(other, Image) and self.__dict__ == other.__dict__: return True return False def __ne__(self, other): return not self.__eq__(other) def __lt__(self, other): return self.__dict__ < other.__dict__ ... But how should the __hash__ method look like? Equal Images should return equal hashes... def __hash__(self): # won't work !?! return hash(self.__dict__) Is the way I try to use __eq__, __ne__, __lt__, __hash__, ... recommend?

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