The hashing tag has no wiki summary.
0
votes
1answer
63 views
Linear probing hashing collision resolution
So I have a quick question about the linear probing method of collision resolution in hash tables. So by definition a linear probing method would look like:
while (hashTable[hash] != null)
hash = ...
1
vote
1answer
93 views
Max number of items mapped to same location in hashmap
I have a question about hashmaps.
If you have this hashmap with m slots, and need to map n items to it, and n > m. There will be collisions for sure. But assuming there is simple uniform hashing ...
-1
votes
1answer
160 views
strongest free c++ user password storage encryption/hashing library? [closed]
If performance is of no concern, what free c++ library has the strongest encryption/hashing for user password storage?
Ease of use would be nice, but the prime concern is security.
1
vote
6answers
375 views
Would md5 hashes allow detection of synced files?
We have to develop our own file management system in Java web application. We need to sync files between our main server and client severs and find out whether all the client server has all the latest ...
4
votes
2answers
403 views
How can “hash functions” be used to implement hash maps at all?
My understandment is that hash maps allow us to link, say, a string, to certain memory location. But if every string were to be linked to a unique place in memory it would need a huge block of empty ...
5
votes
1answer
339 views
How do scalable bloom filters work?
I was reading up on scalable bloom filters and could not understand how each time a constituent bloom filters fills up, a new bloom filter with larger size is added.
The elements that contributed to ...
8
votes
1answer
400 views
Hash function classification interview question
In several places on the Internet there's the interview question
Classify the Hashing Functions based on the various methods by which the key value is found.
with answers like
Direct method
...
4
votes
4answers
222 views
Concept behind SHA-1 Checksum
What's the basis behind SHA-1 or SHA-2 or other Checksum algorithms?
I read about it here http://en.wikipedia.org/wiki/SHA-1#Data_Integrity
But I am still wondering about an answer in a layman's ...
0
votes
1answer
181 views
How to test if a hashing algorithm is good? [duplicate]
Possible Duplicate:
Which hashing algorithm is best for uniqueness and speed?
I have created a hash algorithm and would like to test if it is usable. What do I need to test and how?
0
votes
3answers
244 views
Basic memcached question
I have been reading up on distributed hashing. I learnt that consistent hashing is used for distributing the keys among cache machines. I also learnt that, a key is duplicated on mutiple caches to ...
2
votes
1answer
167 views
Hash Algorithm Randomness Visualization
I'm curious if anyone here has any idea how the images were generated as shown in this response: Which hashing algorithm is best for uniqueness and speed?
Ian posted a very well-received response but ...
1
vote
2answers
186 views
Looking for a non-cryptographic hash function that returns a single character
Suppose I have a dictionary of ASCII words stored in uppercase. I also want to save those words into separate files so that the total word count of each file is approximately the same. By simply ...
2
votes
2answers
278 views
History of Associative Array?
In quite a lot of modern scripting languages (e.g. Perl, Python, Ruby, PHP, Lua, JavaScript), associative arrays are supported as a primitive or first-class data type (with various names like map, ...
3
votes
1answer
253 views
Directory structure (file system design)
I was looking at how file systems are designed and noticed that most places say that the directory hierarchy can be implemented using a hash table.
Could someone please explain me how using a hash ...
0
votes
0answers
45 views
Built-in Context-and-Input-to-Output-Hashing in Compilers
Why doesn't (open source) compilers contain builtin funtionality for (shared) caching and reuse-fetching (using SHA1-hash of compiler-version, build-flags, target-platform and inputs) of executable ...
1
vote
1answer
197 views
hash with file instead of array
Is it possible to use hash function but with File instead of Array, and it's gonna be saving the record in a file position and then search will fseek to that position, but I'm not sure how to open a ...
5
votes
1answer
143 views
Using account (login) password in generated PDF?
Ever since I heard about programming, I was told that any password (especially the one used on login) should be stored in database using any kind of one-way hashing algorithm, and never ever as plain ...
-3
votes
1answer
269 views
Writing-Reading a hashtable to a text file
I'm implementing a hashtable structure for a dictionary. Dictionary is in a text file. There are 2 words on each line. I'm generating the hashtable by using the first word as a key. I'm holding the ...
11
votes
6answers
767 views
What makes a hashing algorithm “secure”?
After reading this interesting question, I felt like I had a good idea of which insecure hashing algorithm I'd use if I needed one, but no idea why I might use a secure algorithm instead.
So what is ...
5
votes
3answers
2k views
How does a web browser save passwords?
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. ...
-1
votes
2answers
177 views
Best way to generate permalinks
I'm looking to create a database of goods and I don't think an incrementing id would be adequate:
http://example.com/0001
http://example.com/0002
So with 4 digits I can address 10000 items IIUC.
I ...
8
votes
8answers
3k views
What are some common examples of a Hash Table?
I was just wondering if there were some "standard" examples that everyone uses as a basis for explaining the nature of a problem that requires the use of a Hash table. What are some well-known ...
10
votes
5answers
2k views
Is it more secure to hash a password multiple times?
I've read a few times that when storing passwords, it's good practice to 'double hash' the strings (eg. with md5 then sha1, both with salts, obviously).
I guess the first question is, "is this ...
2
votes
1answer
856 views
How costly are the Python dict and set in-built types?
I have undertaken a project concerning database deduplication. I did some research and have found that the Python dict type actually is a hashmap that uses open addressing.
In the deduplication ...
-2
votes
2answers
530 views
One global HashMap vs. many local HashMaps?
Which is more efficient; which is faster? Trade-offs?
Goal is for fast look-ups in a web application.
UUIDs are the keys, so global will work.
Approx 50 million values.
A global cache is ...
2
votes
4answers
506 views
Convert filenames to their checksum before saving to prevent duplicates. Is is a smart thing to do?
TL;DR:what the title says
I am developing some sort of image board in PHP. I was thinking of changing each image's filename to it's checksum prior to saving it. This way, I might be able to ...
3
votes
7answers
454 views
How do i speedily traverse a file system while extracting/extrapolating various data and provide user feedback?
I'm working on a system file scanner that reveals info about various files (e.g. size, last used, duplicates, etc). Currently I'm traversing the file system once just to get a good measure of the ...
3
votes
5answers
309 views
Is it possible to insert the hash of an executable into the executable itself without changing the resulting hash? What's the best alternative?
I've been thinking about this problem recently and it really doesn't seem like it's possible, but I figured that I'd ask just in case.
Assume a simple program, in pseudocode:
run hash on an ...
15
votes
9answers
6k views
Why almost no webpages hash passwords in the client before submitting (and hashing them again on the server), as to “protect” against password reuse?
Relevant XKCD
There are many sites on the Internet that require login information, and the only way to protect against password reusing is the "promise" that the passwords are hashed on the server, ...
12
votes
3answers
3k views
I'm trying to understand hash tables - can someone explain it to me - clearly?
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 ...
6
votes
5answers
2k views
Where should salt hash values come from?
When adding salt values to a hash value for something like a password that cannot be stored in plain text, what is the best place to get the salt values come from? For context, let us suppose this is ...
285
votes
9answers
66k views
Which hashing algorithm is best for uniqueness and speed?
I was just wondering which hashing algorithm is best for uniqueness and speed? Example (good) uses include hash dictionaries.
I know there are things like sha256 and such, but these algorithms are ...
5
votes
3answers
263 views
Hashing growth strategy
What is a good growth strategy for hash tables? If the number of elements exceeds the number of buckets, I increase the number of buckets with the following formula:
n = int(n * 1.618033988749895) | ...
