A hash algorithm is a function which takes a variable size input and produces a fixed size output. The algorithm tries to make it difficult to predict the output for a given input, find two inputs with the same output, or reconstruct the input from the output.

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606 views

How to properly anonymize data, if hashing isn't enough?

Today there are news on Bruce Schneier's blog and ArsTechnica about how NY City released information about Cab/Taxi drivers, their trips, and so on. Basically, sensitive information was simply MD5 ...
16
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8answers
3k views

Won't all hashes collide after enough iterations (with a static salt)?

We all know that we're supposed to take a fairly slow hashing algorithm, salt the password, and run the hash for many iterations. Let's say that I'm following almost everything except for one rule, ...
0
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3answers
56 views

How to secure Password and Salt on a deployed application

I have a question regarding one step of protection more than salt/hash. I work on an application that is distributed to many clients and then deployed on their networks. If I set a password on one ...
0
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1answer
77 views

Using hashed password as secret key for hmac to avoid exchange of secret between server and client

I'm currently trying to improve our API to be more restful, therfore avoid any state on the server. I want to accomplish this with a hmac token, appended on every request. The hmac will be made with ...
1
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1answer
101 views

I know scrypt is newer than bcrypt, but is there any reason it would be weaker?

From what I read, scrypt is (on paper) more secure than bcrypt, but it's pretty new so it's better to let it get time-tested and scrutinized first. However, is there any good, compelling reason to ...
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5answers
2k views

When hashing passwords, is it ok to use the hashed password as the salt?

I don't like this idea. But I can not come up with a technical argument against it. Can somebody explain it to me? The basic idea is: $passwd = 'foo'; $salt = hash($passwd); $finalHash = hash($passwd ...
1
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1answer
223 views

Cracking MD5 passwords with the same salt

How long would it take to crack passwords up to 10 letters long if you knew the hashes were MD5 with a salt (that you know)?
9
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3answers
4k views

How often do two users use the same password

If no two users use the same password, then in theory salting the password hash is not needed. How often, in practice, do two users have the same password?
1
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1answer
149 views

Theoretical home grown password options, or what is it that SCrypt, BCrypt, PBKDF2 does that is so special?

I'm developing a personal web framework, nothing internetty, and probably not even anything that will ever go on my personal LAN. And looking for password advice people seem to only recommend those ...
2
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2answers
110 views

Breach informing

I am a staff member of a large fanfic site, but not the head administrator with control over the site itself. Recently, we had a security breach and the databases were copied, which included the ...
42
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5answers
4k views

Is it safe to tell your users what kind of hashing algorithm you use?

For example, on the user registration page, is it safe to tell people "Your password will be stored as a one-way hash using the (whatever) algorithm."
4
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3answers
162 views

Is it good practice to SHA512 passwords prior to passing them to bcrypt?

I want to allow any-sized passwords to be allowed to be submitted. I currently use bcrypt as a key derivation function for passwords, however I have realized that it has a maximum input length of 72. ...
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2answers
214 views

Storing multiple hashes to prevent collisions, security risk?

This is all just for curiosity's sake, so discussion on which hashing algorithm is harder/better/faster/stronger is irrelevant. But my question/thought is this.. With regards to password storage, and ...
1
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4answers
166 views

Hashing Email Address and Contacting User

I am thinking about a log-in web service that would store a users username, password, and (optional) email address. If they forget their username or password, they can have their username and a ...
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4answers
101 views

Is salted MD5 or salted SHA considered secure?

Is using something like bcrypt or scrypt necessary? The hashes are so much longer to store in a database. Can one get away with using salted MD5 or SHA and still be secure?
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2answers
89 views

Is a long salt usually sufficient for security purposes, even with MD5?

I always hear that MD5 is too fast for effective password crypto because you can crack up to 6 characters very quickly (or is this number higher now)? But what if the salt you use is really long and ...
0
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2answers
65 views

Why RSA signatures based on the hash of the message? [closed]

Why RSA signatures based on the hash of the message rather than the message itself?
2
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2answers
459 views

Protecting hidden form fields

The scenario is as follows: An application has a web interface through which data can be configured. The data to consider for this question is Users with a many-to-many relationship with Groups. ...
1
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1answer
55 views

Log file checksums

I am told that you can tell if the log file (like from ripping a CD) has been modified by its checksum. How? How do you bypass this if you wanted to modify it?
2
votes
1answer
67 views

Identical lanman hashes on AD accounts?

I ran metasploit's smart_hashdump module against my (2008r2) domain controllers, trying to find any accounts that may still have lanman hashes in place. These should have been disabled long ago. I'm ...
4
votes
3answers
373 views

comparing password hashing algorithms - PoC ideas?

OK so I just started working for a security consulting firm and we recommend SHA 256 (with salt) for password hashing because MD5 is too weak. I have read some brilliant answers (the list is too ...
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1answer
117 views

What are the enhancements of SHA1 compared to MD5?

I am looking for enhancements of SHA1 when its compared to MD5. But I am not talking about just heap sizes. I am talking about different enhancements than heap size. Also, I think md5 is faster than ...
3
votes
1answer
86 views

Is it possible to slow down the Blue Midnight Wish cryptographic hash function?

In the Blue Midnight Wish (BMW) cryptographic hash function, is there a variable I can use to increase memory/CPU resource consumption to slow down the password hashing process? Call me crazy, but I ...
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2answers
41 views

Can I save & store a user's data in a way that proves that the information has not been altered, and that the timestamp is accurate?

There are many situations where the validity of the timestamp attached to a certain post (submission of information) might be invaluable for the post owner's legal usage. I'm not looking for a service ...
3
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2answers
140 views

MySQL ENCRYPT salt is not random?

I know there's little reason to still use ENCRYPT() nowadays, what with bcrypt being almost ubiquitous and MySQL providing better hashes such as SHA1. But while dabbling with ENCRYPT() on MySQL ...
0
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2answers
124 views

Why do file storage sites have a long unique id for their download links?

I'm creating a file storage site and what I would do is just have the download links format as: https://www.domain.com/[id]/[file name] //id would just be 1, 2, 3 etc. Dropbox and many others have ...
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2answers
60 views

A manual function for hasing identity?

I hope you won't close the question. Even though there are no computers involved, it is still about information and security, and I think that security experts are the ones who will be able to help ...
9
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3answers
960 views

HMAC Based Request Signing - Storing the Salt

I'm working on a (non high security) project that currently isn't live but might go live at some point. We have a REST API (implemented using Restlet and Neo4j) running on a server and an Android ...
0
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4answers
351 views

What are the advantages/disadvatages of hashing over encryption?

I know that hashing is a one way function and encrypted messages could be retrieved if you know the corresponding key to which you encrypted the message. Other than the ability to retrieve, what ...
4
votes
1answer
66 views

Will my method for managing account data work?

I'm looking at whats nessecary to create a small accounts server for a video game I'm programming in my spare time. User privacy is a very important topic for me, and I don't want to keep anything ...
2
votes
2answers
382 views

Content-Security-Policy hash of script

<?php header("Content-Security-Policy: default-src 'sha256-".base64_encode(hash('sha256', 'console.log("Hello world");', true))."'"); ?> <script>console.log("Hello world");</script> ...
0
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0answers
41 views

Algorithm to Transaction Data Signing

Transaction Data Signing I need an idea to develop a very secure algorithm to authenticate online operations using PHP in the server and an Android app in the user's device. What is the idea? The ...
112
votes
11answers
26k views

Why are hash functions one way? If I know the algorithm, why can't I calculate the input from it?

Why can't a password hash be reverse engineered? I've looked into this ages ago and have read lots on it, but I can't find the explanation of why it can't be done. An example will make it easier to ...
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3answers
132 views

What part of the CSR is hashed in order to create its signature?

I'd like to change the CSR before it is transferred to the CA without going through the CSR creation process again. To do that I need to know how to calculate the signature of the CSR after I modified ...
4
votes
3answers
500 views

Is there a hash algorithm that can identify similar files or strings?

Is there a hash algorithm that will help you identify similar files or strings? For example, the hash for ABC and XBC would be similar rather than radically different as is usually the case. I know of ...
2
votes
2answers
178 views

Locality Sensitive Hash (LSH) function to approximately match old passwords

Recently, I ran across a website that requires me to change my password after X number of days had passed since I had last created one. Intelligently, the service made sure that the password did not ...
5
votes
9answers
4k views

What is the best way of securing a website logon without SSL or preshared keys?

Today I sniffed some unencrypted wlan traffic during class and I found quite a few passwords by a simple search for "pass" and "user" in wireshark. Turns out about half the sites we use for school ...
15
votes
2answers
539 views

Can client-side hashing reduce the denial-of-service risk with slow hashes?

When storing user's passwords that you need to verify against (but not use as plaintext) the current state of the art is: Hash the password Use a salt Use a slow hash function - bcrypt, scrypt, etc. ...
264
votes
4answers
77k views

Do any security experts recommend bcrypt for password storage?

On the surface bcrypt, an 11 year old security algorithm designed for hashing passwords by Niels Provos and David Mazieres, which is based on the initialization function used in the NIST approved ...
18
votes
2answers
10k views

Why are GPUs so good at cracking passwords?

What is it about GPUs that lets them crack passwords so quickly? It seems like the driving force behind adopting good key-derivation functions for passwords (bcrpyt, PBKDF2, scrypt) instead of ...
4
votes
11answers
4k views

Definitely safest password storage scheme?

I already asked this on StackOverflow but I was suggested this would be a better suited place and I found no way to "move" the question so I have to copy it. Believe, I know, there are hundreds ...
4
votes
5answers
480 views

Expanding/Inverse Hash function

First off, before I ask my question, let me explain what I am NOT asking. I am NOT asking for a way/method to reverse a hash output; by definition, a hashing function is one-way. Is there such a ...
10
votes
5answers
3k views

What is a good practical (and sane) way to manage all your passwords for online sites?

I am just a mere mortal that wants to have a somewhat secure way of managing all my passwords. This is something that I have been putting off, but since LinkedIn decided to give away one of my ...
6
votes
5answers
2k views

Whenever an unhandled exception somehow makes it into production, is it safe, viable, etc. to print an encrypted stack trace to the end user?

Whenever an unhandled exception makes it into production somehow - whatever the reason - there's generally an option (especially with .NET programs) to print out a stack trace to the end user before ...
268
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12answers
45k views

How to securely hash passwords?

If I hash passwords before storing them in my database, is that sufficient to prevent them being recovered by anyone? I should point out that this relates only to retrieval directly from the ...
1
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1answer
174 views

Any reason I shouldn't be salting and hashing before putting through bCrypt?

I've been reading up on password storage and such, and have come to the conclusion that I need to be using bCrypt. I've got an implementation working correctly, but I'm wondering the best way to move ...
0
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1answer
57 views

Find hash-function if original and hash are given? [duplicate]

I was thinking whether or not you can find the hash function(s) used if you have the original message and the hash. So assume that no salt is used during the hashing process, just multiple hashing and ...
0
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1answer
151 views

How do we estimate the time taken to crack a hash using brute force techniques

A German hacker famously managed to brute force crack a 160 bit SHA1 hash with passwords between 1 to 6 digits in 49 minutes. Now keeping everything constant (hardware, cracking technique - here ...
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1answer
100 views

Hash leaked online

Recently I Googled the email address of one of my friends, as I was just curious of what would come up. Lo and behold, he saw what presumably is his Gmail hash. It is part of a list of 10,170 email ...
0
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0answers
32 views

Hashing / How easy is it to infer the original input if the a slight variation of the input, the hash result and the hashing algorithms are known [duplicate]

Given that I have an initial input that is publicly known (e.g. "ABCDEFGHIJ") a slight variation of (1) (e.g. "BACDEFGHIJ") that is used as the input to a hashing algorithm (3) an modern one-way ...