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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Is the following authentication scheme secure?

I was trying to design an authentication system that would make it much harder to guess a password via brute force, and reduce the risk to a user if the hashed password was stolen through a snooping ...
5
votes
2answers
355 views

Is cascading cryptographic algorithm better than using a single one?

Am I wrong to think that scrypt(bcrypt(password)) would be better than using sole (s|b)crypt? Especially when considering two different key for the two algorithms. I am also interested in some ...
35
votes
3answers
2k views

Am I wrong to believe that passwords should never be recoverable (one way hash)?

I recently forgot my password for our cable provider online account, only to discover that they sent it to us via plain text in an email. I quickly sent an email to customer support asking them if ...
4
votes
1answer
326 views

self-signatures using SHA1

This page says: self-signatures must not use SHA1 You can check this by doing: gpg --export-options export-minimal --export <keyid> | gpg --list-packets |grep -A 2 signature|grep ...
35
votes
15answers
6k views

Why do people think that this is bad way to hash passwords?

Well, please tell me, what's wrong with this code: $password = "hello"; $password = md5($password); for($i=1;$i<20;$i++){ $password = md5($password); } It's exactly the same as this one: ...
4
votes
1answer
610 views

Is this security/encryption scheme secure?

I'm rolling my own, personal threetags.com-style 'encrypted data in the cloud' webapp (I didn't like the UI, and lack of non-browser client). However, I have absolutely no experience with security ...
14
votes
2answers
3k views

What are the most common password salting methods?

I learned that the Sun guys used the login name as salt for password hashing. Is this a common approach? What are the most common salt values?
2
votes
4answers
534 views

Hash/Digest of string; multiple clients and reverse lookup must be impossible

Ok so i need a technique (could be a system or just an algorithm) to generate a hash/digest of a string on a client app without me (admin of a server app) being able to determine what the original ...
7
votes
2answers
2k views

How difficult is it to modify an ISO image and still have the old md5 check sum?

If I want to download the ubuntu11.04.iso then: UBUNTUMIRRORSRV -> ISP -> ISP -> etc. -> MYPC I just want to ask that how difficult is to spoof the original MD5 sum (e.g.: the md5sum would be ...
6
votes
2answers
786 views

How do I use Skein's Stream Cipher?

I understand the NIST hash function competition candidate Skein comes with a built-in block cipher, Threefish, that is turned into a stream cipher by using Unique Block Iteration chaining (is that ...
6
votes
2answers
916 views

Is it better to hash n*x times in sha1 or n times in sha512 on the client side?

I already know I"m going to hash the user's password n times in either sha512 or n*x in sha1 before it is sent to the server. Once at the server, I'm going to use bcrypt set to use ~1/100th of a ...
5
votes
4answers
846 views

mathematically / theoretically, what is the chance that 2 different inputs would have the same results of 2 different hash functions?

mathematically / theoretically, what is the chance that 2 different inputs would have the same results of 2 different hash functions? As an example, i will use 2 weaker hash algorithms, the MD5 ...
4
votes
2answers
6k views

Can DES-based hashed password be recovered if salt is known?

Can a hashed password be recovered if the hashing is done with DES based crypt function in PHP and both the hash and salt are known by the attacker? Consider the following example: $salt = 'mysalt'; ...
14
votes
2answers
1k views

Salting password with the first 8 bit of the password itself

Do you guys think salting password with the first 8 bit of the password itself will have same result as using stored salt to hash password? [Clarification] I am not storing salt but creating from the ...
6
votes
3answers
1k views

chosen plaintext attacks against MD5 and SHA1

According to http://tools.ietf.org/html/rfc2617#section-4.9, having the server chose a nonce but not having the client chose a nonce opens up Digest Access authentication to chosen plaintext attacks. ...
7
votes
4answers
4k views

when people say a file has a checked md5 hash, what exactly does that mean?

ok I was just reading this site: http://www.zdnet.com/blog/bott/stay-safe-online-5-secrets-every-pc-and-mac-owner-should-know/3542?pg=4&tag=mantle_skin;content and thought of something I always ...
12
votes
2answers
1k views

Is there any advantage of bcrypt over multiple iterations of SHA-x/MD5?

I know that a good password hashing algorithm should be slow. MD5, SHA256, etc. are fast. So I've been adding multiple iterations of SHA-256 hashing to my web apps (around 50000). Getting the hash of ...
15
votes
3answers
2k views

What's the mathematical model behind the security claims of symmetric ciphers and digest algorithms?

Why can SHA-1 be considered a secure hash function? That's something I still wonder about. I understand the concepts of why modern asymmetric algorithms are deemed to be secure. They are founded on ...
15
votes
3answers
570 views

What is gained by hashing the last block on-device?

Recently I encountered the notion of "hashing the last block on-device". It means that when computing a digital signature, the hash that serves as input for the actual signature computation is not to ...
4
votes
3answers
473 views

Hashed passwords - How many variations of rainbow tables?

First off...I passed the CISSP exam. WOOOO. I had to get that out. GCIH and CEH by Sept. 11' So, while studying for the technical side of things, I see that there are rainbow tables. They are ...
5
votes
4answers
1k views

Using password hash as session ID?

For a rich client web app, on the server I need to verify that each call comes from a legally logged in user. Obviously user ID is not enough, because that's easy to guess. I have an idea I am ...
21
votes
4answers
3k views

What to transfer? Password or its hash?

Let's say in my database I store passwords hashed with salt with a fairly expensive hash (scrypt, 1000 rounds of SHA2, whatever). Upon login, what should I transfer over the network and why? Password ...
28
votes
6answers
28k views

Most secure password hash algorithm(s)?

What is/are currently the most cryptographically secure hashing algorithm(s)? (available in PHP) Speed is irrelevant, because I'm iterating the hash over a fixed time (rather than a fixed number of ...
9
votes
4answers
5k views

moving from MD5 to SHA-512

This question is more of a security policy than a technical security question. Many years ago I developed an asp.net site, implemented Forms Authentication, and stored the user passwords as MD5 ...
37
votes
4answers
24k views

Are salted SHA-256/512 hashes still safe if the hashes and their salts are exposed?

Scenario: a database of hashed and and salted passwords, including salts for each password, is stolen by a malicious user. Passwords are 6-10 chars long and chosen by non-technical users. Can this ...
6
votes
2answers
735 views

Implementing Secure Remote Password: Constructing the verifier

The SRP protocol as described in RFC 2945 generates the password verifier: x = SHA(<salt> | SHA(<username> | ":" | <raw password>))` v = g^x % N I have three questions: why use ...
18
votes
2answers
5k views

Why is it always `HASH( salt + password )` that we recommend?

Browsing over this site, many forums, online articles, there's always one specific way we're suggesting to store a password hash: function (salt, pass) { return ( StrongHash(salt + pass) ) } But ...
3
votes
0answers
199 views

Checking whether a password is derived from previous passwords [duplicate]

Possible Duplicate: How can a system enforce a minimum number of changed characters in passwords, without storing or processing old passwords in cleartext? On a system I used several years ...
3
votes
0answers
172 views

Files for download and their hash numbers

I'm far from being an expert in the IT security and I have this maybe naive question. Many downloadable files are deployed on websites together with the corresponding hash numbers to ensure their ...
5
votes
1answer
355 views

How valid is the concern over narrow pipe hash function designs?

Narrow pipe hash function designs have recently come under fire, particularly in reference to some SHA-3 candidates. Is this criticism valid? Can it be explained more simply than this paper does? I'm ...
4
votes
3answers
152 views

OS Kernel Hashing

Has anyone had experience with or is aware of any products that hash the OS kernel? This would be used, ideally, for watching for system compromises, auditing, change management, etc. I am looking ...
90
votes
4answers
20k views

Recommended # of iterations when using PKBDF2-SHA256?

I'm curious if anyone has any advice or points of reference when it comes to determining how many iterations is 'good enough' when using PBKDF2 (specifically with SHA-256). Certainly, 'good enough' is ...
23
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12answers
4k views

Can a file contain its md5sum inside it?

Just wondering if it is possible to create a file which has its md5sum inside it along with other contents too.
21
votes
1answer
2k views

Has SHA-3 Arrived?

I know NIST called for contenders (in 2007) regarding the new hash algorithm to replace SHA-2. Has there been a selection, or finalists selected?
23
votes
4answers
13k views

how long does it take to actually generate rainbow tables?

I've been reading up about rainbow tables as I think they're quite interesting cause they're actually a pretty simple concept. Anyway, I was wondering, has anyone been involved in actually generating ...
9
votes
2answers
941 views

Stretching a hash, many iterations versus longer input string

I have been reading up on various password hashing schemes, for example the SHA-based Crypt proposed by Ulrich Drepper and used in some Linux versions. A recurring theme here is to 'strengthen' or ...
96
votes
6answers
36k views

Password Hashing add salt + pepper or is salt enough?

Please Note: I'm aware that the proper method for secure password storage hashing is either scrypt or bcrypt. This question isn't for implementation in actual software, it's for my own understanding. ...
5
votes
4answers
5k views

Brute force vs other methods of recovering passwords from shadow file

Do you know any good approach for de-hashing/actually bruteforcing hashed passwords in the shadow file? On various operating systems, any good solutions/methods/programs. Or is it better to upload ...
32
votes
2answers
12k views

HMAC - Why not HMAC for password storage?

Nota bene: I'm aware that the good answer to secure password storage is either scrypt or bcrypt. This question isn't for implementation in actual software, it's for my own understanding. Let's say ...
18
votes
1answer
3k views

Collision rate for different hash algorithms

Is there any collision rate measure for popular hashing algorithms (md5, crc32, sha-*)? If that depends only from output size, it's quite trivial to measure, but I suppose that depends also of ...
18
votes
3answers
4k views

MySQL OLD_PASSWORD cryptanalysis?

The password hash used for MySQL passwords prior to version 4.1 (now called OLD_PASSWORD()) seems like a very simple ad-hoc hash, without salts or iteration counts. See e.g an implementation in ...
5
votes
2answers
206 views

Complexity of web certificate attacks

I heard a while ago about someone exploiting md5 weaknesses to create a web certificate with the same md5 that a different certificate has. They were able to create a certificate through bad issuing ...
2
votes
3answers
261 views

Identify client based on computed hash

I'm currently developing a web application which will serve data to iPhone clients. In order to be the owner of the data, I don't want other clients to be able to get it. I thought I could use a ...
14
votes
4answers
2k views

Looking for example of well-known app using unsalted hashes

Does anyone know of a well-known application that still uses unsalted hashes for password storage? I'm looking for an example for an upcoming lecture on Rainbow Tables, and I think it would add ...
29
votes
3answers
4k views

Is there any advantage to splitting a password?

I've been reading about the LANMAN (LM) hash and I'm curious about a particular part of the algorithm. The LM hash is computed as follows: The user’s ASCII password is converted to uppercase. ...
3
votes
1answer
984 views

How to apply FIPS to Microsoft Access database with custom VBA

As the software engineer on a project, I have been asked to make a Microsoft Access application, with custom interfaces running custom VBA. That part is going just fine. Recently though I was asked to ...
14
votes
2answers
40k views

What are the differences between MD5, SHA and RSA?

MD5 tools output hexadecimal values. In the same manner, do SHA and RSA together produce a hexadecimal (or any other) output? What are the differences between the MD5, SHA and RSA algorithms?
3
votes
2answers
379 views

MD5 display format

When I run MD5 algorithm I am getting an output in numeric and a few lower case letters. Obviously it uses all numeric digits and rarely i saw some lower case alphabet letter. I need to understand ...
5
votes
2answers
3k views

Reference implementation of C# password hashing and verification

Does anyone have a reference implementation (ideally 3rd party certified, or government approved) way one-way hash a password for C# and or Java? Ideally,I'd like to see something that includes a ...
3
votes
2answers
552 views

BlackBerry client authenticating to Java Web Service

I already asked this question at StackOverflow here: http://stackoverflow.com/questions/4970681/blackberry-app-security and was directed to this site, can anyone pitch in as to how I can solve this ...