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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Secure authentication: partial client-side key stretching… please review/criticize my idea

I am trying to figure out what would be the 'perfect' authentication system for a website. On one end, we know that simple hashing algorithms can be brute-forced or cracked in other ways. Hence why ...
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SHA-512 unix passwords. How secure are those hashes, really?

I came across this very alarming sounding thread which indicates a GPU with about half the compute capacity of the GPU currently powering the monitor I type this on is capable of 11.5k c/s. I'm not ...
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Revisting the Username Hash

There are a few questions which ask for inputs on the wisdom of storing (possibly salted) username hashes for the purpose of authenticating end user access to some information resource. Most of the ...
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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 ...
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What is the meaning of the term “simple string” for the SALT string in Unix crypt using SHA-256 and SHA-512?

In Unix crypt using SHA-256 and SHA-512 the author, Ulrich Drepper, introduces the SALT string as the following (highlight by me): For the SHA-based methods the SALT string can be a simple string ...
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How should I choose a difficulty factor for my password hashing function?

Assuming that I'm doing password hashing properly and using bcrypt, scrypt or PBKDF2, how should I go about choosing an appropriate difficulty factor? i.e rounds for bcrypt, iterations for PBKDF2 and ...
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Keeping user data private in a cloud environment like Google App Engine

I am writing an open-source Java application for Google App Engine (GAE). The application will let users create content that is intended to be private. I want to provide reasonable assurances that ...
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Use the hash of the password to encrypted password

I have a app which transmit the password in clear text. I was planning to use the hash of the password (SHA-512) as the key for encrypting the plain text password. Then send the encrypted text to the ...
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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 ...
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Does Hash/Salted password really help when DB is compromised?

I came across this article and got a basic understanding hash, salt and brute force attack. My question is in the article, the author emphasises how hard it is to reverse the hash/salted password to ...
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388 views

What is the purpose of a Pepper?

I've been trying to find out exactly what a pepper is. The only things I could accurately determine are that a Pepper: Is theoretically unique from site to site and hard-coded in the site's source ...
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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'; ...
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usernames and passwords

I was thinking about usernames and passwords and I was wondering how secure it would be to instead of the server having a list of usernames and accompanying hash of the passwords, just have a list of ...
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Rounds of MD5 and SHA512 Hashing Algorithms

What is the exact number of rounds employed by the MD5 and SHA512 hashing algorithms? According to various sources, the SHA512 hashing algorithm employs a total of 80 rounds ...
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184 views

Salting a public hash

Does it make any sense at all to salt a hash which might be available publicly? It doesn't really make sense to me, but does anyone actually do that? UPDATE - Some more info: An acquaintance of ...
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179 views

Would secure storing of past used/generated passwords be a good idea?

Let's assume an organisation that generates ~100 Passwords a week; these Passwords are 32-Characters long and randomly generated. The consultants that need passwords generated use a Password-generator ...
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933 views

What security purpose do hashes of files serve?

Many websites offering downloads also provide the MD5 or SHA1 hashes of the files which are available for download. An example- What is the security purpose behind providing such a facility to the ...
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How does processor architecture affect password hashing speed?

Does hashing speed vary significantly using different architectures (x86 vs ARM)? Scenario I am investigating the possibility of using a cluster of Raspberry Pi for cracking passwords hashed with ...
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symetric key encryption vs hashing

This is a fascinating document: top 100 passwords from adobe breach I have a question about one part of it: However, thanks to Adobe choosing symmetric key encryption over hashing, selecting ...
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Bank account number and account holder in check exposed?

I'm not sure if this is standard practice in all banking institutions but almost all banks where I've received checks the account number of the issuer is exposed (some even the account name). Isn't ...
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386 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 ...
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496 views

What is the purpose of using Youtube-style alphanumeric ids as URL slugs?

I asked a question on StackOverflow on how to generate the alphanumeric/base64 resource IDs that Youtube, Instragram, and others use to identify videos/pictures/etc. Discussion led to the question of ...
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124 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 ...
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Is it safe to use PBKDF2 for hashing?

I would like to get a few opinions on whether it would be safe or not to use PBKDF2 to generate a hash of a password. For my purposes I'd like to assume that the hash itself will be posted on the ...
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303 views

User password as key instead of hashing it

I was reading here on Hashes and Salts and I thought about another method to do user authentication. I need your thoughts on this as I might be overlooking something. Scenario: For web application ...
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Could a password hash that's prone to more collisions provide better overall security?

Website security breaches seem to be a common occurrence, giving the attacker password hashes that he can conduct a brute force attack against, often given him a list of passwords that will work on ...
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323 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 ...
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316 views

Hashing a key: less entropy than the key itself

A web API needs to store a 'key' for authentication, in much the same fashion as a password but at 128 characters. My concern is that the salted SHA1 hash for the key has less entropy than the key ...
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Is it a good idea to have a “master” password?

Though I do have a good memory of passwords, it is quite impossible to have one password per application. Yet, it should be... My current way to deal with passwords is to have five passwords and to ...
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What steps can you take to make offline cracking of SRP harder?

In the aftermath of the Blizzard hack, what steps can I take to make offline cracking of SRP more difficult? My question assumes that your database is already gone and that you implemented SRP more ...
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Can hash functions be used with CTR or OFB mode?

I have been writing a class that encrypts and decrypts with block ciphers. I want to use Counter Mode(CTR/CM). We know that Counter Mode generates a keystream basing on counters, then XOR the ...
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Is encrypting a salt value with a password/plaintext a viable alternative to straight up hashing?

The basic problem, as far as I can tell, is that hashing's flaw is that the password is in the hash. Asymmetric encryption's flaw is that the password is encrypted and can be reversed. The posts ...
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615 views

Truncating the output of SHA256 to 128 bits

suppose we need/prefer 128 bit hash output. for example to generate a 128 bit encryption key or, in other applications (e.g. file integrity verifications), to consume less storage space. i don't know ...
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490 views

Reducing password length with hash function

Suppose I would like to use a very long string as a password. As an example we can just say this string is 100 characters in length. However, suppose the application for which I would like to use ...
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What about combining pkdf2 with scrypt? [duplicate]

Possible Duplicate: Would it make sense to use Bcrypt and PBKDF2 together? How does the following password hashing scheme look to you? iterations1 = scrypt iterations required to spend ...
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710 views

Bcrypt as a key derivation function?

I read a lot of entries at stack exchange about bcrypt and why it is supposed to be better than PBKDF2 in terms of password storage. I'm asking now if bcrypt is better than PBKDF2 in terms of key ...
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openssl_digest vs hash vs hash_hmac? Difference between SALT & HMAC?

openssl_digest vs hash vs hash_hmac I want to use SHA512 for storing password. Which of the above methods are best to use? Why? What is the difference between SALT & HMAC? I just read ...
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Is BCrypt enough when saving a password into a database?

In order to allow users to connect to my website, I encrypt their password using BCrypt since it is one of the slowest algorithms to decrypt (making a compromised database longer to be decrypted). ...
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PHP Vulnerability May Halt Millions of Servers - max_input_vars!

Recent version of PHP 5.3.9 has been released a couple days ago, and Hash Collisions have been fixed, most of the servers actually didn't upgrade their server until now, including my website's server. ...
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1answer
70 views

Standards for CA cert revocation and time-constrained cryptographic algorithm parameters

I'm working on software that will be in use for foreseeable future (15 years+) that will need to validate XAdES-A signatures (long term archival, similar to PAdES-A, but for XML). That means, it will ...
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129 views

Why is password strength often underestimated and uncertain in the context of password hashing?

An aspect of security has bugged me for a long time: Why is there positive certainty about the importance of hashing algorithms and salts, but password strength is either never mentioned at all or ...
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Rainbow tables, generation and lookup, preferably using GPU

1a) What software can I use to generate my own rainbow tables, preferably software that can utilize CUDA or ATI Stream? One of the reasons I want to make my own, is that I want to use a specific ...
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405 views

Is every hash format that nginx accepts for HTTP Basic Auth weak against brute force?

According to http://nginx.org/en/docs/http/ngx_http_auth_basic_module.html nginx can read password hashes of these types: crypt(), apr1, SHA1 & SSHA. This is how I understand how these hashes ...
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Is it possible to detect password length from hash? Does doubling your password add more security?

Assuming a service doesn't store a plain text password, am I right in saying that the answer to this question depends on the service? On a bad service, the hash length is related to the password ...
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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 ...
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4answers
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How to tell if a site is securely storing passwords? [closed]

A site I frequent has a policy to make you change your password every 90 days. That's a cool policy, but I stumbled upon an old xkcd and facepalmed myself, because lots of doxing happens on this site. ...
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Is there a table that compares hashing algorithms by speed, relatively (machine independent)

As far as I understood*, one of the major criteria when choosing a password / salt hashing algorithm is it's speed. To prevent brute force attacks, a slower algorithm is better (and also makes it more ...
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Irreversible hashing without collision

We are looking to allow users to log on with a smart card. The smart card reader can read the smart card ID and send it to us. We are, however, not allowed to store the smart card ID. Not in ...
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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 ...
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What is better salted hash or openssl encryption?

Im using php and I was looking to store passwords in a mysql database. I was wondering what would be safer to use a salted hash or openssl encryption? If i use a unique random generated salted hash ...