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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Doesn't adding requirements to a password, such as must contain 2 digits, decrease the strength? [duplicate]

Possible Duplicate: Doesn’t imposing a minimum password length make the password weaker by reducing the number of possible combinations? Doesn't any constraints added to a password policy ...
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7answers
770 views

To salt, or not to salt? [duplicate]

Possible Duplicate: Why is using salt more secure? Why would salt not have prevented LinkedIn passwords from getting cracked? Recently I decided that I wanted to learn more about web ...
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2answers
1k views

Do OpenPGP/GnuPG apply slow hash to password when encrypting/decrypting key?

Password space is quiet small. Therefore slow hash should be applied to password before using it for encryption. Should slow hash function (like bcrypt) be applied to password before using it with ...
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1answer
262 views

Password protection of encryption and signature keys

I would like to store encrypted backup of text files on my computer. I'm developing a python script using Pycrypto to achieve that, based on this code to use the library. (current code) The basic ...
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3answers
2k views

what is the fastest and cheapest way to crack this kind of hash - md5(md5($password) + salt))?

I'm looking for a program that can use any GPU (ATI\NVIDIA) and can brute force a vBulletin hash - md5(md5($password) + salt)). I have the salt and hash. the password contains the symbols - ...
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3answers
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Is my session-less authentication system secure?

So, I've created an authentication system. Poured over it for any kind of security flaws and tested the crap out of it. I think it's fairly secure, but there is one "different" by-design aspect of it ...
2
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5answers
557 views

Does shuffling a hashed password increase its security?

I am making a web app and I'm now stuck on making the login secure. I'm thinking of adding a salt to a user-inputted password and then hash it. (md5 or sha for example) and then I will reshuffle the ...
2
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1answer
2k views

Clarification on how rainbow tables work

If you goto : http://www.hanewin.net/encrypt/aes/aes-test.htm for "Key in Hex" enter 00000000000000000000000000000056 for "Plaintext in Hex" enter 00000000000000000000000000000000 and click on ...
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5answers
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Hashed password storage with random salt

Ever since I've been making sites that require a user to log in with a username and password I've always kept the passwords somewhat secure by storing them in my database hashed with a salt phrase. ...
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6answers
2k views

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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1answer
110 views

How are root CAs for SSL distributed?

For internet explorer or whatever, I get it... It's in essence a sneakernet, you get them on the physical media from which you install your system and browser. But what about for firefox and chrome? ...
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3answers
713 views

Key stretching an hash

if I implement an function which hashes the first half of my password with MD5 and the second half with SHA2 and MD5. Is there a security issue when I put these two hashes together to a 64 character ...
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1answer
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Replacing weak SSH fingerprint algorithms

Even though MD5 has been broken for years and its vulnerabilities have been used to create real-world rogue X.509 CAs and other horrible things, OpenSSH and PuTTY still use MD5 as the default public ...
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2answers
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Is AES slower to encrypt than MD5?

Is this the right interperation of this diagram: http://www.cryptopp.com/benchmarks.html AES/CCM MiB/Second:61 Cycles Per Byte:28.6 MD5 MiB/Second:255 Cycles Per Byte:6.8 And does that ...
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0answers
164 views

Finding pre-image of MD5 hash [closed]

I have the following requirement for hashing using MD5. H(A,B,C,X); Where values A,B & C are given. However X is not given. I would like to find out what value of X would give a hash beginning ...
3
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1answer
323 views

Is there a better way to take advantage of current 'approved', 'proven', and memory/cpu-expensive algorithms while using salts and peppers?

I've read about the concepts presented in these two questions: Pre-hash password before applying bcrypt to avoid restricting password length Would it make sense to use Bcrypt and PBKDF2 together? I ...
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2answers
1k views

Program binaries or files with same MD5 hash

I'm looking for 2 different program binaries or 2 different files with the same MD5 hash to prove its weakness and the collisions in the algorithm.
10
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2answers
3k views

Estimating the size of a rainbow table

What are rainbow tables and how are they used? Gives a very precise answer about what rainbow tables are and how they are used. I had always confused hash-tables and rainbow tables. My question is ...
11
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3answers
855 views

Does the salt need to be unique or not predictable?

I always thought that salts is simply used to prevent rainbow tables to be used. Other have suggest they should be unique on a per account basis. Currently i have been using a config file to use as ...
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5answers
4k views

What's the practical limit for rainbow-table based bruteforce?

Say we have a hash of a password. The password can be considered to be made of of totally random characters and has a fixed length of N. The hash is SHA1(password+salt), where the salt is of length M. ...
14
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6answers
807 views

Is there any security risk in storing hashed variations of passwords?

For example, if hypothetically an application requirement was to tell users when their password might have failed because caps-lock was turned on, and hypothetically there was no way for the ...
19
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4answers
2k 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 ...
26
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4answers
9k views

https security - should password be hashed server-side or client-side?

I am building a web application which requires users to login. All communication goes through https. I am using bcrypt to hash passwords. I am facing a dilemma - I used to think it is safer to make a ...
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2answers
673 views

Password entropy match for alphanumeric but there are special characters in password

I have a problem cracking some of the fundamentals on passwords' entropies. Namely: I have read this article about a guy cracking DKIM of Google (maybe more noticing that the keys are only 512 bits) ...
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2answers
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Is it okay to widely share the RSA key fingerprint for a host?

When you ssh into a remote box for the first time or if the remote host's key fingerprint has changed (from what's stored in your known_hosts file) you get a warning and you are shown the fingerprint ...
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3answers
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MD5 collision attacks: are they relevant in password hashing?

DISCLAIMER: This is not an endorsement of MD5 as a password hashing function. I know about parallelization, GPUs, and dedicated password hashing functions like bcrypt and scrypt. With that out of ...
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3answers
344 views

Password Security: Encrypting salt [duplicate]

Possible Duplicate: Password Hashing add salt + pepper or is salt enough? I'm new to security and trying to understand why encrypting or hiding a salt is not considered useful. I've read ...
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3answers
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rsa encrypted hash == rsa signature

$ echo -n "1327943823" > test_ok.txt $ openssl dgst -sha1 -binary -out test_ok.sha1 test_ok.txt $ echo "GURbsl4CFPCG83RCZxsEpoRleXicXQhH1OC4Fk77b7EMj2g8aHUhD/L+sm ...
4
votes
3answers
444 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 ...
2
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1answer
232 views

Seeding GPG keygen with a hashed secret [duplicate]

Possible Duplicate: Tool for public key cryptography where password is the private key? I was wondering if you guys could clue me in to potential problems with using a hashed password as ...
2
votes
1answer
909 views

Password authentication using DynamoDB

I'm working on a Mac app. I have users stored using DynamoDB. Authentication is needed to enforce access control on system-internal operations, such as uploading files to Amazon S3. Of course, I ...
2
votes
1answer
180 views

Security of re-encryption with a list of pre-computed password based keys

I have a problem where an encrypted file stored on a server needs to be decrypted through a precomputed list of passwords that are used one time only - OTP applied to encryption basically. The file is ...
3
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3answers
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How to know if its the same User?

I asked a question awhile ago asking how to make an efficient encrypted chatroom. What I ended up doing was Making each user generate a 4096 bit RSA KeyPair, share their public Keys, and then one of ...
18
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1answer
851 views

Doing a dictionary attack on RSA if you have the public key?

I'm trying to learn exactly how RSA works. Currently I have a very, very simplictic overview that goes like this. Having the public key allows you to encrypt things. Encrypting the same message ...
18
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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 ...
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2answers
1k views

Is there an index of all md5 collisions?

I am about to build a caching system based on md5 to generate file names out of lists of natural numbers. The inputs would be groups like: 1,18,94,100,266,1854. I know there are some collisions in ...
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2answers
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BCrypt's 72-character limit and using it as a general digest algorithm

Goal: have token/cookie-based authentication that doesn't require keeping sessions on the server TL;DR: What, if any, is the accepted mechanism to work around the 72-character limitation of BCrypt? ...
2
votes
3answers
1k views

Preventing dictionary attacks against hashed passwords [duplicate]

Possible Duplicate: How to securely hash passwords? I have a website and on that website I use SHA-256 and salt my user's passwords. What I'm doing right now is padding each letter of the ...
21
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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?
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0answers
185 views

Recomended hash algorithm [duplicate]

Possible Duplicate: How to securely hash passwords? Do any security experts recommend bcrypt for password storage? What would you choose between: PBKDF2 SHA256 (270,000 iterations) ...
6
votes
2answers
2k views

Should we start using SHA-3? [duplicate]

Possible Duplicate: What is SHA-3 and why did we change it? SHA-3 has been finalized! So, what does secuirty.se think about the new hash funciton? Should we start replacing all uses of ...
4
votes
5answers
618 views

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 ...
0
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3answers
2k views

Are there flaws in this simple key exchange?

I'm reviewing for a computer security exam. Here is a simple scenario: Suppose that someone suggests the following way to confirm that the two of you are both in possession of the same secret key. ...
7
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1answer
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PHP crypt() trims the salt as it would be too long

I am using Blowfish with PHP crypt() for password hashing but I noticed something weird. Quoting PHP documentation: CRYPT_BLOWFISH - Blowfish hashing with a salt as follows: "$2a$", "$2x$" or ...
4
votes
2answers
828 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 ...
3
votes
2answers
564 views

Implementing brute force attacks on hash values in Javascript

I'm working for my bachelor thesis at the end of which I aim to implement a proof-of-concept Javascript-based hash cracker. The idea is to work like this: Users can submit a hash value along with ...
5
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3answers
3k views

bcrypt: random salt vs computed salt

I'm pretty new to the whole password hashing business, so I might be missing something obvious. I was looking at the bcrypt algorithm, in particular BCrypt.Net, and I was wondering if it wouldn't be ...
12
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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 ...
2
votes
3answers
2k views

Proper hash_hmac key creation

I'm looking for, but unable to find, some definitive information on how long to make the secret and what characters are useable in creating a HMAC signature in PHP using SHA256. I found some ...
4
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1answer
79 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 ...