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.

learn more… | top users | synonyms (1)

19
votes
2answers
2k views

Should password reset tokens be hashed when stored in a database?

Passwords are hashed so that if someone gains access to a database of passwords then they won't know what the actual passwords are and so they can't log in. If I can get a valid password reset token ...
13
votes
1answer
3k views

Should I hash my passwords even if I am only allowed to generate limited traffic?

At this moment I'm busy working on an webapp with a friend of mine. The main problem we have is that we are only allowed to generate 50 GB a month in datatraffic. My question is: Does hashing the ...
10
votes
3answers
8k views

How secure are sha256 + salt hashes for password storage [duplicate]

I started reading about password hashing recently on multiple sites like this page on crackstation and others, and for what I have understood, I should avoid using hashing algorithms like md5 and sha1 ...
10
votes
4answers
1k views

Does hashing a PRNG make it cryptographically secure?

Would hashing the result of a regular random number generator produce a cryptographically secure PRNG? For example, would sha1(rand()) effectively be a secure PRNG? Assuming it doesn't, how would ...
10
votes
2answers
1k 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 '...
9
votes
1answer
1k 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 ...
8
votes
1answer
916 views

Is there repetition in the Solaris 11 hash routine? Can I add some?

Solaris 11 now uses SHA-256, so we can have longer than 8 character passwords now, by default. That is nice. I'll just make it clear that this password is never used as a line of defence. Only a ...
6
votes
3answers
1k views

SHA and “Bits of Security”

I've researched several forms of encryption/hashing and have often come across the term "bits of security". For example, at least one source claimed SHA-256 = AES128 = ECC256 = 128 bits of security. ...
5
votes
4answers
450 views

What's to stop someone from just MITMing a checksum?

A lot of sites offer MD5 or SHA sums to verify the validity of your download, but why do some things rely almost entirely on this? Is there anything in place to prevent people from just replacing ...
5
votes
2answers
646 views

How facebook knows my new password is too similar to my old password? [duplicate]

I am still very new to Information Security field and as far as I know, websites use hashing algorithm on user's passwords before storing it and they don't know the plain-text password of a user. ...
5
votes
1answer
376 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 '...
1
vote
2answers
1k views

which hashing algorithm is better to use to store a password, sha256 or sha512? [duplicate]

which hashing algorithm is better to use to store a password, sha256 or sha512? I know that sha512 is more secure than sha256 but I was wondering if it has some disadvantages or it is completely ...
24
votes
4answers
2k views

In hashing, does it matter how random a salt is?

I recently had a comment made to me in an online discussion after I'd stated that randomness in a salt doesn't matter -- and I got the following response: Salts may not have to be "secure," but ...
13
votes
6answers
2k views

Does prepending a salt to the password instead of inserting it in the middle decrease security?

I read somewhere that adding a salt at the beginning of a password before hashing it is a bad idea. Instead, the article claimed it is much more secure to insert it somewhere in the middle of the ...
12
votes
1answer
305 views

Securing a prediction about a future event

I want to make a prediction about a future event, but only reveal that prediction after the event occurs lest knowledge of my prediction affect the outcome. For example, suppose Alice predicts that ...
11
votes
4answers
2k views

How secure is the SRP that Blizzard uses to protect passwords?

Blizzard very recently announced that their network was compromised, but they assure users in their statement that the password information that the attackers had access to was saved in a secure way: ...
10
votes
2answers
3k views

How does Google not care about “spaces” in Application-specific passwords?

I have recently setup "2-step verification" for my Google account. One of the features is the ability to create "Application-specific passwords " for devices that do not support the 2 step process. (...
10
votes
4answers
6k 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 hashs....
8
votes
3answers
825 views

Downloaded file checksums

More than often next to the download button of a file there is a variety of checksums. When I download a file what security risks am I exposed to if I don't check for its integrity?
7
votes
2answers
2k views

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 ...
6
votes
3answers
250 views

How could one detect if Apple/Google/etc. has modified a third party application distributed through their App Stores?

Are there any realistic methods for verifying that Apple or whoever has not tampered with third party application distributed through their App Store? You might for example have an open source ...
5
votes
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 ...
5
votes
2answers
424 views

Is there a strong reason to salt and hash passwords when password reuse is not an issue?

I am dealing with a system (in development) that uses randomly generated (not user provided), unique, strings to authenticate services that will consuming an API. Right now, these strings are stored ...
5
votes
3answers
25k views

What are the differences between dictionary attack and brute force attack?

Can someone explain the major differences between a Brute force attack and a Dictionary attack. Does the term rainbow table has any relation with these?
4
votes
3answers
2k views

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
2k views

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 ...
4
votes
2answers
393 views

is it easier to get the original password if you have multiple hashes of it?

Most users tipically use the same password for multiple applications. Let's say all of these applications hash the password in some way. Would it be easier for an attacker to get the original password ...
0
votes
2answers
2k views

Knowing Hash Algorithm from Hashed String [duplicate]

I found an application which stored its password in database as: A69F00623BE6B8 It's a 14-character string length. How do I know this password algorithm? What's the keyword to describe this 14-...
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?
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 ...
14
votes
6answers
1k 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 ...
13
votes
3answers
1k views

Trying to understand why signatures in root certs “are not used”?

Taken from here: Don't worry if the root certificate uses SHA1; signatures on roots are not used (and Chrome won't warn about them. Why are the signatures not used? Are not root certificates ...
11
votes
1answer
563 views

“Please Enter Nth Character” without HSM

This question has been asked a few times, but always in the format "How does examplewebsite.com implement their 'please enter xth yth and zth characters of your password' function?" And the ...
9
votes
4answers
906 views

How to evaluate the strength of a hashing algorithm?

At work the hashing algorithm we use for passwords appears to be bespoke. Obviously that's a pretty bad idea, but the management don't seem bothered. The algorithm always produces 20 character long ...
8
votes
3answers
592 views

Increase the security of an already stored password hash

Right now we're using 1024 byte PBKDF2 with 256 byte user-specific salt and variable iterations. However, I would much prefer to be able to, perhaps once every year or two, to be able to flat out ...
8
votes
3answers
2k views

Using MD5 for malware ids: collision attack risks?

It has been known since 2004 that the MD5 hash is vulnerable to collision attacks (update - not "preimage" attacks - my mistake....). Yet it still seems that people are using it to identify malware. ...
7
votes
2answers
2k views

Is it bad practice to ask only for individual characters of a password? [duplicate]

Some financial websites that I use use passwords in a peculiar way. Instead of asking me the whole password string, they only ask me to enter e.g. "3rd, 5th and 8th character of your password", i.e. a ...
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. ...
6
votes
2answers
3k views

What algorithms are best be cracked by GPU?

What algorithms are best being attacked by a GPU powered password cracker? For example, I heard that md5crypt that is being used in unix shadow file, is not the best choice for GPU cracking because it ...
5
votes
5answers
952 views

When hashing passwords, is it okay to store the algorithm used right there in the database?

Since hashing password has become a hot topic recently, it is only natural to expect things to change and assume that some time down the road you might want to replace/tweak the algorithm used in your ...
5
votes
2answers
673 views

Scrypt + Bcrypt = cascade hashing [duplicate]

I've read here that hashing with differents algorithms would be a good idea. Can you confirm that? In your experience, is it useful and safe? Does it entail any security holes?
5
votes
1answer
718 views

Why do major sites(Facebook, Google, etc) still send passwords unhashed? [duplicate]

QUICK SUMMARY: It seems like modern websites, for security's sake, should all have the client hash their own passwords before sending them to the server, who will rehash them, in order to avoid ...
5
votes
3answers
1k views

Is it safe to use different derived keys but from the same passphrase for AES CBC encryption followed by HMAC SHA256 hashing?

I am working on a cross platform (JS/iOS/Android) list manager application that persists data through a REST API and I want to ensure that any textual data is properly encrypted on the client side so ...
5
votes
2answers
647 views

Can a HSM be used to make password hashing stronger?

Say a database server has a HSM which is in use for encrypting (reversibly of course) credit card numbers. Is there any way a HSM could be used to add strength to a password hashing scheme? (Or are ...
4
votes
5answers
565 views

Am I required to hash passwords

Is one required to hash passwords by law in the US or elsewhere? If not required by law, are there legal ramifications if unhashed passwords are stolen? If not required in the US, but required in the ...
3
votes
1answer
1k views

Verify CDN javascript's integrity

CDNs speed up the loading of websites by allowing caching for frequently used javascript libraries like jquery. How do we know if they have modified the javascript before serving it to my clients? E....
3
votes
1answer
241 views

How secure is Visual host key, and how is SHA2 converted into that representation?

SHA2 has 256 bits of possibilities. Visual host key seems to have the following upper and lowercase = 26*2 numbers and symbols = 20 Additional symbols = 22 Total 94 characters represented in ...
3
votes
1answer
3k views

John the Ripper - Calculating brute force time to crack password

I'm using incremental mode (brute force) mode in John the Ripper to crack Linux MD5 passwords. I'm trying to calculate the time it will take to run through all combinations of 12 passwords (with 12 ...
3
votes
2answers
427 views

Is there any way to cryptographically hash a human thumbprint?

Is there any way to cryptographically hash a human thumbprint into a form that can be consistently reproduced by thumbprint readers? Assuming that it would be possible to create a database of ...
2
votes
2answers
231 views

Keyed-hashing a password with a hash of the password + salt as the key, is it safe?

I was looking at our authentication system which hashes passwords differently than I was taught. The salt is a constant byte array and it uses the password + the salt as a key for the password hashing ...