Questions tagged [hash]

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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9
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7answers
600 views

Proving running code on a website is unchanged

Can it be proved to the user that the running code behind a website with security related code is the same as published? I'm currently looking at a few new project ideas and one involves secure ...
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2answers
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Does password-hashing “busy-work” need to be cryptographically secure

All modern password hashing schemes are deliberately designed to include a huge amount of "busy-work", to limit the speed with which an attacker would be able to conduct password hashing attempts. ...
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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 ...
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1answer
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PRF, IKE and hash function

The term PRF is mentioned in the documentation of the IKE (Internet Key Exchange) protocol. What is a PRF? What is the difference between a PRF and a hash function? What PRFs are used in the IKE ...
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1answer
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What is the collision chance of a 128-bit hashing function if it is always fed with 256-bits of data?

I mean "normal" collisions not based on any attack. How do i calculate it?
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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 ...
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2answers
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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-...
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2answers
10k 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 verification), to consume less storage space. I don't know ...
18
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1answer
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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 "...
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2answers
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File security when encrypting files directly with the openssl command / and what about SHA1 hashing password first?

I've been using this command to encrypt files for a while now: openssl aes-256-cbc -a -salt -in secrets.txt -out secrets.txt.enc Then I type in a password. Can someone tell me, roughly speaking, ...
6
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3answers
722 views

Similarity comparisons with hashed passwords possible?

At a company I worked at, I had to change my password every 90 days and I could only reuse a password after 8 iterations. This no-reusal included passwords being too similar to the old one, e.g. when ...
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3answers
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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 ...
5
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2answers
834 views

Keepass Dictionary Attack Protection Strategy

Though pretty interested, I'm everything but an expert in Information Security, please redirect me to any helpful resources if my question is stupid or correct me if my assumptions are wrong. When ...
5
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2answers
1k 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 ...
5
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1answer
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How big is the risk of hash fixed points/cycles?

It's established wisdom to hash password multiple times with a salt to increase the time it takes per brute force iteration. At the same time (unless the algorithm guarantees otherwise) there's a ...
4
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2answers
820 views

Why does LastPass store password hashes on the server at all?

While reading about LastPass' breach, I was wondering why would LastPass store strengthened password hashes at all on the server side? Could they only store the AES encrypted data and when the user ...
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5answers
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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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2answers
1k views

Using a password hash…as the password? [duplicate]

Ok, this is probably a really stupid idea, but I can't really see why it would be a bad idea. Maybe someone can enlighten me. Why couldn't you enter a password good hashing algorithm like bcrypt, ...
2
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1answer
451 views

truncated hash for message authentication?

I am using hash for authenticating the signature of the message. since the hash will be part of a url that is used for QR code, I would like to keep the hash as short as possible in order to generate ...
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2answers
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How can this website crack MD5 hashes? [closed]

I have heard that hashing, such as MD5, is one-way and cannot be cracked. But there are some websites that can decrypt hash, like www.md5hashing.net and some scripts like findmyhash.py. I tested some ...
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1answer
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How to implement iterations when hashing passwords?

To securely hash passwords, algorithms such as PBKDF2 do many iterations of a common hash such as SHA1. Are there certain ways that these iterations need to be done to be safe? In particular, from ...
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2answers
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Generating authentication token from PHP sessions

I have a traditional PHP site which uses sessions. I've developed a real-time app in nodejs and wish to authenticate users here based on their PHP session. The procedure would go something like this: ...
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1answer
814 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 ...
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1answer
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client side and server side hash password [duplicate]

Another question about client or server side password hashing, I know. After reading many other post about this topic I'm still a little confused and not completely sure what is the best, because I ...
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5answers
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create a variants of MD5

I have also asked similar q here : To create a variants of MD5, I made following changes : MD5 uses a non-linear sin(i)* pow(2,32) ----> i plane to use cos(i)*pow(2,32) Instead ...
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3answers
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Parameters for PBKDF2 for password hashing

I use PBKDF2 with SHA-256 to store hashes of passwords. I use the following parameters: number of iterations desired = 1024 length of the salt in bytes = 16 length of the derived key ...
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3answers
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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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3answers
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NTLMv2 resistance to bruteforcing

I have a question regarding NTLMv2 resistance to password bruteforcing. I know that some modern graphic processors (like Radeon 6990) are able to calculate billions hashes per second and crack NTLM ...
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4answers
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Can I brute-force a password hash even if I don't know the hash-algorithm used?

Can I brute-force a password hash even if I don't know the underlying algorithm? For example if I get hold of a database with password hashes and the used hash algorithm is unknown, like a random ...
6
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3answers
618 views

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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2answers
137 views

Understanding digitial certifications

q1) Does that mean that every time information is exchanged, both the original data + digital certification is sent? Meaning data + signature for each and every exchange. q2) Can any kind soul here ...
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4answers
717 views

Why is a password accompanied by a username deemed 'safer'?

While browsing this community I notice that some people say that the main advantage of usernames accompanied by passwords is as they take more tries to be brute forced, however I don't think that is ...
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3answers
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Why are MD5 collisions dangerous?

I understand that the MD5 algorithm isn't collision resistant, and that collisions between data of arbitrary size can be found with more efficient methods than brute-forcing. However, I have read ...
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2answers
553 views

Can a weak password generate the same hash as a strong password?

Conventional password advice encourages the use of long passwords with the rationale being hashing the entire password space (rainbow table or brute force) takes longer with each character added. ...
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3answers
4k views

Recompute Rainbow table with salt?

So, as I understand it, you prepend a password with salt before you hash it so that the resulting hash can't be used with a rainbow table to find the original password, as you could if the password ...
3
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2answers
698 views

When hashing, do longer messages have a higher chance of collisions?

While discussing maximum password lengths, a poster made this comment: The longer the allowed input, the easier to supply an input that could cause a hash collision To explain (since the lack of ...
3
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1answer
11k views

John the ripper passwd file format with salt not working

I'm trying test password strength in one of our e-commerce sites. I'm using john the ripper to brute-force a password file. The algorithm used by PHP is: $hash = md5($salt . $pass) No other ...
3
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2answers
301 views

How does my bank knows my second and forth chars of my password [duplicate]

I see that the new login mechanism used by some banks in UK and also used by visa debit authentication is to ask for three random characters from your password at login (for example second, ninth and ...
2
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1answer
342 views

Securing communication

The problem: I have an open-source client (a Firefox add-on written in JavaScript) and a server containing somewhat sensible user information: username and user history (all from YouTube). The client ...
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1answer
133 views

How to verify that a clientside-generated object is genuine?

I know that general best-practice states not to trust anything generated by the client. With that in mind, I want to write an HTML5 app that utilises the browser to generate various objects client-...
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1answer
815 views

Please help clarify password hashing - salted, multiple iterations of MD5 vs bcrypt/sha2, etc [duplicate]

I was reading an article about the Ars Technica hack here and had a couple of questions. The commenter said: "PHPass uses salted and iterated MD5 to hash passwords" My question is that if I were ...
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2answers
869 views

Separate database column for salt

Is it advisable to store the salt in a separate database column or should we concatenate it together with the password? Is there any difference? I have come across implementations of both types. ...
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5answers
885 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 ...
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1answer
20k views

Is BCRYPT easy do decrypt?

I know that bcrypt doesn't encrypt, but how easy would it be to get the password from a stored bcrypt hash? I wanna split my question about bcrypt into 2: I read over here that bcrypt generates ...
1
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1answer
242 views

What are attacks against hash collision resistance property?

From the definition, a collision would mean you would have to find any two arbitrary x and y such that h(x) = h(y) where h is some cryptographic hash function. This is different from a second pre-...
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3answers
88 views

Why are there Hashes next to downloads? [duplicate]

I've seen several sites wehre they would put the hash of the downloadable file next to the file. Why do they do this ? I understand the purpose of comparing the hash of your file with the online hash ...
0
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1answer
185 views

Using multiple hashes to verify a file

I'm dreaming of a service where a client sends my service a hash of a file that they generate locally from that file. The idea is that having such a hash would be enough to show that the user is ...
77
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3answers
22k views

How can I create a password that says “SALT ME!” when hashed?

How can I create a password, which when directly hashed (without any salt) with md5 will return a string containing the 8 characters "SALT ME!". The hope is that a naive developer browsing through his ...
43
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7answers
26k views

Hashing a credit card number for use as a fingerprint

What's the best way to hash a credit card number so that it can be used for fingerprinting (i.e. so that comparing two hashes will let you know if the card numbers match or not)? Ideally, I'm looking ...
49
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3answers
40k views

Is bcrypt better than scrypt [duplicate]

Possible Duplicate: Do any security experts recommend bcrypt for password storage? I'm no security expert and do not pretend to be that's why I'm asking here. I write many PHP based applications ...