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)

17
votes
7answers
3k views

Tripwire - Is it security Theater?

Tripwire type intrusion detection systems supposedly protect your system from rootkits, by monitoring the checksums of important binaries for changes. Let's say I have tripwire configured to run ...
17
votes
1answer
2k views

Password hashing : Using 2 salts [duplicate]

I'm developing an authentication service. I know the practice of generating a unique salt per user, stored in the DB with the hashed password, to prevent rainbow tables attacks. I just had the idea ...
17
votes
2answers
2k views

How safe are signed git tags? Only as safe as SHA-1 or somehow safer?

How safe are signed git tags? Especially because git uses SHA-1. There is contradictory information around. So if one verifies a git tag (git tag -v tagname), then checksouts the tag, and checks that ...
16
votes
2answers
54k 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?
16
votes
8answers
3k views

Won't all hashes collide after enough iterations (with a static salt)?

We all know that we're supposed to take a fairly slow hashing algorithm, salt the password, and run the hash for many iterations. Let's say that I'm following almost everything except for one rule, ...
16
votes
3answers
3k views

Have weaknesses in SHA-1 and MD5 ever actually been successfully used in an attack?

Pretty much every guide, how-to, and reference for dealing with passwords and hashing has a warning in big or bold letters stating something along the lines of: SHA-1 and MD5 are NOT secure and ...
16
votes
4answers
6k views

How quickly can these password schemes really be beaten?

If you use a quick hashing algorithm like MD5 or SHA-1 to hash passwords and you don't use any salt at all, how quickly could one expect a hacker to find my password out? If I use a truly random salt ...
16
votes
5answers
3k views

The AES Crypt implementation hashes a password 8192 times to generate the key. Is this necessary?

I'm considering encrypting some small files (hundreds of kb apiece) using the AES Crypt reference implementation. Looking at the source, it seems that the encryption key is derived from the IV and the ...
16
votes
3answers
585 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 ...
16
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
7answers
834 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 ...
15
votes
7answers
13k views

What are the realistic, and most secure crypto for Symmetric, Asymmetric, Hash, Message Authentication Code ciphers?

I'm interested in updating this two pronged question for 2011: What cryptology is most appropriate for low-powered devices (such as a cellphone), and yet still effective? What cryptology is most ...
15
votes
6answers
5k views

Client side password hashing

Edit: Updated to put more emphasis on the goal - peace of mind for the user, and not beefing up the security. After reading through a few discussions here about client side hashing of passwords, I'm ...
15
votes
7answers
4k views

Why does some popular software still use md5?

Nowadays no one dares to defend md5 for any use, and of course they should not! However, much popular software still uses md5 in applications such as password hashing (although it's not simple/plain ...
15
votes
3answers
12k views

What's the advantage of using PBKDF2 vs SHA256 to generate an AES encryption key from a passphrase?

I'm looking at two comprable pieces of software which need to encrypt data on disk using a passphrase. One uses PBKDF2 to generate the encryption key from a passphrase, while the other uses two rounds ...
15
votes
6answers
4k views

Do salts have to be random, or just unique and unknown?

First of all, my motive is to avoid storing the salt in the database as plain text. As far as this question is concerned, the salt is not stored in the database. After discussion in comments and in ...
15
votes
3answers
7k views

Is a HMAC-ed password is more secure than a bcrypt-ed or scrypt-ed password?

Given an option , which one should I choose , a HMAC for storing a password securely or a bcrypt or scrypt library?
15
votes
2answers
684 views

Trustworthiness of kernel.org post attack

What are the security implications of the compromise of kernel.org on the trustworthiness of the code base hosted on the site’s Git repository? The announcement today explained the mitigations ...
15
votes
3answers
9k views

Cracking MS-CACHE v2 hashes using GPU

As most people here will know, Windows caches domain/AD credentials in a format known as MS-Cache v2. Obviously, these would be excellent passwords to gain during a penetration test when local access ...
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
5answers
4k views

What are the differences between an encryption seed and salt?

Today I had a hard time explaining the difference to a friend. I know seeds are used when generating "random" strings. And salts are used when providing different outcomes to a hash. What is 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 ...
14
votes
4answers
8k views

Does symmetric encryption provide data integrity?

Let's say I have one server that encrypts a file with a symmetric key, e.g. AES-CBC, and sends it to clients that decrypt it. Does that provide data integrity when decrypted? Or is it possible for ...
14
votes
3answers
2k views

Content hashes to help protect resources being fetched from a CDN

During a conversation in The DMZ, it was suggested that an SHA256 hash could be used to check that content being delivered from a CDN hasn't changed before being executed, similar to how Kim Dotcom's ...
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?
14
votes
6answers
965 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 ...
14
votes
2answers
568 views

Password Salts and Randomness

Alright, so I understand that users are the kind of beasts who like to use one password and make it short and easy to remember (like "doggies"). If I understand correctly, that's one reason we use ...
14
votes
2answers
3k views

Insecure versions of crypt hashes

I read at crackstation not to use these variants of bcrypt* ($1$, $2$, $2a$, $2x$, $3$),but I've used bcrypt ($2a$) in various sensitive implementations recently. Can any security expert clarify why ...
14
votes
2answers
7k views

With PBKDF2, what is an optimal Hash size in bytes? What about the size of the salt?

When creating a hash with PBKDF2, it allows the developer to choose the size of the hash. Is longer always better? Also, what about the size of the random salt? Should that be the same size as the ...
13
votes
2answers
2k views

Are SHA-2 certificates considered obsolete, or current?

I read here that I should be using SHA-2 certificates to secure a HTTPS webserver. Are SHA-2 certificates considered obsolete, or current for TLS/SSL website certificates? (as of 11/20/2015). If ...
13
votes
6answers
8k views

Is PBKDF2-based System.Cryptology.RFC2898DeriveBytes() “better” for Unicode Password hashing than traditional methods?

When is it appropriate to use RFC2898DeriveBytes versus a typical hash? Update I now understand that a KDF is typically used to create a symmetric key for possible use in encrypting a stream. I ...
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 ...
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 ...
13
votes
3answers
2k views

What is a good enough salt for a SaltedHash?

Since I'm hashing all passwords with each their own salt, is there a benefit to the salt being really random, or would an incremental counter or a guid be good enough? Also, is there a benefit of ...
13
votes
3answers
15k views

Choosing a session ID algorithm for a client-server relationship

I am developing an application which has a client-server relationship, and I am having trouble deciding on the algorithm by which the session identifier is determined. My goal is to restrict ...
13
votes
3answers
1k views

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? ...
13
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
4answers
3k views

How can I make sure password hashing is secure on computers while not being prohibitively slow on mobile devices?

I'm new to cryptography and its implementations. I'm designing an Android app where an user enters a password to retrieve some encrypted data. After some research on possible solutions I ended up with ...
13
votes
1answer
504 views

What did Blackberry do wrong?

The NIST defines a vulnerability in RIM Blackberry encryption discovered last October. Apparently, Blackberry's flavour of PBKDF2 was weak. They say: The offline backup mechanism in Research In ...
12
votes
5answers
2k views

What is the best way to transmit password hash over unreliable TLS?

I have TLS connection between my server and client. I have no certificate, so the connection is susceptible to the Man-in-the-middle attack. I fear that attacker could intercept the password hash ...
12
votes
5answers
2k views

Is this way of encoding cryptographic hashes safe?

I'm looking at the code of a particular web application that handle file uploads. For some reason, instead of using the cryptographic hash function (SHA-256 in this case), they derive an ID from it, ...
12
votes
4answers
3k views

Handling passwords in a web application

I am trying to learn how a secure web application is developed. Particularly, I am unsure of how passwords are sent from the client to the server. For a typical user/password login form. If the client ...
12
votes
4answers
2k views

At what point does adding more iterations to PBKDF2 provide no extra security?

If my true passphrase is used only to generate a hash which is used as the cipher's actual key, doesn't that mean it's possible to try and brute force the cipher itself? I know it would take an ...
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 ...
12
votes
1answer
716 views

General purpose slow/unique hash routine for dup checking of private data, without storing the data itself?

I am wondering if there is a percentage of uniqueness known to be lost with every repeat of various hash routines, like MD5, SHA1, and how that might compare with other algorithms. If theoretically I ...
12
votes
2answers
2k views

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 ...
12
votes
4answers
1k views

MS-SQL Password Storage

What would be your recommendation for replacement of an MD5 hash approach to password storage within an MS-SQL database be?
12
votes
4answers
3k views

Is there a length beyond which increasing password length provides no additional security?

Assuming that the password is stored hashed and salted, and that it is a string of random characters, is there a point where adding to password length doesn't add security? Since the hash will have a ...
12
votes
4answers
1k views

Encrypting IP addresses in a MySQL database

I'd like to encrypt IP addresses in my MySQL database, with the following constraints: Does not need to be resistant to attackers that can execute queries. Must be resistant to attackers that have ...
12
votes
5answers
6k views

Why is client-side hashing of a password so uncommon?

There are very few websites that hash the users password before submitting it to the server. Javascript doesnt even have support for SHA or other algorithms. But I can think of quite a few advantages, ...