Can I safely distribute a hashed password? - security

I have an application whose source code is checked into a public repository. This source code includes configuration files, and in those configuration files are SHA-256 hashed passwords.
My understanding is that when it comes to hashed passwords, an end user doesn't actually have to enter the password you used to generate the hash, but any password that generates the same hash value. I believe this is called a collision.
So can I display my hashed passwords in public with a reasonable assurance that someone can't take that hash and then generate a password (or generate a collection) that can be used to get access to my application? Is that a guarantee that these hashing algorithms try to make?

There are no known practical attacks against SHA-2 in the general case. It's generally considered better to keep hashed passwords secret, though, because there are rainbow tables, dictionary attacks, and other such things. If you took the proper precautions such as salting, round robin hashing, and having a nice long passphrase, it should be perfectly safe.
It's still better to not do this, though. You never know what cryptographic attacks might be developed in the future.

It is not likely for someone to reverse a HASH, SHA1, SALT etc. There are some ways out there to reverse one, but if you think your at that much of a risk I'd use SHA1 and SALT for maximum security. Having a long password makes it difficult to reverse, but unless they are real seasoned coders, your not very like to be a victim of it.
Read up on the algorithms at Wikipedia...
SHA1: http://en.wikipedia.org/wiki/SHA-1
SALT: http://en.wikipedia.org/wiki/Salt_(cryptography)
Just use a unique password and you should be fine ;-)

Related

Why can't we store every hashed password ever in storage(HDD) and use that to match the hashed password instead of use brute force password cracking?

So let's say we somehow got the hashed password of a victim.
So the brute force approach is to take every possible string, hash it and check if it matches the victims hashed password. If it does we can use that string is the password and hence hacked.
But this requires a great deal of computational power and good amount of time even for strings with 6-8 characters.
But what if we can hash every possible string with less than 10(some) characters and store it in storage like a sorted database before hand. So that when you get the hashed password you can easily look up the table and get the password.
P.S:-
For this example let's say we are working with only one type of hashing algorithm and have huge data servers to store data.
I'm new to security and this a very very basic question but for some reason the answer to the question was really hard to find on the internet.
This is called a rainbow table, and is very much a known concept.
It is also the reason you should never just store the hash of passwords. A salt (a random string added to the password and then stored with the hash as plaintext for verification) can easily mitigate this attack by effectively making it impossible to use a rainbow table and force recomputation.
Also just for completeness it's important to note that plain cryptographic hashes are not adequate anymore to be used for credentials (passwords), because they are too fast, which means it's too fast to generate a rainbow table for a given salt, effectively bruteforcing a password. Specialized hardware makes it feasible to recover relatively strong passwords if only hashed with a plain crypto hash, even if using a salt.
So the best practice is to use a key derivation function (KDF) to generate your password hashes in a way that makes it very slow (infeasible) to brute force, but fast enough to verify. Also in most known implementations adding a random salt to each hash is automatic and the whole thing is just secure.
Such algorithms are for example PBKDF2, bcrypt, scrypt or more recently, Argon2. Each of these have different characteristics, and are more resistant against different attacks.

One way functions, Hash algorithms

Basically One-way functions have two properties:
1. Irreversible
2. Collision-Resistance(which means no two same words have the same hash value correct me if im wrong)
On the other hand i see that Salted Hash Passwords are used to provide more security to hash values of passwords and also provide collision-avoidance to passwords which have the same plain value.
So why does this happen, aren't hash functions supposed to have Collision-Resistance, why does Salt have to provide this when hash functions already have that property?
Thank you in advance.
It would be wonderful if one-way hash functions were really one-way.
What happens if two users choose the same password? Without salt, they get the same hash.
Guess what? People are not good at choosing passwords. These creatures of limited memory and lacking in natural internal cryptographic randomness often choose passwords that are short, low entropy, and brute-forceable.
If you want to crack the hash of a password that didn't involve salt, then just Google it.
Salt helps fix the problem, but it is not the panacea. With salt, two people who choose the same password do not get the same password hash, assuming the salt is different for both users. Salts also help prevent rainbow table attacks, which is a time-memory trade-off to hack out passwords.
Still, this does not solve all problems. If your database becomes public, salt + cryptographic hash is not enough because attackers can still brute force-passwords using low cost GPUs.
So what is the solution? You not only need salt, but you also need brute forcing to be a slow process. That's why we don't use hash functions for passwords, instead we use password hashing functions. Don't blame me for the stupid terminology, I fully agree. Bottom line: choose from bcrypt, scrypt, argon2, pbkdf2. I personally recommend bcrypt.
Just want to add a detail to #TheGreatContini s answer.
For passwords hashed without a salt, you will probably find an
already prebuilt rainbow-table.
If you use a single salt for all passwords, an attacker has to build 1 rainbow-table using this salt,
to get all passwords.
If each password gets its unique salt, an attacker would have to build a rainbow table for each password. Building a full rainbow-table to only get 1 password doesn't make sense, that's why we can say that unique salt prevents rainbow table attacks.

Importance of salt when using Rfc2898DeriveBytes to create secure passwords from clear text passwords

I'd like to incorporate the encryption and decryption of files in one of my C# .NET apps. The scenario is simple: User A sends an AES256-encrypted file to user B. The clear text password is exchanged on a different channel (e.g. phone call or whatever).
From what I understand I should use Rfc2898DeriveBytes for converting the user's clear text password into a more secure password using maybe 10,000 rounds. (see this article).
What I don't understand is the role of salt in my scenario. Usually salt is used in hashing passwords to prevent dictionary attacks. But in my scenario the PBKDF2 algo is used to compensate weaknesses of short or easy to guess clear text passwords by adding extra calculations required by the PBKDF2-rounds.
If I choose a random salt then the receiver will need to know that salt also in order to decrypt correctly. If I use a constant salt, then hackers can easily reverse engineer my code and run brute force attacks using my constant salt (although they'll be really slow thanks to the PBKDF2 iterations).
From what I understand I have no choice but to use a constant salt in my scenario and enforce a good clear text password rule to make up for the weakness of constant salt. Is my assumption correct?
Salts, in the context of password hashing (and key derivation), are used to prevent precomputation attacks like rainbow tables.
Note that the salt must be different and unpredictable (preferably random) for every password. Also note that salts need not be secret – that's what the password is for. You gain no security by keeping the salt secret.
The recommended approach in your case is to generate a random salt every time a file is encrypted, and transmit the salt along with the ciphertext.
Is there a specific reason you're using AES-256 by the way? It's around 40% slower than AES-128 due to the extra rounds, and it offers no practical security benefit (particularly not in the case of password-based encryption).
It's also worth considering using a well-established standard like PGP rather than building your own protocol from cryptographic primitives, because building secure protocols is so hard that even experts don't always get it right.
Your assumption is correct. If they have access to the password, they will also have access to the salt. The BCrypt implementations I've seen put the number of iterations, the hash, and the salt all in the same result string!
The idea is: your hash should be secure even if the salt and number if iterations is known. (If we could always know that the salt and number of iterations and even the algorithm would be unknown to attackers, security would get a whole heck of a lot easier! Until attackers politely decline to read our salts, we must assume they will have access to them in the event of a breach.) So you're right, they can brute force it - if they have a few supercomputers and a couple million years of computing time at their disposal.

Storing salt+password hash in DB and protecting against password attack

Please help me with my understanding. Also I am not talking about SSL or DH key exchange.
As the salt is stored in DB and is a secret to the attacker to just protect the user original password (Rainbow tables), in case attacker gets their hand on the actual DB itself. Then how will how you protect against brute/dictionary based attacks. Once again, logging the wrong requests and denying IP of many bad request is known, I am talking about cryptography here. As the password is same for user1, attacker got it from other websites, how does salt protects here. I guess not, then what are the best solutions available to stop such attacks. Assume data is really important like credit card numbers + CVV(I know don't store CVV, but that is not the question).
EDIT: By the way, I came up with some stupid idea, and it looks like a known method for stopping dictionary attacks. Read more this question: High cost encryption but less cost decryption
May be we can discuss some other methods here, to protect against brute/dictionary/social engineering password attack
It's a little unclear to me what your actual question is, but if it is "How does a salt help protect me against brute force attacks?" the answer is that technically it does not. There is nothing about a salt that makes brute force attacks more difficult, salts instead make it difficult to brute force multiple accounts simultaneously. Essentially salts artificially inflate search space required to do a brute force attack, making it computationally difficult to pre-calculate every possible password and then check them against the entire database. Salts can be stored in the clear, so long as they are unique to each password.
If you want to make brute forcing passwords more difficult, what you want is an adaptive hashing scheme. These schemes allow you to dictate how long hashing should take. Because an honest client should only have to authenticate on the order of tens of times, but an attacker will need to do it on the order of millions or billions of times, slower hashes make the task near impossible for the attacker while introducing little overhead in the system.
What this all boils down to is that you should use bcrypt if you are hashing passwords. It is designed to incorporate a salt and is an adaptive hashing system. For more info, see this article on security.stackexchange.com
About salt : If you search the "MD5" encrypted password using search engine like google, here you may find the original plain password. But if you mix the salt in your plain password and then apply "MD5" encryption, you wont be able to find it. If any hacker anyhow hacks your database and if you are using just MD5 encryption then he may use above method to hack passwords. For e.g. Search this string on google : 5f4dcc3b5aa765d61d8327deb882cf99, you'll get original password string. Salt is mainly added to protect against such attacks.
Check out here. Look at Just content and concept here to understand. This is from Spring security docs.
The purpose of a salt is not to prevent dictionary attacks; it is to prevent precomputation attacks such as rainbow tables. Having a salt requires the attacker to attack each password individually, after they gain access to the database; they can't precompute hashes for passwords in the dictionary, or reuse this effort across users.
Password Stretching is a way to make dictionary attacks more difficult, by increasing the amount of work the attacker has to do to test each candidate password.
Without salt, an attacker can use an offline attack to precalculate the hash of common passwords: "secret" "qwerty" etc. No salt allows an attacker to tell when different users are using the same password, as they will have the same hashes. Salt prevents precalculation and avoids the matching hash problem.
An attacker with access to the datbase will also have access to the salts. She will need to attack each password separately, because of the different salts.
Using stretching (repeated hashing) can also slow down an attacker. Rather than storing hash(password + salt) you store hash^n(password + salt), where n is large enough for the overall calculation to take at least 0.1 second . That limits the attacker to around ten trials a second while having no discernible impact on the user.

Difference between Hashing a Password and Encrypting it

The current top-voted to this question states:
Another one that's not so much a security issue, although it is security-related, is complete and abject failure to grok the difference between hashing a password and encrypting it. Most commonly found in code where the programmer is trying to provide unsafe "Remind me of my password" functionality.
What exactly is this difference? I was always under the impression that hashing was a form of encryption. What is the unsafe functionality the poster is referring to?
Hashing is a one way function (well, a mapping). It's irreversible, you apply the secure hash algorithm and you cannot get the original string back. The most you can do is to generate what's called "a collision", that is, finding a different string that provides the same hash. Cryptographically secure hash algorithms are designed to prevent the occurrence of collisions. You can attack a secure hash by the use of a rainbow table, which you can counteract by applying a salt to the hash before storing it.
Encrypting is a proper (two way) function. It's reversible, you can decrypt the mangled string to get original string if you have the key.
The unsafe functionality it's referring to is that if you encrypt the passwords, your application has the key stored somewhere and an attacker who gets access to your database (and/or code) can get the original passwords by getting both the key and the encrypted text, whereas with a hash it's impossible.
People usually say that if a cracker owns your database or your code he doesn't need a password, thus the difference is moot. This is naïve, because you still have the duty to protect your users' passwords, mainly because most of them do use the same password over and over again, exposing them to a greater risk by leaking their passwords.
Hashing is a one-way function, meaning that once you hash a password it is very difficult to get the original password back from the hash. Encryption is a two-way function, where it's much easier to get the original text back from the encrypted text.
Plain hashing is easily defeated using a dictionary attack, where an attacker just pre-hashes every word in a dictionary (or every combination of characters up to a certain length), then uses this new dictionary to look up hashed passwords. Using a unique random salt for each hashed password stored makes it much more difficult for an attacker to use this method. They would basically need to create a new unique dictionary for every salt value that you use, slowing down their attack terribly.
It's unsafe to store passwords using an encryption algorithm because if it's easier for the user or the administrator to get the original password back from the encrypted text, it's also easier for an attacker to do the same.
As shown in the above image, if the password is encrypted it is always a hidden secret where someone can extract the plain text password. However when password is hashed, you are relaxed as there is hardly any method of recovering the password from the hash value.
Extracted from Encrypted vs Hashed Passwords - Which is better?
Is encryption good?
Plain text passwords can be encrypted using symmetric encryption algorithms like DES, AES or with any other algorithms and be stored inside the database. At the authentication (confirming the identity with user name and password), application will decrypt the encrypted password stored in database and compare with user provided password for equality. In this type of an password handling approach, even if someone get access to database tables the passwords will not be simply reusable. However there is a bad news in this approach as well. If somehow someone obtain the cryptographic algorithm along with the key used by your application, he/she will be able to view all the user passwords stored in your database by decryption. "This is the best option I got", a software developer may scream, but is there a better way?
Cryptographic hash function (one-way-only)
Yes there is, may be you have missed the point here. Did you notice that there is no requirement to decrypt and compare? If there is one-way-only conversion approach where the password can be converted into some converted-word, but the reverse operation (generation of password from converted-word) is impossible. Now even if someone gets access to the database, there is no way that the passwords be reproduced or extracted using the converted-words. In this approach, there will be hardly anyway that some could know your users' top secret passwords; and this will protect the users using the same password across multiple applications. What algorithms can be used for this approach?
I've always thought that Encryption can be converted both ways, in a way that the end value can bring you to original value and with Hashing you'll not be able to revert from the end result to the original value.
Hashing algorithms are usually cryptographic in nature, but the principal difference is that encryption is reversible through decryption, and hashing is not.
An encryption function typically takes input and produces encrypted output that is the same, or slightly larger size.
A hashing function takes input and produces a typically smaller output, typically of a fixed size as well.
While it isn't possible to take a hashed result and "dehash" it to get back the original input, you can typically brute-force your way to something that produces the same hash.
In other words, if a authentication scheme takes a password, hashes it, and compares it to a hashed version of the requires password, it might not be required that you actually know the original password, only its hash, and you can brute-force your way to something that will match, even if it's a different password.
Hashing functions are typically created to minimize the chance of collisions and make it hard to just calculate something that will produce the same hash as something else.
Hashing:
It is a one-way algorithm and once hashed can not rollback and this is its sweet point against encryption.
Encryption
If we perform encryption, there will a key to do this. If this key will be leaked all of your passwords could be decrypted easily.
On the other hand, even if your database will be hacked or your server admin took data from DB and you used hashed passwords, the hacker will not able to break these hashed passwords. This would actually practically impossible if we use hashing with proper salt and additional security with PBKDF2.
If you want to take a look at how should you write your hash functions, you can visit here.
There are many algorithms to perform hashing.
MD5 - Uses the Message Digest Algorithm 5 (MD5) hash function. The output hash is 128 bits in length. The MD5 algorithm was designed by Ron Rivest in the early 1990s and is not a preferred option today.
SHA1 - Uses Security Hash Algorithm (SHA1) hash published in 1995. The output hash is 160 bits in length. Although most widely used, this is not a preferred option today.
HMACSHA256, HMACSHA384, HMACSHA512 - Use the functions SHA-256, SHA-384, and SHA-512 of the SHA-2 family. SHA-2 was published in 2001. The output hash lengths are 256, 384, and 512 bits, respectively,as the hash functions’ names indicate.
Ideally you should do both.
First Hash the pass password for the one way security. Use a salt for extra security.
Then encrypt the hash to defend against dictionary attacks if your database of password hashes is compromised.
As correct as the other answers may be, in the context that the quote was in, hashing is a tool that may be used in securing information, encryption is a process that takes information and makes it very difficult for unauthorized people to read/use.
Here's one reason you may want to use one over the other - password retrieval.
If you only store a hash of a user's password, you can't offer a 'forgotten password' feature.

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