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Irreversibly converting user-selected passwords into authentication tokens that can be safely stored e.g. in a user database. Typically done with a salted password-based key derivation function (PBKDF), ideally with a memory-hard mixing stage to thwart brute-force attacks using parallel hardware.

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22 views

Cryptographically secure hash function vulnerable to length extension attacks both to front and to back?

Is there any hash function where both $\text{hash}(m\|k)$ and $\text{hash}(k\|m)$ are vulnerable to length extension, but $\text{hash}(m)$ is itself secure?
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1answer
50 views

Does having an SHA256 hash compromise PBKDF2 secrecy?

If I have a password pwd, and I hash it with SHA256 and send it to a server for authentication (server will apply ...
12
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3answers
5k views

What password hash function for the next 50 years?

According to this report : http://www.ecrypt.eu.org/csa/documents/D5.4-FinalAlgKeySizeProt.pdf SHA2-512, SHA3-512, Whirlpool and Blake2b are hash functions that could be safe for the next 50 years. ...
1
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1answer
77 views

How can a user-input password be used to generate a natural-like dictionary corpus?

I'm curious about the implications of cryptography and the generation of natural text (i.e using Markov chains), and I am wondering if there has been any cryptographic protocols that involved ...
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2answers
55 views

Should number of iterations of PBKDF2 stay secret?

Let's say I encrypt my passwords with PBKDF2 and store it somewhere. Now let's say it was stolen and the hacker, who stole it knows it was hashed with PBKDF2. Does a knowledge of number of iterations ...
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3answers
113 views

Recommended minimum entropy for online passwords in 2018

Assume a simple case, that an attacker knows the password creation scheme, and that we're not dealing with state actors, nor with sites which keep passwords in plain text. We're trying to defend ...
2
votes
2answers
76 views

Why is it recommended to hash passwords with a secret salt?

NIST recommends doing an additional round of hashing using a secret salt: In addition, verifiers SHOULD perform an additional iteration of a key derivation function using a salt value that is ...
3
votes
1answer
69 views

Ciphering the output of a password hash

In an article on password hashing security, Anthony Ferrara suggests using bcrypt to hash passwords and then using a "strong cipher (AES-128-CBC) with a key rotation policy". This seems like a good ...
3
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2answers
111 views

The logic of preferring PBKDF2 over iterative SHA2

I have studied PBKDF2 for the application of hashing passwords, and frankly I don't understand the justification for the complexity of PBKDF2 over iterative hashing with a cryptographic hash function. ...
3
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6answers
399 views

How does a salt get chosen?

I feel like I am missing some information regarding salting. How does one choose the salt? If you reuse the same salt for all passwords, can it just be figured out and then used in conjunction with ...
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1answer
38 views

One-way hashing using singular matrices?

In matrix encoding, we convert our message into some numerical value and then create a matrix out of those numbers. The matrice encryption is based on the fact that a matrix multiplied by its inverse ...
0
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0answers
52 views

Signal database passphrase in version <= 4.15.4

Signal Android's documentation (https://github.com/signalapp/Signal-Android/wiki/Data-Storage-Documentation) says "messages are optionally encrypted by a passphrase" for older version which I assume ...
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3answers
72 views

Authorities on password hashing best practice

I am trying to understand how best practices on password hashing come about. With password hashing, I mean specifically for the case of storing user passwords in a database in a hashed representation, ...
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2answers
58 views

Can't salt be easily removed from hashed password if access to the database was obtained?

After playing around with bcrypt I see that the database stores the salt and the hashed password is prepended with the salt. I read this article on how hashing should be properly used which also ...
3
votes
0answers
51 views

Did “The Catena Password-Scrambling Framework” make an error in the reduction of its pseudorandomness?

I was reviewing the most recent version of the Catena paper and they made some claims that I find questionable in their reduction of the pseudorandomness of the output of Catena (p. 32). First I will ...
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vote
2answers
116 views

Zencash uses your passphrase to identify AND unlock a wallet - how is this secure?

When looking into Zencash I stumbled into myzenwallet.io (by the Zencash creators), which gives you the option to enter a passphrase to generate a wallet (seems normal), but then after creating your ...
0
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2answers
102 views

Security of password hash with known prefix and appendix

Assume I have a password that is exactly 32 characters long. I hash it the following way: Prepend 1524 bytes (known to an attacker) Append 3356 bytes (known to an attacker) Do the checksum It is ...
2
votes
2answers
106 views

Hashing items of different Bytes but same length would enable a timing attack?

I am following this paper which comes highly recommended as a secure Registration/Login system over TLS which uses client side computation for the Password Processing Function (PPF). What my main ...
0
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1answer
223 views

How long will brute force of salted SHA-512 hash will take, if salt is known and possible characters in password are known?

Suppose I know that the password is composed of characters [A-Za-z0-9], length is unknown, but maybe less than 8. If I have information about the salt use to perform hashing, and also hashing ...
2
votes
2answers
105 views

Salt passwords with the username?

Salts should be unique so that an attacker can't brute force multiple passwords at once. However, since usernames are unique, wouldn't it be possible to use some representation of the username as a ...
1
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2answers
151 views

Why SHA-256 (or any other) is too fast for passwords but “slow” for collisions to be found?

Normally, the standard answers of why passwords shouldn't be stored using a groups of hash algorithms, including SHA-256 or higher, even if salted, are "because they are 'fast' hashes", "the attacker ...
0
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1answer
90 views

Salt length for a single password

So I've been reading about salt, and am confused about why the length is so critical. From my understanding salt is used for protection against pre-computed attacks. Say I have a single password ...
2
votes
2answers
145 views

How do I calculate a password space if the password only has eight alphabetic characters (not case sensitive)

I read this wiki article and saw this formula for random password's information entropy. Also the wiki article mention that the symbol count for non case sensitive is 36. Is there a way I can ...
2
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0answers
52 views

Fixed vs variable memory access pattern in password hashing

What are, quantitatively, the pros and cons of fixed versus variable memory access pattern in Password-Based Hashing, Entropy-Stretching Key Derivation functions, and Proof-of-Work applications? ...
3
votes
4answers
194 views

How many bits of entropy are leaked for every derived password from a master?

Given a master password that has a lot of entropy (similar to Bitcoin HD wallet seed words, 130 bits of entropy or more) how many bits of entropy are lost per leaked generated password? Let's take an ...
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vote
4answers
227 views

salt usage for hashed password storage - design consideration

This is part of my academic assignment and hence to ensure no one feels i'm asking for the answer. I've given my opinion. Hashing is mathematical one way function that takes arbitrary length data ...
0
votes
2answers
60 views

Limiting password length to “prevent hash function splitting into multiple hashes”?

Given we are using well-known hashing functions for passwords, i.e. SHA256, SHA512, BCrypt or, PBKDF2. Our Information Assurance SMEs have advised that we truncate the input into these hashing ...
2
votes
1answer
249 views

Salt and pepper at both client and server sides?

Putting aside that it may sound paranoid. I know that many users tend to use the same password on many sites. Then, from an ethical point of view, I should not only be concerned about security breaks ...
3
votes
2answers
128 views

How can a hash function be suitable for hashing passwords, but not for deriving enctyption keys, and vice versa?

Not being a specialist in this field, I am nevertheless constantly trying to keep up with which methods are being considered secure for storing passwords and for encrypting data. During my research ...
1
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1answer
348 views

Use sha3 for passwords hashing

Is use of sha3 justifiable? Is sha3 better than sha2 in (m)any aspects? P.S. I want to use hashing for passwords in a database
0
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3answers
163 views

What is the probability of a SHA-512 hash containing both digits (0-9) and alphabets (a-f) all the time?

Quite curious to know if ever a SHA-512 hash will contain only digits or only alphabets. Thanks in advance.
2
votes
2answers
85 views

PBKDF2 with longer than native output length - Will hashing the result help?

I've seen it mentioned more than once that PBKDF2 should not be used to create a longer key than the native output (such as 160 bits when used with HMACSHA1). Since an attacker could test only the ...
0
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2answers
92 views

How much less secure is an algorithm that gives feedback that the password is one character off?

If we had a stupid login procedure (SLP for short) like in this comic; it gives feedback on login, if the submitted password is one character off. Would a longer password be less secure? What would ...
2
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1answer
154 views

Does this PBKDF2-SHA1 payload hint at a cryptographic security issue?

Blockchain first 16 encrypted bytes, IV, and iter_count – all encoded in Base64: Yms6xqrzCfFsQadVZ5gQonMtnQAAAAAAAAAAAAAAAAAAAAAQJwAA69tYNg== Does it looks like “...
14
votes
2answers
2k views

Password hash that can be upgraded without plaintext password

Most password hashes have a cost parameter that indicates how long the algorithm should take. Is there an algorithm where you can increase that cost for a particular hash, without access to the ...
2
votes
1answer
46 views

Pepper and key derivation/stretching

I understand the pepper concept of adding but not storing a secret and iterating through the set of possible secret values for verifying. But is pepper also useful when it comes already to the use of ...
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2answers
166 views

Comparing different hashes to confirm they came from the same string

Is there any safe hashing algorithm that returns a different hash each time (like bcrypt) but has the possibility to compare 2 different hashes and determine that they were hashed from the same ...
0
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2answers
63 views

hashing and message input size

If a hash function like Whirlpool or Sha512 would take a byte array of 1 MB in size filled with the output of a Secure RNG as its input message, would this be considered a strong input message, a ...
0
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2answers
29 views

Prevent communication with a node assuming full transparency

I have an IoT device that I have set up to communicate with AES-256-GCM encryption. The working version has the encryption key stored in plaintext in a file on the device (this is going to be improved)...
4
votes
4answers
626 views

Rehashing PBKDF2 hashes - do iterations stack?

Let's suppose I have a bunch of PBKDF2 hashes in a database. For the sake of keeping this simple, let's say I've used 10 iterations. A few years later I decide to upgrade to 20 iterations. I want to ...
0
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1answer
114 views

Security trade-off when using low number of rounds with SHA256

I have a web application that stores hashed password reset tokens in a database table. The tokens are randomly generated 256-bit values. I'm currently using Python's passlib sha256_crypt function to ...
0
votes
1answer
279 views

scrypt and argon2: binary safe?

for bcrypt it's probably common knowledge that it isnt binary safe because it uses null termination, which means that when bcrypt is used you need to make sure that no one does these (e.g. by hashing ...
15
votes
2answers
3k views

Mixing algorithms for password hashing good or bad?

So I've come across the following algorithm for hashing passwords ...
0
votes
1answer
120 views

Generating secure hash using iPhone Secure Enclave

I need to turn a password plus salt into a 256 bit hash. The hash is used as a key to encrypt / decrypt a database on an iPhone, so it need never be generated outside the phone. It also need not be ...
9
votes
2answers
395 views

What math makes it safe to offer a stolen-password check service?

The database provider HIBP has 4 billion stolen passwords, and wishes to offer an API for websites to use during new-user signup (and password change) operations, so they can refuse to allow users to ...
3
votes
1answer
414 views

Can pbkdf2 be used with a fixed salt to give a deterministic slow hash?

I need a password hashing function that is deterministic. Correlation attacks are not a concern. The same password must produce the same hash. I just want to protect the password against dictionary ...
4
votes
1answer
140 views

Password derived hash to encrypt known plaintext as password check

The title sounds way too adventurous for what it actually is. I am currently building a system which features some encryption. There is already a system in place, which is built after that scheme if ...
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2answers
820 views

How to crack hash: MD5(MD5(SHA1(SHA1(MD5($pass)))))

I have a hash that I know is MD5(MD5(SHA1(SHA1(MD5($pass))))), which I want to decrypt. However I have yet to find any tools which can decrypt this. Right now my best idea is to write a python script ...
15
votes
1answer
3k views

Why use argon2i or argon2d if argon2id exists?

So I am currently working on a github project of mine and I want to implement Argon2 . The Problem is that I dont really know a lot about it . Internet research is not really helpful , because Argon2 ...
16
votes
3answers
1k views

Why did Argon2 win the PHC?

I've been reading up on Argon2 (and, to a lesser extent, other recent password hashers). I'm trying to understand why it won the competition versus the other finalists, like Catena, Lyra2, Makwa or ...