Passwords are secret keys which human beings can memorize.

learn more… | top users | synonyms (1)

3
votes
1answer
714 views

What's the most secure way to derive a key from a password repeatably?

I'm trying to write a cloud storage application where everything the user uploads is unreadable by the server, encrypted client-side before being sent. Currently, the flow looks like this: User ...
3
votes
1answer
1k views

Ideal passphrase length: old diceware method (5 words) vs. your Bitcoin wallet.dat passphrase lenght (8 words) and doubling passwords?

I made a cool 5 word passphrase back then using the old Diceware method and use it as a master password. The question is as computing power increases will we need to add more and more words to our ...
3
votes
2answers
97 views

Long passwords and Bcrypt

I need to store passwords for a web application, and was looking at Bcrypt for a possible solution. After some research, it appears only the first 72 bytes influence the final hash output. While it is ...
3
votes
1answer
93 views

gpg --gen-random quality level: is higher “better”?

The GNU Privacy Guard manual pages have this to say about using the gpg --gen-random 0|1|2 count command: Emit count random bytes of the given quality level 0, ...
3
votes
1answer
126 views

Is there a practical upper limit for password rehashing?

When using PBKDF2, is there a practical upper limit to the iteration count above which we lose security? Note: If you answer “No”, that's fine. But if you answer: “There can't be an upper limit“, ...
3
votes
1answer
202 views

salting with password hash to improve security?

Would something like the following improve security (against rainbow attacks, not brute force)? Assume that $P$ is a user-chosen password, and the objective is to obtain a hash $H$ for password ...
3
votes
1answer
968 views

estimate of time required to crack sha512crypt password with JtR + OpenCL

OK, I have a shadow file with a password that I know, it is 4 letters followed by two numbers. Using John The Ripper with OpenCL support, on a laptop with AMD Radeon Mobility graphics, how long would ...
3
votes
1answer
257 views

Seed a PRNG with random data and a password

I'd like to combine a random key file with a password to generate a secure seed for a CSPRNG. The key file is assumed to have very high entropy, but the password will be whatever the user provides. ...
3
votes
1answer
42 views

Generating passwords from a master password using rules

I realize it's generally considered bad idea to use the same password everywhere. I can use icloud / lastpass to generate my passwords for me, but that leaves me clueless when I don't have access to ...
3
votes
1answer
53 views

Attacks on WinRAR volumes reusing same password?

I have quite a few WinRAR volumes that are all encrypted with the same password. The password is long and unbruteforceable, but I recently read that WinRAR uses PBDKF2 as its key-derivation function ...
3
votes
1answer
619 views

Recommended password complexity for SSH key encryption using AES-256-CBC

When protecting SSH private keys with password-based encryption, what would be a good minimum password complexity+length standard to make cracking the password too difficult to be worthwhile anytime ...
3
votes
1answer
64 views

Public SRP verifiers or public hash chain “public keys” when secret is low entropy password

I want to set up the following: An untrusted server should host user sessions and authenticate users without knowing their passwords or being capable of creating a fake user session in the user's ...
3
votes
1answer
128 views

How can I generate a good password from a SHA512 hash?

I have to change local administrator passwords on machines. I don't want to store password in a database. I have to generate a password that I can find later to connect to the machine again. So I ...
3
votes
1answer
239 views

PBKDF2 Salt and Password Ordering

I am currently reading about PBKDF2, and understand that the salt is used only once, while the password is used multiple times in the computation of the final key (see this question). How would the ...
3
votes
2answers
239 views

Using PBKDF2 twice with different argument order

I'm pretty sure this is a really bad approach (in theory), but one of my clients is doing this and I was wondering… How bad it is to perform pbkdf-2 in this way (with 2000 iterations)? ...
3
votes
1answer
4k views

Is AES restricted to only 64 characters for the key/password?

I am wondering if AES only supports 64 character passwords? When using truecrypt, the maximum character limit on passwords is 64 characters; however, when using WinRAR, the limit is 128 characters. ...
3
votes
1answer
84 views

What is wrong with simple concatenation in salted password hashes?

I once heard that if implementing a password hashing scheme, simply concatenating the password and salt together before hashing could lead to some subtle vulnerabilities, and I'm trying to figure out ...
3
votes
1answer
43 views

On the security definition of password-authenticated key exchange

I found in all PAKE papers, the security is defined as something like this: Let $Succ(A)$ be the probability that an attacker $A$ successfully distinguished the session key from a random string. Then ...
2
votes
5answers
3k views

“123456” and “password” as crack standards

I know that when we encrypt, we use standard encryption technologies and to store data it's often stored as a hash. By encrypting a common password, for example "password" using ...
2
votes
2answers
273 views

Idea for user/pass hashing to prevent rainbow tables, would it work?

I'm very new to cryptography (and security in general, for that matter), but I had an idea that I'm sure is very flawed, but is worth asking. If a computer user, online account, etc, needs to verify a ...
2
votes
2answers
368 views

Generate secure password hashes without access to PBKDF2 or bcrypt

Given is a system, which does provide only implementations of fast hash algorithms (MD5, SHA1, SHA-256, SHA-512). There is no implementation of PBKDF2, bcrypt or scrypt available. The system does ...
2
votes
1answer
199 views

How can encryption software accept password lengths which are not one of the AES key lengths?

AES comes with key sizes of 128, 192, and 256 bit. But in Truecrypt or other crypto software we can use passwords of different length, even less than 128 bit or more than 256 bit. How is this ...
2
votes
1answer
153 views

Is it true that 7zip doesn't use any salt with its KDF?

This issue claims that 7zip does not use any salt with its key derivation function: https://github.com/magnumripper/JohnTheRipper/issues/1679 If that's true, wouldn't that mean you can crack multiple ...
2
votes
1answer
317 views

XTEA: patterns in plain text

I'm using XTEA to encrypt passwords that I store in a database. (I need to be able to decrypt these passwords later to log in on another system.) But now I have noticed something: if I decrypt a ...
2
votes
1answer
80 views

Rapidly changing passwords?

Suppose you need to authenticate yourself to a program with the password - but the program's source code is public, the program doesn't have access to any private information and all your ...
2
votes
1answer
86 views

Do I need to use a CSPRNG when creating salts for user accounts?

I'm not sure about the need of using CSPRNG to create salts for each user account. I found “Cryptographically Secure Pseudo-Random Number Generator in Qt/C++ (Cross platform)” (at StackOverflow) with ...
2
votes
1answer
373 views

Strange Password Hashing

I know about PBKDF2, bcrypt, scrypt, etc. and while I'm not a crypt professional, I think I understand why are they better than just "hash(pass+salt)". But a colleague of mine surprised me with the ...
2
votes
1answer
161 views

password generation: random length or max length

In short: Is it cryptographically stronger to have a known length password of the maximum length allowed, or a random length password somewhere in the range of the longest length possible? Does the ...
2
votes
2answers
313 views

Could completely public passphrase hashes ever be reliably secure?

This is a hypothetical question and I only have a basic understanding of Cryptography. If one were to follow the very best cryptographic practices for storing passphrases, could it ever be possible ...
2
votes
2answers
590 views

Is rainbow table attack applicable to any hash?

Typically when rainbow tables are discussed MD5 hash is used as an example. It's not quite clear whether this attack is specific just to MD5 or to a certain subset of hashes or to just any hash ...
2
votes
1answer
163 views

Extension of a password hashing algorithm using Fibonacci

I am right now taking a class named Applied Cryptography and our final project is to create a password hashing method using at least one existing algorithm and then add additional steps to make it ...
2
votes
1answer
371 views

Why are some key stretching methods better than others?

I'm trying to understand why some key stretching methods are better than others. The wikipedia article presents 3 different key stretching methods: A collision prone simple key stretching ...
2
votes
2answers
257 views

What is the entropy per Diceware word if a random symbol is inserted into a random position in the word?

On the Diceware page is this little gem: For extra security without adding another word, insert one special character or digit chosen at random into your passphrase... Inserting a letter at ...
2
votes
1answer
3k views

Bcrypt VS Scrypt, Again?

I found this article on SO, but the answer was short, and the subject was closed, What i don't understand, is: Which one of the two limits memory usage to avoid custom Hardware to break the password? ...
2
votes
3answers
2k views

Dictionary attack on pass-phrases on common algorithms

I don't yet perfectly understand the difference between brute-force and dictionary attack since this differentiates one attacking the key and another attacking password: apparently attacking passwords ...
2
votes
1answer
98 views

How secure is Shamir's Secret Sharing for password sharing when attacker has t-1 shares?

I am designing protocol to share a random generated n long password between k parties using Shamir's Secret Sharing. I know that share alone does not reveal much information about the original ...
2
votes
1answer
204 views

Hashing passwords

The common way to store passwords in web applications is this form: $$hash(password||salt)$$ Does it make sense to store them in the following form instead:? $$hash_1(hash_2(...hash_n(password||salt))...
2
votes
2answers
450 views

Maximum password length in PBKDF2

Haven't found any clear cut answer in Google so its up to you guys: DK = PBKDF2(PRF, Password, Salt, c, dkLen) Here, what is the upper limit of password length? ...
2
votes
2answers
240 views

Splitting a password for dual roles [duplicate]

I would like to prompt users for a single passphrase to establish trust with separate, normally (but not always) complementary systems from one password input. I'm essentially looking for a box where ...
2
votes
1answer
82 views

How does the possible attack on passwords and salts mentioned in PKCS#5 v2.1 work?

From PKCS#5 v2.1, 4.1 Salt (page 6, emphasis by me), also in v2.0, RFC 2898: In password-based encryption, the party encrypting a message can gain assurance that these benefits are realized ...
2
votes
2answers
731 views

Using salted hash as password for easy memorization without reuse?

I had an idea earlier: Secure passwords are a) long, and b) unpredictable. A hash is both of these. Would it be safe to reuse a key between sites, and include the site's name as a salt? For example: <...
2
votes
1answer
74 views

Can the salting function complexity improve the hash robustness?

I'm quite novice in security, and all examples I saw seem to salt the password by concatenating it, or by applying a simple binary OR or XOR. So the hash is based on "salt + password", "salt | ...
2
votes
2answers
120 views

Client login without sending a password

I would love to have a system where the password is never send in plaintext (even with TLS) to authenticate a user. I've come up with this protocol, but I'd rather use something proven. Registration: ...
2
votes
1answer
98 views

How does the small n attack work?

I'm studying the Lamport's Hash one-time password scheme. This is the scheme: Alice wants to authenticate herself to Bob from a workstation that knows nothing about her. Alice only knows her ...
2
votes
1answer
235 views

Extracting a WinRAR password

If I have an original file and a WinRAR password protected .rar file containing that file, than can I extract the password?
2
votes
1answer
696 views

Strong key generation using PBKDF

I know that PBKDF2 is very useful for generating strong keys. I'm trying to know is there any additional contribution of the given password to produce even stronger keys. Which key is more secure: ...
2
votes
1answer
93 views

Is concatenated data hashed with scrypt vulunarable to a length extension attack?

scrypt takes a salt, and a password plus some cost paramters to generate a key. So say we define it as this: key = scrypt(password, salt, cost) I am interested ...
2
votes
2answers
654 views

Which is more secure, using just bcrypt or SRP?

OK, here's the two different ways I was thinking about making the authentication for the login thing to store the passwords securely. The first is the following. Client hashes password bcrypt(...
2
votes
2answers
212 views

How can I store a combination of multiple pass phrases?

Let's assume we have 2 phrases, one is the real password from a user, and the other is generated from the real password and almost impossible to guess. You would need both to authenticate a user. What ...
2
votes
1answer
68 views

Salting in asp.net?

I have spent the past hour reading up on salting and still don't understand how it is achieved. Forgive me if im wrong, but the way I am thinking of salting is, storing an ArrayList of random strings ...