Specific to the security of passwords: hashing, entropy, cracking, resets, lockouts, etc.

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19
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7answers
2k views

Appropriate password requirements for a login (OpenID) service/provider/delegate/thing

This is with regards* to Stack Exchange's upcoming OpenID provider (and in particular, discussion about password requirements). Currently, password requirements are: Must contain 3 of: lower case ...
8
votes
4answers
850 views

Doesn't imposing a minimum password length make the password weaker by reducing the number of possible combinations?

I thought the strength of a password depended on the total number of possible combinations. Therefore, allowing longer passwords should be safer because you then have more possibilities. But why do ...
19
votes
4answers
4k views

The registration confirmation email contains my password: do they keep it in plaintext?

I was kind of shocked when I just received my confirmation mail from the shop where I just registered myself: they sent my username (which is my email address) and the password I typed in. The ...
9
votes
3answers
2k views

How often should passwords change?

I'm asking two very related questions As an admin what policies should be enforced regarding the frequency of password changing? I have an idea that users should be forced to change their ...
8
votes
2answers
2k views

Does bcrypt compare the hashes in “length-constant” time?

I saw this function slowEquals() while reading Salted Password Hashing - Doing it Right, which uses a byte-level xor comparison to avoid timing attacks. I was wondering whether this is what Bcrypt ...
7
votes
2answers
6k views

How expensive is it to guess a 15 character password, and should I be worried?

I'm currently using AES encryption (at home) on GNU/Linux (one of LUKS AES-256 variants with xts) and on Windows 7 (Truecrypt) with a 15 characters password (alphanumeric lowercase only plus _). ...
4
votes
8answers
819 views

Does it take longer to brute force a password starting with z than one starting with a?

I was wondering about the following: If someone tries to get my password with Brute Force, will a password starting with "a" guessed faster than one starting with "z" ? In this case assume the ...
12
votes
9answers
2k views

Why do we authenticate by prompting a user to enter both username and password? Does prompting the password only suffice?

I don't know why do we authenticate by prompting the user to enter both username and password. In my mental model, prompting password only suffices. The reason is as follows: Assume there are x ...
10
votes
3answers
2k views

What are the security implications of using TOTP for single factor authentication?

(Note: I am not actually planning to do this. This question is strictly theoretical.) TOTP is commonly used as the second factor in Two Factor Authentication. It is an open standard with available ...
6
votes
2answers
385 views

Is cascading cryptographic algorithm better than using a single one?

Am I wrong to think that scrypt(bcrypt(password)) would be better than using sole (s|b)crypt? Especially when considering two different key for the two algorithms. I am also interested in some papers....
9
votes
1answer
999 views

Would it make sense to use Bcrypt and PBKDF2 together?

I've read various opinions about whether Bcrypt or PDBKF2 is a better key derivation hashing method. The answer seems to depend on a lot of complicated factors that are not easy to analyze. Would ...
2
votes
5answers
768 views

passphrases - lowercase and dictionary words

Amid all the discussion about password length vs. complexity (summarized by the famous xkcd strip and the followup dicussion) I am trying to make up my mind about passphrases made up with dictionnary ...
34
votes
4answers
21k views

Demystifying Web Authentication (Stateless Session Cookies)

I'm currently researching user authentication protocols for a website I'm developing. I would like to create an authentication cookie so users can stay logged in between pages. Here is my first bash:...
75
votes
14answers
8k views

How to store passwords written on a physical notebook?

Answers to the question "How safe are password managers like LastPass?" suggest that storing personal passwords on a physical notebook might be a reasonable option: I know someone who won't use ...
33
votes
6answers
12k views

Length of passwords that are rainbow table safe

With large computing power (like what you can get in the Amazon cloud for example) you can generate huge rainbow tables for passwords. There also seems to be some large rainbow tables reachable that ...
57
votes
11answers
46k views

Are password-protected ZIP files secure?

Following my answer. If I can list contents of a password-protected ZIP file, check the file types of each stored file and even replace it with another one, without actually knowing the password, then ...
36
votes
15answers
7k views

Why do people think that this is bad way to hash passwords?

Well, please tell me, what's wrong with this code: $password = "hello"; $password = md5($password); for($i=1;$i<20;$i++){ $password = md5($password); } It's exactly the same as this one: ...
24
votes
2answers
1k views

Can client-side hashing reduce the denial-of-service risk with slow hashes?

When storing user's passwords that you need to verify against (but not use as plaintext) the current state of the art is: Hash the password Use a salt Use a slow hash function - bcrypt, scrypt, etc. ...
18
votes
3answers
5k views

MySQL OLD_PASSWORD cryptanalysis?

The password hash used for MySQL passwords prior to version 4.1 (now called OLD_PASSWORD()) seems like a very simple ad-hoc hash, without salts or iteration counts. See e.g an implementation in ...
17
votes
2answers
2k views

Essential things to think about before outsourcing authentication with OpenID, OAuth, or SAML

It's clear there there is no consistent set of features among any of the popular authentication providers. Below is an attempt to aggregate the similarities and differences I've noticed, but I ...
10
votes
2answers
14k views

How weak is MD5 as a password hashing function ?

A professor told us today, that MD5 is weak. I understand his chain of thought but pointed out, that IMHO MD5 is a good way to go if you would use a long (even really long) dynamic salts and static ...
26
votes
6answers
3k views

Are there secure alternatives to single-use password reset links?

We currently have what I believe to be a pretty standard scheme for dealing with password resets. Our reset links are single-use links: They expire immediately after they've been visited, even if the ...
21
votes
6answers
2k views

Hash function change

I have user account passwords stored in a database using an unsafe (old) cryptographic hash function. What is the best/usual approach to changing password hash function? Only two ideas come to my ...
26
votes
1answer
3k views

Facebook password lowercase and uppercase

Recently I logged into my Facebook account and then noticed that my caps lock was on. So I tried to log in again with and without capslock on. I got in both times. Then I tried to log in with the ...
22
votes
13answers
4k views

Why do we even use passwords / passphrases next to biometrics?

In the last couple of days there were a lot of talking about passwords and passphrases, not only here, but on several blogs and forums I follow (especially after XKCD #936 saw the light of this world)....
20
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6answers
5k views

What is a good practical (and sane) way to manage all your passwords for online sites?

I am just a mere mortal that wants to have a somewhat secure way of managing all my passwords. This is something that I have been putting off, but since LinkedIn decided to give away one of my ...
20
votes
7answers
1k views

At what length does a password stop making sense?

I'm going to recommend that our users start using a password manager and start creating strong random passwords. Though I don't know what size of a password to recommend. Is it possible for a ...
11
votes
2answers
8k views

Is it safe to store the password hash in a cookie and use it for “remember-me” login?

I want to store an encrypted string of the password hash in a cookie and use the hash to lookup the user and log them in (if they want to be remembered). Is this safe? The password is one-way hashed ...
38
votes
10answers
5k views

Is there any point in using 'strong' passwords?

Let's say I'm setting up a new account on a website. Should I bother using a strong password? My reasoning is this: Password strength is a rough measure of how long it would take to brute-force my ...
25
votes
8answers
24k views

Why do people still use/recommend MD5 if it is cracked since 1996?

It's still commonly recommended way of hashing passwords, even if it's insecurity had been proven in 1996 Therefore we suggest that in the future MD5 should no longer be implemented in ...
15
votes
6answers
5k 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 ...
14
votes
7answers
1k views

Aren't password managers still incredibly risky?

I understand the utility in having one application remember a bunch of long, randomized passwords, but all you'd need is one well-placed phishing scam or a keylogger and they get all the keys to the ...
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 ...
26
votes
12answers
8k views

How secure are passwords made of whole english sentences

I often read as an advice to build strong passwords, just to think about a sentence and then take the initial letters. For example take a nonsense sentence like "I watch Grey's Anatomy at 9.40" gives ...
18
votes
3answers
9k views

Password in file .php

My connection.php file stores the credentials to connect to the database. <?php $objConnect = mysql_connect("localhost","username","password"); mysql_select_db("selectDB", $objConnect); ?...
14
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 ...
10
votes
2answers
1k views

How should I make diceware passphrases more memorable?

I find that truly random diceware passphrase, more often than not, either contain a word that is easily misspelled or has an order that is illogical. I think there are three ways to make a diceware ...
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 ...
7
votes
6answers
4k views

Is denying login after incorrect attempts ineffective?

Generally denying login attempts after X amounts of incorrect attempts for Y amount of tries is a very basic way to prevent bruteforce attempts or malicious login attempts. Yet, surely doing this is ...
26
votes
6answers
5k views

Why do some sites prevent users from reusing their old passwords?

I have always wondered why it is that bad to reuse old passwords; it should not be the end of the world if we happen to use an old password that we previously used. After all, I believe most of the ...
12
votes
1answer
3k views

How will security need to be changed if P=NP?

If we suppose that it is found that P=NP, how will security measures need to be changed? I'd like to know the major security measures that are affected, and how they would need to be changed. We can ...
10
votes
5answers
6k views

How can one secure a password/key in source code [duplicate]

If there is a need for source code to have a password in it, how should this be secured? This is purely an example, but say there is an app that is using an API, and you don't want to expose your ...
8
votes
2answers
5k views

Practices for storing username/password in Web applications

I have read the following question: Storing password in Java application but I don't find the answers useful for my case. So here is my question somehow related to that. I have a Java Web application ...
6
votes
3answers
633 views

How can Microsoft validate a shorter password on Microsoft accounts (MSDN)?

I recently ran across this when logging into MSDN. (I saw this screen after typing my initial credentials.) I have a 20+ digit password, however there's apparently a new requirement for Microsoft ...
20
votes
8answers
3k views

Why should I hash passwords?

I've read that every good web application should hash passwords. I found many articles about hashing. So I started implementing hashing on my website and then I asked myself why should I do it? When a ...
18
votes
5answers
1k views

Is there any legal reason to save a cleartext password?

I called customer service of a well known company and discovered that the operator had the ability to view my website password in clear text on her screen. I asked her about this and she defended the ...
16
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5answers
1k views

Is it legal to log passwords from failed logins?

Is it legal to store/log mistyped passwords? How many of you have seen this happen in a log file or DB?
15
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2answers
3k views

Tamper-proof BIOS password & settings storage with Trusted Platform Module?

In the olden days, one could trivially bypass BIOS passwords on most PCs by removing the BIOS battery and clearing the CMOS. My question is: On modern PCs equipped with a Trusted Platform Module (TPM)...
8
votes
3answers
807 views

An alternative to traditional passwords: is there some merit to this idea?

If you've got a website aimed at people that are not neccessarily technically proficient, letting new users choose their own password isn't very secure because of the simple fact that a lot of people ...
8
votes
2answers
583 views

Can the human brain generate cryptographically secure random numbers?

A security conscious friend of mine was attempting to generate entropy using random dice rolls to generate a random password, and I became curious about the security of random number generators and ...