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120

Well, let's start with math: If we assume that your password consists of lowers, uppers, and numbers, that's 62 characters to choose from (just to keep the math easy, real passwords use symbols too). A password of length 1 has 62 possibilities, a password of length 2 has 62^2 possibilities, ..., a password of length n has 62^n possibilities. So that means ...


55

See this site for a summary of the key strength estimates used by various researchers and organizations. Your "512-bits in 12μs" is completely bogus. Let's see from where it comes. 1999 was the year when the first 512-bit general factorization was performed, on a challenge published by RSA (the company) and called RSA-155 (because the number consisted in ...


52

One related question that you missed in your list is this one: How critical is it to keep your password length secret? The accepted answer there (disclaimer: mine) shows that if you have a password scheme which allows all 95 printable ascii characters, then the key space ramps insanely quickly every time you increase the length of the password by 1. You ...


42

Apart from the maths detailed by @Mike, consider also that the password length leaks all over the place: When it is typed, a sneaky bystander can learn it, either by counting the '*' on the screen, or listening to the keystrokes (in the latter case, he can record the sound with his smartphone and play it as his leisure). In a classic "Web browser" ...


37

The question doesn't state how many rounds of hashing are performed. And the whole answer hinges on that point. All hash functions are unsafe if you use only one iteration. The hash function, whether it is SHA-1, or one of the SHA-2 family, should be repeated thousands of times. I would consider 10,000 iterations the minimum, and 100,000 iterations is not ...


35

It is very common. Many botnets try to spread that way, so this is a wide scale mindless attack. Mitigation measures include: Use passwords with high entropy which are very unlikely to be brute-forced. Disable SSH login for root. Use an "unlikely" user name, which botnets will not use. Disable password-based authentication altogether. Run the SSH server on ...


32

In that order of magnitude (1000 passwords), I don't see any down sides from a security point of view. If anything, I'd say it's a good idea. Granted, you'll be shrinking the pool of possible passwords which, theoretically, decreases the security. In practice, however, those most commonly used passwords will be one of the first wordlists an attacker would ...


32

For starters, that article misuses terminology. Whatever vulnerability they may be referring to it seems pretty blatant that it is not "brute force" as that would contradict the premise of that very sentence. As another answer suggested it's possible that some form of social engineering was employed, but in this case any rounds of "guessing" left would not ...


31

You don't need to find out how they got your IP - the entire Internet is constantly being scanned by malicious individuals, bots etc. If you have an FTP server on the Internet, one of these scans will find it and a whole series of attack attempts will commence. Your downside is - you can't secure an FTP server. FTP just wasn't designed to provide encryption ...


28

I assume that your intention with the failure delay is to prevent brute force attacks: if an attacker is trying to guess a user's password, she will first fail many times; if we can make those failures take a substantial amount of time longer, then it will make the attack an order of magnitude harder, and thus unlikely to succeed (in a reasonable time ...


27

What you see in the movies is a plot device to ratchet up tension, every time a character is determined it gives the audience a kick. Reality is a bit different. Brute-force attacks do exist, however it's all or nothing - you either get the whole passcode right or wrong. There's no way to know whether you have guessed a correct character. Passcodes are ...


26

A rainbow table is "just" a compact representation of a table of precomputed hash values. During the construction of the rainbow table, many possible inputs are tried and hashed. Each input which has been encountered during table construction will be successfully attacked with that table, and none other. The hash evaluation concentrates most of the table ...


26

An important one that hasn't been added to the list is the crackstation wordlist The list contains every wordlist, dictionary, and password database leak that I could find on the internet (and I spent a LOT of time looking). It also contains every word in the Wikipedia databases (pages-articles, retrieved 2010, all languages) as well as lots of ...


25

You misunderstand what remember does for pam_pwcheck; see the man page: remember=XX Remember the last XX passwords and do not allow the user to reuse any of these for the next XX password changes. XX is a number between 1 and 400. With this option, pam_pwcheck will reject attempts at reusing a password which was previously used by the same user. ...


24

Some additional ones to add to those already suggested ftp://ftp.ox.ac.uk/pub/wordlists/ - Lists by language, may be an important point depending on the locations of the users... http://www.openwall.com/passwords/wordlists/ - The openwall project lists. While not strictly a dictionary site (although it does have some) ...


24

To complete @Terry's answer: a GPU has a lot of cores (hundreds). Each core is basically able to compute one 32-bit arithmetic operation per clock cycle -- as a pipeline. Indeed, GPU work well with extreme parallelism: when there are many identical work units to perform, actually many more than actual cores ("identical" meaning "same instructions", but not ...


23

Let's say they randomly chose alphanumeric (A-Za-z0-9 no symbols) for both salt and password; e.g., the sample space is (62)^M possible salts and (62)^N passwords. Say they have a million GPUs in a farm at their disposal that can each generate a billion hashes a second (assuming a simple MD5 or SHA type hashes - bcrypt or PBKDF based hashes are much ...


20

When I put this in a password, does it pretty much guarantee that it will never be brute forced? A brute force attack on a password tends to happen one of two ways: either an attacker obtains a hashed password database, or an attacker attempts to login to a live system with a username (or other account identifier) and password. A common method of ...


19

Space reduction does occur, but not like that. Secure hash functions are supposed to behave like what a random function would do on average (i.e., a function chosen uniformly among the set of possible functions with the same input and output lengths). MD5 and SHA-1 are known not to be ultimately secure (because we can find collisions for them more ...


19

Same problem happened to me when I was playing with DVWA. The reason is that you're trying to brute-force YOUR_SERVER/dvwa/vulnerabilities/brute/index.php which needs authentication. Try to visit that page in your browser and you'll be prompted to enter a username and a password (different form from the one you're trying to brute-force) So while you're ...


18

There are mostly two kinds of attackers: the automatic, and the targeted. Automatic attackers are not humans; they are infected machines, part of various botnets, which try to expand their basis by finding other machines to infect. Their strategy is mostly random: they try random IP address for an open SSH server, then try common passwords for common ...


18

A) Yep you got it. Same in that they both result from a failed login attempt(s), though they differ in things like logging, the resulting UX implementation, and when one is used. If a user is temporarily locked out, this is email-worthy. You should send an email or text-message to them notifying them that enough failed attempts were made to warrant a ...


17

Some UX specialists says that it's not a good idea to refuse a password. One of the arguments is the one you provide : "but if you ban them, users will use other weak passwords", or they will add random chars like 1234 -> 12340, which is stupid, nonsensical and will then force the user to go through the "lost my password" process because he can't remember ...


17

Your quote describes symmetric key strength, but your counter examples (1024, 2048 bits) reference keys used for asymmetric cryptography. The number of bits required for strength is different between the two. Your quote is from section 7.1 of Applied Cryptography; if you move ahead to section 7.2, for example, you'll see Schneier's predictions on what ...


16

Not sure can it be of any help to you, but once I managed to describe entropy to a child. After I said that entropy is a measure of chaos in system (to a group of people), a 12 (year more or less) year old said he doesn't understand me. I replied with - "Well, when your room is untidy, entropy is high. But when you clean your room, entropy is low - ...


16

Short version: I think there is no danger doing short-cut comparison of salted hashes of passwords, if the salt is hidden to the attacker. Long version: Using timing attacks in this case will in no way tell an attacker more than what he would know if he had the actual stored hash and salt ... and brypt's security parameter (iteration count exponent) should ...


16

Another thing you can do is add an iptables 'bruteforce' rule. This will allow ip's to make NEW connections x times within y seconds. After these limits have been reached the packets will be dropped. This prevents brute-forces from continuously attacking your server. I have such protection on common scanned ports like FTP, SSH, IMAP, POP3, SMTP, etc.... ...


16

Kali linux is a distribution designed for penetration testing and computer forensics, both which involve password cracking. So you are right in thinking that word lists are involved in password cracking, however it's not brute force. Brute force attacks try every combination of characters in order to find a password, while word lists are used in dictionary ...



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