Hot answers tagged brute-force
30
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 ...
25
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 ...
25
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 ...
23
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 ...
19
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 ...
18
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 ...
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 ...
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....
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15
There are lots of programs trawling the internet looking for vulnerable hosts. Certainly there are people who target their attacks - but starting from torrent logs will not yield very interesting targets.
Have a look at the sans.org site for basic checklists on securing your server.
15
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 ...
14
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) ...
14
I do not know if your question is about dictionary attacks in general, or dictionary attacks in the case of a WiFi network with password protection.
For the general question of dictionary attacks: there are two kinds of dictionary attacks, the online attacks and the offline attacks. An offline attack is one such that the attacker got enough data to "test" ...
13
One-Time Pad and Shamir's Secret Sharing are two examples of cryptographic algorithms, where some secret value is involved, and which are nonetheless immune to brute force, even against attackers with unlimited computing abilities. Their key feature is "lack of key redundancy": there is no way to filter out "bad" keys. This shows in the fact that OTP ...
13
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 - ...
13
These rules basically mean that instead of having one valid password for an account, there are three of them (two, if the original password already begins with an uppercase letter). Theoretically, this divides attacker effort by up to 3, but actually a bit less than that because "pASSWORD" is much less probable as a user-chosen password than "Password".
So, ...
13
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 ...
13
MS-Cache is a pretty simple format - it's an MD4 hash of the password, followed by the username in lower case, and hashed together MD4( MD4(Unicode(password)) + Unicode(tolower(username)) ). I'm not sure of the technical difference between MS-Cache and v2; but nothing I can find suggests they're not susceptible to a RainbowTable attack (in fact, Cain & ...
12
How long does it take to generate a rainbow table for a very simple hash, using just a single iteration? It takes one hour! Or less, if you want it to.
While the answers above are entirely correct, there is one important development that they're not mentioning. Amazon EC2 and other 'cloud computing' server providers.
Today everybody with a credit card can ...
12
John the Ripper works by trying out possible passwords, very quickly. It will not always break a DES-based crypt, or at least not easily.
With the DES-based hashing function, passwords may have up to 8 characters, and only 7 bits are used for each character (the upper bit is ignored). Considering that the password is typed at some point by a user on a ...
12
For most cracking attacks, the average attack cost is about half the cost of the worst case. Simply put, if there are N possible passwords, you will hit the right one after about N/2. Note that this is an average: you can always "get lucky" or "get unlucky" on any single instance. This can be quantified: the probability of finding the right password after ...
12
There are a few ways I can think of.
Require certain character combinations
This is a commonly used technique. Require users to input a certain combination of characters like a mix of capitalized words, non-capitalized words, numbers and symbols. Enforce a minimum password length. Do not be overly restrictive though, as it might force users to mix ...
12
For a simple solution I would say to implement an exponentially increasing delay per user per IP address.
Required delay between attempts 1 and 2 from IP a.b.c.d for user x: 1 seconds
...attempts 2 and 3: 2 seconds
...attempts 3 and 4: 4 seconds
...
...attempts 7 and 8: 1 minute 4 seconds
That way an adversary can't DoS access from an IP address or an ...
11
This is a good summary article on CATPCHA:
http://www.smashingmagazine.com/2011/03/04/in-search-of-the-perfect-captcha/
I think you are right not to use CAPTCHA. Research has show that CAPTCHA can lower your conversion rates by 3% and potentially up to 30%. Even employing someone to manually filter or using mechanical turk, yourmaninindia.com etc maybe ...
11
Short answer: The easiest method would be to use the prime number theorem, but be aware it's an approximation. Estimate how long it would take you to try each of those primes; time per prime*number of primes gives you the total time. This will give you an estimate for brute force searching.
You could also use the running time estimation for the quadratic ...
11
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 ...
10
So because I had to know I generated an NTLM rainbow table using the non print character alt 0160 (and non-keyboard represented)0161-0164. The table recognized the non-print character in hex.
The table was able to recognize the non-print character after dumping the hash. (It was a dummy account with a 4 character password for demonstration purposes)
...
10
The salt may be considered public practically by definition.
As for what hash to use and how "safe" it is, I would stick with the recommendations NIST makes for U.S. government agencies. As the Wikipedia article says:
SHA-1 is being retired for most government uses; the U.S. National Institute of Standards and Technology says, "Federal agencies should ...
10
Sometimes people estimate how long it will take to crack a password based on the worst case; sometimes, based upon the average time to crack it. Usually, the average time to crack the password is half of the worst-case time.
Sure, it's possible someone could get lucky and crack the password a lot quicker than expected. Heck, no matter how strong your ...
10
If all the access is via SSL, then it's reasonably secure.
Basic authentication without SSL only sends the username/password as base64 encoded - so it's trivial to extract the tokens via MITM or sniffing.
Digest authentication without SSL is a lot better (a challenge based mechanism) but still not as secure as an encrypted connection. However there are few ...
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