# Tag Info

129

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 ...

119

You can't hide your IP address on the internet. They aren't secret. Pretty much what @DeerHunter said. It's trivial to scan the entire internet. If they want, they can target all-known digital ocean droplets that are online. They can do this on a timer so that when you go offline, or online, it will just keep trying as those may be high-value targets that ...

68

Sure it's possible, but it doesn't really help. The number of possibilities is just too large. Consider that a 256-bit key has 2256 possible values. That's 12✕1076, or 12 followed by 76 zeroes. If we generously assume that a computer can test a trillion (that's 1012) possible keys a second, and that we have a trillion computers (where will we get them from?)...

67

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 ...

64

Yes it looks like you are experiencing a brute force attack. The attacker is in on a class B private address, so it is likely to be someone with access to your organization's network that is conducting the attack. From the usernames it looks like they are running though a dictionary of common usernames. Have a look at 'How to stop/prevent SSH bruteforce' (...

58

A simple answer, NO. It is like asking, if I know, that x%4 = 3, is it possible to find the value of x? No. Surely, there would be infinite values of x satisfying this equation, but you wouldn't simply know which one is correct. Similarly, many(or infinite) video clips could result in a given hash value(obviously, infinite video clips have to be mapped to ...

54

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 ...

52

The IPv4 address space is limited to only 4,294,967,296 addresses.[note 1] Given enough bandwidth, it becomes trivial to scan every single IP address out there, especially if you're the owner of a botnet consisting of thousands of hacked devices. With IPv6[note 2], things are a bit more tricky: with over 300,000,000,000,000,000,000,000,000,000,000,000,000 ...

52

You really can't, if you're just encrypting / decrypting text. If you know that the encrypted string is "kdo" and the encryption method is a Caesar shift, the plaintext could just as easily be "IBM" as "HAL". You'd have to have some idea of what the plaintext "looks like". For instance, if you know the plaintext is the name of a Stanley Kubrick character, ...

49

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 ...

49

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" scenario,...

49

I'm choosing to assume you're asking why it's a risk rather than how to hack. GPUs are very good at parallelising mathematical operations, which is the basis of both computer graphics and cryptography. Typically, the GPU is programmed using either CUDA or OpenCL. The reason they're good for brute-force attacks is that they're orders of magnitude faster than ...

49

In some cases yes, you can guess the most frequently used keys by the wear marks. That's how I know that apparently I use the L, M, N, A and E keys a lot - the keys are now just black, the letter is faded. But most people don't use the keyboard for just their passwords, and the wear pattern is also influenced by the stroke direction, angle and pressure - ...

47

People have given great answers here that directly answer your question, but I'd like to give a complementary answer to explain more in depth why GPUs are so powerful for this, and other applications. As some have pointed out, GPUs are specially designed to be fast with mathematical operations since drawing things onto your screen is all math (plotting ...

40

Yes, this looks exactly like a brute-force attack and after googling admins phoenix piglet rainbow it looks like this is the wordlist the attacker is using: https://github.com/hydrogen18/kojoney/blob/master/fake_users Check out line 116 onwards. The wordlist is being used in the exact same order. This appears to be a generic wordlist as it also present on ...

39

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 ...

38

I did a calculation on this one once. Let's assume AES can only be broken using brute force. Clearly we are going to need a counter, which counts from 0 to 2^256-1, and on average it will need to count to 2^255. Running this counter takes energy. How much energy does it take? As it turns out, there is a thermodynamic limit here, Landauer's principle. ...

35

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 "...

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

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 ...

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 ...

30

I would say that you should do both. If you only rate limit on IP address, an attacker controlling a bot net could brute force an account with a weak password. If you have 10 000 computers with unique IPs and each one is allowed four attempts per hour you can try almost a million passwords per day. If you only rate limit on username, an attacker with a ...

30

Any practical brute-force algorithm will take into account the method a password was generated with. If a password was randomly generated. You should assume brute-force algorithm also to be truly random. You don't know what it is, you can't claim one password is faster to find than the other, you can only tell that on average passwords would be discovered ...

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 frame)....

28

Yes, you're being bruteforced. But I don't think you should worry about any bruteforce you detect coming from the internet. You should, however, be worried about brute-force attacks coming from your own network. Being bruteforced is very common, and as long you don't use passwords for SSH (or use good passwords), the attack won't be successful at all (...

27

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 ...

27

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 ...

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 ...

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