Questions tagged [brute-force]

An attack using every possible input to attempt to produce the correct output. Typically the method of last resort when no weakness allows the use of a more restricted input set. E.g. trying all possible (or likely) passwords, in an attempt to guess the correct one.

130
votes
10answers
257k views

Where can I find good dictionaries for dictionary attacks?

I’m wondering where I can find good collections of dictionaries which can be used for dictionary attacks? I've found some through Google, but I’m interested in hearing about where you get your ...
116
votes
10answers
16k views

How critical is it to keep your password length secret?

Is keeping your password length secret critical to security? Does someone knowing that you have a password length of say 17 make the password drastically easier to brute force?
97
votes
5answers
30k views

Someone is trying to brute-force(?) my private mail server… very… slowly… and with changing IPs

This has been going on for about 1-2 days now: heinzi@guybrush:~$ less /var/log/mail.log | grep '^Nov 27 .* postfix/submission.* warning' [...] Nov 27 03:36:16 guybrush postfix/submission/smtpd[7523]:...
92
votes
7answers
13k views

Script Kiddies - how do they find my server IP?

I've set up a site on Digital Ocean without a domain yet, so there is only the IP. Despite telling no-one of its existence or advertising it, I get hundreds of notices from fail2ban that various IP's ...
92
votes
8answers
16k views

Can secret GET requests be brute forced? [duplicate]

Say, I have on my server a page or folder which I want to be secret. example.com/fdsafdsafdsfdsfdsafdrewrew.html or example.com/fdsafdsafdsfdsfdsafdrewrewaa34532543432/admin/index.html If the ...
90
votes
9answers
18k views

Is it possible make brute-force attacks ineffective by giving false positive answers to failed log-in attempts?

I don't have any experience or scientific knowledge in security, I just wanted to ask if this is possible because I am interested in it. What if I encrypt data and every password decrypts it, but ...
68
votes
8answers
21k views

Am I experiencing a brute force attack?

When checking the auth log of a server with the command: grep sshd.\*Failed /var/log/auth.log | less I see thousands of lines like this: Jan 12 11:27:10 ubuntu-leno1 sshd[8423]: Failed password ...
64
votes
3answers
103k views

How to estimate the time needed to crack RSA encryption?

How to estimate the time needed to crack RSA encryption? I mean the time needed to crack Rsa encryption with key length of 1024, 2048, 3072, 4096, 5120, 6144, 5120, 7168, 8192, 9216, 10240, 11264, ...
58
votes
6answers
11k views

Wrong password - number of retries - what's a good number to allow?

Most sites & software seem to have a default of auto lock or time lock after 3 wrong tries. I feel that the number could be much higher - not allowing retries is mainly to prevent automated ...
51
votes
7answers
24k views

How are GPUs used in brute force attacks?

I have read that GPUs can be used in brute force attacks? But how can this be done and is there a need for any other hardware devices (hard disks for instance)? Note: I'm more interested in web ...
51
votes
4answers
48k views

Are salted SHA-256/512 hashes still safe if the hashes and their salts are exposed?

Scenario: a database of hashed and and salted passwords, including salts for each password, is stolen by a malicious user. Passwords are 6-10 chars long and chosen by non-technical users. Can this ...
45
votes
7answers
52k views

Invalid users trying to log in to my server

I'm seeing a lot of log entries that appear to be failed login attempts from unknown IP addresses. I am using private and public keys to log in with SSH but I have noticed that even with private ...
41
votes
9answers
8k views

Do non-keyboard characters make my password less susceptible to brute forcing?

I can put characters in my password for which there are no keys on a keyboard. On Windows, Alt+#### (with the numpad) inserts the character for whatever code you type in. When I put this in a ...
41
votes
3answers
7k views

Should Failed Login Attempts Be Logged

Should failed login attempts be logged? My doubt is that if there is a distributed brute force attack, it might exhaust the available disk space of the database. What is the best practice for this? I'...
39
votes
8answers
5k views

Find matching phone numbers without actually knowing them

We have a mobile app that, given two users, needs to let them see what common contacts they have based on their phone numbers. How can we do this in a cryptographically secure way and respecting the ...
38
votes
8answers
14k views

Is brute force a probable threat even if you enable CAPTCHA and rate limit logins?

Let's assume CAPTCHA is enabled with account lock out control (after five continuous failed attempts, the account will be locked for 15 min) on a system. Is brute force still a probable threat?
36
votes
7answers
5k views

How to know if a file is decrypted or not

For school, I have to do an exercise in which I have to decrypt files by brute force attack. There are a lot of different files in different file formats. The files have been encrypted using XOR or ...
36
votes
7answers
8k views

Is it possible to improve brute-force guessing of a password with a picture of the keyboard used to enter it?

Is it a bad idea to post a photo of your keyboard to social media? Can I look at a photo of a keyboard and determine the password of an account? Assuming a certain (set of) password(s) is the most ...
33
votes
5answers
8k views

SSH - If Eve has the passphrase and public key, can she derive the private key?

I have used ssh-keygen for creating an RSA 4096-bit SSH private and public key pair. I used a passphrase for the private key. If an attacker, Eve, knows the passphrase in addition to the public key: ...
33
votes
2answers
36k views

Why are GPUs so good at cracking passwords?

What is it about GPUs that lets them crack passwords so quickly? It seems like the driving force behind adopting good key-derivation functions for passwords (bcrpyt, PBKDF2, scrypt) instead of ...
30
votes
12answers
8k views

Could I recover the content of file from its checksum/hash?

Let's say I have a video file that is split into multiple parts. Each piece is 2 Megabytes. I also have a list of the *insert hash name here* for each piece and also for the full file. Now assume ...
30
votes
5answers
2k views

What are the security implications of storing password blacklist?

I want to add a password blacklist that would prevent the 1000 most common passwords from being used in order to mitigate shallow dictionary attacks. Is there any negative implication of storing this ...
27
votes
3answers
5k views

Use multiple computers for faster brute force [duplicate]

I've watched Mr. Robot lately and can't stop thinking why it was so hard to decrypt files encrypted using AES encryption with a 256-bit key. Let us say the only method to find the key is through brute ...
27
votes
1answer
9k views

How does the attacker know what algorithm and salt to use in a dictionary attack?

I am curious about password cracking methods like dictionary and brute force attacks. Nowadays passwords are stored as hashes and not plaintext on the server. Then how can the plaintext passwords in ...
27
votes
4answers
23k views

how long does it take to actually generate rainbow tables?

I've been reading up about rainbow tables as I think they're quite interesting cause they're actually a pretty simple concept. Anyway, I was wondering, has anyone been involved in actually generating ...
27
votes
11answers
9k views

Best password strength checker

In XKCD #936: Short complex password, or long dictionary passphrase? Jeff claimed that password cracking with "dictionary words separated by spaces", or "a complete sentence with punctuation", or "...
26
votes
8answers
6k views

How to respond to a SSH brute force attack on a single VPS?

I logged onto my VPS this morning to find millions of failed login attempts for the root user and other users that don't even exist. I took the below measures to try and obfuscate the attackers ...
26
votes
4answers
8k views

How practical is it to bruteforce a 10-digit number via URL

Example URL www.[somewebsite].com/[10_digit_number] Getting the correct number loads a page. I know there would be 10 billion possible digits to choose from, but how long would it take? What are the ...
26
votes
2answers
37k views

What's the purpose? Strange login attemps “sshd[***] Received disconnect from **.**.**.**: 11: Bye Bye [preauth]”

I've seen something like: sshd[***]: Invalid user oracle from **.**.**.** // 1st line sshd[***]: input_userauth_request: invalid user oracle [preauth] // 2nd line ...
25
votes
6answers
9k views

What would be the key size for a picture used as a key?

I'm working on a cryptosystem that uses colour pictures as keys for encryption. I'm trying to guess what is the key size of my cryptosystem in order to find the feasibility of a brute force attack. My ...
25
votes
6answers
125k views

Is it possible to brute force all 8 character passwords in an offline attack?

This article states: Brute-force techniques trying every possible combination of letters, numbers, and special characters had also succeeded at cracking all passwords of eight or fewer characters. ...
25
votes
5answers
10k views

What's the practical limit for rainbow-table based bruteforce?

Say we have a hash of a password. The password can be considered to be made of of totally random characters and has a fixed length of N. The hash is SHA1(password+salt), where the salt is of length M. ...
24
votes
3answers
10k views

Is this what a brute force SSH attack looks like?

I reviewed the auth.log file on my Ubuntu server to find: [preauth] Feb 22 17:39:18 code-storage sshd[17271]: Disconnected from 147.135.192.203 port 49408 [preauth] Feb 22 17:40:15 code-storage sshd[...
23
votes
3answers
7k views

Rate limit login attempts: count by IP or username

I need to limit login attempts. One option is to count attempts by IP address and then block the IP. The disadvantage is that different users may have the same IP address. Another option is to limit ...
23
votes
4answers
7k views

Should I implement incorrect password delay in a website or a webservice?

With arguments expressed in this answer, there is a few seconds delay between user enters an incorrect password and when he/she actually learns, that password was incorrect. This security solution is ...
23
votes
7answers
9k views

Are reCAPTCHA enough to prevent brute-force password guesses?

I was wondering if reCAPTCHA were strong enough to prevent BruteForce from bots or if I needed to add more security, such as sending a unique mail to the user every 5 tries that someone try to log on ...
23
votes
3answers
50k views

Why does Hydra return 16 valid passwords when none are valid?

I've been playing around with Hydra and DVWA and I've hit a bit of a snag - Hydra responds letting me know that the first 16 passwords in my password list are correct when none of them are. I assume ...
23
votes
1answer
6k views

Timing attacks on password hashes

Timing attacks can have a devastating impact in scenarios where the secret is involved, often in cases where byte-wise array comparison is used. Now there are those that advertise using constant ...
23
votes
4answers
8k views

Protection against account lockout DoS

Any ideas on how to protect against the following scenario? Company x uses active directory for authentication of it's employees. The company has multiple authentication points that are semi-public ...
22
votes
2answers
7k views

Do Veracrypt encrypted volumes have any kind of brute force protection?

I have a 10mb encrypted volume which I made with Veracrypt and was planning to upload it to the internet. I have a pretty strong password but was worried about its protection against brute force ...
22
votes
2answers
42k views

Brute Forcing Password to a Truecrypt-encrypted file with Partial Knowledge

A while back, I encrypted a few files with Truecrypt, and stored the password in my head. Now I need to access it again, the password isn't working. I'm sure most of it is right, but I'm off by one or ...
21
votes
4answers
17k views

How is Gmail susceptible to brute-force attacks?

In the Atlantic article "Hacked!" it says: My wife’s password was judged as “strong” when she first chose it for use with Gmail. But it was a combination of two short English words followed by ...
21
votes
5answers
1k views

What concrete parameters can I change to make my passphrase-protected private gpg key more secure

There are several questions which discuss the resistance of passphrase-protected private gpg keys against brute force attacks. It seems, this kind of discussion could go on forever. Rather than ...
20
votes
5answers
7k views

Would allowing shorter passwords sometimes be more secure?

Does the act of requiring certain criteria for passwords make them easier to brute-force? It's always seemed to me that when websites limit the use of "insecure" passwords, it might make it easier ...
20
votes
5answers
107k views

How to generate dictionary for a dictionary attack?

I need to crack my own password. Advantage is that I know possible characters and maximum length. What I need is to create a dictionary. The dictionary should contain all the combos of characters ...
19
votes
7answers
1k views

Are common passwords at particular risk?

The question Should we disallow common passwords like “password” and “12345”? on User Experience immediately made me think that these common passwords were extremely dangerous not because they are ...
18
votes
5answers
12k views

How unlikely is it that a Google Doc link is guessed?

Most (if not all) of us know that a Google Doc link looks something like this: https://docs.google.com/document/d/13P3p5bA3lslqEJT1BGeTL1L5ZrQq_fSov_56jT9vf0I/edit There are becoming several tools (...
17
votes
6answers
2k views

Is there a brute-force attack similar to what they demonstrate in movies [duplicate]

Since I was a teenager (that's 20 years ago) and till now-days you see movies with professionals stealing a super-computer and use it to crack a password or a home security system using brute-force (I ...
17
votes
3answers
3k views

Why check to see if a password is already used by another user?

This is coming from a joke originally in French: Enter your password. carrot Sorry, your password must be more than 8 characters. carottegéante (giant carrot) Sorry, your ...
16
votes
5answers
10k views

What is the difference between login throttling and temporary account lockout?

I am currently working on the redesign of a login page. I have initially suggested that login be throttled whereby pauses (incremental - in number of seconds) are introduced between each failed login ...