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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.

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139 votes
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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 ...
Chris Dale's user avatar
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126 votes
10 answers
18k 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?
Crizly's user avatar
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102 votes
5 answers
32k 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]:...
Heinzi's user avatar
  • 3,778
93 votes
6 answers
14k 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 ...
microwth's user avatar
  • 2,483
93 votes
8 answers
17k 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 ...
Kargari's user avatar
  • 921
91 votes
9 answers
19k 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 ...
Tweakimp's user avatar
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71 votes
3 answers
128k 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, ...
Predator's user avatar
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67 votes
8 answers
28k 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 ...
syldor's user avatar
  • 761
67 votes
4 answers
16k views

How did the brute-forcers get my IP address so quickly?

This is probably a massive noob question, but Google results aren’t being helpful and I couldn’t find something specific here. I made this server that just hosts IRC, HTTP and SSH for some friends. I ...
Architect's user avatar
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59 votes
6 answers
16k 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 ...
user93353's user avatar
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56 votes
7 answers
72k 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 ...
mk_89's user avatar
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53 votes
7 answers
38k 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 ...
Mahmood Muhammad Nageeb's user avatar
52 votes
4 answers
52k 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 ...
Seppo Erviälä's user avatar
43 votes
9 answers
9k 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 ...
jnm2's user avatar
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42 votes
1 answer
19k 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 ...
andjava's user avatar
  • 608
42 votes
3 answers
11k 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'...
John L.'s user avatar
  • 741
39 votes
8 answers
6k 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 ...
liviucmg's user avatar
  • 493
38 votes
8 answers
17k 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?
Sayan's user avatar
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37 votes
2 answers
9k views

When could 256 bit encryption be brute forced?

Assuming quantum computing continues to improve and continues to perform like this: ... quantum computer completes 2.5-billion-year task in minutes is it reasonable to expect that 256 bit encryption ...
stevec's user avatar
  • 1,300
36 votes
7 answers
9k 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 ...
formicophobia's user avatar
35 votes
7 answers
7k 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 ...
juan michelle's user avatar
35 votes
2 answers
43k 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 ...
Nick's user avatar
  • 455
34 votes
5 answers
7k views

Does it matter if a brute force search for a password returns a collision and not the password?

Assume the following very basic hashing algorithm. h(k) = k mod 17 Let's say we create a password 12345 for a website that uses this very basic hashing algorithm. That would yield the hash of 3. ...
MikeSchem's user avatar
  • 2,351
34 votes
5 answers
24k 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 (...
Wayne Werner's user avatar
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34 votes
2 answers
51k 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 ...
iceX's user avatar
  • 443
33 votes
5 answers
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: ...
unseen_rider's user avatar
32 votes
12 answers
15k 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 ...
beppe9000's user avatar
  • 565
30 votes
5 answers
3k 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 ...
Gajus's user avatar
  • 553
28 votes
3 answers
7k 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 ...
Mero55's user avatar
  • 845
28 votes
6 answers
175k 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. ...
Stephen Ostermiller's user avatar
28 votes
4 answers
11k 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 ...
trejder's user avatar
  • 3,639
28 votes
3 answers
86k 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 ...
DKNUCKLES's user avatar
  • 9,217
27 votes
4 answers
28k 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 ...
stickman's user avatar
  • 1,590
27 votes
3 answers
15k 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 ...
Moshe Shaham's user avatar
27 votes
11 answers
12k 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 "...
Misha's user avatar
  • 2,789
26 votes
4 answers
11k 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 ...
test's user avatar
  • 289
26 votes
5 answers
12k 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. ...
mhswende's user avatar
  • 866
26 votes
5 answers
2k 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 ...
Martin Vegter's user avatar
25 votes
6 answers
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 ...
Daniel Esteban Ladino Torres's user avatar
25 votes
8 answers
8k 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 ...
Aage Torleif's user avatar
25 votes
3 answers
15k 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[...
David Kamer's user avatar
24 votes
7 answers
11k views

After a password leak, is there a Levenshtein distance from which one a newly derivated password can be considered safe?

After a password leak, is there a Levenshtein distance from which one a newly derivated password can be considered safe? I assume yes, given that if e.g. the word was "password", and the new ...
kaiya's user avatar
  • 452
24 votes
7 answers
18k 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 ...
JohnnyBgud's user avatar
24 votes
2 answers
55k 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 ...
Robyn's user avatar
  • 241
24 votes
4 answers
12k 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 ...
Josh Brower's user avatar
  • 1,387
23 votes
2 answers
20k 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 ...
Eka's user avatar
  • 569
22 votes
5 answers
119k 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 ...
RhymeGuy's user avatar
  • 323
22 votes
3 answers
22k 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 ...
Mr. Bultitude's user avatar
22 votes
1 answer
8k 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 ...
emboss's user avatar
  • 4,348
21 votes
4 answers
9k views

Does password length / complexity make any difference if hashes are leaked?

Password length/complexity only mitigates a brute force attack, correct? In the event of a hash leak, since any algorithm is a fixed length, there could potentially be a pre-image* with a very short / ...
thegr33k's user avatar
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