In modern zip utilities like 7zip, you can specify a password when creating a .ZIP file. But, how secure is this? What encryption algorithm(s) are used to secure password-protected zip files?
3 Answers
7-zip uses AES-256 encrpytion for 7z/zip archives.
http://7-zip.org/7z.html says:
7-Zip also supports encryption with AES-256 algorithm. This algorithm uses cipher key with length of 256 bits. To create that key 7-Zip uses derivation function based on SHA-256 hash algorithm. A key derivation function produces a derived key from text password defined by user. For increasing the cost of exhaustive search for passwords 7-Zip uses big number of iterations to produce cipher key from text password.
The help files of 7-zip says this about the security of a passworded 7z file:
Brute force attacks are a waste of time. I won't go into details why, I will instead direct you to Jeff Atwood's blog, specifically Brute Force Key Attacks Are for Dummies.
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8Brute force attacks aren't always a waste of time, most users don't put an awful lot of thought into passwords, and a dictionary attack against the password they use can be a very effective way to decrypt a file. A brute force attack is only a waste of time (at present it becomes easier by the year) against a secure key.– Mike1980Apr 10, 2010 at 17:21
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6A brute force attack is a waste of time. Dictionary attacks are not brute force, and are a LOT faster than trying every possible combination of a set of characters up to a specific length. Apr 10, 2010 at 21:10
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+1 For posting a link to a blog with a link to a blog with that discusses an email that pertains to the original question.– OorangJul 25, 2010 at 0:36
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As secure as the length of the password:
From my personal experience trying to crack 7zip, password protected files by the combo of dictionary and brute-force attack the way to go is:
- Dictionary attack 200k^1
1.1 dictionary attack with the first letter capitalized 200k^1
1a. Dictionary and brute-force 3 digits at the back (idiot123
) 10^3*200k
1a.1 Dictionary with the first letter capitalized and brute-force 3 digits at the back (Boston777
) 10^3*200k
Less than an hour.
If above didn't fly you have less than 1 in 10 to crack with following (using cRARk
).
All numbers (0-9) 9 digits long (10^9) - will take about a day, will unlock all pins (
4-5
digits) and all dates(20191111
,10102019
)Latin lower and digits (a-z0-9) 6 symbols (25^6) will take about 2 days, have cracked some this way (
asdfaf
)Latin lower and upper and digits and . and - (a-zA-Z0-9.-) 5 symbols (60^5) will take another day, have scored some (
A.1983
)
After this point, it's a longshot (Nowadays I stop here)
- Dictionary combo 2 words 200k^2
4.1 Dictionary combo with 2 words first letter cap 200k^2
4.2 Dictionary combo 2 words space in between 200k^2
4.3 Dictionary combo with 2 words first letter cap space in between 200k^2
another two to three days
After this point just give up, lol