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From the article: 

Softips: A Fistfull of Reasons for Compressing Data Using the 7z Archive Format

"7-Zip also supports encryption with the AES-256 algorithm. This algorithm uses a cipher key with length of 256 bits. To create the key, 7-Zip uses a derivation function based on an SHA-256 hash algorithm. A key derivation function produces a derived key from a text password defined by the user. To increase the cost of an exhaustive search for passwords, 7-Zip uses a big number of iterations to produce the cipher key from the text password."

The following table taken from the above article gives the time taken to crack a simple password created using only lower case letters. When using a larger character set, that includes all printable characters available on the keyboard, these numbers become greater. For such a set, 10 characters correspond to the 14 characters Password Length entry, which provide a high degree of security.

Password Length Single User Attack Organization Attack
1 2 s 1 s
2 1 min 1 s
3 30 min 1 s
4 12 hours 1 s
5 14 days 1 s
6 1 year 1 s
7 10 years 1 s
8 19 years 20 s
9 26 years 9 min
10 37 years 4 hours
11 46 years 4 days
12 55 years 4 months
13 64 years 4 years
14 73 years 13 years
15 82 years 22 years
16 91 years 31 years
17 100 years 40 years