7z Format

7z is a new archive format, providing a high compression ratio.

The main features of the 7z format:

7z has an open architecture, so it can support any new compression methods.

The following methods currently are integrated into 7z:
Method Description
LZMA Improved and optimized version of LZ77 algorithm
PPMD Dmitry Shkarin's PPMdH with small changes
BCJ Converter for 32-bit x86 executables
BCJ2 Converter for 32-bit x86 executables
BZip2 Standard BWT algorithm
Deflate Standard LZ77-based algorithm

LZMA is the default and general compression method of 7z format. The main features of the LZMA method:

The LZMA compression algorithm is very suitable for embedded applications. If you want to use LZMA code, you can ask for consultation, custom code programming, and required developer licenses at


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.

Tips for selecting password length

Here is an estimate of the time required for an exhaustive password search attack, when the password is a random sequence of lowercase Latin letters.

We suppose that one user can check 10 passwords per second and an organization with a budget of about $1 billion can check 10 billion passwords per second. We also suppose that the processor in use doubles its performance every two years; so, each additional Latin letter of a long password adds about 9 years to an exhaustive key search attack.

The result is this estimate of the time to succeed in an attack:

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