| Server IP : 85.214.239.14 / Your IP : 3.148.144.139 Web Server : Apache/2.4.62 (Debian) System : Linux h2886529.stratoserver.net 4.9.0 #1 SMP Tue Jan 9 19:45:01 MSK 2024 x86_64 User : www-data ( 33) PHP Version : 7.4.18 Disable Function : pcntl_alarm,pcntl_fork,pcntl_waitpid,pcntl_wait,pcntl_wifexited,pcntl_wifstopped,pcntl_wifsignaled,pcntl_wifcontinued,pcntl_wexitstatus,pcntl_wtermsig,pcntl_wstopsig,pcntl_signal,pcntl_signal_get_handler,pcntl_signal_dispatch,pcntl_get_last_error,pcntl_strerror,pcntl_sigprocmask,pcntl_sigwaitinfo,pcntl_sigtimedwait,pcntl_exec,pcntl_getpriority,pcntl_setpriority,pcntl_async_signals,pcntl_unshare, MySQL : OFF | cURL : OFF | WGET : ON | Perl : ON | Python : ON | Sudo : ON | Pkexec : OFF Directory : /proc/2/task/2/cwd/proc/2/cwd/usr/share/doc/p7zip/DOC/MANUAL/general/ |
Upload File : |
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">
<HTML>
<HEAD>
<META http-equiv="Content-Type" content="text/html; charset=Windows-1252">
<TITLE>7z Format</TITLE>
<LINK href="style.css" rel="stylesheet" type="text/css">
</HEAD>
<BODY>
<H1>7z Format</H1>
<P><B>7z</B> is a new archive format, providing a high compression ratio.</P>
<P>The main features of the <B>7z</B> format:</P>
<UL>
<LI>Open architecture
<LI>High compression ratio
<LI>Strong AES-256 encryption
<LI>Ability to use any compression, conversion or encryption method
<LI>Supports files with sizes up to 16000000000 GB
<LI>Unicode file names
<LI>Solid compression
<LI>Archive headers compression
</UL>
<P><B>7z</B> has an open architecture, so it can support any new compression methods.</P>
The following methods currently are integrated into <B>7z</B>:<P>
<TABLE cellspacing ="2" cellpadding ="4">
<TR> <TH class="Title" width="60">Method</TH> <TH class="Title">Description</TH> </TR>
<TR> <TD class="Item">LZMA</TD> <TD class="Item">Improved and optimized version of LZ77 algorithm</TD></TR>
<TR> <TD class="Item">LZMA2</TD> <TD class="Item">LZMA-based compression method. It provides better multithreading support than LZMA</TD></TR>
<TR> <TD class="Item">PPMD</TD> <TD class="Item">Dmitry Shkarin's PPMdH with small changes</TD></TR>
<TR> <TD class="Item">BCJ</TD> <TD class="Item">Converter for 32-bit x86 executables</TD></TR>
<TR> <TD class="Item">BCJ2</TD> <TD class="Item">Converter for 32-bit x86 executables</TD></TR>
<TR> <TD class="Item">BZip2</TD> <TD class="Item">Standard BWT algorithm</TD></TR>
<TR> <TD class="Item">Deflate</TD> <TD class="Item">Standard LZ77-based algorithm</TD></TR>
</TABLE>
<P><B>LZMA</B> is the default and general compression method of <B>7z</B> format.
The main features of the <B>LZMA</B> method:</P>
<UL>
<LI>High compression ratio
<LI>Variable dictionary size (up to 4 GB)
<LI>Compression speed: about 1 MB/s on 2 GHz CPU
<LI>Decompression speed: about 10-20 MB/s on 2 GHz CPU
<LI>Small memory requirement for decompression (depends from dictionary size)
<LI>Small code size for decompression: about 5 KB
<LI>Supports multi-threading and P4's hyper-threading
</UL>
<P>The <B>LZMA</B> compression algorithm is very suitable for embedded applications.
If you want to use <B>LZMA</B> code, you can ask for consultation, custom code programming,
and required developer licenses at
<P><A href="http://www.7-zip.org/support.html" target="_blank">www.7-zip.org/support.html</A></P>
</P>
<H2>AES encryption</H2>
<P>7-Zip 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.</P>
<H2>Tips for selecting password length</H2>
<P>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.</P>
<P>The most complex task for password search attack is SHA-256 calculation.
Special SHA-256 hardware or GPU can be used to accelerate password search attack.
Now modern GPU can provide about 10 times more performance for SHA-256 calculation
than modern CPU. And special SHA-256 hardware can provide about 20 times more
performance than GPU.</P>
<P>We suppose that one user with a budget of about $2000 (for GPUs) can check
10000 passwords per second and an organization with a budget of about
10^9 USD (one thousand million US dollars) can check 3 * 10^12 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.</P>
<P>The result is this estimate of the time to succeed in an attack:</P>
<TABLE>
<TR align=center>
<TH>Password Length</TH>
<TH>Single User Attack</TH>
<TH>Organization Attack</TH>
</TR>
<TR align=center> <TD> 1</TD> <TD> 1 s</TD> <TD> 1 s</TD> </TR>
<TR align=center> <TD> 2</TD> <TD> 1 s</TD> <TD> 1 s</TD> </TR>
<TR align=center> <TD> 3</TD> <TD> 2 s</TD> <TD> 1 s</TD> </TR>
<TR align=center> <TD> 4</TD> <TD> 1 min</TD> <TD> 1 s</TD> </TR>
<TR align=center> <TD> 5</TD> <TD> 30 min</TD> <TD> 1 s</TD> </TR>
<TR align=center> <TD> 6</TD> <TD> 12 hours</TD> <TD> 1 s</TD> </TR>
<TR align=center> <TD> 7</TD> <TD> 14 days</TD> <TD> 1 s</TD> </TR>
<TR align=center> <TD> 8</TD> <TD> 1 year</TD> <TD> 1 s</TD> </TR>
<TR align=center> <TD> 9</TD> <TD> 10 years</TD> <TD> 2 s</TD> </TR>
<TR align=center> <TD>10</TD> <TD> 19 years</TD> <TD> 1 min</TD> </TR>
<TR align=center> <TD>11</TD> <TD> 28 years</TD> <TD> 30 min</TD> </TR>
<TR align=center> <TD>12</TD> <TD> 37 years</TD> <TD> 12 hours</TD> </TR>
<TR align=center> <TD>13</TD> <TD> 46 years</TD> <TD> 14 days</TD> </TR>
<TR align=center> <TD>14</TD> <TD> 55 years</TD> <TD> 1 year</TD> </TR>
<TR align=center> <TD>15</TD> <TD> 64 years</TD> <TD> 10 years</TD> </TR>
<TR align=center> <TD>16</TD> <TD> 73 years</TD> <TD> 19 years</TD> </TR>
<TR align=center> <TD>17</TD> <TD> 82 years</TD> <TD> 28 years</TD> </TR>
<TR align=center> <TD>18</TD> <TD> 91 years</TD> <TD> 37 years</TD> </TR>
<TR align=center> <TD>19</TD> <TD>100 years</TD> <TD> 46 years</TD> </TR>
</TABLE>
</BODY>
</HTML>