1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
|
<!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>
<P>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.</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>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.</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>2 s</TD>
<TD>1 s</TD>
</TR>
<TR align=center>
<TD>2</TD>
<TD>1 min</TD>
<TD>1 s</TD>
</TR>
<TR align=center>
<TD>3</TD>
<TD>30 min</TD>
<TD>1 s</TD>
</TR>
<TR align=center>
<TD>4</TD>
<TD>12 hours</TD>
<TD>1 s</TD>
</TR>
<TR align=center>
<TD>5</TD>
<TD>14 days</TD>
<TD>1 s</TD>
</TR>
<TR align=center>
<TD>6</TD>
<TD>1 year</TD>
<TD>1 s</TD>
</TR>
<TR align=center>
<TD>7</TD>
<TD>10 years</TD>
<TD>1 s</TD>
</TR>
<TR align=center>
<TD>8</TD>
<TD>19 years</TD>
<TD>20 s</TD>
</TR>
<TR align=center>
<TD>9</TD>
<TD>26 years</TD>
<TD>9 min</TD>
</TR>
<TR align=center>
<TD>10</TD>
<TD>37 years</TD>
<TD>4 hours</TD>
</TR>
<TR align=center>
<TD>11</TD>
<TD>46 years</TD>
<TD>4 days</TD>
</TR>
<TR align=center>
<TD>12</TD>
<TD>55 years</TD>
<TD>4 months</TD>
</TR>
<TR align=center>
<TD>13</TD>
<TD>64 years</TD>
<TD>4 years</TD>
</TR>
<TR align=center>
<TD>14</TD>
<TD>73 years</TD>
<TD>13 years</TD>
</TR>
<TR align=center>
<TD>15</TD>
<TD>82 years</TD>
<TD>22 years</TD>
</TR>
<TR align=center>
<TD>16</TD>
<TD>91 years</TD>
<TD>31 years</TD>
</TR>
<TR align=center>
<TD>17</TD>
<TD>100 years</TD>
<TD>40 years</TD>
</TR>
</TABLE>
</BODY>
</HTML>
|
