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<h2 class="style1">Compression and encryption</h2>
<p>Cobian Backup 9 uses two methods of compression: the
standard Zip format or the 7zip method. The standard zip format has
restrictions about the size and the quantity of files that an
archive can handle. If the archive gets large enough Cobian Backup 9
will automatically use Zip64. This is a new enhanced format that
will handle huge archives and is compatible with the last
version of PKWARE's PKZip. You can also create archives in "Blocked"
mode. In this case, the archive will be split into blocks. This is
useful if you wish then to copy the archive into removable media
such as CDs. In this version the zip files can store your file names
as unicode.<p>
The 7zip format has the advantage of having a better compression than
ZIP, but can be a lot slower as well. In the current version of
Cobian Backup 9 you can use the 7zip format to create archives but
<span class="style2">not to update existing ones</span>. This means
that if you are not creating new backups, separated by timestamps,
then a 7zip backup <span class="style2">will always be full</span>.
If you separate the backups with timestamps, then you can have
incremental and differential backups because there is no need to
update an archive. This limitation may be eliminated on future
versions of the program.<p>
Cobian Backup 9 can use strong encryption to protect your files. You
can set a passphrase into the <a href="tasks_en.htm">Task dialog
box</a> and then you can use one of four methods to
encrypt:<p>
<font color="#FF00FF">RSA</font>-<font color="#FF00FF">Rijndael
- </font>This combined method encrypts the file using the
Rijndael method (see further) using a RANDOMLY created
256-bits key. This key is then asymmetrically encrypted with a
public 1024-bit RSA key and embedded into the resulting file. To
decrypt a file that has been encrypting using this method, you need
to use the private key. You can create a RSA key pair using
the Decrypting tool in the Tool menu.<p>
<font color="#FF00FF">Blowfish</font>: Bruce Schneier
designed Blowfish in 1993. It is a symmetric block cipher with key
lengths from 32 bits to 448 bits (Cobian Backup 9 implementation uses
a 128 bits key).The algorithm is patent, royalty and license free.
Since its introduction, Blowfish has been extensively analyzed, with
papers being published by many cryptographers. It is acknowledged as
a strong cipher, especially with the recommended number of rounds.
There have been attacks and weaknesses published on using Blowfish
with fewer rounds, but note that Cobian Backup 9 implements the
recommended number and so doesn t suffer from these problems. </p>
<p><font color="#FF00FF">Rijndael</font>: The
Rijndael encryption algorithm was the finalist in the Advanced
Encryption Standard (AES) selection process run by the National
Institute of Standards and Technology (NIST).</p>
<p>Two Belgian cryptographers, Joan Daemen and
Vincent Rijmen, devised Rijndael for the AES competition in 1998. It
is a symmetric block cipher with variable key lengths and block
sizes. In their paper, the authors promoted key lengths of 128, 192,
and 256 bits, with block sizes of 128, 192, and 256 bits. Cobian Backup 9
supports 128 bit keys and 128-bit blocks. Rijndael (pronounced
"Rhine Dahl") is interesting from a cryptographic viewpoint as,
unlike many of the ciphers invented since DES, is it not a Feistal
cipher.</p>
<p><font color="#FF00FF">DES</font>: The Data
Encryption Standard (DES) algorithm was the first encryption
standard. It was adopted as a federal standard in 1976. IBM proposed
the algorithm to the National Bureau of Standards (the precursor of
the National Institute of Standards and Technology) based upon an
earlier algorithm called LUCIFER. The National Security Agency
refined some internal aspects of the algorithm during a review
process. The algorithm is free of royalties and licenses.<p>
DES is a symmetric block cipher. The key length is usually quoted as
64 bits, but in reality only 56 bits of these 64 participate in the
encryption algorithm. The other eight bits are parity or check bits
and are stripped prior to the encryption or decryption process. The
block size is 64 bits (8 bytes).<p>During its
acceptance phase, DES was extensively analyzed and is now accepted
to be a strong algorithm, except for one area: the key length. A
56-bit key is within the reach of brute-force attacks using a
network of high-powered machines. DES should therefore only be used
for temporary data; data that would be out-of-date before someone
brute-force cracked an encrypted message or data that doesn't need a
very strong encryption.<br>
<p>Please note that encryption can be a
<font color="#FF00FF">VERY lengthy operation</font> for large
files.<p class="style1"><a href="index_en.htm">Index</a></td>
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<p class="style1">⌐2000-2008 by Luis Cobian<br>
All rights reserved</td>
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