What is security?
A computer operating system stores and processes information in the form of electronic data. In doing so, a computer operating system (also known as an operating system, a computer system, or simply a system) provides an interface between you, the user of the computer, and the computer. An operating system provides you with commands, library routines, functions, and programs that allow you to tell the computer how to store and process the information that belongs to you.
The need for computer security comes mainly from the multiuser nature of computer systems. If every computer user had a locked office containing a private computer, then there would be no need for a secure operating system. But most computer systems have many users who share resources. The security mechanisms in UnixWare provide for the controlled sharing of computer resources, and therefore provide security. Even single-user systems require security if they are eventually used to export information.
Security, for a computing system, means that the information on the system is protected from unauthorized disclosure. For the purposes of this discussion, security also encompasses the concept of integrity, that is, the assurance that information is protected from unauthorized modification or corruption. There are many ways in which the security of a computer system can be violated. Unauthorized access to read or write files can be the result of the abuse of privileges by users or administrators malicious programs that surreptitiously gain privileges or access to files idle browsing of files that are inadequately protected by existing security mechanisms
To perform its storage and processing functions correctly, a computer system must keep data separate from other data and must also restrict access to data. Computer systems typically have mechanisms that identify users to the system, keep data separate, and limit access to data. By making access decisions, these mechanisms enforce rules about who can access what, supplying basic security.
Most computer systems make access decisions based on a unique identity assigned to each user on the system, typically known as a login. While you are logged in, all data you enter, create, and process belongs to you. Data is stored in named files on the computer system. Each file you own is kept separate from the rest of your files and from the files belonging to other users.
Retrieve by 27 February 2010 at 8 pm
( http://uw713doc.sco.com/en/SEC/_admin/_What_ Is_Security.html )
The followings are some steps regarding computer security:-
Step 2:
Click the " FILE " tab.
Step 3:
Click " SAVE AS ".
Step 4:
This is will be appear.
Step 5 :
Type any name you desire for your file.
Step 6 :
Type any password you desire for.
ZIP FILE
What is zip file?
The ZIP file format is a data compression and archive format. A ZIP file contains one or more files that have been compressed to reduce file size, or stored as-is. The ZIP file format permits a number of compression algorithms, but as of 2009, the method continues to be dominant.
The format was originally created in 1986 by Phil Katz for PKZIP,[1] and evolved from the previous ARC compression format by Thom Henderson. The PKZIP format is now supported by many software utilities other than PKZIP (see List of file archivers). Microsoft has included built-in ZIP support (under the name "compressed folders") in versions of its Windows operating system since 1998. Apple has included built-in ZIP support in Mac OS X 10.3 and later, including other compression formats.
ZIP files generally use the file extensions ".zip" or ".ZIP" and the MIME media type application/zip, although the ZIP file format has also been used by many programs, usually under a different name. Examples of this usage are Java JAR files, Mozilla Firefox Add-ons (.xpi), id Software .pk3/.pk4 files, Activity Bundles (.xo) for the Sugar learning platform, Winamp and Windows Media Player skins, OpenDocument format and Office Open XML.
Encryption
ZIP supports a simple password-based symmetric encryption system which is documented in the ZIP specification, and known to be seriously flawed. In particular it is vulnerable to known-plaintext attacks which are in some cases made worse by poor implementations of random number generators.[4]
New features including new compression and encryption (e.g. AES) methods have been documented in the .ZIP File Format Specification since version 5.2. A WinZip-developed AES-based standard is used also by 7-Zip, XCeed, and DotNetZip, but some vendors use other formats.[5] PKWARE SecureZIP also supports RC2, RC4, DES, 3DES encryption methods, Digital Certificate-based encryption and authentication (X.509), and archive header encryption.[6]
ZIP64
The original ZIP format had a 4GB limit on various things (uncompressed size of a file, compressed size of a file and total size of the archive), as well as a limit of 65535 entries in a zip archive. In version 4.5 of the specification (which is not the same as v4.5 of any particular tool), PKWARE introduced the "ZIP64" format extensions to get around these limitations. Zip64 support is emerging. For example, the File Explorer in Windows XP does not support ZIP64, but the Explorer in Windows Vista does. Likewise--some libraries, such as DotNetZip and IO::Compress::Zip in Perl, support ZIP64, while others, such as Java's built-in java.util.zip, still lack it.
Advantages and Disadvantages of the Approach
Compressing files separately, as is done in ZIP files, allows for random access: individual files can be retrieved without reading through other data. It may allow better overall compression by using different algorithms for different files. Even when confining the possibility to DEFLATE compression, the use of different compression dictionaries for each file may result in a smaller archive overall.
This approach is less well-suited, in general, to archival of a large number of small files. In the ZIP archive format, the metadata for each entry--the information about each individual entry--is not compressed. This limits the maximum achievable compression ratio, especially as the size of the individual entries diminishes and approaches the size of the metadata for the entry.
An alternate approach is used in a compressed tar archive (.tar.gz, or .tgz), in which the file data and metadata is compressed as a unit using gzip. The downside of this approach is the loss of random-access efficiency.
Combining ZIP with other file formats
The ZIP file format allows for a comment containing any data to occur at the end of the file after the central directory.[7] Also, because the central directory specifies the offset of each file in the archive with respect to the start, it is possible in practice for the first file entry to start at an offset other than zero.
This allows arbitrary data to occur in the file both before and after the ZIP archive data, and for the archive to still be read by a ZIP application. A side-effect of this is that it is possible to author a file that is both a working ZIP archive and another format, provided that the other format tolerates arbitrary data at its end, beginning, or middle. Self-extracting archives (SFX), of the form supported by WinZip and DotNetZip, take advantage of this--they are .exe files that conform to the PKZIP AppNote.txt specification and can be read by compliant zip tools or libraries.
This property of the ZIP format, and of the JAR format which is a variant of ZIP, can be exploited to hide harmful Java classes inside a seemingly harmless file, such as a GIF image uploaded to the web. This so-called GIFAR exploit has been demonstrated as an effective attack against web applications such as Facebook
What is zip file?
What is zip file?
The ZIP file format is a data compression and archive format. A ZIP file contains one or more files that have been compressed to reduce file size, or stored as-is. The ZIP file format permits a number of compression algorithms, but as of 2009, the method continues to be dominant.
The format was originally created in 1986 by Phil Katz for PKZIP,[1] and evolved from the previous ARC compression format by Thom Henderson. The PKZIP format is now supported by many software utilities other than PKZIP (see List of file archivers). Microsoft has included built-in ZIP support (under the name "compressed folders") in versions of its Windows operating system since 1998. Apple has included built-in ZIP support in Mac OS X 10.3 and later, including other compression formats.
ZIP files generally use the file extensions ".zip" or ".ZIP" and the MIME media type application/zip, although the ZIP file format has also been used by many programs, usually under a different name. Examples of this usage are Java JAR files, Mozilla Firefox Add-ons (.xpi), id Software .pk3/.pk4 files, Activity Bundles (.xo) for the Sugar learning platform, Winamp and Windows Media Player skins, OpenDocument format and Office Open XML.
Encryption
ZIP supports a simple password-based symmetric encryption system which is documented in the ZIP specification, and known to be seriously flawed. In particular it is vulnerable to known-plaintext attacks which are in some cases made worse by poor implementations of random number generators.[4]
New features including new compression and encryption (e.g. AES) methods have been documented in the .ZIP File Format Specification since version 5.2. A WinZip-developed AES-based standard is used also by 7-Zip, XCeed, and DotNetZip, but some vendors use other formats.[5] PKWARE SecureZIP also supports RC2, RC4, DES, 3DES encryption methods, Digital Certificate-based encryption and authentication (X.509), and archive header encryption.[6]
ZIP64
The original ZIP format had a 4GB limit on various things (uncompressed size of a file, compressed size of a file and total size of the archive), as well as a limit of 65535 entries in a zip archive. In version 4.5 of the specification (which is not the same as v4.5 of any particular tool), PKWARE introduced the "ZIP64" format extensions to get around these limitations. Zip64 support is emerging. For example, the File Explorer in Windows XP does not support ZIP64, but the Explorer in Windows Vista does. Likewise--some libraries, such as DotNetZip and IO::Compress::Zip in Perl, support ZIP64, while others, such as Java's built-in java.util.zip, still lack it.
Advantages and Disadvantages of the Approach
Compressing files separately, as is done in ZIP files, allows for random access: individual files can be retrieved without reading through other data. It may allow better overall compression by using different algorithms for different files. Even when confining the possibility to DEFLATE compression, the use of different compression dictionaries for each file may result in a smaller archive overall.
This approach is less well-suited, in general, to archival of a large number of small files. In the ZIP archive format, the metadata for each entry--the information about each individual entry--is not compressed. This limits the maximum achievable compression ratio, especially as the size of the individual entries diminishes and approaches the size of the metadata for the entry.
An alternate approach is used in a compressed tar archive (.tar.gz, or .tgz), in which the file data and metadata is compressed as a unit using gzip. The downside of this approach is the loss of random-access efficiency.
Combining ZIP with other file formats
The ZIP file format allows for a comment containing any data to occur at the end of the file after the central directory.[7] Also, because the central directory specifies the offset of each file in the archive with respect to the start, it is possible in practice for the first file entry to start at an offset other than zero.
This allows arbitrary data to occur in the file both before and after the ZIP archive data, and for the archive to still be read by a ZIP application. A side-effect of this is that it is possible to author a file that is both a working ZIP archive and another format, provided that the other format tolerates arbitrary data at its end, beginning, or middle. Self-extracting archives (SFX), of the form supported by WinZip and DotNetZip, take advantage of this--they are .exe files that conform to the PKZIP AppNote.txt specification and can be read by compliant zip tools or libraries.
This property of the ZIP format, and of the JAR format which is a variant of ZIP, can be exploited to hide harmful Java classes inside a seemingly harmless file, such as a GIF image uploaded to the web. This so-called GIFAR exploit has been demonstrated as an effective attack against web applications such as Facebook.
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How to compress a file..
The ZIP file format is a data compression and archive format. A ZIP file contains one or more files that have been compressed to reduce file size, or stored as-is. The ZIP file format permits a number of compression algorithms, but as of 2009, the method continues to be dominant. The format was originally created in 1986 by Phil Katz for PKZIP,[1] and evolved from the previous ARC compression format by Thom Henderson. The PKZIP format is now supported by many software utilities other than PKZIP (see List of file archivers). Microsoft has included built-in ZIP support (under the name "compressed folders") in versions of its Windows operating system since 1998. Apple has included built-in ZIP support in Mac OS X 10.3 and later, including other compression formats.
ZIP files generally use the file extensions ".zip" or ".ZIP" and the MIME media type application/zip, although the ZIP file format has also been used by many programs, usually under a different name. Examples of this usage are Java JAR files, Mozilla Firefox Add-ons (.xpi), id Software .pk3/.pk4 files, Activity Bundles (.xo) for the Sugar learning platform, Winamp and Windows Media Player skins, OpenDocument format and Office Open XML.
Encryption
ZIP supports a simple password-based symmetric encryption system which is documented in the ZIP specification, and known to be seriously flawed. In particular it is vulnerable to known-plaintext attacks which are in some cases made worse by poor implementations of random number generators.
New features including new compression and encryption (e.g. AES) methods have been documented in the .ZIP File Format Specification since version 5.2. A WinZip-developed AES-based standard is used also by 7-Zip, XCeed, and DotNetZip, but some vendors use other formats. PKWARE SecureZIP also supports RC2, RC4, DES, 3DES encryption methods, Digital Certificate-based encryption and authentication (X.509), and archive header encryption.
ZIP6 The original ZIP format had a 4GB limit on various things (uncompressed size of a file, compressed size of a file and total size of the archive), as well as a limit of 65535 entries in a zip archive. In version 4.5 of the specification (which is not the same as v4.5 of any particular tool), PKWARE introduced the "ZIP64" format extensions to get around these limitations. Zip64 support is emerging. For example, the File Explorer in Windows XP does not support ZIP64, but the Explorer in Windows Vista does. Likewise--some libraries, such as DotNetZip and IO::Compress::Zip in Perl, support ZIP64, while others, such as Java's built-in java.util.zip, still lack it.
Advantages and Disadvantages of the Approach Compressing files separately, as is done in ZIP files, allows for random access: individual files can be retrieved without reading through other data. It may allow better overall compression by using different algorithms for different files. Even when confining the possibility to DEFLATE compression, the use of different compression dictionaries for each file may result in a smaller archive overall.
This approach is less well-suited, in general, to archival of a large number of small files. In the ZIP archive format, the metadata for each entry--the information about each individual entry--is not compressed. This limits the maximum achievable compression ratio, especially as the size of the individual entries diminishes and approaches the size of the metadata for the entry. An alternate approach is used in a compressed tar archive (.tar.gz, or .tgz), in which the file data and metadata is compressed as a unit using gzip. The downside of this approach is the loss of random-access efficiency. Combining ZIP with other file formats The ZIP file format allows for a comment containing any data to occur at the end of the file after the central directory. Also, because the central directory specifies the offset of each file in the archive with respect to the start, it is possible in practice for the first file entry to start at an offset other than zero.
This allows arbitrary data to occur in the file both before and after the ZIP archive data, and for the archive to still be read by a ZIP application. A side-effect of this is that it is possible to author a file that is both a working ZIP archive and another format, provided that the other format tolerates arbitrary data at its end, beginning, or middle. Self-extracting archives (SFX), of the form supported by WinZip and DotNetZip, take advantage of this--they are .exe files that conform to the PKZIP AppNote.txt specification and can be read by compliant zip tools or libraries.
This property of the ZIP format, and of the JAR format which is a variant of ZIP, can be exploited to hide harmful Java classes inside a seemingly harmless file, such as a GIF image uploaded to the web. This so-called GIFAR exploit has been demonstrated as an effective attack against web applications such as Facebook.
There are some graphics step to make easy your task.
Step 1:
What is zip file?
Step 2:
Step 3 :
2. Perkhidamatan yang di tawarkan di internet?
Tajuk Tugasan : Perbandingan antara yahoo dan Google
Pengenalan
Terdapat beberapa kelebihan di antara Google dan Yahoo. Kedua-duanya menawarkan produk yang menarik kepada semua pelangan mereka. Dengan kata lain kedua-duanya menawarkan versi untuk kegunaan pelangan yang sama seperti (Maps, Local Search, Image Search) tetapi dapatkah kedua-dua versi ini dibezakan. Rajah di bawah akan menerangkan kebaikan dan kelemahan di antara perkhidmatan yang diberikan kepada pelangan.
JADUAL PERBANDINGAN ANTARA GOOGLE’S DESIGN DAN YAHOO’S DESIGN
RUJUKAN :
http://www.lukew.com/ff/entry.asp?189
