








Data compression (bit-rate reduction) involves encoding
information using fewer bits than the original
repre...








The lossless data compression method essentially has two steps: Analyze the files
and then eliminate the redun...










Lossy data compression is the converse of lossless data compression. In these
schemes, some loss of informa...






Data compression works by finding patterns in data that occur frequently,
and changing their representation to so...


After you encode it, it will look like ACBABBACCCBABABBAC. Notice that
this is shorter than the original, because your ...




The objective of image compression is to
reduce irrelevance and redundancy of the
image data in order to be able to ...






Lossless compression is preferred for archival purposes and
often for medical imaging, technical drawings, clip a...
Methods for lossless image compression are:
 Run-length encoding – used as default method
in PCX and as one of possible
i...






Lossy compression methods, especially when used at low bit
rates, introduce compression artifacts.
Lossy methods ...







Methods for lossy compression:
Reducing the color space to the most common colors in the image. The
selected co...


What is the so-called image compression
coding?

To store the image into bit-stream as compact
as possible and to displ...






The image file is converted into a series of
binary data, which is called the bit-stream.
The decoded receives th...
GIF – Graphics Interchange Format
 Compressed but do not lose any of the
original data (loseless)
 Limited to 256 colors...









JPEG: Joint Photographic Experts Group – an
international standard since 1992.
Compresses the data but can...








“Audio compression is a way to reduce the
size of the audio file.”
A form of data compression designed to
redu...
2 types of Audio Compression
 Lossless - allows one to preserve an exact copy
of one's audio files
Usage: For archival pu...


Codecs:
Lossless

Lossy

Free Lossless Audio Codec
(FLAC)

MP2- MPEG-1Layer 2 audio
codec

Apple Lossless

MP3 – MPEG-1...





Motion Picture Experts Group
An ISO standard for high-fidelity audio
compression.
An ISO/IEC working group, establ...


MPEG-1

-

Designed for up to 1.5 Mbit/sec.
Is used to compress video and is designed for
specially for Video CD (VCD)....

-

-

-

MPEG-4

Designed specially for the Internet.
Provides greater audio and video interactivity than
previous MPEG ...
Audio
Input

Time to
Frequency
Mapping Filter
bank

Psychoacoustic
Model

Bit
Allocation, Qu
antize and
coding

Bit stream...

-


-

MP3
The name of the file extension and also the
name of the type of file for MPEG.
A popular audio file that can...

-

-

Ogg
Is an audio compression format, comparable
to other formats used to store and play
digital music, but differs ...

-

-

WMA
Short for Windows Media Audio
WMA is a Microsoft file format for encoding
digital audio files similar to MP3 t...








Once a video signal is digital, it requires a large amount
of storage space and transmission bandwidth.
To red...








Video compression technique is used to compress the data for
these applications because it less storage space...




video compression standards do not require the
encoding of all the details and some of the less
important video deta...








To accomplish this, an application known as a “codec”
analyzes the video frame by frame, and breaks each frame...






Intra frame ( I )
-Typically about 12 frames between 1 frame
-every MB of the frame is coded using spatial redund...
Lossy
 Lossy compression reduce file size by considerably graeter
amount than lossless compression but lose both informat...
Lossless
 Lossless compression is exactly what it sounds like,
compression where none of the information is lost.
 produ...




Start by encoding the first frame using a still image
compression method.
It should then encode each successive fram...
Intraframe
 Intra frame compression is a brute-force method that
often requires significantly more CPU time than inter
fr...
Interframe
 Inter frame video compression considers frames one at
a time, seeing them only as still images. It can analyz...










Flow Control and Buffering
Temporal Compression
-Adjacent frames highly
Spatial Compression
-Nearby pixel...
Example:
 AVI: Audio Video Interleave
-use to store audio and video data in file
-formatted as .AVI
 JPEG2000: Compressi...










The ISO/IEC, or International Organization for Standardization and the
International Electrotechnical Commi...


Step 1: Add Video File



Click the +FILE button in the upper left of the program
interface. Choose the video you want...


Step 2: Choose the Format or Device Preset



Choose the desired video format or target mobile device from the list of...


Step 3: Define Quality and Size Values



Return to the source file list and click on the value displayed in
the Quali...
Step 4: Start the Video Compression



Press the Convert button to start the compression process. After the operation is
...
Alternative approaches to the data
representation problem:
1. ASN.1
2. XDR
3. MIME
Abstract Syntax Notation One (ASN.1) is a standard and notation that
describes rules and structures for representing, enco...
The notation provides a certain number of pre-defined
basic types such as:
 integers (INTEGER),
 booleans (BOOLEAN),
 c...












ASN.1 sends information in any form anywhere it needs to be
communicated digitally. ASN.1 only covers th...
The standard ASN.1 encoding rules include:
 Basic Encoding Rules (BER)
 Canonical Encoding Rules (CER)
 Distinguished E...
ASN.1's abstract syntax is similar in form to that of any high level programming language.
For example, consider the follo...










ASN.1 has been adopted in the communications protocol specification of
Telecommunications, including 3GP...






The eXternal Data Representation (XDR) is a standard for the description and
encoding of data. XDR uses a languag...
there is a user named "john" who wants to store his lisp program
"sillyprog" that contains just the data "(quit)". His fil...


MIME (Multipurpose Internet Mail
Extensions) is a standard in order to expand
upon the limited capabilities of email, a...
MIME adds the following features to email
service:
 Be able to send multiple attachments with a
single message;
 Unlimit...
MIME uses special header directives to describe the format
used in a message body, so that the email client can interpret
...


Encryption is a method used to enhance the
security of a file or message by scrambling
the contents so that it can be r...


Symmetric keys- only one, same key used to
encrypt and decrypt information transmitted.


Asymmetric keys- use receiver’s public key to
encrypt and receiver’s private key to decrypt.




Preserve confidentiality of the file or
message.
Save money on extra protection software as
the machine that uses th...






If the key to unlock the encrypted file is lost
then the data is no longer protected and
could also be lost.
Over...
Pbl1
Pbl1
Pbl1
Pbl1
Pbl1
Pbl1
Pbl1
Pbl1
Pbl1
Pbl1
Pbl1
Upcoming SlideShare
Loading in …5
×

Pbl1

957 views
861 views

Published on

Published in: Technology, Art & Photos
0 Comments
1 Like
Statistics
Notes
  • Be the first to comment

No Downloads
Views
Total views
957
On SlideShare
0
From Embeds
0
Number of Embeds
0
Actions
Shares
0
Downloads
104
Comments
0
Likes
1
Embeds 0
No embeds

No notes for slide

Pbl1

  1. 1.      Data compression (bit-rate reduction) involves encoding information using fewer bits than the original representation. The process of reducing the size of a data file is popularly referred to as data compression, although its formal name is source coding (coding done at the source of the data before it is stored or transmitted).[ Compression can be either lossy or lossless. Lossless compression reduces bits by identifying and eliminating statistical redundancy. No information is lost in lossless compression. Lossy compression reduces bits by identifying unnecessary information and removing it.
  2. 2.     The lossless data compression method essentially has two steps: Analyze the files and then eliminate the redundant data found within them. For example, if a file compressor analyzed and eliminated all the repeated words in a document file, the result would be a document with about 60 percent fewer words. Such is the case with compressed files. Your application analyzes the file and removes all the equivalent superfluous data bits, and shrinks the overall size of the file. However, if you attempted to read the article with the omitted words, it wouldn't make any sense. Therefore, the file compression applications insert placeholders where those eliminated words were. When you extract the file, the application automatically restores the repeated words to their places, making the file readable. Because no data is lost, this method is called lossless compression.
  3. 3.      Lossy data compression is the converse of lossless data compression. In these schemes, some loss of information is acceptable. Dropping nonessential detail from the data source can save storage space. Lossy data compression schemes are informed by research on how people perceive the data in question. For example, the human eye is more sensitive to subtle variations inluminance than it is to variations in color. JPEG image compression works in part by rounding off nonessential bits of information. There is a corresponding trade-off between information lost and the size reduction. A number of popular compression formats exploit these perceptual differences, including those used in music files, images, and video.
  4. 4.    Data compression works by finding patterns in data that occur frequently, and changing their representation to something short, so that the total amount of data is reduced without sacrificing any useful information. For example, suppose you have a stream of data that consists of only ones and zeros, like this: 10100001010101001. And suppose that you know that this data stream usually contains a lot more zeros than ones; that is, a stream is more likely to be 100000100000101000000 than 111110111011011111. In this case, you can develop a way of abbreviating the zeros so that they take up less space. You can define A as representing a one, B as representing a single zero, and C as representing four consecutive zeros. Now suppose you have a data stream like this: 100000100100000000000001010010000
  5. 5.  After you encode it, it will look like ACBABBACCCBABABBAC. Notice that this is shorter than the original, because your encoding method helped abbreviate long strings of consecutive zeros. This is data compression.  In order for data compression to work, the data stream must not be random. There has to be some sort of pattern in it, or you can't compress it. For example, if the stream contains ones and zeros, but there's no pattern, and neither ones nor zeroes are more common, then you can't compress the data stream, because there's nothing predictable about it.  If you want a more formal definition, data compression consists of a way of encoding a set of input messages into a set of output messages such that the most common input messages encode to the shortest output messages, and the least common input messages encode to the longest output messages. As long as the input messages are not randomly distributed, this will result in an output stream that is shorter than the input stream. It's all information theory.
  6. 6.   The objective of image compression is to reduce irrelevance and redundancy of the image data in order to be able to store or transmit data in an efficient form. Image compression may be lossy or lossless.
  7. 7.    Lossless compression is preferred for archival purposes and often for medical imaging, technical drawings, clip art, or comics. Lossless compression is possible because most real-world data has statistical redundancy. For example, an image may have areas of colour that do not change over several pixels; instead of coding "red pixel, red pixel, ..." the data may be encoded as "279 red pixels". This is a basic example of run-length encoding; there are many schemes to reduce file size by eliminating redundancy.
  8. 8. Methods for lossless image compression are:  Run-length encoding – used as default method in PCX and as one of possible in BMP, TGA, TIFF  DPCM and Predictive Coding  Entropy encoding  Adaptive dictionary algorithms such as LZW – used in GIF and TIFF  Deflation – used in PNG, MNG, and TIFF  Chain codes 
  9. 9.    Lossy compression methods, especially when used at low bit rates, introduce compression artifacts. Lossy methods are especially suitable for natural images such as photographs in applications where minor (sometimes imperceptible) loss of fidelity is acceptable to achieve a substantial reduction in bit rate. The lossy compression that produces imperceptible differences may be called visually lossless. Lossy image compression can be used in digital cameras, to increase storage capacities with minimal degradation of picture quality. Similarly, DVDs use the lossy MPEG-2 Video codec for video compression.
  10. 10.     Methods for lossy compression: Reducing the color space to the most common colors in the image. The selected colors are specified in the color palette in the header of the compressed image. Each pixel just references the index of a color in the color palette, this method can be combined with dithering to avoid posterization. In contrast to lossless compression, which retains the integrity of the original file, the so-called lossy data compression method scans the file being compressed to determine what information the file can do without. It then eliminates those bits completely, with no method to retrieve that data. This method is akin to taking picture with your camera phone, opening a photo-editing app, cropping off the edges of the picture and then sending it to a friend. The recipient of that message cannot restore the pixels you cropped off before you sent the image. Such is the case with lossy compression. While this is method is more effective at reducing the size of the file, you won't be able to restore the file to its original state when you extract the file on the back end of the process.
  11. 11.  What is the so-called image compression coding? To store the image into bit-stream as compact as possible and to display the decoded image in the monitor as exact as possible.
  12. 12.    The image file is converted into a series of binary data, which is called the bit-stream. The decoded receives the encoded bitstream and decoded it to reconstruct the image. The total data quantity of the bit-stream is less than the total data quantity of the original image.
  13. 13. GIF – Graphics Interchange Format  Compressed but do not lose any of the original data (loseless)  Limited to 256 colors  Still patented in a few countries PNG – Portable Network Graphics  Up to 48 bits worth of color  New graphic format
  14. 14.        JPEG: Joint Photographic Experts Group – an international standard since 1992. Compresses the data but can lose some of the original content (lossy). Contains millions of colors. Works with colour and greyscale images. Up to 24 bit colour images (Unlike GIF) Target photographic quality images (Unlike GIF) Suitable for many applications e.g.,satellite, medical, general photography.
  15. 15.     “Audio compression is a way to reduce the size of the audio file.” A form of data compression designed to reduce the size of audio files Audio compression can be lossless or lossy Audio compression algorithms are typically referred to as audio codecs.
  16. 16. 2 types of Audio Compression  Lossless - allows one to preserve an exact copy of one's audio files Usage: For archival purposes, editing, audio quality.  Lossy - irreversible changes , achieves far greater compression, use psychoacoustics to recognize that not all data in an audio stream can be perceived by the human auditory system. Usage: distribution of streaming audio, or interactive applications
  17. 17.  Codecs: Lossless Lossy Free Lossless Audio Codec (FLAC) MP2- MPEG-1Layer 2 audio codec Apple Lossless MP3 – MPEG-1 Layer 3 audio codec MPEG-4 ALS MPC Musepack Monkey's Audio Vorbis Ogg Vorbis Lossless Predictive Audio Compression (LPAC) AAC Advanced Audio Coding (MPEG-2 and MPEG-4) Lossless Transform Audio Compression (LTAC) WMA Windows Media Audio AC3 AC-3 or Dolby Digital A/52
  18. 18.    Motion Picture Experts Group An ISO standard for high-fidelity audio compression. An ISO/IEC working group, established in 1988 to develop standards for digital audio and video formats.
  19. 19.  MPEG-1 - Designed for up to 1.5 Mbit/sec. Is used to compress video and is designed for specially for Video CD (VCD).  MPEG-2 - - Designed for between 1.5 and 15 Mbit/sec. Similar to MPEG-1, but it can be used for more applications. Transmission rates are more than double the transmission for MPEG-1. Works with HDTV and DVD.
  20. 20.  - - - MPEG-4 Designed specially for the Internet. Provides greater audio and video interactivity than previous MPEG versions. It allows developers to control objects independently in a scene. MPEG-4 includes the capability of representing natural and synthesized sound and also support natural textures, images, photograph, natural video and animated video.
  21. 21. Audio Input Time to Frequency Mapping Filter bank Psychoacoustic Model Bit Allocation, Qu antize and coding Bit stream formatting Encoded Bit Stream
  22. 22.  -  - MP3 The name of the file extension and also the name of the type of file for MPEG. A popular audio file that can be opened in Windows Media Player and many other players. WAV WAV files are a format for sound files developed by Microsoft with a .wav file extension.
  23. 23.  - - Ogg Is an audio compression format, comparable to other formats used to store and play digital music, but differs in that it is free, open and unpatented. It uses Vorbis, a specific audio compression scheme that's designed to be contained in Ogg.
  24. 24.  - - WMA Short for Windows Media Audio WMA is a Microsoft file format for encoding digital audio files similar to MP3 though can compress files at a higher rate than MP3. WMA files, which use the ".wma" file extension, can be of any size compressed to match many different connection speeds, or bandwidths.
  25. 25.     Once a video signal is digital, it requires a large amount of storage space and transmission bandwidth. To reduce the amount of data, several strategies are employed that compress the information without negatively affecting the quality of the image. Storing and transmitting uncompressed raw video is not an efficient technique because it needs large amounts of storage and bandwidth. Digital Versatile Disk (DVD), DSS, and internet video, all use digital data because it take a lot of space to store and large bandwidth to transmit
  26. 26.      Video compression technique is used to compress the data for these applications because it less storage space and less bandwidth to transmit data. With efficient compression techniques, a significant reduction in file size can be achieved with little or no adverse effect on the visual quality. The video quality can be affected if the file size is further lowered by raising the compression level for a given compression technique. Videos are sequences of images displayed at a high rate. Each of these images is called a frame. Human eye can not notice small changes in the frames such as a slight difference in color. Typically 30 frames are displayed on the screen every second.
  27. 27.   video compression standards do not require the encoding of all the details and some of the less important video details are lost because lossy compression is used due to its ability to get very high compression ratios. less efficient during sequences of fast movement because fewer MBs in the same position from frame to frame. In fact, users may note video artifacts during these sequences if the file is over compressed.
  28. 28.     To accomplish this, an application known as a “codec” analyzes the video frame by frame, and breaks each frame down into square blocks known as “macro blocks.” One macro block(MB) consists of four pixels. Typically, the codec then analyzes each frame, checking for changes in the MBs. Areas where the MBs do not change for several frames in a row are noted and further analyzed. If the video compression codec determines that these areas can be removed from some of the frames, it does so, thus reducing overall file size.
  29. 29.    Intra frame ( I ) -Typically about 12 frames between 1 frame -every MB of the frame is coded using spatial redundancy Predictive frame ( P ) -Encode from previous I or P reference frame -most of the MBs of the frame are coded exploiting temporal redundancy in the past Bi-directional frames ( B ) -Encode from previous and future I or P frames -most of the MBs of the frame are coded exploiting temporal redundancy in the past and in the future
  30. 30. Lossy  Lossy compression reduce file size by considerably graeter amount than lossless compression but lose both information and quantity.  The compressed file has less data in it than the original file.  It can lose a relatively large amount of data before you start to notice a difference.  Lossy compression makes up for the loss in quality by producing comparatively small files.  For example, DVDs are compressed using the MPEG2format, which can make files 15 to 30 times smaller, but we still tend to perceive DVDs as having high-quality picture.
  31. 31. Lossless  Lossless compression is exactly what it sounds like, compression where none of the information is lost.  produces a less compressed file, but maintains the original quality.  reducing the file size by encoding image information more efficiently.  If file size is not an issue, using lossless compression will result in a perfect-quality picture.  For example, a video editor transferring files from one computer to another using a hard drive might choose to use lossless compression to preserve quality while he or she is working.
  32. 32.   Start by encoding the first frame using a still image compression method. It should then encode each successive frame by identifying the differences between the frame and its predecessor, and encoding these differences. If the frame is very different from its predecessor it should be coded independently of any other frame.
  33. 33. Intraframe  Intra frame compression is a brute-force method that often requires significantly more CPU time than inter frame, but it can achieve a better balance between file size and quality loss.  occurs within individual frames  designed to minimize the duplication of data in each  picture(Spatial Redundancy)
  34. 34. Interframe  Inter frame video compression considers frames one at a time, seeing them only as still images. It can analyze brightness and color and search for areas that can be optimized, but it does not consider macro blocks.  compression between frames  designed to minimize data redundancy in successive  pictures(Temporal redundancy)
  35. 35.        Flow Control and Buffering Temporal Compression -Adjacent frames highly Spatial Compression -Nearby pixels often correlated(as in still images) Discrete Cosine Transform (DCT) Vector Quantization (VQ) Fractal Compression Discrete Wavelet Transform (DWT).
  36. 36. Example:  AVI: Audio Video Interleave -use to store audio and video data in file -formatted as .AVI  JPEG2000: Compression standard for still image -Lower latency -Type of lossless compression  MPEG2 & MPEG4: Video Compression Standard -widely used to DVD Discs and digital television broad casting -used in as encoder before transmission
  37. 37.      The ISO/IEC, or International Organization for Standardization and the International Electrotechnical Commission, have a group called the Moving Pictures Experts Group or MPEG. MPEG is responsible, for example, for the familiar compression formats MPEG-1, MPEG-2 and MPEG-4. The ITU-T standardizes formats for the International Telecommunications Union, a United Nations Organization. Some popular ITU-T compression formats include the H.261 and H.264 formats. There are other compression formats, such as Intel Indeo and RealVideo (based on the ITU-T H.263 codec). These are just as useful as the ones standardized by the international groups, although some video sharing websites won’t accept them. There are also a few different formats to consider when exporting for the web: MPEG4 (which includes .MV4 files), MPEG2, H.264, DivX, Quicktime, Window Media Video(WMV), etc. It’s important not to get video compression formats mixed up with media container formats. A media container is a file format that contains data that had been compressed using a video compression format. So the media container is the end product of video.
  38. 38.  Step 1: Add Video File  Click the +FILE button in the upper left of the program interface. Choose the video you want to convert in the Add File dialog box and press Open.
  39. 39.  Step 2: Choose the Format or Device Preset  Choose the desired video format or target mobile device from the list of presets. You can also use the Search function to quickly find the format or device you need. Next, choose the output folder for the compressed videos by clicking Browse and selecting the desired destination. By default, the output video will be saved in C:Users%your username%VideosMovavi Library.
  40. 40.  Step 3: Define Quality and Size Values  Return to the source file list and click on the value displayed in the Quality/Size column. A dialog box will open. Move the slider bar to adjust the output file size and bitrate to meet your needs. Note that the output video size value is only an estimate; the actual size of the converted video file may differ slightly Check out our detailed article for other ways to reduce video size.
  41. 41. Step 4: Start the Video Compression  Press the Convert button to start the compression process. After the operation is complete, the output folder with the converted video will open automatically.
  42. 42. Alternative approaches to the data representation problem: 1. ASN.1 2. XDR 3. MIME
  43. 43. Abstract Syntax Notation One (ASN.1) is a standard and notation that describes rules and structures for representing, encoding, transmitting, and decoding data in telecommunications and computer networking.
  44. 44. The notation provides a certain number of pre-defined basic types such as:  integers (INTEGER),  booleans (BOOLEAN),  character strings (IA5String, UniversalString...),  bit strings (BIT STRING),  etc., and makes it possible to define constructed types such as:  structures (SEQUENCE),  lists (SEQUENCE OF),  choice between types (CHOICE),  etc.
  45. 45.       ASN.1 sends information in any form anywhere it needs to be communicated digitally. ASN.1 only covers the structural aspects of information there are no operators to handle the values once these are defined or to make calculations with. Therefore it is not a programming language. One of the main reasons for the success of ASN.1 is that this notation is associated with several standardized encoding rules such as the BER (Basic Encoding Rules), or more recently the PER (Packed Encoding Rules), which prove useful for applications that undergo restrictions in terms of bandwidth. Encoding rules describe how the values defined in ASN.1 should be encoded for transmission regardless of machine, programming language, or how it is represented in an application program. ASN.1's encodings are more streamlined than many competing notations, enabling rapid and reliable transmission of extensible messages, this is an advantage for wireless broadband. Because ASN.1 has been an international standard since 1984, its encoding rules are mature and have a long track record of reliability and interoperability. ASN.1 is widely used in industry sectors where efficient (low-bandwidth,
  46. 46. The standard ASN.1 encoding rules include:  Basic Encoding Rules (BER)  Canonical Encoding Rules (CER)  Distinguished Encoding Rules (DER)  XML Encoding Rules (XER)  Canonical XML Encoding Rules (CXER)  Extended XML Encoding Rules (E-XER)  Packed Encoding Rules (PER, unaligned: UPER, canonical: CPER)  Generic String Encoding Rules (GSER)
  47. 47. ASN.1's abstract syntax is similar in form to that of any high level programming language. For example, consider the following C structure: struct Student { char name[50]; /* ``Foo Bar'' */ int grad; /* Grad student? (yes/no) */ float gpa; /* 1.1 */ int id; /* 1234567890 */ char bday[8]; /* mm/dd/yy */ } Its ASN.1 counterpart is: Student ::= SEQUENCE { name OCTET STRING, -- 50 characters grad BOOLEAN, -- comments preceded gpa REAL, -- by ``--'' id INTEGER, bday OCTET STRING -- birthday }
  48. 48.         ASN.1 has been adopted in the communications protocol specification of Telecommunications, including 3GPP mobile phones Intelligent Transport Systems ITS Internet voice communications technology in the VoIP Multimedia standards Security-related systems, including smart-cards and certificates - the basis for e-commerce Embedded systems communications Air traffic control
  49. 49.    The eXternal Data Representation (XDR) is a standard for the description and encoding of data. XDR uses a language to describe data formats, but the language is used only for describing data and is not a programming language. Protocols such as Remote Procedure Call (RPC) and the Network File System (NFS) use XDR to describe their data formats. XDR is an alternative to ASN.1. XDR is much simpler than ASN.1, but less powerful. For instance: ◦ XDR uses implicit typing. Communicating peers must know the type of any exchanged data. In contrast, ASN.1 uses explicit typing; it includes type information as part of the transfer syntax. ◦ In XDR, all data is transferred in units of 4 bytes. Numbers are transferred in network order, most significant byte first. ◦ Strings consist of a 4 byte length, followed by the data (and perhaps padding in the last byte). Contrast this with ASN.1. ◦ Defined types include: integer, enumeration, boolean, floating point, fixed length array, structures, plus others. One advantage that XDR has over ASN.1 is that current implementations of ASN.1 execute significantly slower than XDR.
  50. 50. there is a user named "john" who wants to store his lisp program "sillyprog" that contains just the data "(quit)". His file would be encoded as follows: OFFSET HEX BYTES ASCII ------ -------------0 00 00 00 09 .... 4 73 69 6c 6c sill 8 79 70 72 6f ypro characters ... 12 67 00 00 00 g... 16 00 00 00 02 .... 20 00 00 00 04 .... 24 6c 69 73 70 lisp 28 00 00 00 04 .... 32 6a 6f 68 6e john 36 00 00 00 06 .... 40 28 71 75 69 (qui 44 74 29 00 00 t).. COMMENTS ----------------------- length of filename = 9 -- filename characters -- ... and more ------ ... and 3 zero-bytes of fill filekind is EXEC = 2 length of interpretor = 4 interpretor characters length of owner = 4 -- owner characters -- length of file data = 6 -- file data bytes ... -- ... and 2 zero-bytes of fill
  51. 51.  MIME (Multipurpose Internet Mail Extensions) is a standard in order to expand upon the limited capabilities of email, and in particular to allow documents (such as images, sound, and text) to be inserted in a message.
  52. 52. MIME adds the following features to email service:  Be able to send multiple attachments with a single message;  Unlimited message length;  Use of character sets other than ASCII code;  Use of rich text (layouts, fonts, colors, etc)  Binary attachments (executable, images, audio or video files, etc.), which may be divided if needed.
  53. 53. MIME uses special header directives to describe the format used in a message body, so that the email client can interpret it correctly:  MIME-Version: This is the version of the MIME standard used in the message. Currently only version 1.0 exists.  Content-type: Describes the data's type and subtype. It can include a "charset" parameter, separated by a semicolon, defining which character set to use.  Content-Transfer-Encoding: Defines the encoding used in the message body  Content-ID: Represents a unique identification for each message segment  Content-Description: Gives additional information about the message content.  Content-Disposition: Defines the attachment's settings, in particular the name associated with the file, using the attribute filename.
  54. 54.  Encryption is a method used to enhance the security of a file or message by scrambling the contents so that it can be read only by someone who has the right key to unscramble it. For example, the information used for transaction such as purchasing online (e.g address, phone number, and credit card number) is usually encrypted to help keep it safe.
  55. 55.  Symmetric keys- only one, same key used to encrypt and decrypt information transmitted.
  56. 56.  Asymmetric keys- use receiver’s public key to encrypt and receiver’s private key to decrypt.
  57. 57.   Preserve confidentiality of the file or message. Save money on extra protection software as the machine that uses the encrypted message does not have to be secured.
  58. 58.    If the key to unlock the encrypted file is lost then the data is no longer protected and could also be lost. Overall performance of the machine that use the data will decrease since it takes a lot of energy, processing and computer power to do the encryption process. Difficult to use the encrypted message as some limitations have been placed on it.

×