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Chapter 5
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  • 1. Edmond Wong Sing Huat B031110038 Khor Yong Jian B031110173 Goh Zong Wei B031110071 Fairus Binti Aziz B031110326
  • 2.  Abstract Syntax Notation (ASN.1) is an ISO standard that addresses the issue of representing, encoding, transmitting, and decoding data structures. It consists of two parts: 1. An abstract syntax that describes data structures in an unambiguous way. Use “ integers”, “character strings”, and “structures” rather than bits and bytes. 2. A transfer syntax that describes the bit stream encoding of ASN.1 data objects.
  • 3.  The main reasons for the success of ASN.1 is that it is associated with several standardized encoding rules such as: ◦ Basic Encoding Rules (BER) - X.209 ◦ Canonical Encoding Rules (CER) ◦ Distinguished Encoding Rules (DER) ◦ Packed Encoding Rules (PER) and ◦ XER Encoding Rules (XER).  These 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.
  • 5. Though initially used for specifying the email protocol within the Open Systems Interconnection environment, ASN.1 has since then been adopted for a wide range of other applications, as in network management, secure email, cellular telephony, air traffic control, and voice and video over the Internet.
  • 6. Though initially used for specifying the email protocol within the Open Systems Interconnection environment, ASN.1 has since then been adopted for a wide range of other applications, as in network management, secure email, cellular telephony, air traffic control, and voice and video over the Internet.
  • 7.  Sun Microsystems's External Data Representation (XDR) is much simpler than ASN.1, but less powerful. For instance: 1. 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. 2. In XDR, all data is transferred in units of 4 bytes. Numbers are transferred in network order, most significant byte first.
  • 8. 4 bytes of XDR message:
  • 9. 3. Strings consist of a 4 byte length, followed by the data (and perhaps padding in the last byte). 4. 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.
  • 10. " The message “£100 is about !150” could become Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=ISO-8859- 15 MIME-Version: 1.0 =A3100 is about =A4150
  • 11. or Content-Transfer-Encoding: base64 Content-Type: text/plain; charset=ISO-8859- 15 MIME-Version: 1.0 ozEwMCBpcyBhYm91dCCkMTUwCg=49
  • 12. Reduces the number of bits contained in the information. Sometimes programs need to send more data in a timely fashion than the bandwidth of the network supports. Need to compress the data at the sender and decompress it at the receiver.
  • 13. In terms of storage, the capacity of a storage device can be effectively increased with methods that compresses a body of data. The bandwidth of a digital communication link can be effectively increased by compressing data at the sending end and decompressing data at the receiving end.
  • 14. Lossless Compression – data is compressed and can be uncompressed without loss of information. These are referred to as bit-preserving or reversible compression systems. Lossy Compression – aim to obtain the best possible fidelity for a given bit-rate or minimizing the bit-rate to achieve a given fidelity measure. Most suited to video and audio compression techniques
  • 15. Lossless - Image quality is not reduced. Use in: artificial images that contain sharp- edged lines such as technical drawings, textual graphics, comics, maps or logos.
  • 16.  Lossy - reduces image quality. Cannot get the original image back & lose some information. Use in: natural images such as photos of landscapes
  • 17.  Lossless - allows one to preserve an exact copy of one's audio files Usage: For archival purposes, editing, audio quality.
  • 18.  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
  • 19. • 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.
  • 20. In the video compression literature, a frame that is coded using its predecessor is called inter frame (or just inter), while a frame that is coded independently is called intra frame (or just intra).
  • 21. • To carry sensitive information, a system must be able to assure privacy. • One way to safeguard data from attacks is encrypting the data.
  • 22. • Encryption – sender transform original information (plaintext) to another form (ciphertext) by a function that is parameterized by a key. • Decryption – reverses the original process to transform the message (ciphertext) back to its original form (plaintext).
  • 23. Plaintext Plaintext Ciphertext
  • 24. Symmetric Keys – use same key to encrypt and decrypt a message.
  • 25. Asymmetric Keys -2 keys are needed (public key and private key); 1 key to encrypt, another key to decrypt and vice versa.
  • 26. Protection Description Confidentiality Allow only authorized users to access information. Authentication Verify who the sender was and trust the sender is who they claim to be. Integrity Trust the information has not been altered No repudiation Ensure that the sender or receiver cannot deny that a message was sent or received. Access Control Restrict availability to information.