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Networks - Coggle Diagram

- - - - Content Distributed Network
        
        Servers and nodes will provide contents on the servers
        
        Improve content delivery and processing :
        
        Caching
        
        Step 1: Using Browser's cache on client side
        
        Step 2: Caching on node: Web proxy is a node which will respond for user, if other users have accessed the same website the site is saved on web proxy to be used by other clients prior connecting the server.
        
        Server Farms with Load Balancers
        
        Mirroring the main server for different locations
        
        DNS will provide IP address of requested URL of server for the closest area user is located with the best bandwidth
      - Peer-to-Peer Network
        
        An overlay n/w consists of computer resources without any central point of control
        
        An overlay n/w is a comp. nn/w bulit on top of another IP comp. n/w, on top of the internt
        
        Role of client and server is interchangeable
        
        example?? watch lecture
        
        Bit-Torrent
        
        A concept which shares files between peers (clients)
        
        Torrent: Is file description of content, contains information about server and list of chunks with equal pieces which contains the content, the torrent is residing on tracker server.
        
        Tracker server has the list of peers(swarm) knows about activities, such as upload and downloads.
        
        Swarm : A group of peers using tracker
        
        Seeders: Peers who have all the information on chunks
        
        The peers will upload chunks they have, and download those they don't have.
        
        The chunks(content) will be available on many peers
        
        DHTs - Distributed Hash Tables
        
        A concept that decentralizes the indexes to the contents, indexes are not on one node.
        
        Each node will access fast part of index list
        
        A mathematical method as hash is used to turn a variable length string into a fixed length number.
        
        A good hashing function will have a minimum probability of collisions (2 different strings producing the same hash output)
        
        Nodes in a P2P n/w can be found by using a key acts as identifier for the peer node
        
        Peer nodes keep a table of a limited number of known neighbors nodes in the form of hash table for routing at the application layer
        
        When the content is to be stored in an overlay n/w, the hash function is used to determine where it is stored.
        
        The key (index) is the hash of content description in file-sharing P2P n/w or simply the hash of the IP address in a P2P communication networks
        
        Chord Protocol
        
        Ring Architecture
        
        Algorithm : SHA -1
        
        Works similar to doubly linked list - keeping track of predecessor node and successor node
        
        Joining and LEaving the Ring
        
        Download content
        
        O(log n): Binary search in hash table to search from n(no. of contents key entries)
    - - 7.4.1 Digital Audio
        
        Protocols used:
        
        HTTP - Client connects to webserver, gets metafile (contains URL(IP of server) location of media
        
        RTSP - Client will connect to Media Server using TCP port 554, receives media, using RTP over TCP or UDP
        
        Media Player will decompress and display the video
        
        RTSP controls to play, pause, teardown, record, forward in zoom, youtube
        
        Error Corrention
        
        FEC : Recovery at receiver (client)
        
        Interleaving : Sampled media (voice or video) are gro
        uped in odd and even groups each in one packet and transmitted
      - 7.4.2 Digital Video
      - 7.4.3 Streaming Stored Media
      - 7.4.4 Streaming Live Media
        
        Live IPTV (TV broadcasting over Internet)
        
        Live IPTV will be buffered in Media Payer then browser will display
        
        Rate cannot be changed it is constant
        
        Multicast streaming is used, using UDP, RTP, RTCP (Multicast Routers are used in between client and Netflix data server to handle user logic.
        
        Cable operators use multicast
        
        Live Video Conferencing
        
        provided voice and video in real time over ip network
        
        Delays and Latencies
        
        packet size
        
        network delay, jitter (can be overcome by using jitter buffer)
        
        propogation Latency
        
        processing
      - 7.4.5 Real-Time Conferencing
        
        H.323 and SIP both have same features (Marketing and competitor issues)
        
        Voice over IP Protocol Stack for H.323
        
        ex. Zoom.com uses H.323
        
        TCP Port 120 : Reserved Port for H.225
        
        RAS : Authentication Request
        
        UDP : cannot acknowledge every packet or it slows down
        
        SIP: Session Initiation Protocol
        
        Setting up conferencing, telephony, multimedia (3GPP - multimedia wireless std)and other type of communication sessions on the internet
        
        eg. SKYPE
      - Introduction
- - - - Firewalls
      - VPN
      - IPsec
        
        IP Sec Headers
      - Wireless Security
        
        802.11 Security
        
        Bluetooth Security
    - - Use certificates for secure distribution of public keys
        
        A centralized online server that gives the public trusted keys if other parties will become the source of bottleneck or the failure
        
        (Certified Authority) is the org. that certifies public keys
        
        Certificates binds the public key to a person or org.
        
        An authority issues these certificates to users who asked for.
        
        The receiver of certificate can send it to certification site or a process, the site or process will send after encryption with public key and a random number to user, if the user can decrypt and send back, this shows the certificate is valid.
        
        For every session a new random number can be used.
        
        Note : Certificate can contain objects, attribute (citizenship, age)
        
        Public Key infrastructures
        
        We need Public key of a user to communicate with user, need to get certificate which contains that:
        
        Certificate Authority certificate should be approved by Regional Authority and the Root should approve Regional Authority certificate
        
        User we want to connect will provide the CA and RA certificates, we use the Root's public key to verify the top level certificate
        
        Chain of trust or certification path are the requests sent to Root.
        
        There are many roots which can provide the high level authority to users, the browsers will provide public keys of 100 Roots called trusted anchors.
        
        There is no need for a central worldwide Root.
        
        Revocation
        
        Certification Revocation list contains revoked certificates
        
        Directories
        
        Where are certificates stored?
        
        DNS can provide the certificates at the time provide the IP address.
        
        X.509 directory server can provide certificates using X.500 naming.
        
        Certificates
        
        X.509
        
        It is the std for certificates, is not required to communicate with CA, it uses encoding ASN.1 (Abstract syntax Notation 1)
        
        Format: /c=Country/O= Organisation/OU=Org Name/CN=Common Name
        
        Version
        
        Serial number
        -algo Info
        
        Issuer distinguished name
        
        Validity
        
        Subject distingueshed name
        
        Subject public key info
        
        extensions
    - - DS binding the entity (User, Company) to digital data
        
        Can be verified by receiver or by third part
        
        Calculated from data and secret key it is known only by signer (Originator)
        
        8.4.3 Message Digests
        
        Provides authentication does not encrypts the whole message
        
        Using hash algo with variable input text length the output is fixed bit length text
        
        It computes fast, very good encrypts, very strong packet integrity
        
        Originator -> Plaitext+MD -> Destination
        
        Secure Hash Algo (SHA)
        
        An algo used by MD
        
        operates on 512 bytes input texts and creates 160 bits output
        
        eg. content not secret but integrity guaranteed
        
        SHA-1
        
        SHA-2
        
        Message Digest 5 (MD5)
        
        Weakness : May create multiple outputs with same hash
        
        8.4.1 Symmetric-Key Signatures
        
        8.4.4 The Birthday Attack
        
        8.4.2 Public-Key Signatures
    - - -Different keys re used to encrypt and decrypt it is different than symmetric key
        
        Receiver uses a unique decryption key, known as private key
        
        Receiver should publish its public key for encryption
        
        Requires third party to certify public key belongs to certain entity (person, company)
        
        Public and private keys are related algorithmically
        
        8.3.1 RSA
        
        each peer needs to generate public and private key
        
        8.3.2 Other Public-Key Algorithms
    - - 8.1.5 Two Fundamental Cryptographic Principles
        
        Redundancy
        
        All messages should have redundancy information:
        
        Add capability to compute the correct message
        
        Information not required to understand the message
        
        Type of Methods
        
        Hash
        
        Cyclic Redundancy Check (CRC)
        
        Freshness
        
        Message contain timestamps, old messages will be discarded - not allowing the intruder to inject new messages
      - 8.1.4 One-Time Pads
        
        = (Convert Text String into Bits) XOR (Key Bit String)
        
        Quantum Cryptography
        
        Original Photons are transmitted through perpendiculat polarizers, 90degree
        
        Photons by receiver are using the right polarizers to reconstruct the original signal
        
        Real life Application 2014-15 : Vienna and Beijing using satellites to send message
      - 8.1.3 Transposition Ciphers
        
        Reorder the content but don't replace them
      - 8.1.2 Substitution Ciphers
        
        Easy could be broken
      - 8.1.1 Introduction to Cryptography
        
        Terms :check:
        
        Ciphering - Changing the contents of packet ( a secret way of writing code)
        
        Use Encryption key to change the content
        (Apply Encryption Key -> Plain Text -> Encrypted Text)
        
        Key length is relevant for breaking the key (64 bits, 128 bits,256 bits)
        
        Applied in 3 Levels:
        
        Physical Layer - Signal Monitoring
        
        Data Link Layer - Link Security (Check Sum)
        
        Network Layer - Firewall
        
        Transport Layer - Transport Layer Security
        
        Application Layer - Authentication
    - - Same key used for encryption and decrytion
        
        Block Cipher: convert n bits of plaintext into n bits of ciphered text in H/W or S/W
        
        Conversion could be in form of substitution or transposition
        
        Substituion:
        
        S- BOX - converts n i/p bits to m i/p bits
        
        P-BOX (permutation)
        
        Transposition : Using bit shuffling over S-BOX inputs
        
        8.2.1 DES - The Data Encryption Standard
        
        Algorithm :
        
        Function "F" scrambles half a block together with some of the key
        
        The output of "F" is then merged with other half of the block
        
        64 bits block is divided into 32 bits block and processed alternately (Feistel Function)
        
        Fesitel Function Algo:
        
        5 more items...
        
        IP (Initial Phase) Permutation
        
        Before the next round the 32 bits halves are swapped
        
        Final Phase (FP) permutation
        
        Developed By IBM
        
        Key Schedule
        
        Procedure to generate sub keys
        
        The 56 bits are split into two 28 bits segments and processed separately each is rotated left by one or two bits
        
        Each segment could be used as sub key
        
        From initial 64 bits are 56 bits used in PC-1 (Permutation Choice 1) to generate 48 bits
        
        PC2 (Permutation choice 2) will select the 48 bits generated by PC-1 from left and right 28 bits
        
        Are split into two 28 bits segments each is rotated left by one or two bits
        
        We create 16 sub keys
        
        Triple DES (ANSI X9.52)
        
        Encrypt-Decrypt-Encrypt or 2-key Triple DES (2DES)
        
        It provides 112 bits, it is sufficient for current computers, Key 1 and Key 2 are used.
        
        To be backward compatible with DES, Key1, key 2 and key 3 can be equal
        
        Encrypt-Encrypt-Encrypt or 3Key Triple DES (3TDES)
        
        Not used much due to overhead
        
        8.2.5 Cryptanalysis
        
        8.2.2 - AES - The Advanced Encryption Standard
        
        AES is replacing DES because DES has too small key size and easy to attack
        
        Rijindael Algorithm
        
        Rijindael Decryption Algorithm
        
        Reverse order of the Rijindael Encryption algorithm
        
        Rijindael Encryption Algorithm
        
        Step 2: Shift Rows
        
        1 more item...
        
        Step 3: Mix Columns
        
        1 more item...
        
        Step 1: Byte Subsitution
        
        1 more item...
        
        Step 4: Round key added
        
        It has 3 main segments:
        
        Also, used 10 rounds for 128 bits key, 12 rounds for 192bits key, 14 rounds for 256 bits key
        
        Each round uses different 128 bits key
        
        Key - 16 bytes
        
        Plaintext - places in a 16 bytes arranged in 4 columns and rows of matrix
        
        Cipher Text - an array of 16 bytes
        
        Rijindael algo is base fir AES, operates on Bytes
        
        Supports symmetric key and symmetric blocks
        
        The algorithm Supporting block size is 128 bits andkey 128, 192 or 256 bits
        
        Is a public domain algorithm, using permutation and substitution
        
        PERMUTATIONS: involve shuffling the bits
        SUBSTITUTIONS: replacing inputs by specific outputs
        
        8.2.4 Other Ciphers
        
        Steps:
        
        Phase I: Permutation of input bits
        Phase II: 6 bits decoder will select one of 8 bits and modify
        (PBOX output used in SBox)
        
        Most implementations are 64 or 256 inputs
        
        8.2.3 Cipher Modes
        
        Mono-alphabetic substitution, when same plaintext in same encrypted text out. Easy to break the key.
        
        Counter Mode
        
        Cipher Block Chaining Mode
        
        prevents the replacement of blocks in ciphered text
        
        Stream Cipher Mode
        
        used to encrypt text using cipher key, algorithm to apply on each bit
        
        Asynchronous stream cipher
        
        Cipher Feedback Mode
        
        data is ciphered in the smaller units than block size
        
        This method could be used to cipher one bit or one byte before transmission
        
        Electronic Code Book Mode
        
        Plaintext -> Cipher Text (old code books: Words -> Digits)
        
        AES and DES
        
        Plain Text divided in 8 bytes blocks and encrypted in order with one key
        
        If requires leftover Byte will be padded to 64 bits