1. 3rd Theorical
Carmen Suárez Palomares
Abraham José Silva Orozco
Gabriela García Cárdenas
Sunday, November 20, 11
2. Net working
Devices interconnected
Share information, files, and resources.
Sunday, November 20, 11
3. NETWORKING
A sending system:
Segments -> adds header bytes
Packets
Protocol:
1) Format and Order -> Message exchanges
2) Actions taken of a message
Sunday, November 20, 11
4. Socket
Sockets allow the implementation
of a client-server model.
Communication must be started by
one of the clients. The server waits
for the client to start the
communication.
A socket is a process or an
existing thread in the client and
server machine, it allows the
client and server to read and write
information. !
Sunday, November 20, 11
5. NETWORK CONNECTIONS
1. Fully connected network 2
2. Partially connected network
3. Hierarchical Network
4. Star Network
1
5. Ring Network
6. Multiaccess bus network (shared link)
7. Hybrid Networks
4 3
6 7
5
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6. Client-Server
Clients connected to server
Example: Accessing a web
page
Chat
Client: Sends a demand or !
messages
Server: Listen for incoming calls
or messages
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7. Nachos
Nachos/code/network
-m 1 -o 0 Server
(Buffer)
Me Receiver
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8. PING
Ping test the state
of connection of Protocol
host with one or
others computers,
sending package
ICMP Ping works in the network layer, this
use the encapsulate the message, in the
package and then it send
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9. Example
You
Sister
n.n Lost
You
Sister
n.n
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10. Ok, she is n.n n.n
alive
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11. Pseudocode
///request
Ping() ////answer
ping.txt receive_request()
validate() validate(request)
verify structure if request = true{
execute() answer->send
do ping->send }
receive_ans(answer)
validate()
if answer = true{
echo “Connected”
}
else{
echo “Not Connected”
}
Sunday, November 20, 11
12. SECURITY
Virus
Malware
Warms
Zombies
Trojans
Others
Botnets Funny
DoS
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14. Important Points
Sending Pings (easy)
Server attacks
Receive Information
Broke elisa’s server
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15. Cryptography
rap hy En c r y p t at i o
t o g io n
yp i t n
Cr f in de f i n i t i o n
de
C = E( P, K e )
C i ph e r te x
t
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16. Cryptography
De c r y p t i o n
of f s’s de f i n i t i o n
k h le
e rc c i p
K in P = D(C, K d)
pr
P l a i n te x t
Sunday, November 20, 11
17. Secret-key criptography
Definition symmetric encryption
Example In this example the plaintext HELLO would become the cyphertext SVOOL.
All As are replaced by Zs, all Bs by Ys, all Cs by Xs and so on
key
Plaintext: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
Ciphertext: Z Y X W V U T S R Q P O N M L K J I H G F E D C B A
encryption key
Monoalphabetic sustitution
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19. Public-key cryptography
ri v a te
di f f e re n t k e ys y, p
ke )
p ub lic e y
( k
ic
r n App l ic at i o n
e t t io
m a -A u t h e n t ic s:
m pt at io n
sy r y
a c - D igi t a l S ig
n at u re s
en Prov ides:
-Con fide ntia lity
- Inte grit y
Sunday, November 20, 11
21. Pseudocode
a = “xxx”;
b = encrypt_algorithm
ke = encrypt_key
t_encrypt = b ( a, key)
t_encrypt = send ( )
receive ( t_encrypt)
kd = decrypt_key
if (kd == true){
t_decrypt = b (t_encrypt, kd)
a = t_decrypt
}
else
{
print “you need the key to decrypt”
Sunday, November 20, 11
