1. חישוב ציון תרגילי בית: מי שלא יגיש את הפרויקט בזמן (PA3):
ממוצע של כל 7 תרגילי הבית
מי שיגיש את הפרויקט בזמן (PA3):
ממוצע של 6 תרגילי בית:
הפרויקט (PA3)
חמשת הטובים (מתוך ששת) התרגילים האחרים
משקל כל תרגיל (מתוך השישה) יהיה זהה (1/6)
הערה: חייבים להקפיד על הגשה בזמן!

2. Chapter 7: Network security
January 13, 2010
Chapter 7: Network security
Foundations:
what is security?
cryptography
authentication
message integrity
key distribution and certification
Security in practice:
application layer: secure
transport layer: Internet commerce, SSL, SET
network layer: IP security
Firewalls
Lecture 13: Network Security

3. What is network security?
January 13, 2010
What is network security?
Confidentiality: only sender, intended receiver should “understand” message contents
sender encrypts message
receiver decrypts message
Authentication: sender, receiver want to confirm identity of each other
Message Integrity: sender, receiver want to ensure message not altered (in transit, or afterwards) without detection
Access and Availability: services must be accessible and available to users
Lecture 13: Network Security

4. Internet security threats
January 13, 2010
Internet security threats
Packet sniffing:
broadcast media
promiscuous NIC reads all packets passing by
can read all unencrypted data (e.g. passwords)
e.g.: C sniffs B’s packets A C
src:B dest:A payload B
Lecture 13: Network Security

5. Internet security threats
January 13, 2010
Internet security threats
IP Spoofing:
can generate “raw” IP packets directly from application, putting any value into IP source address field
receiver can’t tell if source is spoofed
e.g.: C pretends to be B A C
src:B dest:A payload B
Lecture 13: Network Security

6. Internet security threats
January 13, 2010
Internet security threats
Denial of service (DOS):
flood of maliciously generated packets “swamp” receiver
Distributed DOS (DDOS): multiple coordinated sources swamp receiver
e.g., C and remote host SYN-attack A A C
SYN
SYN
SYN
SYN
SYN B
SYN
SYN
Lecture 13: Network Security

7. Cryptography Principles
January 13, 2010
Cryptography Principles
Lecture 13: Network Security

8. Friends and enemies: Alice, Bob, Trudy
January 13, 2010
Friends and enemies: Alice, Bob, Trudy
well-known in network security world
Bob, Alice (lovers!) want to communicate “securely”
Trudy (intruder) may intercept, delete, add messages
Alice
Bob
channel
data, control messages
secure
sender
secure
receiver
data
data
Trudy
Lecture 13: Network Security

9. Who might Bob, Alice be? … well, real-life Bobs and Alices!
January 13, 2010
Who might Bob, Alice be?
… well, real-life Bobs and Alices!
Web browser/server for electronic transactions (e.g., on-line purchases)
on-line banking client/server
DNS servers
routers exchanging routing table updates
other examples?
Lecture 13: Network Security

10. The language of cryptography
January 13, 2010
The language of cryptography
Alice’s
encryption
key
Bob’s
decryption
key K A K B
encryption
algorithm
plaintext
ciphertext
decryption
algorithm
plaintext
symmetric key crypto: sender, receiver keys identical
public-key crypto: encryption key public, decryption key secret (private)
Lecture 13: Network Security

11. Symmetric Key Cryptography
January 13, 2010
Symmetric Key Cryptography
Lecture 13: Network Security

12. Symmetric key cryptography
January 13, 2010
Symmetric key cryptography
substitution cipher: substituting one thing for another
monoalphabetic cipher: substitute one letter for another
plaintext: abcdefghijklmnopqrstuvwxyz
ciphertext: mnbvcxzasdfghjklpoiuytrewq
E.g.:
Plaintext: bob. i love you. alice
ciphertext: nkn. s gktc wky. mgsbc
Q: How hard to break this simple cipher?:
brute force (how hard?)
other?
Lecture 13: Network Security

13. Perfect cipher [Shannon 1948]
January 13, 2010
Perfect cipher [Shannon 1948]
Definition:
Let C = E[M]
Pr[C=c] = Pr[C=c | M]
Example: one time pad
Generate random bits b1 ... bn
E[M1 ... Mn] = (M1  b1 ... Mn  bn )
Cons: size
Pseudo Random Generator
G(R) = b1 ... bn
Indistinguishable from random (efficiently)
Lecture 13: Network Security

14. Symmetric key crypto: DES
January 13, 2010
Symmetric key crypto: DES
DES: Data Encryption Standard
US encryption standard [NIST 1993]
56-bit symmetric key, 64 bit plaintext input
How secure is DES?
DES Challenge: 56-bit-key-encrypted phrase (“Strong cryptography makes the world a safer place”) decrypted (brute force) in 4 months
no known “backdoor” decryption approach
making DES more secure
use three keys sequentially (3-DES) on each datum
use cipher-block chaining
Advanced Encryption Standard (AES)
Lecture 13: Network Security

15. Symmetric key crypto: DES
January 13, 2010
Symmetric key crypto: DES
DES operation
initial permutation
16 identical “rounds” of function application, each using different 48 bits of key
final permutation
Lecture 13: Network Security

16. Block Cipher chaining How do we encode a large message Encoding:
January 13, 2010
Block Cipher chaining
How do we encode a large message
Would like to guarantee integrity
Encoding:
Ci = E[Mi  Ci-1]
Decoding:
Mi = D[Ci]  Ci-1
Malfunctions:
Loss
Reorder/ integrity
Lecture 13: Network Security

17. Cipher Block Chaining Mode
Cipher block chaining. (a) Encryption. (b) Decryption.
7: Network Security 17

18. Diffie-Hellman key exchange protocol
January 13, 2010
Diffie-Hellman key exchange protocol
Goal: Allow strangers establish a shared secret key for later communication
Assume two parties (Alice and Bob) want to establish a secret key.
Alice and Bob agree on two large numbers, n and g
usually, these are publicly known, and have some additional conditions applied (e.g., n must be prime)
Lecture 13: Network Security

19. Diffie-Hellman Key Exchange
January 13, 2010
Diffie-Hellman Key Exchange
Alice picks large x, Bob picks large y (e.g., 512 bits)
Lecture 13: Network Security

20. Man in the middle attack
January 13, 2010
Man in the middle attack
Eavesdropper can’t determine secret key (gxy mod n) from (gx mod n) or (gy mod n)
However, how does Alice and Bob know if there is a third party adversary in between?
Lecture 13: Network Security

21. Exponentiation Compute gx mod n Expg,n (x) Assume x = 2y + b
January 13, 2010
Exponentiation
Compute gx mod n
Expg,n (x)
Assume x = 2y + b
Let z = Expg,n (y)
R=z2
If (b=1) R = g R mod n
Return R
Complexity: logarithmic in x
Lecture 13: Network Security

22. Public Key Cryptography
January 13, 2010
Public Key Cryptography
Lecture 13: Network Security

23. Public Key Cryptography
January 13, 2010
Public Key Cryptography
symmetric key crypto
requires sender, receiver know shared secret key
Q: how to agree on key in first place (particularly if never “met”)?
public key cryptography
radically different approach [Diffie-Hellman76, RSA78]
sender, receiver do not share secret key
encryption key public (known to all)
decryption key private (known only to receiver)
Lecture 13: Network Security

24. Public key cryptography
January 13, 2010
Public key cryptography +
Bob’s public
key K B -
Bob’s private
key K B
plaintext
message, m
encryption
algorithm
ciphertext
decryption
algorithm
plaintext
message
K (m) B +
m = K (K (m)) B + -
Lecture 13: Network Security

25. Public key encryption algorithms
January 13, 2010
Public key encryption algorithms
Two inter-related requirements: . . 1
need d ( ) and e ( ) such that B B
d (e (m)) = m B 2
need public and private keys
for d ( ) and e ( ) . B
RSA: Rivest, Shamir, Adelson algorithm
Lecture 13: Network Security

26. RSA: Choosing keys 1. Choose two large prime numbers p, q.
January 13, 2010
RSA: Choosing keys
1. Choose two large prime numbers p, q.
(e.g., 1024 bits each)
2. Compute n = pq, z = (p-1)(q-1)
3. Choose e (with e<n) that has no common factors
with z. (e, z are “relatively prime”).
4. Choose d such that ed-1 is exactly divisible by z.
(in other words: ed mod z = 1 ).
5. Public key is (n,e). Private key is (n,d). K B + K B -
Lecture 13: Network Security

27. RSA: Encryption, decryption
January 13, 2010
RSA: Encryption, decryption
0. Given (n,e) and (n,d) as computed above
1. To encrypt bit pattern, m, compute
c = m mod n e
(i.e., remainder when m is divided by n)
2. To decrypt received bit pattern, c, compute
m = c mod n d d
(i.e., remainder when c is divided by n)
m = (m mod n) e
mod n d
Magic
happens!
Lecture 13: Network Security

28. Bob chooses p=5, q=7. Then n=35, z=24.
January 13, 2010
RSA example:
Bob chooses p=5, q=7. Then n=35, z=24.
e=5 (so e, z relatively prime).
d=29 (so ed-1 exactly divisible by z). e
c = m mod n e
letter m m
encrypt: l 12 17 c d
m = c mod n d c
letter
decrypt: 17 12 l
Lecture 13: Network Security

29. RSA: Why x y mod n = x (y mod (p-1)(q-1) ) mod n m = (m mod n) e mod n
January 13, 2010
RSA: Why
m = (m mod n) e
mod n d
Number theory result:
IF pq = n, p and q primes then:
x y mod n = x (y mod (p-1)(q-1) ) mod n
(m e)d mod n = m (ed mod (p-1)(q-1)) mod n
But ed – 1 divisible by (p-1)(q-1) i.e., ed mod (p-1)(q-1) = 1
= m 1 mod n = m
Always there is a solution, and satisfies (Chinese Remainder)
Lecture 13: Network Security

30. modified Diffie-Hellman Key Exchange
January 13, 2010
modified Diffie-Hellman Key Exchange
Encrypt 1 with Bob’s public key, 2 with Alice’s public key
Prevents man-in-the-middle attack
Actually, nonces and a third message are needed to fully complete this exchange (in a few slides)
Lecture 13: Network Security

31. January 13, 2010
Authentication
Lecture 13: Network Security

32. Protocol ap1.0: Alice says “I am Alice”
January 13, 2010
Authentication
Goal: Bob wants Alice to “prove” her identity to him
Protocol ap1.0: Alice says “I am Alice”
“I am Alice”
Failure scenario??
Lecture 13: Network Security

33. Authentication Goal: Bob wants Alice to “prove” her identity to him
January 13, 2010
Authentication
Goal: Bob wants Alice to “prove” her identity to him
Protocol ap1.0: Alice says “I am Alice”
in a network,
Bob can not “see” Alice, so Trudy simply declares
herself to be Alice
“I am Alice”
Lecture 13: Network Security

34. Authentication: another try
January 13, 2010
Authentication: another try
Protocol ap2.0: Alice says “I am Alice” in an IP packet
containing her source IP address
“I am Alice”
Alice’s
IP address
Failure scenario??
Lecture 13: Network Security

35. Authentication: another try
January 13, 2010
Authentication: another try
Protocol ap2.0: Alice says “I am Alice” in an IP packet
containing her source IP address
Trudy can create
a packet “spoofing”
Alice’s address
“I am Alice”
Alice’s
IP address
Lecture 13: Network Security

36. Authentication: another try
January 13, 2010
Authentication: another try
Protocol ap3.0: Alice says “I am Alice” and sends her
secret password to “prove” it.
“I’m Alice”
Alice’s
IP addr
password
Failure scenario?? OK
Alice’s
IP addr
Lecture 13: Network Security

37. Authentication: another try
January 13, 2010
Authentication: another try
Protocol ap3.0: Alice says “I am Alice” and sends her
secret password to “prove” it.
Alice’s
IP addr
Alice’s
password
“I’m Alice”
playback attack: Trudy records Alice’s packet
and later
plays it back to Bob OK
Alice’s
IP addr
“I’m Alice”
Alice’s
IP addr
password
Lecture 13: Network Security

38. Authentication: yet another try
January 13, 2010
Authentication: yet another try
Protocol ap3.1: Alice says “I am Alice” and sends her
encrypted secret password to “prove” it.
“I’m Alice”
Alice’s
IP addr
encrypted
password
Failure scenario?? OK
Alice’s
IP addr
Lecture 13: Network Security

39. Authentication: another try
January 13, 2010
Authentication: another try
Protocol ap3.1: Alice says “I am Alice” and sends her
encrypted secret password to “prove” it.
Alice’s
IP addr
encrypted
password
“I’m Alice”
record
and
playback
still works! OK
Alice’s
IP addr
“I’m Alice”
Alice’s
IP addr
encrypted
password
Lecture 13: Network Security

40. Authentication: yet another try
January 13, 2010
Authentication: yet another try
Goal: avoid playback attack
Nonce: number (R) used only once –in-a-lifetime
ap4.0: to prove Alice “live”, Bob sends Alice nonce, R. Alice
must return R, encrypted with shared secret key
“I am Alice” R
K (R)
A-B
Alice is live, and only Alice knows key to encrypt nonce, so it must be Alice!
Failures, drawbacks?
Lecture 13: Network Security

41. “send me your public key”
January 13, 2010
Authentication: ap5.0
ap4.0 requires shared symmetric key
can we authenticate using public key techniques?
ap5.0: use nonce, public key cryptography
“I am Alice”
Bob computes R
(K (R)) = R A - K +
K (R) A -
and knows only Alice could have the private key, that encrypted R such that
“send me your public key” K A +
(K (R)) = R A - K +
Lecture 13: Network Security

42. sends m to Alice encrypted with Alice’s public key
January 13, 2010
ap5.0: security hole
Man (woman) in the middle attack: Trudy poses as Alice (to Bob) and as Bob (to Alice)
I am Alice
I am Alice R T
K (R) - R A
K (R) -
Send me your public key T K +
Send me your public key A K + T
K (m) +
Trudy gets T
m = K (K (m)) + - A
K (m) +
sends m to Alice encrypted with Alice’s public key A
m = K (K (m)) + -
Lecture 13: Network Security

43. January 13, 2010
ap5.0: security hole
Man (woman) in the middle attack: Trudy poses as Alice (to Bob) and as Bob (to Alice)
Difficult to detect:
Bob receives everything that Alice sends, and vice versa. (e.g., so Bob, Alice can meet one week later and recall conversation)
problem is that Trudy receives all messages as well!
Lecture 13: Network Security

44. Message Integrity (Signatures etc) January 13, 2010
Lecture 13: Network Security

45. January 13, 2010
Digital Signatures
Cryptographic technique analogous to hand-written signatures.
Sender (Bob) digitally signs document, establishing he is document owner/creator.
Verifiable, nonforgeable: recipient (Alice) can verify that Bob, and no one else, signed document.
Assumption:
eB(dB(m)) = dB(eB(m))
RSA
Simple digital signature for message m:
Bob decrypts m with his private key dB, creating signed message, dB(m).
Bob sends m and dB(m) to Alice.
Lecture 13: Network Security

46. Digital Signatures (more)
January 13, 2010
Suppose Alice receives msg m, and digital signature dB(m)
Alice verifies m signed by Bob by applying Bob’s public key eB to dB(m) then checks eB(dB(m) ) = m.
If eB(dB(m) ) = m, whoever signed m must have used Bob’s private key.
Alice thus verifies that:
Bob signed m.
No one else signed m.
Bob signed m and not m’.
Non-repudiation:
Alice can take m, and signature dB(m) to court and prove that Bob signed m.
Lecture 13: Network Security

47. January 13, 2010
Message Digests
Computationally expensive to public-key-encrypt long messages
Goal: fixed-length,easy to compute digital signature, “fingerprint”
apply hash function H to m, get fixed size message digest, H(m).
Hash function properties:
Many-to-1
Produces fixed-size msg digest (fingerprint)
Given message digest x, computationally infeasible to find m such that x = H(m)
computationally infeasible to find any two messages m and m’ such that H(m) = H(m’).
Lecture 13: Network Security

48. Hash Function Algorithms
January 13, 2010
Hash Function Algorithms
MD5 hash function widely used.
Computes 128-bit message digest in 4-step process.
arbitrary 128-bit string x, appears difficult to construct msg m whose MD5 hash is equal to x.
SHA-1 is also used.
US standard
160-bit message digest
Internet checksum would make a poor message digest.
Too easy to find two messages with same checksum.
Lecture 13: Network Security

49. Digital signature = signed message digest
January 13, 2010
Alice verifies signature and integrity of digitally signed message:
Bob sends digitally signed message:
large
message m
H: Hash
function
KB(H(m)) -
encrypted
msg digest
H(m)
digital
signature
(encrypt)
Bob’s
private
key
large
message m K B -
Bob’s
public
key
digital
signature
(decrypt) K B +
KB(H(m)) -
encrypted
msg digest
H: Hash
function +
H(m)
H(m)
equal ?
Lecture 13: Network Security

50. Key Distribution Centers
January 13, 2010
Key Distribution Centers
Lecture 13: Network Security

51. Problems with Public-Key Encryption
January 13, 2010
Problems with Public-Key Encryption
A way for Trudy to subvert public-key encryption.
Lecture 13: Network Security

52. Trusted Intermediaries
January 13, 2010
Trusted Intermediaries
Problem:
How do two entities establish shared secret key over network?
Solution:
trusted key distribution center (KDC) acting as intermediary between entities
Problem:
When Alice obtains Bob’s public key (from web site, , diskette), how does she know it is Bob’s public key, not Trudy’s?
Solution:
trusted certification authority (CA)
Lecture 13: Network Security

53. Key Distribution Center (KDC)
January 13, 2010
Key Distribution Center (KDC)
Alice,Bob need shared symmetric key.
KDC: server shares different secret key with each registered user.
Alice, Bob know own symmetric keys, KA-KDC KB-KDC , for communicating with KDC.
Alice communicates with KDC, gets session key R1, and KB-KDC(A,R1)
Alice sends Bob KB-KDC(A,R1), Bob extracts R1
Alice, Bob now share the symmetric key R1.
Lecture 13: Network Security

54. Certification Authorities
January 13, 2010
Certification Authorities
Certification authority (CA) binds public key to particular entity.
Entity (person, router, etc.) can register its public key with CA.
Entity provides “proof of identity” to CA.
CA creates certificate binding entity to public key.
Certificate digitally signed by CA.
When Alice wants Bob’s public key:
gets Bob’s certificate (Bob or elsewhere).
Apply CA’s public key to Bob’s certificate, get Bob’s public key
Lecture 13: Network Security

55. X.509 is the standard for certificates
January 13, 2010
X.509 is the standard for certificates
The basic fields of an X.509 certificate.
Lecture 13: Network Security

56. Public-Key Infrastructures
January 13, 2010
Public-Key Infrastructures
PKIs are a way to structure certificates
(a) A hierarchical PKI. (b) A chain of certificates.
Lecture 13: Network Security

57. Example revisited (solved with certificates)
January 13, 2010
Example revisited (solved with certificates)
Trudy presents Alice a certificate, purporting to be Bob, but Alice is unable to trace Trudy’s certificate back to a trusted root
Be wary if your browser warns about certs!
Lecture 13: Network Security

58. January 13, 2010
Secure
Lecture 13: Network Security

59. January 13, 2010
Secure
Alice wants to send confidential , m, to Bob.
KS( ) .
KB( ) + -
KS(m )
KB(KS ) m KS KB
Internet
Alice:
generates random symmetric private key, KS.
encrypts message with KS (for efficiency)
also encrypts KS with Bob’s public key.
sends both KS(m) and KB(KS) to Bob.
Lecture 13: Network Security

60. January 13, 2010
Secure
Alice wants to send confidential , m, to Bob.
KS( ) .
KB( ) + -
KS(m )
KB(KS ) m KS KB
Internet
Bob:
uses his private key to decrypt and recover KS
uses KS to decrypt KS(m) to recover m
Lecture 13: Network Security

61. Secure e-mail (continued)
January 13, 2010
Secure (continued)
Alice wants to provide sender authentication message integrity.
H( ) .
KA( ) - +
H(m )
KA(H(m)) m KA
Internet
compare
Alice digitally signs message.
sends both message (in the clear) and digital signature.
Lecture 13: Network Security

62. Pretty good privacy (PGP)
January 13, 2010
Pretty good privacy (PGP)
Internet encryption scheme, a de-facto standard.
Uses symmetric key cryptography, public key cryptography, hash function, and digital signature as described.
Provides secrecy, sender authentication, integrity.
Inventor, Phil Zimmerman, was target of 3-year federal investigation.
A PGP signed message:
---BEGIN PGP SIGNED MESSAGE---
Hash: SHA1
Bob:My husband is out of town tonight.Passionately yours, Alice
---BEGIN PGP SIGNATURE---
Version: PGP 5.0
Charset: noconv
yhHJRHhGJGhgg/12EpJ+lo8gE4vB3mqJhFEvZP9t6n7G6m5Gw2
---END PGP SIGNATURE---
Lecture 13: Network Security

63. Secure Socket layer (SSl)
January 13, 2010
Secure Socket layer (SSl)
Lecture 13: Network Security

64. Secure sockets layer (SSL)
January 13, 2010
Secure sockets layer (SSL)
Server authentication:
SSL-enabled browser includes public keys for trusted CAs.
Browser requests server certificate, issued by trusted CA.
Browser uses CA’s public key to extract server’s public key from certificate.
Visit your browser’s security menu to see its trusted CAs.
PGP provides security for a specific network app.
SSL works at transport layer. Provides security to any TCP-based app using SSL services.
SSL: used between WWW browsers, servers for E-commerce (https).
SSL security services:
server authentication
data encryption
client authentication (optional)
Lecture 13: Network Security

65. Tools  Internet options  Content  Certificates
January 13, 2010
Internet Explorer:
Tools  Internet options  Content  Certificates
Lecture 13: Network Security

66. Internet Explorer: Error Message
January 13, 2010
Internet Explorer: Error Message
Lecture 13: Network Security

67. SSL (continued) Encrypted SSL session:
January 13, 2010
Encrypted SSL session:
Browser generates symmetric session key, encrypts it with server’s public key, sends encrypted key to server.
Using its private key, server decrypts session key.
Browser, server agree that future msgs will be encrypted.
All data sent into TCP socket (by client or server) is encrypted with session key.
SSL: basis of IETF Transport Layer Security (TLS).
SSL can be used for non-Web applications, e.g., IMAP.
Client authentication can be done with client certificates.
Lecture 13: Network Security

68. January 13, 2010
SSL basics
Lecture 13: Network Security

69. Access Control in the Network
January 13, 2010
Access Control in the Network
Lecture 13: Network Security

70. Firewalls Two firewall types: packet filter application gateways
January 13, 2010
Firewalls
To prevent denial of service attacks:
SYN flooding: attacker establishes many bogus TCP connections. Attacked host alloc’s TCP buffers for bogus connections, none left for “real” connections.
To prevent illegal modification of internal data.
e.g., attacker replaces CIA’s homepage with something else
To prevent intruders from obtaining secret info.
firewall
isolates organization’s internal net from larger Internet, allowing some packets to pass, blocking others.
Two firewall types:
packet filter
application gateways
Lecture 13: Network Security

71. January 13, 2010
Packet Filtering
Internal network is connected to Internet through a router.
Router manufacturer provides options for filtering packets, based on:
source IP address
destination IP address
TCP/UDP source and destination port numbers
ICMP message type
TCP SYN and ACK bits
Example 1: block incoming and outgoing datagrams with IP protocol field = 17 and with either source or dest port = 23.
All incoming and outgoing UDP flows and telnet connections are blocked.
Example 2: Block inbound TCP segments with ACK=0.
Prevents external clients from making TCP connections with internal clients, but allows internal clients to connect to outside.
Lecture 13: Network Security

72. Virtual Private Networks
January 13, 2010
Virtual Private Networks
Using firewalls and IPsec encryption to provide a “leased-line” like connection over the Internet
(a) A leased-line private network. (b) A virtual private network.
Lecture 13: Network Security

73. January 13, 2010
Application gateways
host-to-gateway
telnet session
gateway-to-remote
host telnet session
application
gateway
router and filter
Filters packets on application data as well as on IP/TCP/UDP fields.
Example: allow select internal users to telnet outside.
1. Require all telnet users to telnet through gateway.
2. For authorized users, gateway sets up telnet connection to dest host. Gateway relays data between 2 connections
3. Router filter blocks all telnet connections not originating from gateway.
Lecture 13: Network Security

74. Limitations of firewalls and gateways
January 13, 2010
Limitations of firewalls and gateways
IP spoofing: router can’t know if data “really” comes from claimed source
If multiple app’s. need special treatment, each has own app. gateway.
Client software must know how to contact gateway.
e.g., must set IP address of proxy in Web browser
Filters often use all or nothing policy for UDP.
Tradeoff: degree of communication with outside world, level of security
Many highly protected sites still suffer from attacks.
Lecture 13: Network Security

75. Network Security (summary)
January 13, 2010
Network Security (summary)
Basic techniques…...
cryptography (symmetric and public)
authentication
message integrity
…. used in many different security scenarios
secure
secure transport (SSL)
IP sec
Firewalls
Lecture 13: Network Security