Chapter 37 Network SecurityChapter 37 Network Security

Aspects of Security Aspects of Security

data integrity– data received should be same as data sent

data availability– data should be accessible when there is a legitimate need.

data confidentiality and privacy– data should be protected from unauthorized users– implemented via username/password mechanism,but data

traversing network is still susceptible to eavesdropping

EncryptionEncryption

Encrypted message = encrypt (Key, Message)Message = decrypt(Key, Encrypted message) = decrypt(Key, encrypt(Key,

Message))

Symmetric Key EncryptionSymmetric Key Encryption

Same key used for encrypting and decrypting message

Key known only by sender and receiverEg. DES, RC4

Public Key Encryption Public Key Encryption

Aka Asymmetric encryption uses a pair of keys

– a private key known only to a user– a public key that is published along with name of user.

message encrypted with private key can only be decrypted with public key and visa versa. 

Used by SSL protocol to send symmetric key M = decrypt (public key, encrypt(private key, Message))

– good for guarantee authenticity of sender M = decrypt (private key, encrypt(public key, Message))

– good for guarantee privacy of message

Authenticity and Authenticity and Confidentiality of messageConfidentiality of message

two levels of encryption is used to guarantee that a message is both authentic and private

double encrypted message

= encrypt( public key receiver, encrypt (private key sender, Message))

Message = decrypt (public key sender, decrypt(private key receiver, double encrypted message))

Digital CertificatesDigital Certificates

Electronic document used to identify an individual, a server, or a company associated with a public key

Analogous to driver’s license or passportDigital certificates are issued by Certificate

Authority

Digital SignatureDigital Signature

Used to sign an electronic document A one-way hash (media digest) of electronic

document is encrypted using sender’s private key. Recipient can verify that document has not been

tampered by using sender’s public key to recover the media digest and verifying that this value is the same as the one-way hash value calculated.

Packet Filters Packet Filters

Implement via Internet firewalls or routers used to prevent certain packets from passing

through operates by examining fields in the header of each

packet network manager specifies boolean combination

of various filter parameters such as source and destination IP address, or specific protocol service such FTP or HTTP

Virtual Private NetworksVirtual Private Networks

Using pubic network to create “private” network(fig 37.4)

minimizes network connection costs VPN using routers (fig 37.5)IPsecPPTP

Network Attacks Network Attacks

denial of service – Deprives network bandwidth or server resource– eg. ping flooding via running multiple “ping –s

destIPaddress 12000&”– Exploits vulnerability in operating system or

application software– Eg. Viruses and worms, buffer overflow

Good Security PracticesGood Security Practices

http://www.itc.virginia.edu/pubs/docs/Respcomp/videos