Download Security

Network Security
MET CS-625 Unit 6
1-1
Objectives
• Discuss security tradeoffs
• Examine specific threats in an enterprise
network
• Discuss development of a site security policy
1-2
Changes in security requirements
• It used to be that computers were kept in
locked rooms
• Often users did not even have an account on
the computer
• Now everyone has a computer that attaches
to a network of secure and insecure devices
• When attached to the Internet the machine is
potentially open to anyone in the world
1-3
The Orange Book
• Government publication describing security of
computing systems
• Uses a gradation of security from D (insecure
ie DOS) to A1 (super secure)
• Security is not black and white...it is a
continuum
1-4
Tradeoffs in security design
• Services offered versus level of security
• Ease of use versus security
• Cost of security versus cost of loss
1-5
Extending the definition of
security
• Security doesn’t only mean theft or
compromise of data
• Can also mean complete loss of data or
assets
– Example: A fire destroys your disk farm
• For our discussion we’ll assume that the
earthquake won’t hit
1-6
Why have a security policy?
• Inform users of the requirements for
protecting information and assets
• Spell out procedures mechanisms to meet the
requirements
• Provides a baseline to audit the site for
compliance
• May also include an appropriate use policy
1-7
Physical threats
• Orange Book A1 security requires a machine
in a vault with no external
connections...including power
• It points out that if someone can touch your
machine, it can be compromised
• This extends to all components of the
network...switches, phone lines, etc
1-8
Social engineering
• Kevin Mitnick testified before Congress that
most of his hacker work was accomplished
without the use of technology
• Users are surprisingly naive when confronted
by technology
• Humans tend to fall into easily discernible
patterns
• Part of the security policy must acknowledge
and plan for this
1-9
Network threats
• Any time a computer is connected to a
network it is open to a variety of threats
• We’ll look at three broad categories
– Unauthorized access
– Impersonation
– Denial of service
1-10
Unauthorized access
• Intruder gains access to information
• Hardest to protect against
• Many avenues
– Social engineering
– Packet snooping
– Eavesdropping
1-11
Impersonation
• Related to unauthorized access
• Means the ability to present credentials to
make it seem you are someone or something
you are not
• Spoofing
• Replay
1-12
Sequence number attack
• TCP packets use a sequence number that
increments in a known, non-random way for
identification of a connection
• By making valid connections to a machine it
may be possible to deduce the next sequence
• Attacker then starts sending packets to server
with valid sequence numbers (possibly using
DoS attack on some other machine)
1-13
Session hijacking
• Intruder monitors traffic between two
machines
• Captures packets
• Starts to send packets with authorized
machine’s credentials
• Somewhat easier than sequence number
attack
1-14
Denial of service (DoS)
• Purpose: prevent use of a network resource
• Many scenarios
• Most rely on incapacitating a server with an
overload of traffic
• Often very difficult to trace
– SYN
– Ping of Death
– SMURF
1-15
SYN attack (LAND.C)
• Not used much anymore due to updates in
server code
• Send forged packets to server with the
server’s address in the destination field
• Standard SYN flood generates multiple SYN
requests to a server using bogus destination
addresses
– Server must allocate buffers for each connection
– Eventually memory is exhausted
1-16
Ping of death
• Max size of an IP packet is 64k
• However packets may be fragmented
• Fragments rely on sequence numbers and
offsets
• Using an offset with multiple large IP packets
can result in buffer overflows and server
crashes
• This one is extremely difficult to trace
1-17
SMURF
• Smurfing also uses ICMP Echo packets
(pings)
• In this attack the destination and source
addresses are forged to be broadcast
addresses
• In a poorly protected network this may
generate a cascade of thousands of echo
responses for each individual smurf packet
1-18
teardrop.c
• Teardrop attacks use IP fragment
vulnerabilities
• Ping of Death simply sends an extremely
large IP packet
• Teardrop sends fragments that overlap
• Result: Server crash
1-19
SMTP/Email attacks
• Bombing
– Multiple identical messages to a single recipient
• Spamming
– Multiple messages to multiple recipients
• Filters are useful in preventing an attack,
however spam continues to be used as a
marketing tool
1-20
Session replay
• Record an entire TCP/IP stream
• Modify the stream
• Replay it
1-21
Cookie Poisoning
• Analyze the format of data stored in a cookie
– Not all sites encrypt data
• Modify cookie
• Log back on to site
• Ex:
LastPageVisited%2Fkidpub%2Fschools%2Fkidpubschoolsdirectory.phpwww.kidpub.com/102424989729282960
4757327755579229604673*AuthorIDP3c2236b9bc02
9www.kidpub.com/102462152012829604682327735
579229604673*
1-22
Parameter tampering
• Change parameters in URL request strings
– Ex:
http://www.com/order?price=9.99&item=1234
• Can also examine hidden fields in forms
• Simple to avoid by using POST instead of GET
in http sources
1-23
Buffer overflows
• Attacker crafts code that overwrites a portion
of stack
• Code replaces return address on stack with
one attacker chooses
• Return address point either to Attacking code
or somewhere else malicious
• Results can be crash or control
1-24
Cross-site scripts
• Insert script code (such as JavaScript) into
form fields
• Script is executed on the browser
• Social engineering attack
• To avoid, use server-side parsing of inputs
(data validation)
1-25
Code injection
• Pass extra SQL commands on http request
string
• Ex: http://my.com/getCart?SQL=‘select
creditCard from master where ID=12345’
• Mod: http://my.com/getCart?SQL=‘select
creditCard from master where
ID=12345’+’OR ID=*’
1-26
File enumeration
• Examine source code and site to find file
names, directories, etc
• Use files to determine if site is vulnerable to
other attack modes
1-27
Forceful browsing
• Access site pages out of order
• May be able to bypass security checks
• Data validation may also be weak on pages
deep in site
• Can be used with other attacks such as
parameter tampering
1-28
Other vulnerabilities
•
•
•
•
Weak encryption
Open access to admin pages
Information leakage
Access to logs
1-29
Way to avoid problems
• Practice least privilege
– Users get no more access than what they need to
do job
• Secure defaults
• Validate all data from external sources
– Data are called ‘tainted’ if from outside
• Prevent information leakage
• Defense in depth
1-30
Application layer options
• SHTML
• PGP
• Block encryption
–
–
–
–
3DES
Blowfish
IDEA
RC5
• Message digests (MD5 etc)
1-31
Hashing
• Used to provide evidence that message has
not been tampered with
• No key involved
• Algorithms are collision resistant
• Hash algorithm is one-way
– SHA1 and MD5 are in common use
• Typically will hash an encrypted message
twice
– Original + encrypted
1-32
SHTML
• Uses encryption of data stream between
client and server
• Only recently has strong encryption become
available in the US
• Still vulnerable to certain attacks because key
exchange must happen in the clear
1-33
Symmetric vs asymmetric
cryptography
• Symmetric
– Algorithm uses same key on both sides of
transaction
– Keys must be exchanged in trusted manner
– Rotation keys often used
• Asymmetric
– Only one key is available to public
– No need to exchange keys
– PGP/PKI is example
1-34
PGP
•
•
•
•
Pretty Good Privacy
Uses private/public key encryption
Extremely strong encryption
Used both for encryption and digital
signatures
• Until recent;y PGP was a controlled
technology
1-35
1-36
Public-Key Encryption
Components
•
•
•
•
•
Plaintext
Encryption algorithm
Public and private key
Ciphertext
Decryption algorithm
1-37
Public-Key Encryption Operation
1-38
Public-Key Signature Operation
1-39
Characteristics of Public-Key
• Computationally infeasible to determine the
decryption key given knowledge of the
cryptographic algorithm and the encryption
key
• Either of the two related keys can be used for
encryption, with the other used for decryption
1-40
Steps in Public Key Encryption
• Each user generates a pair of keys to be used for the encryption and
decryption of messages.
• Each user places one of the two keys in a public register or other
accessible file. This is the public key. The companion key is kept
private.
• If Bob wishes to send a private message to Alice, Bob encrypts the
message using Alice's public key.
• When Alice receives the message, she decrypts it using her private
key. No other recipient can decrypt the message because only Alice
knows Alice's private key.
1-41
Digital Signature Process
1-42
RSA Encryption Algorithm
• Developed in 1977, first published in 1978
• Widely accepted and implemented approach to public-key
encryption
• For plaintext block M and ciphertext block C
– C = Me mod n
– M = Cd mod n = (Me)d mod n = Med mod n
• Both sender and receiver must know values of n and e;
only receiver knows value of d
• Public key of KU = {e, n}
• Private key of KR = {d, n}.
1-43
RSA Requirements
• It is possible to find values of e, d, n such that Med
= M mod n for all M < n.
• It is relatively easy to calculate Me and Cd for all
values of M < n.
• It is infeasible to determine d given e and n.
– This requirement can be met with large values of e and
n
1-44
Approaches to Defeating RSA
• Brute force approach: try all possible private keys.
– The larger the number of bits in e and d, the more secure the
algorithm.
– However, the larger the size of the key, the slower the system will
run.
• Cryptanalysis: factoring n into its two prime factors
– A hard problem, but not as hard as it used to be
– Currently, a 1024-bit key size is considered strong enough for
virtually all applications
1-45
Key Management
• Symmetric encryption requires both parties to
share a secret key
• Secure distribution of keys is the most
difficult problem for symmetric encryption
• Public key encryption solves this problem, but
adds the issue of authenticity
• Public key certiciates address this issue
1-46
Public Key Certificates
1-47
Public Key Certificate Process
1. A public key is generated by the user and submitted
to Agency X for certification.
2. X determines by some procedure, such as a face-toface meeting, that this is authentically the user’s
public key.
3. X appends a timestamp to the public key, generates
the hash code of the result, and encrypts that result
with X’s private key forming the signature.
4. The signature is attached to the public key.
1-48
Virtual Private Networks (VPNs)
• Internet connectivity provides easier access for
telecommuters and off-site employees
• Use of a public network exposes corporate traffic to
eavesdropping and provides an entry point for
unauthorized users
• A variety of encryption and authentication packages and
products are available to secure and authenticate remote
access
• Need for a standard that allows a variety of platforms to
interconnect securely
1-49
Applications of IPSec
• Secures communications across a LAN, WANs, and/or
the Internet
• Can encrypt and/or authenticate all traffic at the IP level
• Examples of use:
–
–
–
–
Secure branch office connectivity over the Internet
Secure remote access over the Internet
Establishing extranet and intranet connectivity with partners
Enhancing electronic commerce security
1-50
Benefits of IPSec
• When implemented in a firewall or router, provides
strong security for all traffic crossing the perimeter
• IPSec in a firewall is resistant to bypass
• Runs below the transport layer (TCP, UDP) and so is
transparent to applications
• Can be transparent to end users
• Can provide security for individual users if needed
1-51
IPSec Functions
• IPSec provides three main facilities
– authentication-only function referred to as
Authentication Header (AH)
– combined authentication/encryption function
called Encapsulating Security Payload (ESP)
– a key exchange function
• For VPNs, both authentication and encryption
are generally desired
1-52
ESP Transport and Tunneling
• Transport Mode
– provides protection primarily
for upper-layer protocols.
– Typically used for end-to-end
communication between two
hosts
– encrypts and optionally
authenticates the IP payload
but not the IP header
– useful for relatively small
networks; for a full-blown
VPN, tunnel mode is far more
efficient
• Tunnel Mode
– Provides protection to the
entire packet
– Original packet is
encapsulated in ESP fields,
protecting contents from
examination
– Used when one or both ends is
a security gateway
– Multiple hosts on networks
behind firewalls may engage in
secure communications
without implementing IPSec
1-53
IPSec Key Management
• Manual
– System administrator manually configures each system with
its own keys and with the keys of other communicating
systems
– Practical for small, relatively static environments
• Automated
– Enables the on-demand creation of keys for SAs and
facilitates the use of keys in a large distributed system
– Most flexible but requires more effort to configure and
requires more software
1-54
IPSec and VPNs
• Organizations need to isolate their networks and at the
same time send and receive traffic over the Internet
• Authentication and privacy mechanisms of secure IP allow
for security strategy
• IPSec can be implemented in routers or firewalls owned
and operated by the organization, allowing the network
manager complete control over security aspects of the
VPN
1-55
Transport layer
• Secure socket layer (SSL)
• Secure shell (SSH)
• Socket security (SOCKS)
1-56
Network layer / Link layer
• IPSec (IP Security suite)
• Cisco layer 2 forwarding protocol for VPN
• Point to point tunneling
1-57
Creating security policies
•
•
•
•
•
What are you trying to protect?
What are you protecting it from?
How likely are the threats?
Implement measures to protect your assets
Continuously review and revise your policy
1-58
Resources
• www.rootshell.com
• www.cert.org
1-59