Transcript ppt
Computer Networks Security Autumn 2000 John Kristoff 1 Internet/Telco Comparison Ñ Telephone System Ñ central authority Ñ network in control Ñ billing records per connection Ñ legal issues well understood Ñ provisions for law enforcement (wiretapping) Autumn 2000 Ñ Internet Ñ no central authority Ñ end systems in control Ñ no central knowledge of connections Ñ no per-packet billing Ñ legal issues not well understood Ñ anonymity is easy John Kristoff 2 Internet Security Stinks Ñ Hosts are hard to secure Ñ Bad defaults Ñ Poor software Ñ Fixes rarely applied Ñ Average user/administrator is clueless Ñ An overly secure system is not useful Ñ It’s difficult to coordinate among sites Autumn 2000 John Kristoff 3 What to Protect Ñ Confidentiality Ñ snooping Ñ encryption Ñ Integrity Ñ deletion, changes Ñ backups Ñ Availability Ñ denial of service attacks Autumn 2000 Ñ Authentication Ñ are who you say you are Ñ Nonrepudiation Ñ no denying it Ñ Access Control Ñ don’t touch that! Ñ Reputation Ñ Ensure your good name John Kristoff 4 Where to Put the Protection? Autumn 2000 John Kristoff 5 Physical Security Ñ Trash bins Ñ Social engineering Ñ It’s much easier to trust a face than a packet Ñ Protect from the whoops Ñ Ñ Ñ Ñ power spills the clumsy software really can kill hardware Autumn 2000 John Kristoff 6 Host Based Security Ñ Recall End-to-End Argument Ñ Security is ultimately a host problem Ñ Key idea: protect the DATA Ñ End hosts are in control of data Ñ Users are in control of end hosts Ñ Users can and often will do dumb things Ñ Result: very difficult to protect all hosts Autumn 2000 John Kristoff 7 Internal Security Ñ Most often ignored Ñ Most likely the problem Ñ Disgruntled employee Ñ Curious, but dangerous employee Ñ Clueless and dangerous employee Autumn 2000 John Kristoff 8 Security by Obscurity Ñ Is no security at all. Ñ However ÑIt’s often best not to advertise unnecessarily ÑIt’s often the only layer used (e.g. passwords) Ñ Probably need more security Autumn 2000 John Kristoff 9 Network Based Security Ñ Should augment host based security Ñ Useful for Ñ Protecting groups of users from others Ñ Prohibiting certain types of network usage Ñ Controlling traffic flow Ñ Difficult to inspect traffic Ñ encryption can hide bad things Ñ tunneling can mislead you Good book: Network Security: PRIVATE Communication in a PUBLIC World. Kaufman, Perlman and Speciner. Autumn 2000 John Kristoff 10 Layered Defenses Ñ The belt and suspenders approach Ñ Multiple layers make it harder to get through Ñ Multiple layers take longer to get through Ñ Basic statistics and probability apply Ñ If Defense A stops 90% of all attacks and Defense B stops 90% of all attacks, you might be able to stop up to 99% of all attacks Ñ Trade-off in time, money and convenience Autumn 2000 John Kristoff 11 Perimeter Security Ñ Boundary between a trusted internal network and a hostile external network Autumn 2000 John Kristoff 12 Firewall Solutions Ñ They help, but not a panacea Ñ A network response to a host problem ÑPacket by packet examination is tough Ñ Don’t forget internal users Ñ Need well defined borders Ñ Can be a false sense of security Ñ Careful not to break standard protocol mechanisms! Autumn 2000 John Kristoff 13 Packet Filtering Firewalls Ñ Apply rules to incoming/outgoing packets Ñ Based on ÑAddresses ÑProtocols ÑPorts ÑApplication ÑOther pattern match Autumn 2000 John Kristoff 14 Packet Filtering Firewall Illustrated Autumn 2000 John Kristoff 15 Screened Subnet Autumn 2000 John Kristoff 16 Example Firewall: ipchains -A input -s 192.168.0.0/255.255.0.0 -d 0.0.0.0/0.0.0.0 -j DENY -A input -s 172.0.0.0/255.240.0.0 -d 0.0.0.0/0.0.0.0 -j DENY -A input -s 10.0.0.0/255.0.0.0 -d 0.0.0.0/0.0.0.0 -j DENY -A input -s 224.0.0.0/224.0.0.0 -d 0.0.0.0/0.0.0.0 -j DENY -A input -s 0.0.0.0/0.0.0.0 -d a.b.c.d/255.255.255.255 22:22 -p 6 -j ACCEPT -A input -s 0.0.0.0/0.0.0.0 -d a.b.c.d/255.255.255.255 1024:65535 -p 6 ! -y -j ACCEPT Autumn 2000 John Kristoff 17 Example Firewall: Cisco Router Filters access-list access-list access-list access-list access-list access-list access-list access-list access-list access-list access-list access-list access-list access-list Autumn 2000 100 100 100 100 100 100 100 100 100 100 100 100 100 100 deny deny deny deny deny deny deny permit permit deny deny deny permit deny ip 192.168.0.0 0.0.255.255 any ip 172.0.0.0 0.15.255.255 any ip 10.0.0.0 0.255.255.255 any ip 0.0.0.0 0.255.255.255 any ip 127.0.0.0 0.255.255.255 any ip 224.0.0.0 31.255.255.255 any ip 1.2.0.0 0.0.255.255 any tcp any host 1.2.3.4 eq domain udp any host 1.2.3.4 eq domain tcp any host 1.2.3.5 eq telnet log tcp any host 1.2.3.6 eq syn log ip any host 1.2.3.4 ip any 1.2.0.0 0.0.255.255 ip any any John Kristoff 18 Application Level Gateway Autumn 2000 John Kristoff 19 Encryption Ñ Make a readable message unreadable Ñ Math intensive Ñ Plain text versus cipher text Ñ Algorithms and keys Ñpublic Ñprivate Ñkey size Autumn 2000 John Kristoff 20 Shared Secret Key Ñ Each party knows a secret Ñ The secret is used to decrypt the cipher text ÑBook: Ulysses ÑPage: 7 ÑLine: 23 ÑWord: 4 Ñ Must know the book and keep it a secret Autumn 2000 John Kristoff 21 Shared Secret Key Illustrated Autumn 2000 John Kristoff 22 Public Key Cryptography Ñ Public Key ÑEveryone can use it to encrypt messages to you Ñ Private Key ÑOnly you know this key and only it decrypts messages encrypted with your public key Ñ Keyring Autumn 2000 John Kristoff 23 Public Key Illustrated Autumn 2000 John Kristoff 24 Exploits Overview Ñ Passwords Ñ hacking and sniffing Ñ System specific Ñ NT, UNIX, NetWare, Linux Ñ Application specific Ñ web browser, ftp, email, finger Ñ Protocol specific Ñ spoofing, TCP hijacking, ICMP redirects, DNS Ñ Denial of Service Ñ PING of death, trinoo, tribe flood Autumn 2000 John Kristoff 25 The Process Ñ Reconnaissance Ñ Scanning Ñ Exploit Systems Ñ Keep access with backdoors/trojans Ñ Use system ÑOften as a springboard Ñ Cover any tracks Autumn 2000 John Kristoff 26 Buffer Overflows and Weak Validation of Input Ñ Key idea: overwriting the something on the stack Ñ Popular exploits with CGI scripts Ñ Format strings Ñ Regular users can gain root access Ñ If exploit on TCP/UDP service, remote root can be accomplished Autumn 2000 John Kristoff 27 Network Mapping Ñ Ñ PING DNS mapping (don’t need zone transfer) Ñ dig +pfset=0x2020 -x 10.x.x.x Ñ Ñ rpcinfo -p <hostname> nmap <http://www.insecure.org/nmap/> Ñ very nice! Ñ Microsoft Windows is NOT immune Ñ nbtstat, net commands Ñ Just look around the ‘net! Autumn 2000 John Kristoff 28 Session Hijacking If you can predict sequence numbers and spoof the source address, you might be able to pretend to be one end of the session. It helps if you can keep one end of the session busy while you’re hijacking. Autumn 2000 John Kristoff 29 Session Hijacking Illustrated Autumn 2000 John Kristoff 30 Password Cracking Ñ Very common today Ñ If attacker can get a hold of the password file, they can go offline and process it Ñ Recall Ñpasswords are a form of obscurity Ñmultiple defenses may be needed Ñ Given enough time, passwords alone are probably not safe Autumn 2000 John Kristoff 31 Viruses and Worms Ñ Programs written with the intent to spread Ñ Worms are very common today ÑOften email based (e.g. ILOVEYOU) Ñ Viruses infect other programs ÑCode copied to other programs (e.g. macros) Ñ All require the code to be executed ÑProves users continue to do dumb things ÑSometimes software is at fault too Autumn 2000 John Kristoff 32 Denial of Service (DoS) Ñ Prevents or impairs standard service Ñ SYN flooding Ñ SMURF attacks Ñ Distributed Denial of Service (DDoS) Ñ Most effective when source address can be spoofed Ñ Difficult to differeniate between valid traffic Autumn 2000 John Kristoff 33 Example Denial of Service Illustrated Autumn 2000 John Kristoff 34 Example Distributed Denial of Service Illustrated Autumn 2000 John Kristoff 35 DoS Solutions Ñ Ingress/Egress filtering Ñ ICMP Traceback Ñ Packet Marking Ñ Rate-limiting Ñ Difficult to solve completely! Autumn 2000 John Kristoff 36 Network Address Translation Ñ Removes end-to-end addressing Ñ Standardized in RFC 1918 Ñ NAT has been bad for the Internet Ñ Provides relatively no security with a great deal of cost - this slide shouldn't be here Ñ NAT has been required for sites with IP address allocation problems Ñ NAT may be used for IPv6 transition Autumn 2000 John Kristoff 37 NAT Illustrated Autumn 2000 John Kristoff 38 Virtual Private Networks Autumn 2000 John Kristoff 39 Key Idea A session between two endpoints that is secured from eavesdroppers and all threats on the network in between, usually through the use of encryption technology. Autumn 2000 John Kristoff 40 Why Is This Worthwhile? Ñ Cost, Cost, Cost! ÑAbility to make use of a public, insecure network, rather than building your own private, secure network Autumn 2000 John Kristoff 41 Challenges Ñ Increased overhead Ñ Complexity Ñ Performance Ñ Quality Ñ Management Autumn 2000 John Kristoff 42 Oh, and One More Thing Autumn 2000 John Kristoff 43 Other Areas of Interest Ñ IP multicast Ñ Routing protocols Ñ Privacy issues Ñ IPsec Ñ Intrusion Detection Systems (IDS) Autumn 2000 John Kristoff 44 References bugtraq mailing list (see http://www.securityfocus.com) http://www.cert.org http://www.cerias.purdue.edu http://www.first.org http://packetstorm.securify.com http://www.research.att.com/~smb/ http://cm.bell-labs.com/who/ches/ http://www.denialinfo.com http://www.cs.georgetown.edu/~denning/ http://www.washington.edu/People/dad/ http://www.sans.org http://theory.lcs.mit.edu/~rivest/ http://networks.depaul.edu/security/ Autumn 2000 John Kristoff 45