Lecture 24 Secure Communications CS 450/650 Fundamentals of Integrated Computer Security Slides are modified from Ian Goldberg

Who Attacks Networks Hackers break into organizations from the outside – Challenge – Fame – Money & Espionage – Ideology However, most security breaches are internal, by employees and ex-employees

Threat Precursors Port Scan Social Engineering – Reconnaissance – Bulletin Board / Chat – Docs Packet Sniffers (telnet/ftp in cleartext)

Network Security Threats Interception – If interceptor cannot read, have confidentiality (privacy) – If cannot modify without detection, have message integrity

Network Security Threats Impostors (Spoofing/ Masquerade) – Claim to be someone else – Need to authenticate the sender--prove that they are who they claim to be True Person Impostor

Network Security Threats Remotely Log in as Root User – Requires cracking the root login password – Then control the machine – Read and/or steal information – Damage data (erase hard disk) – Create backdoor user account that will let them in easily later Root Login Command

Security Threats Content Threats – Application layer content may cause problems Viruses In many ways, most severe security problem in corporations today Must examine application messages

Replay Attack First, attacker intercepts a message – Not difficult to do

Replay Attack Later, attacker retransmits (replays) the message to the original destination host – Does not have to be able to read a message to replay it

Replay Attack Why replay attacks? – To gain access to resources by replaying an authentication message – In a denial-of-service attack, to confuse the destination host

Thwarting Replay Attacks Put a time stamp in each message to ensure that the message is “fresh” – Do not accept a message that is too old Place a sequence number in each message – Do not accept a duplicated message Message Sequence Number Time Stamp

Thwarting Replay Attacks In request-response applications, – Sender of request generates a nonce (random number) – Places the nonce in the request – Server places the nonce in the response – Neither party accepts duplicate nonces Nonce RequestResponse

Network Security Threats Denial of Service (DOS) Attacks – Overload system with a flood of messages – Or, send a single message that crashes the machine

Denial of Service (DOS) Attacks Transmission Failure Connection Flooding – Echo-Chargen – Ping of Death – Smurf – Syn Flood – Traffic Redirection – DNS Attacks Distributed Denial of Service

VPNs IETF developing IPsec security standards – IP security – At the internet layer – Protects all messages at the transport and application layers IPsec TCPUDP , WWW, Database, etc.

VPNs IPsec Transport Mode – End-to-end security for hosts Local Network Internet Local Network Secure Communication

VPNs IPsec Tunnel Mode – IPsec server at each site – Secure communication between sites Local Network Internet Local Network Secure Communication IPsec Server

VPNs IPsec Modes Can be Combined – End-to-end transport mode connection – Within site-to-site tunnel connection Local Network Internet Local Network Tunnel Mode Transport Mode

VPNs Another Security System for VPNs is the Point- to-Point Tunneling Protocol (PPTP) – For dial-up connections, based on PPP – Connects user with securely to a remote access server at a site Internet Local Network Remote Access Server Dial-Up Connection PPTP Connection

PKIs To use public key methods, an organization must establish a comprehensive Public Key Infrastructure (PKI) – A PKI automates most aspects of using public key encryption and authentication – Uses a PKI Server PKI Server

PKIs PKI Server Creates Public Key-Private Key Pairs – Distributes private keys to applicants securely – Often, private keys are embedded in delivered software PKI Server Private Key

PKIs PKI Server Provides CRL Checks – Distributes digital certificates to verifiers – Checks certificate revocation list before sending digital certificates PKI Server Digital Certificate

PKIs CRL (Certificate Revocation List) Checks – If applicant gives verifier a digital certificate, – The verifier must check the certificate revocation list PKI Server OK? OK or Revoked CRL

Integrated Security System When two parties communicate … – Their software usually handles the details – First, negotiate security methods – Then, authenticate one another – Then, exchange symmetric session key – Then can communicate securely using symmetric session key and message-by-message authentication

SSL Integrated Security System SSL – Secure Sockets Layer – Developed by Netscape TLS (now) – Netscape gave IETF control over SSL – IETF renamed it TLS (Transport Layer Security) – Usually still called SSL

Location of SSL Below the Application Layer – IETF views it at the transport layer – Protects all application exchanges – Not limited to any single application WWW transactions, , etc. SSL WWW WWW

SSL Operation Browser & Webserver Software Implement SSL – User can be unaware

SSL Operation SSL ISS Process – Two sides negotiate security parameters – Webserver authenticates itself – Browser may authenticate itself but rarely does – Browser selects a symmetric session key, sends to webserver – Adds a digital signature and encrypts all messages with the symmetric key

Importance of SSL Supported by Almost All Browsers – De facto standard for Internet application security Problems – Relatively weak security – Does not involve security on merchant server – Does not validate credit card numbers – Viewed as an available but temporary approach to consumer security

Other ISSs SSL is merely an example integrated security system Many other ISSs exist – IPsec – PPP and PPTP – Etc.

Other ISSs All ISSs have the same general steps – Negotiate security parameters – Authenticate the partners – Exchange a session key – Communicate with message-by-message privacy, authentication, and message integrity

IPsec IPsec (IP security) Security for transmission over IP networks – The Internet – Internal corporate IP networks – IP packets sent over public switched data networks (PSDN) Local Network Internet Local Network

IPsec Why do we need IPsec? – IP has no security – Add security to create a virtual private network (VPN) to give secure communication over the Internet or another IP network Local Network Internet Local Network

IPsec Genesis – Being created by the Internet Engineering Task Force – For both IP version 4 and IP version 6

IPsec Two Modes of operation Tunnel Mode – IPsec server at each site – Secures messages going through the Internet Local Network Internet Local Network Secure Communication IPsec Server

IPsec Tunnel Mode – Hosts operate in their usual way Tunnel mode IPsec is transparent to the hosts – No security within the site networks Local Network Internet Local Network Secure Communication IPsec Server

IPsec Two Modes of operation Transport Mode – End-to-end security between the hosts – Security within site networks as well – Requires hosts to implement IPsec Local Network Internet Local Network Secure Communication

IPsec Transport Mode – Adds a security header to IP packet – After the main IP header – Source and destination addresses of hosts can be learned by interceptor – Only the original data field is protected Protected Original Data Field Original IP Header Transport Security Header

IPsec Tunnel Mode – Adds a security header before the original IP header – Has IP addresses of the source and destination IPsec servers only, not those of the source and destination hosts – Protects the main IP header Protected Original Data Field Protected Original IP Header Tunnel Security Header

IPsec Can combine the two modes – Transport mode for end-to-end security – Plus tunnel mode to hide the IP addresses of the source and destination hosts during passage through the Internet Local Network Internet Local Network Tunnel Mode Transport Mode

IPsec Two forms of protection Encapsulating Security Protocol (ESP) security provides confidentiality as well as authentication Authentication Header (AH) security provides authentication but not confidentiality – Useful where encryption is forbidden by law – Provides slightly better authentication by providing authentication over a slightly larger part of the message, but this is rarely decisive

IPsec Modes and protection methods can be applied in any combination Tunnel Mode Transport Mode ESPSupportedSupported AHSupportedSupported

IPsec Security Associations (SAs) are agreements between two hosts or two IPsec servers, depending on the mode “Contracts” for how security will be performed Negotiated Governs subsequent transmissions Host AHost B Negotiate Security Association

IPsec Security Associations (SAs) can be asymmetrical – Different strengths in the two directions – For instance, clients and servers may have different security needs Host AHost B SA for messages From A to B SA for messages From B to A

IPsec Policies may limit what SAs can be negotiated – To ensure that adequately strong SAs for the organization’s threats – Gives uniformity to negotiation decisions Host AHost B Security Association Negotiations Limited By Policies

IPsec First, two parties negotiate IKE (Internet Key Exchange) Security Associations – IKE is not IPsec-specific – Can be used in other security protocols Host AHost B Communication Governed by IKE SA

IPsec Under the protection of communication governed by this IKE SA, negotiate IPsec- specific security associations Host AHost B Communication Governed by IKE SA IPsec SA Negotiation

IPsec Process of Creating IKE SAs (and other SAs) – Negotiate security parameters within policy limitations – Authenticate the parties using SA-agreed methods – Exchange a symmetric session key using SA-agreed method – Communicate securely with confidentiality, message-by-message authentication, and message integrity using SA-agreed method

IPsec IPsec has mandatory security algorithms – Uses them as defaults if no other algorithm is negotiated – Other algorithms may be negotiated – But these mandatory algorithms MUST be supported

IPsec Diffie-Hellman Key Agreement – To agree upon a symmetric session key to be used for confidentiality during this session – Also does authentication Party AParty B

IPsec Diffie-Hellman Key Agreement – Each party sends the other a nonce (random number) – The nonces will almost certainly be different – Nonces are not sent confidentially Party AParty B Nonce B Nonce A

IPsec Diffie-Hellman Key Agreement – From the different nonces, each party will be able to compute the same symmetric session key for subsequent use – No exchange of the key; instead, agreement on the key Party AParty B Symmetric Key From nonces, independently compute same symmetric session key

Multi-Layer Security Security Can be Applied at Multiple Layers Simultaneously – Application layer security for database, , etc. – Transport layer: SSL – Internet layer: IPsec – Data link layer: PPTP, L2TP – Physical layer: locks

Multi-Layer Security Applying security at 2 or more layers is good – If security is broken at one layer, the communication will still be secure However, – Security slows down processing – Multi-Layer security slows down processing at each layer

Total Security Network Security is Only Part Server Security – Hackers can take down servers with denial-of- service attack – Hacker can log in as root user and take over the server – Steal data, lock out legitimate users, etc.

Total Security Server Security – Occasionally, weakness are discovered in server operating systems – This knowledge is quickly disseminated – Known security weaknesses

Total Security Server Security – Server operating system (SOS) vendors create patches – Many firms do not download patches – This makes them vulnerable to hackers, who quickly develop tools to probe for and then exploit known weaknesses

Total Security Client PC Security – Known security weaknesses exist but patches are rarely downloaded – Users often have no passwords or weak passwords on their computer – Adversaries take over client PCs and can therefore take over control over SSL, other secure communication protocols

Total Security Application Software – May contain viruses Must filter incoming messages – Database and other applications can add their own security with passwords and other protections

Total Security Managing Users – Often violate security procedures, making technical security worthless – Social engineering: attacker tricks user into violating security procedures

Defense in Depth Firewalls Antivirus Intrusion Detection Systems Intrusion Protection Systems