Prof. Shervin Shirmohammadi SITE, University of Ottawa. Security Architecture. Lecture 13: Prof. Shervin Shirmohammadi CEG

Transcription

1 Lecture 13: Security Architecture Prof. Shervin Shirmohammadi SITE, University of Ottawa Prof. Shervin Shirmohammadi CEG

2 Network Assets and Security Threats Assets: Hardware (PC, workstation, etc) Servers Network devices (routers, hubs, ) Software (OS, programs, ) Services (applications, networking services) Data (stores, in-transit, databases, ) Threats: Unauthorized access to assets. Unauthorized disclosure of information Denial of service Theft (data, hardware, software ) Corruption of data, viruses, worms Physical damage Prof. Shervin Shirmohammadi CEG

3 Security Network Security: Protection of network and its services from unauthorized access, modification, destruction, or disclosure. Necessary for the network performing its critical functions correctly. Requirements: Confidentiality: data should be accessible to authorized parties only. Integrity: data can only be modified by authorized parties. Authenticity: receiver should be able to verify the identity of sender. Typically cryptography is used for fulfilling these requirements. Prof. Shervin Shirmohammadi CEG

4 Cryptography The encryption model for a symmetric-key cipher. Prof. Shervin Shirmohammadi CEG

5 Passive Attacks Eavesdropping on transmissions to obtain information Release of message contents Outsider learns content of transmission Traffic analysis By monitoring frequency and length of messages, even encrypted, nature of communication may be guessed Difficult to detect Can be prevented Prof. Shervin Shirmohammadi CEG

6 Active Attacks Masquerade Pretending to be a different entity Replay Modification of messages Denial of Service More easy to detect Detection may lead to deterrent Hard to prevent Prof. Shervin Shirmohammadi CEG

7 Substitution Ciphers Two types of Ciphers: substitution; transposition Substitution: Replace each symbol with another symbol A substitution cipher: a b c d e f g h i j k l m n o p q r s t u v w x y z q w e r t y u i o p a s d f g h j k l z x c v b n m attack QZZQEA Broken using statistical properties of the language. English: e, t, o, a, n, i; th, in, er, re, an; the, ing, and, ion Prof. Shervin Shirmohammadi CEG

8 Transposition Ciphers A transposition cipher: Prof. Shervin Shirmohammadi CEG

9 Symmetric-Key Algorithms Uses a shared secret key between the sender and the receiver. DES The Data Encryption Standard AES The Advanced Encryption Standard Each technique comes with a number of different Cipher Modes for specific situations. Prof. Shervin Shirmohammadi CEG

10 Data Encryption Standard 1977 standard of NSA. Uses 56- bit keys. Takes in 64-bit plaintext segments. (a) General outline (b) details of one iteration Prof. Shervin Shirmohammadi CEG

11 DES problems 56-bit key too short; these days it can be broken by a submillion dollar machine in under 1 day. NSA (National Security Agency) suspected of incorporating secret design to easily break DES for itself. Age of universe 20 billion years = years Prof. Shervin Shirmohammadi CEG

12 Electronic Code Book Mode Cipher Modes add more security for specific situations. The plaintext of a file encrypted as 16 DES blocks: Con: one can switch parts of ciphertext undetectably. Prof. Shervin Shirmohammadi CEG

13 Cipher Block Chaining Mode Cipher block chaining. (a) Encryption. (b) Decryption. Con: need to wait for complete C 0 (typically 64-bit) before decryption can occur Prof. Shervin Shirmohammadi CEG

14 Cipher Feedback Mode (a) Encryption. (b) Decryption. Con: 1 bit error will lead to an 8-byte transmission error Prof. Shervin Shirmohammadi CEG

15 Stream Cipher Mode & Counter Mode Stream Cipher Mode: (a) Encryption. (b) Decryption. Counter Mode: allows for Random Access - the ability to decrypt a specific part of the message. Prof. Shervin Shirmohammadi CEG

16 Public-Key Algorithms Also known as asymmetric algorithm. Uses a pair of keys, one public and one private. The idea is to give away your public key! Encrypt your messages using the public key and you can decrypt it using the private key, and vice versa! Public-key algorithm can be used for both authentication and confidentiality; although differently for each. Main disadvantage: slow processing. Prof. Shervin Shirmohammadi CEG

17 Digital Signatures Similar to a signature on a document, a digital signature validates the authenticity of its signee: It was indeed the signee (and not someone else) who singed this document It was indeed this document (and not some other document), that the signee signed. Upon receiving such digital signature, one can prove, in a court of law, that the document is indeed signed by the person indicated by his/her signature. Typically uses Message Digests Prof. Shervin Shirmohammadi CEG

18 Message Digests Creates a unique, fixed-sized, one-way digest using the message. MD5: takes 512 bit blocks and gives a 128-bit digest Essentially a hash converter. Digital signatures using message digests and public-key encryption: Prof. Shervin Shirmohammadi CEG

19 SHA-1 SHA: Secure Hash Algorithm Takes 512 bit blocks and gives a 160-bit digest Use of SHA-1 and RSA for signing non-secret messages. Prof. Shervin Shirmohammadi CEG

20 PK Management: Certificates Who to get the certificate from? Certificate Authority (CA) A possible certificate and its signed hash Issued by a CA Prof. Shervin Shirmohammadi CEG

21 PK Management: X.509 What format to use for the certificate: One possible one: ITU X.509 The basic fields of an X.509 certificate: Prof. Shervin Shirmohammadi CEG

22 PK Management: Public-Key Infrastructures Obviously we can t have one server for the CA for the whole planet Scalability problems Solution: use multiple servers, but make sure there is a hierarchical infrastructure to maintain integrity and reliability. A hierarchical PKI. Regional Authority Prof. Shervin Shirmohammadi CEG

23 Security Administration Similar to requirements and flow analysis, it is important to find out what security threats affect the network, and how we can protect against them. Consists of two components: Threat analysis In consultation with users, administrators, an operators, assets and risks are recorded and analysed. Policies and procedures Rules of system usage (what to do, and what not to do) Prof. Shervin Shirmohammadi CEG

24 Threat Analysis Effect/ Prob. Unauthorized Access Unauthorized Disclosure Denial of Service User Devices B/A B/C B/B Servers B/B B/B B/B Network Elements C/B C/C B/B Software A/B A/B B/B Services B/C B/C B/B Data A/B A/B D/D Theft A/D B/D B/B A/B C/C A/B Corruption A/C B/C C/C A/B D/D A/B Viruses B/B B/B B/B B/B B/C D/D Physical Damage A/D B/C C/C D/D D/D D/D Effect: A=Destructive B=Disabling C=Disruptive D=No Impact Probability: A=Certain B=Unlikely C=Likely D=Impossible Prof. Shervin Shirmohammadi CEG

25 Policies and Procedures Formal statements on rules for system, network, and information access and use. Understand possible security breaches, and implement policies to deal with these breaches Common security philosophies: Deny specifics/permit all else (open network philosophy) Permit specifics/deny all else (closed network philosophy) Policies should include: Privacy statement (monitoring, logging, access) Accountability statement (auditing, responsibility) Authentication statement (password policies, remote access) Reporting violations (procedures, contact info) Prof. Shervin Shirmohammadi CEG

26 Security Mechanisms 1. Physical Security and Awareness Protection of devices from physical access Security Awareness in order to educate persons 2. Protocol and Application Security Packet filters SNMPv3 IPSec 3. Encryption / Decryption 4. Network Perimeter Firewalls and NAT 5. Remote Access security Not all mechanisms are appropriate/needed for all environments Degree of protection it provides Expertise required for installation and configuration Cost of purchasing, implementing and operating it Amounts of administration and maintenance required Prof. Shervin Shirmohammadi CEG

27 Physical Security and Awareness Physical security Protected access (e.g. to server rooms etc.) Backup power source and power conditioning Off-site storage and retrieval Alarm systems (fire, also illegal entry) Awareness Educating users and their involvement in all aspects of security Training, knowledge of breaches Bulletins and newsletters Prof. Shervin Shirmohammadi CEG

28 Protocol and Application Security Most common mechanisms in this category: IPsec Secures anything that goes in the IP datagram All layers above and including IP will benefit from this Disadvantage? SNMPv3 NOT SNMPv1 or SNMPv2 (they have no security) Only secures network management Packet filtering Port or IP blocking. Prof. Shervin Shirmohammadi CEG

29 IPsec A protocol used to enhance IP with security. Establishes a simplex connection, known as Security Association (SA). Unlike normal IP, that is connectionless. It s a simplex connection, so we d need two SAs for a full-duplex secure connection. Provides Authentication Header (AH), and Encapsulating Security Payload (ESP). AH is used for authentication, ESP is used for : authentication and confidentiality. Used in transport mode (host-to-host), or tunnel mode (gateway-to-gateway). Prof. Shervin Shirmohammadi CEG

30 IPsec AH The IPsec authentication header in transport mode for IPv4. HMAC: Hashed Message Authentication Code Packet, and some IP header fields, are hashed together with a private key to form a digital signature. How to let the receiver know that this packet is an IPsec packet? Set the protocol field in the IP header to be IPsec (value 51) Prof. Shervin Shirmohammadi CEG

31 IPsec ESP Used for both authentication and confidentiality. ESP header has fields similar to the AH header, plus some more for encryption purposes. HMAC is a trailer (rather than a header) due to easier hardware implementation (like Ethernet s CRC). (a) ESP in transport mode. (b) ESP in tunnel mode. (Host to host) (gateway to gateway) Prof. Shervin Shirmohammadi CEG

32 SNMPv3 Security at the message level Authentication Privacy of message via secure communication Flexible access control Who can access? What can be accessed? What MIB views? SNMP Engine (identified by snmpengineid) Dispatcher Message Processing Subsystem Security Subsystem Access Control Subsystem Prof. Shervin Shirmohammadi CEG

33 Packet Filtering Prof. Shervin Shirmohammadi CEG

34 Encryption / Decryption Provides protection of the information from being used by an attacker. Other security mechanisms concentrate on protection against unauthorized access and destruction of resources. Most of these mechanisms work on either symmetric key or asymmetric key encryption. Cons Degrades network performance 15-85% Hardware solution speed things up Administration and maintenance is required Expensive Prof. Shervin Shirmohammadi CEG

35 Network Perimeter Protects the external interfaces of your network: the components in your network that act as connectors to the external networks. Network Address Translation (NAT) is the most commonly used technique to achieve this security NAT was originally developed to solve IP address exhaustion problem by introducing private networks: (class A) (class B) (class C) S-port=8777 S-IP= S-port=63211 S-IP= Router NAT Internet D-port=8777 D-IP= D-port=63211D-IP= NAT port = port=5113 S-IP= NAT port = port=8777 S-IP= NAT port = port=6522 S-IP= Prof. Shervin Shirmohammadi CEG

36 Firewall Firewalls are combinations of one or more security mechanisms, placed at strategic locations within a network. E.g. port filtering, plus NAT Can be standalone devices, or part of other equipment (routers, gateways, etc.) May require knowledge of users requirements (telnet, ftp, etc.) Network performance degradation up to 30% Can complicate LAN/MAN/WAN troubleshooting Prof. Shervin Shirmohammadi CEG

37 Remote Access Security Remote access is a common operation where users need access to internal resources via dial-in, point-to-point sessions, and VPNs. Commonly known as AAAA Authentication, Authorization, Accountability, and Allocation Considerations Server types and locations (DMZs) Interactions with DNS, address pools, other services. PPP/PPPoE Network Network Internet User Computer dial Network Access Server (NAS) RADIUS Server User Computer PPP RADIUS Prof. Shervin Shirmohammadi CEG