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

Prof. Shervin Shirmohammadi

CEG 4185

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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 4185

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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 4185

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Cryptography • The encryption model for a symmetric-key cipher.

Prof. Shervin Shirmohammadi

CEG 4185

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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

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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 4185

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Substitution Ciphers • Two types of Ciphers: substitution; transposition • Substitution: Replace each symbol with another symbol • A substitution cipher: –ab cdefghi jklmnopqrs tuvwxyz –qwer tyuiopasd fg hjklz xcvbnm – 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

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Transposition Ciphers • A transposition cipher:

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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 4185

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Data Encryption Standard • 1977 standard of NSA. • Uses 56bit keys. • Takes in 64-bit plaintext segments. (a) General outline Prof. Shervin Shirmohammadi

CEG 4185

(b) details of one iteration 13-10

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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 = 2 × 1010 years

Prof. Shervin Shirmohammadi

CEG 4185

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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

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Cipher Block Chaining Mode • Cipher block chaining. (a) Encryption. (b) Decryption.

• Con: need to wait for complete C0 (typically 64-bit) before decryption can occur Prof. Shervin Shirmohammadi

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Cipher Feedback Mode • (a) Encryption. (b) Decryption.

• Con: 1 bit error will lead to an 8-byte transmission error Prof. Shervin Shirmohammadi

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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 4185

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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 4185

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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 4185

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Message Digests • Creates a unique, fixed-sized, one-way digest using the 2 3 message. 1 • MD5: takes 512 bit blocks and gives a 128-bit digest – Essentially a hash converter.

• Digital signatures using message digests and public-key encryption:

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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

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PK Management: Certificates • Who to get the certificate from? – Certificate Authority (CA)

• A possible certificate and its signed hash Issued by a CA

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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:

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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

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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 4185

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Threat Analysis Effect/ Prob.

User Devices

Servers

Network Elements

Software

Services

Data

Unauthorized Access

B/A

B/B

C/B

A/B

B/C

A/B

Unauthorized Disclosure

B/C

B/B

C/C

A/B

B/C

A/B

Denial of Service

B/B

B/B

B/B

B/B

B/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

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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

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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

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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

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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 4185

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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

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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

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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. (Host to host) Prof. Shervin Shirmohammadi

(b) ESP in tunnel mode. (gateway to gateway) CEG 4185

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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

Prof. Shervin Shirmohammadi

Message Processing Subsystem

Security Subsystem

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Access Control Subsystem

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Packet Filtering

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CEG 4185

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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 4185

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Network Perimeter 192.168.0.1

192.168.0.2

• 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: – 10.0.0.0 – 10.255.255.255 (class A) – 172.16.0.0 – 172.31.255.255 (class B) – 192.168.0.0 – 192.168.255.255 (class C) S-port=8777

S-port=63211

S-IP=192.168.0.2

Router

S-IP=137.122.20.1

NAT

Internet

137.122.20.1 D-port=8777

192.168.0.10

D-IP=192.168.02

D-port=63211D-IP=137.122.20.1

NAT port = 63210 NAT port = 63211 NAT port = 63212

port=5113 S-IP=192.168.0.10 port=8777 S-IP=192.168.0.2 port=6522 S-IP=192.168.0.1

Prof. Shervin Shirmohammadi

CEG 4185

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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

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CEG 4185

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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) User Computer Prof. Shervin Shirmohammadi

PPP CEG 4185

RADIUS Server

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