Network Security Applications

Network Security Applications

Network Security Applications

Hatem [email protected]

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AgendaAgenda

▪ Introduction

▪ An Authentication Application

▪ A Web Security Standard

▪ Summary

▪ References

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IntroductionIntroduction

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IntroductionIntroduction

Network security applications:

▪ Authentication Applications (Kerberos)

▪ Web Security Standards (SSL/TLS)

▪ Email Security

▪ IP Security

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KerberosAn Authentication Application

KerberosAn Authentication Application

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OverviewOverview

▪ Kerberos is a trusted third-party authentication protocol designed for TCP/IP networks (developed at MIT)

▪ A Kerberos service on the network acts as a trusted arbitrator

▪ Kerberos allows clients to access different entities (clients/servers) on the network

Kerberos

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The Kerberos ModelThe Kerberos Model

▪ Kerberos keeps a database of clients and their secret keys

▪ Services requiring authentication, as well as their clients, register their secret keys with Kerberos

Kerberos

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The Kerberos ModelThe Kerberos Model

▪ Kerberos creates a shared session key and gives it to client and server (or two clients) to encrypt messages

▪ Kerberos uses DES for encryption

▪ Kerberos Version 4 provided a weak nonstandard mode for authentication

▪ Kerberos Version 5 uses CBC mode

Kerberos

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How Kerberos WorksHow Kerberos Works

1. A client requests a ticket for a TGS (Ticket-Granting Service) from Kerberos

2. Kerberos sends the ticket to the client, encrypted in client’s secret key

3. To use a particular service, client requests a ticket from TGS

4. TGS issues and send a ticket to the client, encrypted with server's secret key

Kerberos

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How Kerberos WorksHow Kerberos Works

- The ticket is used by server to ensure that it is the same client to whom the ticket was issued

- Client can use the ticket multiple times to access the server until the ticket expires

5. Client presents ticket to server with an authenticator (the authenticator contains client’s name and a timestamp, encrypted with the shared session key)

Kerberos

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How Kerberos WorksHow Kerberos Works

- Unlike a ticket, an authenticator can only be used once

- The client can generate authenticators as needed using the shared secret key

6. If client credentials (ticket + authenticator) are correct, server provides access to service

Kerberos

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How Kerberos WorksHow Kerberos WorksKerberos

Kerberos TGS

Client Server

1

2 3

4

5

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Security of KerberosSecurity of Kerberos It may be possible to cache and replay old

authenticators. Although timestamps are supposed to prevent this, replays can be done during the lifetime of the ticket

Authenticators assume all clocks in the network are synchronized. If a host is fooled about the correct time, an old authenticator can be replayed

Kerberos

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Security of KerberosSecurity of Kerberos Password-guessing attacks: an intruder can

collect tickets and then try to decrypt them. The average user doesn’t usually choose good passwords

Malicious software: Kerberos rely on that its software is trustworthy. It is possible to replace all client Kerberos software with a version that records passwords

Kerberos

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Security of KerberosSecurity of Kerberos New enhancements to Kerberos include an

implementation of public-key cryptography and a smart-card interface for key management

Kerberos

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SSL/TLSA Web Security Standard

SSL/TLSA Web Security Standard

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OverviewOverview

Web security threats:

▪ Location● Server or client (System Security)● Network traffic (Web Security)

▪ Type● Passive attacks● Active attacks

SSL/TLS

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OverviewOverview

▪ Passive attacks include accessing network traffic between browser and server, accessing restricted information on a website, etc.

▪ Active attacks includes impersonating another user, altering messages in traffic, altering information on a website, etc.

SSL/TLS

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OverviewOverview

▪ Netscape originated the SSL (Secure Socket Layer) protocol to provide a reliable secure service on TCP

▪ TLS (Transport Layer Service) is the Internet standard version of SSL

▪ TLS is very similar to SSLv3

SSL/TLS

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Connections and SessionsConnections and Sessions

▪ A connection is a transport that provides a suitable type of service

▪ An session is an association between a client and a server

▪ Sessions define a set security parameters which can be shared among multiple connections

SSL/TLS

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Connections and SessionsConnections and Sessions

▪ A number of states are associated with each session

▪ During the handshake, pending read and write states are created

▪ Upon successful conclusion of the handshake, the pending states become the current states

SSL/TLS

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SSL ArchitectureSSL Architecture

▪ Layer1 (provides basic security services to higher-layer protocols such as HTTP):● Record Protocol

▪ Layer 2 (manages SSL exchanges):● Handshake Protocol● Change Cipher Spec Protocol● Alert Protocol

SSL/TLS

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SSL ArchitectureSSL ArchitectureSSL/TLS

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1. Record Protocol1. Record Protocol

Provides:

▪ Confidentiality: a shared secret key is used for encryption

▪ Message Integrity: a shared secret key is used to form a MAC (message authentication code)

SSL/TLS

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1. Record Protocol1. Record Protocol

1)Fragments data into blocks

2)Compresses the data (optional)

3)Applies a MAC

4)Encrypts using a symmetric encryption such as AES and RC4

5)Adds a header (length, SSL version, etc.)

6)Transmits in a TCP segment

SSL/TLS

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1. Record Protocol1. Record Protocol

Received data are:

1)Decrypted

2)Verified

3)Decompressed

4)Reassembled

5)Delivered to higher levels

SSL/TLS

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1. Record Protocol1. Record ProtocolSSL/TLS

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2. Handshake Protocol2. Handshake Protocol Used before any data is transmitted Allows the server and client to

authenticate each other through a series of messages. Each message has: Type: one of 10 types Length: length in bytes Content: session id, version, hash, etc.

SSL/TLS

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2. Handshake Protocol2. Handshake ProtocolSSL/TLS

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2. Handshake Protocol2. Handshake ProtocolSSL/TLS

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3. Change Cipher Spec3. Change Cipher Spec Consists of a single message which

consists of a single byte with the value 1 Copies the pending state into the current

state, which updates the cipher suite to be used on this connection

SSL/TLS

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4. Alert Protocol4. Alert Protocol Conveys SSL-related alert messages Each message consists of two bytes:

● Severity– Warning (1): certificate_expired, etc.– Fatal (2) - terminates the connection:

handshake_failure, bad_record_mac, etc.● Code

SSL/TLS

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SSL ProtocolsSSL ProtocolsSSL/TLS

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TLS vs SSLv3TLS vs SSLv3

Differences include: Version number: 3.x vs 3 MAC algorithm Pseudorandom function for key

generation and validation Alert Codes

SSL/TLS

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SummarySummary

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SummarySummary

▪ Kerberos is a trusted third-party authentication protocol that enables clients and servers to establish authenticated communication

▪ SSL provides security services between TCP and applications that use TCP

▪ TLS is the Internet standard version

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SummarySummary

▪ SSL/TLS provides confidentiality using symmetric encryption and message integrity using a MAC

▪ SSL/TLS enables two TCP users to determine the security mechanisms and services they will use

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ReferencesReferences

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ReferencesReferences

▪ Cryptography and Network Security Principles and Practices, 4th Edition,William Stallings

▪ Applied Cryptography, 2nd Edition,Bruce Schneier

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Thank You!Thank You!

Hatem [email protected]