Linux and network security

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Linux and network security

• A short two-part talk introducing
• Basic Linux/Unix system administration
  (CentOS/RHEL5)
• General Computer/Network security
• for the G53SEC module.
• Nick Reynolds.

CentOS 5
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Adding Accounts

• Need entry in /etc/passwd
• Need password in /etc/shadow
• Need home directory /home/username
• Correct Permissions

• man adduser
• adduser ltusernamegt
• man passwd
• passwd ltusernamegt

Gui Alternative redhat-config-users
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The Telnet Server (telnetd)

• Runs on receiving a connection
• man xinted
• Start with
• chkconfig krb5-telnet on
• Stop with
• chkconfig krb5-telnet off

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Configuring the Telnet Server

• Read manual page
• man telnetd
• Set up accounts using
• adduser
• Change account shell
• chsh ltusernamegt
• (Tip man ssh, chkconfig sshd on/off)

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Other Services

• ftp server
• httpd server (apache)
• ssh server

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Network Configuration (Optional)

• redhat-config-network-gui

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Software Installs Distribution

• Searching
• yum search string
• Installing
• yum install package
• Staying up to date
• yum update
• Lots more!
• man yum man yum.conf

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Monitoring The System

• Check logs
• /var/log/
• Monitor network activity
• tcpdump
• Monitor processes
• ps
• top

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Useful Commands

• Move between accounts
• /bin/su username
• Permissions and ownership
• chmod ltmodegt ltfilenamegt
• chgrp ltgroupgt ltfilenamegt
• chown ltusergt ltfilenamegt
• Manual pages
• man ltcommandgt

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Useful Resources

• CentOS5 (RedHat EE) Documentation
• http//netlab-gw.cs.nott.ac.uk/centos/5/docs/
• http//ftp.cs.nott.ac.uk/centos/5/docs/
• Linux Documentation Project
• http//newton.ex.ac.uk/LDP/
• Search Engines!

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Final CentOS Notes

• Many ways to achieve the same result.
• Experiment within a user account.
• Dont make to many changes in one go.
• Stay up to date (yum update)
• Advanced methods to configure servers
• man pam

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General Network/Computer Security

• Encryption
• Access Permissions
• Who/what do you trust?
• Network Infrastructure

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Encryption

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Encryption
Use secure Protocols Insecure Secure telnet
ssh ftp scp imap imaps http https
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Access Permissions
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Access Permissions

• File/directory permissions
• Firewalls

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Who/What do you trust?
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Who/What do you trust?

• DHCP?
• IP Addresses?

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Network Infrastructure
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Network Infrastructure

• Where does your data go?
• Switches? Hubs? Which route?
• Wi-fi

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The End!