Denial of Service and Intrusion Detection

What is a DoS attack and how can it be initiated? Which one is done mostly?

In computing, a denial-of-service (DoS) or distributed denial-of-service (DDoS) attack is an attempt to make a machine or network resource unavailable to its intended users.
A DoS attack generally consists of efforts to temporarily or indefinitely interrupt or suspend services of a host connected to the Internet. As clarification, distributed denial-of-service attacks are sent by two or more people, or bots, and denial-of-service attacks are sent by one person or system. As of 2014, the frequency of recognized DDoS attacks had reached an average rate of 28 per hour. Perpetrators of DoS attacks typically target sites or services hosted on high-profile web servers such as banks, credit card payment gateways, and even root nameservers.
A denial of service (DoS) attack is an attack on the availability of network resources.DoS attacks can be initiated in many ways, including:

• Transmission failure

• Traffic redirection

• DNS attacks

• Connection flooding

Which types of connection flooding attacks do you know?

A connection flooding attack seeks to negatively affect the availability of a network recourse by exhausting or overwhelming the capacity of a communications channel. Types:

• Echo chargen

• Ping of death

• Smurth attack

• SYN flood

• Teardrop

What is an echo chargen attack?

Basically, this attack is a form of an UDP flood attack. The attacker sends a forged UDP echo request packet (with source IP of the target) to the port 19 (chargen) of another computer. This in turn sends a packet with random strings to the echo service port of the target computer responds again. As a result, the bandwidth of the computer is busy fast.

Source: http://image.slidesharecdn.com/12-tcp-dns-140326164729-phpapp01/95/12-tcpdns-14-638.jpg?cb=1395870536



What is the speciality of a ping of death attack?

A correctly formed ping message is typically 56 bytes in size, or 84 bytes when the Internet Protocol (IP) header is considered. Historically, many computer systems could not properly handle a ping packet larger than the maximum IPv4 packet size of 65535bytes. Larger packets could crash the target computer. In early implementations of TCP/IP, this bug was easy to exploit. This exploit affected a wide variety of systems, including Unix, Linux, Mac, Windows, printers, and routers. Generally, sending a 65,536-byte ping packet violates the Internet Protocol as documented in RFC 791, but a packet of such a size can be sent if it is fragmented; when the target computer reassembles the packet, a buffer overflow can occur, which often causes a system crash.



Describe smurf attacks and their impacts?

The smurf attack is an attack in which a system is flooded with spoofed ping messages. This creates high computer network traffic on the victim’s network, which often renders it unresponsive.
Smurfing takes certain well-known facts about Internet Protocol and Internet Control Message Protocol (ICMP) into account. ICMP is used by network administrators to exchange information about network state, and can also be used to ping other nodes to determine their operational status. The smurf program sends a spoofed network packet that contains an ICMP ping. The resulting echo responses to the ping message are directed toward the victim’s IP address. Large number of pings and the resulting echoes can make the network unusable for real traffic.



Show in an example how a teardrop attack is carried out.

In the teardrop attack, packet fragments are sent in a jumbled and confused order. When the receiving device attempts to reassemble them, it obviously won’t know how to handle the request. Older versions of operating systems will simply just crash when this occurs. Operating systems such as Windows NT, Windows 95, and even Linux versions prior to version 2.1.63 are vulnerable to the teardrop attack. As stated earlier, upgrading your network hardware and software is the best way to stay secure from these types of attacks.



Why are DDoS attacks more efficient than DoS attacks?

In a distributed denial of service attack, an attacker uses any convenient method to distribute a Trojan horse to as many target machines as possible. After choosing a victim, a signal is transmitted from the attacker to each zombie machine to initiate the attack. The Trojan horse on each zombie machine then launches a denial of service attack on the target.



How does an Intrusion Detection System work? What is the difference to an Intrusion Prevention System? Which goals do they have?

An intrusion detection system (IDS) is a device that monitors system activities with a view toward detecting malicious or suspicious events

IDS attempt to detect:

• Outsiders breaking into a system

• Insiders attempting to perform inappropriate actions

Goals of IDS:

• Detect wide variety of instrusions

• Previously known and unknown attacks

• Suggest need to learn/adapt to new attacks or changes in behavior

• Detect instrusions in timely fashion

• May need to be real-time especially when system responds to instrusion

• May suffice to report instrusion ocurred a few minutes or hours ago

• Present analysis in simple, easy-to-understand format

• Ideally a binary indicator

• Usually more complex, allowing analyst to examine suspected attack

• User interface critical, especially when monitoring many systems

• Be accurate

• Minimize false positives, false negatives

• Minimize time spent verifying attacks, looking for them

Name the differences between host-based and network-based IDSs.

Host-based:

• IDS runs on a host

• IDS monitors activities on this host only

Network-based:

• The IDS is a stand-alone device

• The IDS monitors the entire network or sub-network

Name the different modes of operation of an IDS. Which one is most efficient for detecting an attack?

Signature-based:

• The looks for known attacks

• To detect an attack, current activities are matched to known attack signatures

• Problem: Unable to detect new attacks (unknown signatures)

Anomaly-based:

• IDS allows only permitted behavior

• Uses models of acceptable user activities

• Raises alarm upon detection of deviation from model behavior

Hybrid:

• IDS is a combination of anomaly, signature, and/or heuristic-based approaches

Heuristic-based:

• The IDS automatically constructs a model of "normal" system behavior

• Current activities are compared to what is considered normal in order to identify unacceptable system activities

What can be done with the responses of an IDS.

• Protect systems and reduce exposure

• Alert a human

• Monitor the attack and collect data

Sources:

http://en.wikipedia.org/wiki/Intrusion_detection_system
http://www.geniusguard.com/AboutDDoS.php
http://en.wikipedia.org/wiki/Denial-of-service_attack
https://www.youtube.com/watch?v=0_59AocrBVo
http://beyondcgpa.com/tag/hacking-website-attack/
http://www.techopedia.com/definition/17294/smurf-attack

Firewalls and Network Security

A video about Firewalls and Network Security you can find at:
https://www.youtube.com/watch?v=XEqnE_sDzSk



Which characteristics make a network vulnerable to attacks?

Several characteristics make networks vulnerable to attack, including:

• System complexity

• Many points of attack

• Unknown boundary

• Resource and workload sharing

• Anonymity

What is a port scanner? How does a network admin use this tool?

Is a software application designed to probe a server or host for open ports. This is often used by administrators to verify security policies of their networks and by attackers to identify running services on a host with the view to compromise it. A network administrator or security analyst can use a port scanner to evaluate the strengths and weaknesses of a network.

A port scan or portscan can be defined as a process that sends client requests to a range of server port addresses on a host, with the goal of finding an active port. While not a nefarious process in and of itself, it is one used by hackers to probe target machine services with the aim of exploiting a known vulnerability of that service. However the majority of uses of a port scan are not attacks and are simple probes to determine services available on a remote machine.



What is a firewall? Which tasks can be fulfilled by a firewall?

A firewall is software or hardware that checks information coming from the Internet or a network, and then either blocks it or allows it to pass through to your computer, depending on your firewall settings.
A firewall can help prevent hackers or malicious software (such as worms) from gaining access to your computer through a network or the Internet. A firewall can also help stop your computer from sending malicious software to other computers.

Quelle: http://res2.windows.microsoft.com/resbox/en/windows%207/main/a253fe23-4fb7-48d2-b52f-f52cb0e82734_57.jpg


Just as a brick wall can create a physical barrier, a firewall creates a barrier between the Internet and your computer.
A firewall isn't the same thing as an antivirus program. To help protect your computer, you need both a firewall and an antivirus and anti-malware program.



What is a firewall security policy? Name some examples!

A firewall security policy is a set of rules that a firewall relies upon to determine which traffic should be allowed to pass through a network boundary.


Examples of firewall security policy rules:

• Block all access from the outside, allow all access to the outside
• Allow access from outside
• Only for certain activities
• Only for certain sub-networks, hosts, applications, or users

Firewalls may have a default security policy:

• Default permit
• Anything that is not expressly prohibited is allowed
• Default deny
• Anything that is not expressly allowed is denied

What can be done by stateful inspection firewall?

A dynamic or "stateful" packet inspection firewall maintains a table of active TCP sessions and UDP "pseudo" sessions. Each entry records the session's source and destination IP address and port numbers, and the current TCP sequence number. Entries are created only for those TCP connections or UDP streams that satisfy a defined security policy. Packets associated with these sessions are permitted to pass through the firewall. Sessions that do not match any policy are denied, as are any packets received that do not match an existing table entry.

Stateful inspection is more secure than packet filtering because it only allow packets belonging to an allowed session. For example, instead of permitting any host or program to send any kind of TCP traffic on port 80, a stateful inspection firewall ensures that packets belong to an existing session. Furthermore, it can authenticate the user when the session is established, it can determine whether the packets really carry HTTP, and it can enforce constraints at the application layer (e.g., filtering URLs to deny access to black-listed sites).



What is an application proxy gateway? How does it increase security?

Also known as application proxy or application-level proxy, an application gateway is an application program that runs on afirewall system between two networks. When a client program establishes a connection to a destination service, it connects to an application gateway, or proxy



What is a circuit-level-gateway?

A circuit-level gateway is a firewall that provides User Datagram Protocol (UDP) and Transmission Control Protocol (TCP) connection security, and works between an Open Systems Interconnection (OSI) network model’s transport and application layers such as the session layer. Unlike application gateways, circuit-level gateways monitor TCP data packet handshaking and session fulfillment of firewall rules and policies.

A proxy server is a security barrier between internal and external computers, while a circuit-level gateway is a virtual circuit between the proxy server and internal client.

For example, when a user Web page access request passes through the circuit gateway, basic internal user information, such as IP address, is exchanged for proper feedback. Then, the proxy server forwards the request to the Web server. Upon receiving the request, the external server sees the proxy server’s IP address but does not receive any internal user information. The Web or real server sends the proxy server a proper response, which is forwarded to the client or end user via the circuit-level gateway.



What are guard firewalls? Which advantages do they have over application proxy gateways?

A firewall is designed to limit traffic to certain services, a guard aims to control the information exchange that the network communication is supporting at the business level. Further, unlike a firewall a guard provides assurance that it is effective in providing this control even under attack and failure conditions.

A guard will typically sit between a protected network and an external network, and ensure the protected network is safe from threats posed by the external network and from leaks of sensitive information to the external network.

A guard is usually dual-homed, though guards can connect more than two networks, and acts as a full application layer proxy, engaging in separate communications on each interface. A guard will pass only the business information carried by the protocols from one network to another, and then only if the information passes configured checks which provide the required protection.



Where is a personal firewall implemented? Can it replace a hardware firewall?

A personal firewall differs from a conventional firewall in terms of scale. A personal firewall will usually protect only the computer on which it is installed, as compared to a conventional firewall which is normally installed on a designated interface between two or more networks, such as a router or proxy server. Hence, personal firewalls allow a security policy to be defined for individual computers, whereas a conventional firewall controls the policy between the networks that it connects.

The per-computer scope of personal firewalls is useful to protect machines that are moved across different networks. For example, a laptop computer may be used on a trustedintranet at a workplace where minimal protection is needed as a conventional firewall is already in place, and services that require open ports such as file and printer sharing are useful. The same laptop could be used at public Wi-Fi hotspots, where strict security is required to protect from malicious activity. Most personal firewalls will prompt the user when a new network is connected for the first time to decide the level of trust, and can set individual security policies for each network.



Name the six truths about firewalls!

• Exert only narrow control over the content that they allow to cross the network boundary

• Protect an environment only if they control the entire perimeter

• Systems should not contain any tools that could help an attacker who penetrates the firewall in subsequent exploits

• Do not protect data outside of the perimeter

• Must be properly configured, and their configuration settings must be periodically evaluated and updated

• From the outside, firewalls are the most visible component of a network, and are hence attractive targets for attack

Does NAT really increase the network security?

NAT does not add any real security to a network while it breaks almost any good concepts of a structured network design.
If you keep your network secure, it is no security leakage if the network is not hidden from the Internet by a NAT device. It is rather cumbersome that NAT breaks the end-to-end communication model and disrupts certain internet protocols.
The usage of NAT has several disadvantages, mainly because it breaks the end-to-end communication model which is essential for proper IP connections. For example, IPsec host-to-host tunnels cannot be used with NAT, the FTP protocol (active mode) does not work, VoIP (SIP) has troubles, and any other peer-to-peer protocols do not work out of the box if they need to establish connections to each other independently. To overcome this disadvantages, a few changes in the just mentioned protocols are proposed to use them also through NAT devices, called NAT traversal.




Sources:

http://en.wikipedia.org/wiki/Port_scanner
http://windows.microsoft.com/en-us/windows/what-is-firewall#1TC=windows-7
http://windows.microsoft.com/en-us/windows/understanding-firewall-settings#1TC=windows-7
https://www.netcetera.co.uk/Products/DedicatedServers/Additions/Firewall/
http://www.eircomictdirect.ie/docs/juniper/wp_firewall.pdf
http://en.wikipedia.org/wiki/Guard_(information_security)
http://www.wikiwand.com/en/Personal_firewall
http://www.slideshare.net/hiwashooter/personal-or-software-firewall
http://en.wikipedia.org/wiki/Network_address_translation
http://www.techopedia.com/definition/24780/circuit-level-gateway

Computer and Network Security - Types of Security Attacks and Services

This video is about security attacks and services:
 https://www.youtube.com/watch?v=LkzWHgX_GDU



What is the difference between trojans, viruses and worms?

Viruses
A computer virus is a type of malware that propagates by inserting a copy of itself into and becoming part of another program. It spreads from one computer to another, leaving infections as it travels. Viruses can range in severity from causing mildly annoying effects to damaging data or software and causing denial-of-service (DoS) conditions. Almost all viruses are attached to an executable file, which means the virus may exist on a system but will not be active or able to spread until a user runs or opens the malicious host file or program. When the host code is executed, the viral code is executed as well. Normally, the host program keeps functioning after it is infected by the virus. However, some viruses overwrite other programs with copies of themselves, which destroys the host program altogether. Viruses spread when the software or document they are attached to is transferred from one computer to another using the network, a disk, file sharing, or infected e-mail attachments.

Worms
Computer worms are similar to viruses in that they replicate functional copies of themselves and can cause the same type of damage. In contrast to viruses, which require the spreading of an infected host file, worms are standalone software and do not require a host program or human help to propagate. To spread, worms either exploit a vulnerability on the target system or use some kind of social engineering to trick users into executing them. A worm enters a computer through a vulnerability in the system and takes advantage of file-transport or information-transport features on the system, allowing it to travel unaided.

Trojans
A Trojan is another type of malware named after the wooden horse the Greeks used to infiltrate Troy. It is a harmful piece of software that looks legitimate. Users are typically tricked into loading and executing it on their systems. After it is activated, it can achieve any number of attacks on the host, from irritating the user (popping up windows or changing desktops) to damaging the host (deleting files, stealing data, or activating and spreading other malware, such as viruses). Trojans are also known to create back doors to give malicious users access to the system. Unlike viruses and worms, Trojans do not reproduce by infecting other files nor do they self-replicate. Trojans must spread through user interaction such as opening an e-mail attachment or downloading and running a file from the Internet.



What is the difference between an active and a passive attack?

Passive Attack
A passive attack monitors unencrypted traffic and looks for clear-text passwords and sensitive information that can be used in other types of attacks. Passive attacks include traffic analysis, monitoring of unprotected communications, decrypting weakly encrypted traffic, and capturing authentication information such as passwords. Passive interception of network operations enables adversaries to see upcoming actions. Passive attacks result in the disclosure of information or data files to an attacker without the consent or knowledge of the user.

Active Attack
In an active attack, the attacker tries to bypass or break into secured systems. This can be done through stealth, viruses, worms, or Trojan horses. Active attacks include attempts to circumvent or break protection features, to introduce malicious code, and to steal or modify information. These attacks are mounted against a network backbone, exploit information in transit, electronically penetrate an enclave, or attack an authorized remote user during an attempt to connect to an enclave. Active attacks result in the disclosure or dissemination of data files, DoS, or modification of data.



How can a passive attack be detected?

Passive attacks are very difficult to detect because they do not involve any alteration of the data. When the messages are exchanged neither the sender nor the receiver is aware that a third party has read the messages. This can be prevented by encryption of data.




Which types of active attacks are typically used?

• In a masquerade attack, the intruder pretends to be a particular user of a system to gain access or to gain greater privileges than they are authorized for. A masquerade may be attempted through the use of stolen login IDs and passwords, through finding security gaps in programs or through bypassing the authentication mechanism.

• In a session replay attack, a hacker steals an authorized user’s log in information by stealing the session ID. The intruder gains access and the ability to do anything the authorized user can do on the website.

• In a message modification attack, an intruder alters packet header addresses to direct a message to a different destination or modify the data on a target machine.

• In a denial of service (DoS) attack, users are deprived of access to a network or web resource. This is generally accomplished by overwhelming the target with more traffic than it can handle.

• In a distributed denial-of-service (DDoS) exploit, large numbers of compromised systems (sometimes called a botnet or zombie army) attack a single target.

What is X.800? Which services are included?

X-800 is an extention recommendation of the recommendation X-200 which describes the reference model for Open System Interconnection (OSI). It establishes a framework for coordinating the development of existing and future recommendations for the system interconnection. The objective of OSI is to permit the interconnection of heterogeneous computer systems so that communication between application process may be achieved. At various times, security controls need to be built in order to protect the information exchanged between application processes,but by doing so the cost and time of obtaining and modifying data will be greater than the potential value of the informations.

The OSI security architecture provides a useful overview of many concepts that take eyes on the mechanisms, services and security attacks which can be described as following :

• Security Attack : any action that compromises the security of information owned by somebody including unauthorized reading of a message of file and traffic analysis.

• Security Mechanism : any process that designed to detect or preventing a security attack to be held.

• Security Service : a process of enhancing / improving the security of data processing system and information exchange between application processes.

How does the ILOVEYOU-worm work?

The ILOVEYOU-worm comes in an e-mail note with "I LOVE YOU" in the subject line and contains an attachment that, when opened, results in the message being re-sent to everyone in the recipient's Microsoft Outlook address book and, perhaps more seriously, the loss of every JPEG, MP3, and certain other files on the recipient's hard disk. Because Microsoft Outlook is widely installed as the e-mail handler in corporate networks, the ILOVEYOU virus can spread rapidly from user to user within a corporation. On May 4, 2000, the virus spread so quickly that e-mail had to be shut down in a number of major enterprises such as the Ford Motor Company. The virus reached an estimated 45 million users in a single day.



What is a VANET? Which security measures need to be considered in those networks?

A VANET turns every participating car into a wireless router or node, allowing cars approximately 100 to 300 metres of each other to connect and, in turn, create a network with a wide range. As cars fall out of the signal range and drop out of the network, other cars can join in, connecting vehicles to one another so that a mobile Internet is created.

Source: http://adrianlatorre.com/projects/pfc/img/vanet_full.jpg




Which security measures are necessary in WMNs? Wich security attacks can happen in WMNs?

A wireless mesh network (WMN) is a mesh network created through the connection of wireless access points installed at each network user's locale. Each network user is also a provider, forwarding data to the next node. The networking infrastructure is decentralized and simplified because each node need only transmit as far as the next node. Wireless mesh networking could allow people living in remote areas and small businesses operating in rural neighborhoods to connect their networks together for affordable Internet connections.




What is the "Byzantine General Problem"?

Reliable computer systems must handle malfunctioning components that give conflicting information to different parts of the system. This situation can be expressed abstractly in terms of a group of generals of the Byzantine army camped with their troops around an enemy city. Communicating only by messenger, the generals must agree upon a common battle plan. However, one or more of them may be traitors who will try to confuse the others. The problem is to find an algorithm to ensure that the loyal generals will reach agreement. It is shown that, using only oral messages, this problem is solvable if and only if more than two-thirds of the generals are loyal; so a single traitor can confound two loyal generals. With unforgeable written messages, the problem is solvable for any number of generals and possible traitors.


Sources:

http://whatis.techtarget.com/definition/active-attack
http://computernetworkingnotes.com/network-security-access-lists-standards-and-extended/types-of-attack.html
http://www.cisco.com/web/about/security/intelligence/virus-worm-diffs.html

Virtual private networks

(see http://en.wikipedia.org/wiki/Virtual_private_network)

First watch the video at https://www.youtube.com/watch?v=4BfL0UHrzDY&spfreload=10. Afterwards please answer the following questions:

What is a VPN used for?

A Virtual Private Network (VPN) is a network technology that creates a secure network connection over a public network such as the Internet or a private network owned by a service provider. Large corporations, educational institutions, and government agencies use VPN technology to enable remote users to securely connect to a private network.

A VPN can connect multiple sites over a large distance just like a Wide Area Network (WAN). VPNs are often used to extend intranets worldwide to disseminate information and news to a wide user base. Educational institutions use VPNs to connect campuses that can be distributed across the country or around the world.

In order to gain access to the private network, a user must be authenticated using a unique identification and a password. An authentication token is often used to gain access to a private network through a personal identification number (PIN) that a user must enter. The PIN is a unique authentication code that changes according to a specific frequency, usually every 30 seconds or so.


Which types of VPNs are used?

There are three kinds of virtual private networks (VPNs). The most common ones are remote access VPNs or virtual private dial-up networks (VPDNs). These are user-to-LAN connections used when employees of a company who are in remote locations need to connect to the company's private network. A company that wants to set up a remote-access VPN usually outsources to an ESP or enterprise service provider. The ESP sets up a NAS (network access server) and also provides remote users with the software they need for their computers. Then users simply dial the NAS using a toll-free number and access the network via their VPN client software. VPNs offer a good third-party service for encrypted, secure connections between remote users within a private network.

The other two types of VPN are both site-to-site, meaning that multiple fixed sites are connected over a public network (like the Internet). A site-to-site VPN requires large-scale encryption and dedicated equipment. An intranet (password-protected site for company employees)-based VPN connects LAN to LAN when a company wants to connect multiple remote connections in one private network. An extranet-based VPN connects LAN to LAN between multiple companies (such as customers and suppliers) so that they can work in a shared environment.


How did VPNs evolve?

Many organisations today operate in complex, distributed environments that encompass multiple branch offices spread across diverse geographical locations, some of which may be subsidiaries or affiliated companies. For most of these, access to centralised IT resources is a must. And they also need to provide access to those IT resources for an expanding army of mobile workers and for external users. Remote access has become a fact of life.

To provide secure remote access to employees - and increasingly to business partners, suppliers and users - virtual private networks (VPN) have emerged as the technology of choice. The majority of VPN deployments are one of two flavours. Secure socket layer (SSL) VPNs require just an internet browser for setting up a VPN connexion and are an effective remote access solution for large numbers of remote and ad hoc users.


What made VPNs possible?

As the public networks evolved, also VPNs became more important. VPNs bring the possibility to get a private connection over a public network.


What are the components of a VPN? How do they work together? Explain that in more detail.

• VPN server: A computer that accepts VPN connections from VPN clients. 
• VPN client: A computer that initiates a VPN connection to a VPN server. A VPN client can be an individual computer or a router.
• Tunnel: The portion of the connection in which your data is encapsulated.
• VPN connection: The portion of the connection in which your data is encrypted. For typical secure VPN connections, the data is encrypted and encapsulated along the same portion of the connection.
• Tunneling protocols: Protocols that are used to manage tunnels and encapsulate private data. Data that is tunneled must also be encrypted to be a VPN connection. The Windows Server 2003 family includes the PPTP and L2TP tunneling protocols. For more information, see Point-to-Point Tunneling Protocol and Layer Two Tunneling Protocol.
• Tunneled data: Data that is usually sent across a private point-to-point link.
• Transit internetwork: The shared or public network crossed by the encapsulated data. For the Windows Server 2003 family, the transit internetwork is always an IP internetwork. The transit internetwork can be the Internet or a private IP-based intranet.

Quelle: https://i-msdn.sec.s-msft.com/dynimg/IC197655.gif


What is tunneling?

Virtual private network technology is based on the idea of tunneling.
VPN tunneling involves establishing and maintaining a logical network connection (that may contain intermediate hops). On this connection, packets constructed in a specific VPN protocol format are encapsulated within some other base or carrier protocol, then transmitted between VPN client and server, and finally de-encapsulated on the receiving side. For Internet-based VPNs, packets in one of several VPN protocols are encapsulated within Internet Protocol (IP) packets. VPN protocols also support authentication and encryption to keep the tunnels secure.


Which algorithms are used for encrpyting the packets?


A data packet can only be sent if the encryption key is known to both parties, and the connection is activated. If the encryption key is not known, a request is sent to the destination using the meta connection to retrieve it.

So, the entire VPN packet is encrypted using a symmetric cipher, including a 32 bits sequence number that is added in front of the actual VPN packet, to act as a unique IV for each packet and to prevent replay attacks. A message authentication code is added to the UDP packet to prevent alteration of packets. Tinc by default encrypts network packets using Blowfish with 128 bit keys in CBC mode and uses 4 byte long message authentication codes to make sure eavesdroppers cannot get and cannot change any information at all from the packets they can intercept. The encryption algorithm and message authentication algorithm can be changed in the configuration. The length of the message authentication codes is also adjustable. The length of the key for the encryption algorithm is always the default length used by OpenSSL.




Which VPN protocols are used very often in industry?

• OpenVPN
• PPTP
• Chameleon
• L2TP/IPsec
• SSL with encryption
• MPLS with constrained distribution of routing information through BGP

What is a split tunnel?

Split tunneling is a computer networking concept which allows a VPN user to access a public network (e.g., the Internet) and a local LAN or WAN at the same time, using the same physical network connection. This connection service is usually facilitated through a program such as a VPN client software application.
For example, suppose a user utilizes a remote access VPN software client connecting to a corporate network using a hotel wireless network. The user with split tunneling enabled is able to connect to file servers, database servers, mail servers and other servers on the corporate network through the VPN connection. When the user connects to Internet resources (Web sites, FTP sites, etc.), the connection request goes directly out the gateway provided by the hotel network.


Explain in short how OpenVPN and IPSec work and which components do they consist of?


OpenVPN:
OpenVPN is an open-source software application that implements virtual private network (VPN) techniques for creating secure point-to-point or site-to-site connections in routed or bridged configurations and remote access facilities. It uses a custom security protocol that utilizes SSL/TLS for key exchange. It is capable of traversing network address translators (NATs) and firewalls. It was written by James Yonan and is published under the GNU General Public License (GPL).

OpenVPN allows peers to authenticate each other using a pre-shared secret key, certificates, or username/password. When used in a multiclient-server configuration, it allows the server to release an authentication certificate for every client, using signature and Certificate authority. It uses the OpenSSL encryption library extensively, as well as the SSLv3/TLSv1 protocol, and contains many security and control features.

OpenVPN has been ported and embedded to several systems. For example, DD-WRT has the OpenVPN server function. SoftEther VPN, a multi-protocol VPN server, has an implementation of OpenVPN protocol.



IPSec:
IPSec is an Internet Engineering Task Force (IETF) standard suite of protocols that provides data authentication, integrity, and confidentiality as data is transferred between communication points across IP networks. IPSec provides data security at the IP packet level. A packet is a data bundle that is organized for transmission across a network, and it includes a header and payload (the data in the packet). IPSec emerged as a viable network security standard because enterprises wanted to ensure that data could be securely transmitted over the Internet. IPSec protects against possible security exposures by protecting data while in transit.


Quellen:
http://whatismyipaddress.com/vpn
http://computer.howstuffworks.com/three-types-of-vpn.htm
http://technet.microsoft.com/en-us/library/cc786563%28v=ws.10%29.aspx
http://compnetworking.about.com/od/vpn/a/vpn_tunneling.htm
http://www.tinc-vpn.org/documentation-1.1/Encryption-of-network-packets.html
http://documentation.netgear.com/reference/enu/vpn/VPNBasics-3-02.html

Pretty Good Privacy (PGP) / GNU Privacy Guard(GPG)

see http://en.wikipedia.org/wiki/Pretty_Good_Privacy
and http://en.wikipedia.org/wiki/GNU_Privacy_Guard

What is PGP?

Pretty Good Privacy (PGP) is a data encryption and decryption computer program that provides cryptographic privacy and authentication for data communication. PGP is often used for signing, encrypting, and decrypting texts, e-mails, files, directories, and whole disk partitions and to increase the security of e-mail communications. It was created by Phil Zimmermann in 1991 while working at PKWARE, Inc.

PGP and similar software follow the OpenPGP standard (RFC 4880) for encrypting and decrypting data.


What is PGP mainly used for?

Pretty Good Privacy can be used to authenticate digital certificates and encrypt/decrypt texts, emails, files, directories and whole disk partitions. Symantec, for example, offers PGP-based products such as Symantec File Share Encryption for encrypting files shared across a network and Symantec Endpoint Encryption for full disk encryption on desktops, mobile devices and removable storage. In the case of using PGP technology for files and drives instead of messages, the Symantec products allows users to decrypt and re-encrypt data via a single sign-on.


How does PGP work?

Quelle: http://upload.wikimedia.org/wikipedia/commons/thumb/4/4d/PGP_diagram.svg/1024px-PGP_diagram.svg.png


What is the web of trust?

Scematic representation of an web of trust:

Quelle: http://upload.wikimedia.org/wikipedia/commons/thumb/4/49/Web_of_Trust_2.svg/800px-Web_of_Trust_2.svg.png



How and why are certificates used? What is a certificate good for?


In the (more recent) OpenPGP specification, trust signatures can be used to support creation of certificate authorities. A trust signature indicates both that the key belongs to its claimed owner and that the owner of the key is trustworthy to sign other keys at one level below their own. A level 0 signature is comparable to a web of trust signature since only the validity of the key is certified. A level 1 signature is similar to the trust one has in a certificate authority because a key signed to level 1 is able to issue an unlimited number of level 0 signatures. A level 2 signature is highly analogous to the trust assumption users must rely on whenever they use the default certificate authority list (like those included in web browsers); it allows the owner of the key to make other keys certificate authorities.


What's the difference between PGP and GPG?

“PGP” stands for “Pretty Good Privacy.” It was developed by Phil Zimmermann. At first it was written as copyrighted freeware under the Gnu Public License. Later, PGP was upgraded and made into a propriety program. The rights for this program are traded around. The reason for this upgrade was legal defense costs and royalty issues related to the export laws of the USA. Now the PGP program is owned by PGP Corporation.

“GPG” stands for “Gnu Privacy Guard.” GPG is a re-write or upgrade of PGP. It does not use the IDEA encryption algorithm. This is to make it completely free. It uses the NIST AES, Advanced Encryption Standard. All the algorithm data is stored and documented publicly by OpenPGP Alliance. The main reason for this change is that AES costs less than IDEA and is considered more secure. Moreover, it is royalty free because it is not patented. GPG is more compatible than the original PGP with OpenPGP. GPG is also based on a command line. Windows frontends are also available for GPG other than the command line.


Which other methods can be used to encrypt E-Mails (see http://en.wikipedia.org/wiki/Email_encryption)?

• Enigmail - Thunderbird plug-in
• Entrust
• Echoworx
• Email authentication
• Email privacy
• Galaxkey - iOS, Android, Windows,BlackBerry and outlook plug-in
• GPGMail - OS X Mail.app plug-in
• MyKolab
• Secure Messaging
• Dark Mail Alliance
• HTTP Secure - a widely used communications protocol for secure communication over a computer network
• Hushmail
• Lavabit
• Mail1Click
• DataMotion, Inc.

How can PGP/GPG be used in popular E-Mail services (gmail, yahoo-mail, outlook)?

To use PGP, you will need to install some extra software that will work with your current email program. You will also need to create a private key, which you will keep private. The private key is what you will use to decrypt emails sent to you, and to digitally sign emails that you send to show they truly came from you. Finally, you'll learn how to distribute your public key—a small chunk of information that others will need to know before they can send you encrypted mail, and that they can use to verify emails you send.


Quellen: http://en.wikipedia.org/wiki/Pretty_Good_Privacy
http://en.wikipedia.org/wiki/GNU_Privacy_Guard
http://searchsecurity.techtarget.com/definition/Pretty-Good-Privacy

Digital Signiture

see http://en.wikipedia.org/wiki/Digital_signature

Please answer the following questions:


What is authentication and integrity?

Authentication:
Although messages may often include information about the entity sending a message, that information may not be accurate. Digital signatures can be used to authenticate the source of messages. When ownership of a digital signature secret key is bound to a specific user, a valid signature shows that the message was sent by that user. The importance of high confidence in sender authenticity is especially obvious in a financial context. For example, suppose a bank's branch office sends instructions to the central office requesting a change in the balance of an account. If the central office is not convinced that such a message is truly sent from an authorized source, acting on such a request could be a grave mistake.

Integrity:
In many scenarios, the sender and receiver of a message may have a need for confidence that the message has not been altered during transmission. Although encryption hides the contents of a message, it may be possible to change an encrypted message without understanding it. (Some encryption algorithms, known as nonmalleable ones, prevent this, but others do not.) However, if a message is digitally signed, any change in the message after signature invalidates the signature. Furthermore, there is no efficient way to modify a message and its signature to produce a new message with a valid signature, because this is still considered to be computationally infeasible by most cryptographic hash functions (see collision resistance).


What are the applications of digital signatures, when are they used?

A digital signature can be used with any kind of message -- whether it is encrypted or not -- simply so the receiver can be sure of the sender's identity and that the message arrived intact. Digital signatures make it difficult for the signer to deny having signed something (non-repudiation) -- assuming their private key has not been compromised -- as the digital signature is unique to both the document and the signer, and it binds them together. A digital certificate, an electronic document that contains the digital signature of the certificate-issuing authority, binds together a public key with an identity and can be used to verify a public key belongs to a particular person or entity.

Most modern email programs support the use of digital signatures and digital certificates, making it easy to sign any outgoing emails and validate digitally signed incoming messages. Digital signatures are also used extensively to provide proof of authenticity, data integrity and non-repudiation of communications and transactions conducted over the Internet.

Digital signatures are often used to implement electronic signatures, a broader term that refers to any electronic data that carries the intent of a signature, but not all electronic signatures use digital signatures.In some countries, including the United States, India, Brazil, and members of the European Union, electronic signatures have legal significance.


How do they work, how is message signed and verified?

Quelle: http://upload.wikimedia.org/wikipedia/commons/thumb/2/2b/Digital_Signature_diagram.svg/1280px-Digital_Signature_diagram.svg.png


What is the hash of a message? Which hash functions are the most popular ones?
What's the difference to an electronic signature?

Producing hash values for accessing data or for security. A hash value (or simply hash), also called a message digest, is a number generated from a string of text. The hash is substantially smaller than the text itself, and is generated by a formula in such a way that it is extremely unlikely that some other text will produce the same hash value.
Hashes play a role in security systems where they're used to ensure that transmitted messages have not been tampered with. The sender generates a hash of the message, encrypts it, and sends it with the message itself. The recipient then decrypts both the message and the hash, produces another hash from the received message, and compares the two hashes. If they're the same, there is a very high probability that the message was transmitted intact.
Hashing is also a common method of accessing data records. Consider, for example, a list of names:

• John Smith
• Sarah Jones
• Roger Adams

To create an index, called a hash table,for these records, you would apply a formula to each name to produce a unique numeric value. So you might get something like:

• 1345873 John smith
• 3097905 Sarah Jones
• 4060964 Roger Adams

Then to search for the record containing Sarah Jones,you just need to reapply the formula, which directly yields the index key to the record. This is much more efficient than searching through all the records till the matching record is found.

Quelle: http://www.webopedia.com/TERM/H/hashing.html



Name some digital signature algorithms:

• Pairing-based schemes such as BLS
• Undeniable signatures
• Rabin signature algorithm
• cryptographic protocols such as zero-knowledge proofs or secure c
• DSA and its elliptic curve variant ECDSA
• Aggregate signature
• RSA-based signature schemes, such as RSA-PSS
• ElGamal signature scheme as the predecessor to DSA, and variants Schnorr signature and Pointcheval–Stern signature algorithm

Which additional security precautions can be used?

• Putting the private key on a smart card
• Using smart card readers with a separate keyboard
• Other smart card designs
• Using digital signatures only with trusted applications
• Using a network attached hardware security module

Quelle: http://en.wikipedia.org/wiki/Digital_signature#Authentication
http://en.wikipedia.org/wiki/Digital_signature
http://www.webopedia.com/TERM/H/hashing.html
http://searchsecurity.techtarget.com/definition/digital-signature

Diffie–Hellman key exchange

(see also on http://en.wikipedia.org/wiki/Diffie%E2%80%93Hellman_key_exchange)

Please watch the following video under http://www.youtube.com/watch?v=YEBfamv-_do and give answers to the following questions:


What's the purpose of this algorithm, when is it used?
This algorythm allows two parties that have no prior knowledge of each other to jointly establish a shared secret key over an insecure communications channel. The key can be used to encrypt subsequent communications using a symmetric key cipher.

What is a one way function?
The one way function is easy to perform but hard to reverse.

Quelle: http://www.cs.cornell.edu/courses/cs513/2007fa/TL01.one-way.png

How does the algorithm work?

Quelle: https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhkUGnMgfk2C3Vt_pHSETdCRFhdlZ9r5bMvGIALosi8XWii94F8sDQDLP_wk40XwO5yqsItDNQ7N0zastpfblYI17k-gDxCRR6opNOHazh1ql3IGe-y0pDZQFyKhbRkl2U2s2o7mzOcTOY/s1600/Unbenannt.PNG


What is clock arithmetic, which characteristics does it have?

In mathematics, modular arithmetic is a system of arithmetic for integers, where numbers "wrap around" upon reaching a certain value - the modulus. The modern approach to modular arithmetic was developed by Carl Friedrich Gauss in his book Disquisitiones Arithmeticae, published in 1801.

A familiar use of modular arithmetic is in the 12-hour clock, in which the day is divided into two 12-hour periods. If the time is 7:00 now, then 8 hours later it will be 3:00. Usual addition would suggest that the later time should be 7 + 8 = 15, but this is not the answer because clock time "wraps around" every 12 hours; in 12-hour time, there is no "15 o'clock". Likewise, if the clock starts at 12:00 (noon) and 21 hours elapse, then the time will be 9:00 the next day, rather than 33:00. Since the hour number starts over after it reaches 12, this is arithmetic modulo 12. According to the definition below, 12 is congruent not only to 12 itself, but also to 0, so the time called "12:00" could also be called "0:00", since 12 is congruent to 0 modulo 12.

Quelle: http://upload.wikimedia.org/wikipedia/commons/thumb/a/a4/Clock_group.svg/560px-Clock_group.svg.png

What is the discrete logarithm problem?

Discrete logarithms are logarithms defined with regard to multiplicative cyclic groups. If G is a multiplicative cyclic group and g is a generator of G, then from the definition of cyclic groups, we know every element h in G can be written as gx for some x. The discrete logarithm to the base g of h in the group G is defined to be x . For example, if the group is Z5*, and the generator is 2, then the discrete logarithm of 1 is 4 because 24 ≡ 1 mod 5.

 The discrete logarithm problem is defined as: given a group G, a generator g of the group and an element h of G, to find the discrete logarithm to the base g of h in the group G. Discrete logarithm problem is not always hard. The hardness of finding discrete logarithms depends on the groups. For example, a popular choice of groups for discrete logarithm based crypto-systems is Zp* where p is a prime number. However, if p−1 is a product of small primes, then the Pohlig–Hellman algorithm can solve the discrete logarithm problem in this group very efficiently. That's why we always want p to be a safe prime when using Zp* as the basis of discrete logarithm based crypto-systems. A safe prime is a prime number which equals 2q+1 where q is a large prime number. This guarantees that p-1 = 2q has a large prime factor so that the Pohlig–Hellman algorithm cannot solve the discrete logarithm problem easily. Even p is a safe prime, there is a sub-exponential algorithm which is called the index calculus. That means p must be very large (usually at least 1024-bit) to make the crypto-systems safe.
Quelle: http://www.doc.ic.ac.uk/~mrh/330tutor/ch06s02.html


Calculate the private shared key, when Alice selects 56 and Bob selects 23 as a random number.
What is authentication? Does the Diffie-Hellman key exchange provide authentication?

Firstly you have to agree on a prime modulus and a generic. For example we can choose 5 as the prime modulus and 17 as generic.

Both parties can generate the private shared key with their random number.

556 mod 17 = 16

523 mod 17 = 10

So the private shard keys are 16 and 11.