Information Security Practical

COURSE TITLE: Information Security

By: Deepak Kumar Rajak

www.earnrupees4you.com COURSE CODE: IT- 801

List of Experiments:-

1. Study of Network Security fundamentals - Ethical Hacking, Social Engineering practices. 2. System threat attacks - Denial of Services. 3. Sniffing and Spoofing. 4. Web Based Password Capturing. 5. Virus and Trojans. 6. Anti-Intrusion Technique – Honey pot. 7. Symmetric Encryption Scheme – RC4. 8. Block Cipher – S-DES, 3-DES. 9. Asymmetric Encryption Scheme – RSA. 10. IP based Authentication.

1. ETHICAL HACKING Ethical hacking is a process in which an authenticated person,who is a computer and network expert, attacks a security system on behalf of it`s owners a security system on behalf of its owners, seeking vulnerabilities that a malicious hacker could exploit. In order to test the system an ethical hacker will use the sameprinciples as the usual hacker uses, but reports those vulnerabilities instead of using them for their own advantage. 1 Analogy with Building Robbing The methodology of a hacker is similar to the one used for usual thefts. Lets consider the case of a bank robbery. The first step will be to find information about the total transaction of the bank, the total amount of money that may be kept in the bank, who is the manager, if the security personals have a gun with them etc. This is similar to the reconnaissance phase of hacking. Methodology of Hacking As described above there are mainly five steps in hacking like reconnaissance, scanning, gaining access, maintaining access and clearing tracks. But it is not the end of  the process. The actual hacking will be a circular one. Once the hacker completed the five steps then the hacker will start reconnaissance in that stage and the preceding stages to get in to the next level. The various stages in the hacking methodology are ● Reconnaissance ● Scanning & Enumeration ● Gaining access ● Maintaining access Social Engineering The best and the most common method used to crack the password is social engineering. In this technique the hacker will come in direct contact with the user through a phone call or some way and directly ask for the password by doing some fraud.

2.DENIAL OF SERVICE denial-of-service attack (DoS attack) or distributed denial-of-service attack (DDoS attack) is an attempt to make a computer resource unavailable to its intended users. Although the means to carry out, motives for, and targets of a DoS attack may vary, it generally consists of the concerted efforts of a person or people to prevent an Internet site or service from functioning efficiently or at all, temporarily or indefinitely. 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. The term is generally used with regards to computer networks, but is not limited to this field; for [1] example, it is also used in reference to CPU resource management.

One common method of attack involves saturating the target machine with external communications requests, such that it cannot respond to legitimate traffic, or responds so slowly as to be rendered effectively unavailable. In general terms, DoS attacks are implemented by either forcing the targeted computer(s) to reset, or consuming its resources so that it can no longer provide its intended service or obstructing the communication media between the intended users and the victim so that they can no longer communicate adequately. Denial-of-service attacks are considered violations of the IAB's Internet proper use policy, and also violate the acceptable use policies of virtually all Internet service providers. They also commonly constitute violations of the laws of individual [ ] nations. citation needed 

Methods of attack A "denial-of-service" attack is characterized by an explicit attempt by attackers to prevent legitimate users of a service from using that service. There are two general forms of DoS [3] attacks: those that crash services and those that flood services. Attacks can be directed at any network device, including attacks on routing devices and web, electronic mail, or Domain Name System servers. 1. Consumption of computational resources, such as bandwidth, disk space, or processor time. 2. Disruption of configuration information, such as routing information. 3. Disruption of state information, such as unsolicited resetting of TCP sessions. 4. Disruption of physical network components. 5. Obstructing the communication media between the intended users and the victim so that they can no longer communicate adequately. A DoS attack may include execution of malware intended to:   

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[citation needed ]

Max out the processor's usage, preventing any work from occurring. Trigger errors in the microcode of the machine. Trigger errors in the sequencing of instructions, so as to force the computer into an unstable state or lock-up. Exploit errors in the operating system, causing resource starvation and/or thrashing, i.e. to use up all available facilities so no real work can be accomplished. Crash the operating system itself.

Denial of Service Techniques

Network protocols attacks These attacks aim at the transmission channel, and therefore target the IP stack which is an entry point for critical resources such as memory and CPU.

SYNFloods SYNFloods are typical concept-based denial of service attacks as they entirely rely on the way TCP connections are established. During the initial 3-way handshake, the server fills up a table, the TCB (Transmission Control Block), which keeps session information in memory. When a server receives the initial SYN packect from a client,it sends backs a SYN-ACK packet and creates an entry in the TCB. The connection is in a TIME_WAIT status, for as long as the server waits for the final ACK packet fromthe client. If this final ACK packet is not received, another SYN-ACK is sent to the client. Finally, if after multiple retries none of the SYN-ACK packets are acknowledged by the client, the session is closed and flushed from the TCB. The period of time between the transmission of the first SYN-ACK and the closure of the session is usually around 30 seconds. SYN-ACK Flood SYN-ACK Floods rely on CPU resource exhaustion. Theoretically this kind of packet is the second step of the TCP 3-way handshake and there should be a corresponding entry in the TCB. Browsing the TCB uses CPU resources, especially when the TCB appears to be large. Then, under heavy load, this resource usage can affect the performance of the system. UDP Flood UDP is also naturally bound to be a vector of Denial of Service attacks. As it is specified, a server receiving a UDP packet on a closed port sends back an ICMP Port Unreachable packet to the source. The data part of the ICMP packet is filled with at least the first 64 bytes of the original UDP packet. As no limit or quota is specified as a standard, it is then possible to send huge amount of packets on closed ports. At very high load, operations necessary to generate ICMP error packets consume a lot of CPU, eventually leading to CPU resource exhaustion. Generating such attacks is once again possible from a simple command. 3.Sniffing and Spoofing. Spoofing is the action of making something look like something that it is not in order to gainunauthorized access to a user's private information. The idea of spoofing originated in the 1980s with the discovery of a security hole in the TCP protocol. Today spoofing exists in various forms namely IP, URL and Email spoofing.All email users might have received an email asking us to update our profile information for ouraccount in either Paypal or other financial institutions. Some of these users might know that these emails are acts of phishing and thus they avoid/delete emails like these, and others might not beaware of this practice and so they navigate to a spoofed Website by clicking on a link provided in the spoofed email. A spoofed Website is designed to look exactly like

the original Website (sometimes even the URL, title bar, and status bar mimic the original Website, this is referred to as a spoofed URL) and a spoofed email appears to be sent from a legitimate source; while in fact it was sent from someone else. Phishing and spoofing are closely related. The paper will address the issue of spoofing and the negative effects on computer users. It will analyze the various types of spoofing, current prevention methods and current research in new technology to prevent spoofing (site-authentication or Certified Mail Delivery). Types of Spoofing IP Spoofing Internet Protocol (IP) is the protocol used for transmitting messages over the Internet; it is a networkprotocol operating at layer 3 of the OSI model. URL Spoofing URL spoofing occurs when one website appears as if it is another. The URL that is displayed is not the real URL of the site, therefore the information is sent to a hidden hi dden web address. Email Spoofing Email spoofing is the act of altering the header of an email so that the email appears to be sent from someone else. Attacks Cause confusion or discredit a person Social Engineering (phishing) Hide identity of the sender (spamming).   

Sniffing Sniffing is the act of intercepting and inspecting data packets using sniffers (Software or hardware devices) over the Net. Sniffing is a passive security attack in which a machine separated from the intended destination reads data on a network. These passive security attacks are those, that do not alter the normal flow of data on a communication link or inject data in to the link, but lead to leakages of different kinds of information like: Passwords, Financial figures, Confidential/Sensitive data & Lowlevel Protocol information. Sniffing is considered as the virtual counterpart of  shoulder surfing. Sniffers are also used as a troubleshooting tool by the Network  Administrators.  

Targets Data Link layer of protocol stack  Sniffer – gathers traffic off network 

This data can include userIDs passwords transmitted by telnet, DNS queries and responses, sensitive emails, FTP passwords, etc. Allows attacker to read data passing a given machine in real time.   Two types of sniffing:  Active Passive  Passive  Attacker must have account on LAN  Done over a hub  Usually once access is gained on one computer attacker uses passwords to get in other computers Active  Attacker still needs an account  Several different attacks: - Parsing . Packets - Flooding - Spoofed ARP Messages - DNS Spoofing - HTTPS and SSH spoofing 

IP Address Spoofing  Three main flavors - Simple Spoofing - Undermining Unix r-Commands - Spoofing with source routing  Doesn’t allow actions to be traced back to an IP  Undermine applications that rely on IP addresses for authentication or filtering

4. WEB BASED PASSWORD CAPTURING: Intruders

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significant issue for networked systems is hostile or unwanted access either via network or local can identify classes of intruders: – masquerader – misfeasor – clandestine user varying levels of competence

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clearly a growing publicized problem

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– from “Wily Hacker” in 1986/87 – to clearly escalating CERT stats may seem benign, but still cost resources may use compromised system to launch other attacks

Intrusion Techniques • •

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aim to increase privileges on system basic attack methodology – target acquisition and information gathering – initial access – privilege escalation – covering tracks key goal often is to acquire passwords so then exercise access rights of owner

Password Guessing • • •

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one of the most common attacks attacker knows a login (from email/web page etc) then attempts to guess password for it – try default passwords shipped with systems – try all short passwords – then try by searching dictionaries of common words – intelligent searches try passwords associated with the user (variations on names, birthday, phone, common words/interests) – before exhaustively searching all possible passwords check by login attempt or against stolen password file success depends on password chosen by user surveys show many users choose poorly

Password Capture •

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another attack involves password capture – watching over shoulder as password is entered – using a trojan horse program to collect – monitoring an insecure network login (eg. telnet, FTP, web, email) – extracting recorded info after successful login (web history/cache, last number dialed etc) using valid login/password can impersonate user users need to be educated to use suitable precautions/countermeasures

Intrusion Detection

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inevitably will have security failures so need also to detect intrusions so can – block if detected quickly – act as deterrent – collect info to improve security assume intruder will behave differently to a legitimate user – but will have imperfect distinction between

Approaches to Intrusion Detection •

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statistical anomaly detection – threshold – profile based rule-based detection – anomaly – penetration identification

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5. VIRUS   

Officially,” in the sense of ELF etc, not a program. Not even a separate file. Code that will reproduce itself, and ... Definition from RFC 1135: A virus .is a piece of code that inserts itself into a host [program], including operating systems, to propagate. It cannot run independently. It requires that its its host program be run to activate it. it.

Macro Virus   

Sometimes considered a worm. Requires a host program to process/run it. Written in Visual Basic for Application for Word, Access, Excel, PowerPoint, and Outlook etc. E.g., Melissa

Trojan Horses  

Trojan horses are programs that appear to have one function but actually perform another function. Modern-day Trojan horses resemble a program that the user wishes to run - a game, a spreadsheet, or an editor. While the program appears to be doing what the user wants, it is also doing something else unrelated to its advertised purpose, and without the user's knowledge.

A trojan is a program which a user or administrator installs on a computer because they are misled into thinking it only performs wanted functionality, when in addition this program contains hidden functionality which the user does not want. The term "trojan" might also apply to "adware" or "spyware" software which is installed from a remote website as part of the normal functioning of a poorly designed web browser without the end user's consent or knowledge.

6. Honeypot In computer terminology, a honeypot is a trap set to detect, deflect, or in some manner counteract attempts at unauthorized use of information systems. Generally it consists of a computer, data, or a network site that appears to be part of a network, but is actually isolated and monitored, and which seems to contain information or a resource of value to attackers.

A honeypot is valuable as a surveillance and early-warning tool. While it is often a computer, a honeypot can take other forms, such as files or data records, or even unused IP address space. A honeypot that masquerades as an open proxy to monitor and record those using the system is known as a "sugarcane". Honeypots should have no production value, and hence should not see any legitimate traffic or activity. Whatever they capture is therefore malicious or unauthorized. One practical application of this is the spamtrap a honeypot that thwarts spam by masquerading as a type of system abused by spammers. These honeypots categorize trapped material 100% accurately: it is all illicit. Honeypots can carry risks to a network, and must be handled with care. If they are not properly walled off, an attacker can use them to break into a system. Victim hosts are an active network counter-intrusion tool. These computers run special software, designed to appear to an intruder as being important and worth looking into. In reality, these programs are dummies, and their patterns are constructed specifically to foster interest in attackers. The software installed on, and run by, victim hosts is dual purpose. First, these dummy programs keep a network intruder occupied looking for valuable information where none exists, effectively convincing an intruder to isolate themselves in what is truly an unimportant part of the network. This decoy strategy is designed to keep an intruder from getting bored and heading into truly security-critical systems. The second part of the victim host strategy is intelligence gathering. Once an intruder has broken into the victim host, the machine or a network administrator can examine the intrusion methods used by the intruder. This intelligence can be used to build specific countermeasures to intrusion techniques, making truly important systems on the network less vulnerable to intrusion.

Types Honeypots can be classified based on their deployment and based on their level of  involvement. Based on the deployment, honeypots may be classified as 1. Production Honeypots 2. Research Honeypots Production honeypots are easy to use, capture only limited information, and are used primarily by companies or corporations; Production honeypots are placed inside the production network with other production servers by an organization to improve their overall state of security. Normally, production honeypots are low-interaction honeypots, which are easier to deploy. They give less information about the attacks or attackers than research honeypots do. The purpose of a production honeypot is to help mitigate risk in an organization. The honeypot adds value to the security measures of an organization. Research honeypots are run by a volunteer, non-profit research organization or an educational institution to gather information about the motives and tactics of the Blackhat community targeting different networks. These honeypots do not add direct value to a specific organization. Instead they are used to research the threats organizations face, and to learn how to better protect against those threats. This information is then used to protect against those threats. Research honeypots are complex to deploy and maintain, capture extensive information, and are used primarily by research, military, or government organizations.

Database honeypot Databases often get attacked by intruders using SQL Injection. Because such activities are not recognized by basic firewalls, companies often use database firewalls. Some of  the available SQL database firewalls provide/support honeypot architectures to let the [6] intruder run against a trap database while the web application still runs as usual.

Honeynets Two or more honeypots on a network form a honeynet . Typically, a honeynet is used for monitoring a larger and/or more diverse network in which one honeypot may not be sufficient. Honeynets and honeypots are usually implemented as parts of larger network  intrusion detection systems. A honeyfarm is a centralized collection of honeypots and [8][9] analysis tools. The concept of the honeynet first began in 1999 when Lance Spitzner, founder of the Honeynet Project, published the paper "To Build a Honeypot":

"A honeynet is a network of high interaction honeypots that simulates a production network and configured such that all activity is monitored, recorded and in a degree, discreetly regulated."

7. Symmetric Encryption Scheme – RC4. RC4. In cryptography, RC4 (also known as ARC4 or ARCFOUR meaning Alleged RC4, see below) is the most widely-used software stream cipher and is used in popular protocols such as Secure Sockets Layer (SSL) (to protect Internet traffic) and WEP (to secure wireless networks). While remarkable for its simplicity and speed in software, RC4 has weaknesses that argue against its use in new [2] systems. It is especially vulnerable when the beginning of the output keystream is not discarded, or nonrandom or related keys are used; some ways of using RC4 can lead to very insecure cryptosystems such as WEP.

RC4 was designed by Ron Rivest of RSA Security in 1987. While it is officially termed "Rivest Cipher 4", the RC acronym is alternatively understood to stand for "Ron's [3] Code" (see also RC2, RC5 and RC6). RC4 was initially a trade secret, but in September 1994 a description of it was [4] anonymously posted to the Cypherpunks mailing list. It was soon posted on the sci.crypt newsgroup, and from there to many sites on the Internet. The leaked code was confirmed to be genuine as its output was found to match that of proprietary software using licensed RC4. Because the algorithm is known, it is no longer a trade secret. The name "RC4" is trademarked, so RC4 is often referred to as "ARCFOUR" or "ARC4" (meaning Alleged RC4) to avoid trademark problems. RSA Security has never officially released the algorithm; Rivest has, however, linked to the English Wikipedia article on [5] RC4 in his own course notes. RC4 has become part of some commonly-used encryption protocols and standards, including WEP and WPA for wireless cards and TLS. The main factors in RC4's success over such a wide range of applications are its speed and simplicity: efficient implementations in both software and hardware are very easy to develop.a RC4 generates a pseudorandom stream of bits (a keystream ). As with any stream cipher, these can be used for encryption by combining it with the plaintext using bit-wise exclusive-or; decryption is performed the same way (since exclusive-or is a symmetric operation). (This is similar to the Vernam cipher except that generated  pseudorandom bits, rather than a prepared stream, are used.) To generate the keystream, the cipher makes use of a secret internal state which consists of two parts: 1. A permutation of all 256 possible bytes (denoted "S" below). 2. Two 8-bit index-pointers (denoted "i" and "j").

The permutation is initialized with a variable length key, typically between 40 and 256 bits, using the key-scheduling algorithm (KSA). Once this has been completed, the stream of bits is generated using the  pseudo-random generation algorithm (PRGA).

Symmetric Encryption Scheme – RC4 In cryptography, RC4 (also known as ARC4 or ARCFOUR meaning Alleged RC4, see below) is the most widely used software stream cipher and is used in popular protocols such as Secure Sockets Layer (SSL) (to protect Internet traffic) and WEP (to secure wireless networks). While remarkable for its simplicity and speed in software, RC4 has [2] weaknesses that argue against its use in new systems. It is especially vulnerable when the beginning of the output keystream is not discarded, or nonrandom or related keys are used; some ways of using RC4 can lead to very insecure cryptosystems such as WEP RC4 was designed by Ron Rivest of RSA Security in 1987. While it is officially termed "Rivest Cipher 4", the RC acronym is alternatively understood to stand for "Ron's [3] Code" (see also RC2, RC5 and RC6). RC6 ). RC4 was initially a trade secret, but in September 1994 a description of it was [4] anonymously posted to the Cypherpunks mailing list. It was soon posted on the sci.crypt newsgroup, and from there to many sites on the Internet. The leaked code was confirmed to be genuine as its output was found to match that of proprietary software using licensed RC4. Because the algorithm is known, it is no longer a trade secret. The name "RC4" is trademarked, so RC4 is often referred to as "ARCFOUR" or "ARC4" (meaning Alleged RC4) to avoid trademark problems. RSA Security has never officially released the algorithm; Rivest has, however, linked to the English Wikipedia article on [5] RC4 in his own course notes. RC4 has become part of some commonly used encryption protocols and standards, including WEP and WPA for wireless cards and TLS. RC4 generates a pseudorandom stream of bits (a keystream ). As with any stream cipher, these can be used for encryption by combining it with the plaintext using bit-wise exclusive-or; decryption is performed the same way (since exclusive-or is a symmetric operation). (This is similar to the Vernam cipher except that generated  pseudorandom bits, rather than a prepared stream, are used.) To generate the keystream, the cipher makes use of a secret internal state which consists of two parts: 1. A permutation of all 256 possible bytes (denoted "S" below). 2. Two 8-bit index-pointers (denoted "i" and "j"). The permutation is initialized with a variable length key, typically between 40 and 256 bits, using the key-scheduling algorithm (KSA). Once this has been completed, the stream of bits is generated using the  pseudo-random generation algorithm (PRGA).

RC4-based cryptosystems  

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WEP WPA (default algorithm, but can be configured to use AES-CCMP instead of  RC4) BitTorrent protocol encryption Microsoft Point-to-Point Encryption [23] Opera Mini Secure Sockets Layer (optionally) Secure shell (optionally) Remote Desktop Protocol Kerberos (optionally)

Implementation Many stream ciphers are based on linear feedback shift registers (LFSRs), which, while efficient in hardware, are less so in software. The design of RC4 avoids the use of  LFSRs, and is ideal for software implementation, as it requires only byte manipulations. It uses 256 bytes of memory for the state array, S[0] through S[255], k bytes of memory for the key, key[0] through key[k-1], and integer variables, i, j, and y. Performing a modular reduction of some value modulo 256 can be done with a bitwise AND with 255 (which is equivalent to taking the low-order byte of the value in question).

8. Block Cipher – S-DES, 3-DES. In cryptography, a block cipher is a symmetric key cipher operating on fixed-length groups of bits, called blocks, with an unvarying transformation. A block cipher encryption algorithm might take (for example) a 128-bit block of plaintext as input, and output a corresponding 128-bit block of ciphertext. The exact transformation is controlled using a second input — the secret key. Decryption is similar: the decryption algorithm takes, in this example, a 128-bit block of ciphertext together with the secret key, and yields the original 128-bit block of plain text. A message longer than the block size (128 bits in the above example) can still be encrypted with a block cipher by breaking the message into blocks and encrypting each block individually. However, in this method all blocks are encrypted with the same key, which degrades security (because each repetition in the plaintext becomes a repetition in the ciphertext). To overcome this issue, modes of operation are used to make encryption probabilistic. Some modes of operation, despite the fact that their underlying implementation is a block cipher, allow the encryption of individual bits. The resulting cipher is called a stream cipher. An early and highly influential block cipher design was the Data Encryption Standard (DES), developed at IBM and published as a standard in 1977. A successor to DES, the Advanced Encryption Standard (AES), was adopted in 2001.

S-DES S-DES is a reduced version of the DES algorithm. It has similar properties to DES but deals with amuch smaller block and key size (operates on 8-bit message blocks with a 10-bit key). It was designed as atest block cipher for learning about modern cryptanalytic techniques such as linear cryptanalysis,differential cryptanalysis and linear-differential cryptanalysis. It is a variant of  Simplified DES [SC96]. The same key is used for encryption and decryption. Though, the schedule of addressing the key bits are altered so that the decryption is the reverse of encryption. An input block to be encrypted is Subjected to an initial permutation  IP. Then, it is applied to two rounds of key-dependent computation. Finally, it is applied to a permutation which is the inverse of the initial permutation. We shall now proceed to a detailed description of the components of S-DES.

Simplified DES

Simplified DES (S-DES) has similar properties and structure to DES with much smaller parameters (See following S-DES scheme).

3-DES [1] In cryptography, Triple DES (3DES ) is the common name for the Triple Data Encryption Algorithm (TDEA or Triple DEA) block cipher, which applies the Data Encryption Standard (DES) cipher algorithm three times to each data block. Because of  the availability of increasing computational power, the key size of the original DES cipher was becoming subject to brute force attacks; Triple DES was designed to provide a relatively simple method of increasing the key size of DES to protect against such attacks, without designing a completely new block cipher algorithm.

Name of the algorithm

The earliest standard that defines the algorithm (ANS X9.52, published in 1998) describes it as the "Triple Data Encryption Algorithm (TDEA)" — i.e. three operations of  the Data Encryption Algorithm specified in ANSI X3.92 — and does not use the terms "Triple DES" or "DES" at all. FIPS PUB 46-3 (1999) defines the "Triple Data Encryption Algorithm (TDEA)", but also uses the terms "DES" and "Triple DES". It uses the terms "Data Encryption Algorithm" and "DES" interchangeably, including starting the specification with: The Data Encryption Standard (DES) shall consist of the following Data Encryption Algorithm (DES) [ sic] and Triple Data Encryption Algorithm (TDEA, as described in ANSI X9.52). [5]

NIST SP 800-67 (2004, 2008 ) primarily uses the term TDEA, but also refers to "Triple DES (TDEA)". ISO/IEC 18033-3 (2005) uses "TDEA", but mentions that: The TDEA is commonly known as Triple DES (Data Encryption Standard). None of the standards that define the algorithm use the term "3DES".

Algorithm Triple DES uses a "key bundle" which comprises three DES keys, K 1, K2 and K3, each of  56 bits (excluding parity bits). bits ). The encryption algorithm is: ciphertext = E K3(DK2(EK1(plaintext))) I.e., DES encrypt with K 1, DES decrypt with K2, then DES encrypt with K 3. Decryption is the reverse: plaintext = D K1(EK2(DK3(ciphertext))) I.e., decrypt with K3, encrypt with K2, then decrypt with K1. Each triple encryption encrypts one block of 64 bits of data. In each case the middle operation is the reverse of the first and last. This improves the strength of the algorithm when using keying option 2, and provides backward compatibility with DES with keying option 3.

9. Asymmetric Encryption Scheme – RSA. In cryptography, RSA (which stands for Rivest, Shamir and Adleman who first publicly described it) is an algorithm for public-key cryptography. [1] It is the first algorithm known to be suitable for signing as well as encryption, and was one of the first great advances in public key

cryptography. RSA is widely used in electronic commerce protocols, and is believed to be sufficiently secure given sufficiently long keys and the use of up-to-date implementations. Operation

The RSA algorithm involves three steps: key generation, encryption and decryption.

Key generation RSA involves a public key and a private key. The public key can be known to everyone and is used for encrypting messages. Messages encrypted with the public key can only be decrypted using the private key. The keys for the RSA algorithm are generated the following way: 1. Choose two distinct prime numbers  p and q. For security purposes, the integers  p and q should be chosen at random, o and should be of similar bit-length. Prime integers can be efficiently found using a primality test. 2. Compute n = pq. n is used as the modulus for both the public and private keys o  p–1)(q–1), where φ is Euler's totient function. 3. Compute φ(n) = ( p Choose an integer e such that 1 < e < φ( n) and gcd( e,φ(n)) = 1, i.e. e and o φ(n) –1 4. Determine d = e mod φ(n); i.e. d  is the multiplicative inverse of  e mod φ(n). This is often computed using the extended Euclidean algorithm. o d is kept as the private key exponent. o The public key consists of the modulus n and the public (or encryption) exponent e. The private key consists of the private (or decryption) exponent d which must be kept secret

Encryption Alice transmits her public key (n,e) to Bob and keeps the private key secret. Bob then wishes to send message M to Alice. He first turns M into an integer m, such that 0 < m < n by using an agreed-upon reversible protocol known as a padding scheme. He then computes the ciphertext c corresponding to e

c = m (mod n).

This can be done quickly using the method of exponentiation by squaring. Bob then transmits c to Alice.

Decryption Alice can recover m from c by using her private key exponent d via computing

m = cd  (mod n). It is generally presumed that RSA is secure if  n is sufficiently large. If  n is 300 bits or shorter, it can be factored in a few hours on a personal computer, using software already freely available. Keys of 512 bits have been shown to be practically breakable in 1999 when RSA-155 was factored by using several hundred computers and are now factored in a few weeks using common hardware.

10 . IP based Authentication. Authentication. . Internet Protocol Security (IPsec) is a protocol suite for securing Internet Protocol (IP) communications by authenticating and encrypting each IP packet of a communication session. IPsec also includes protocols for establishing mutual authentication between agents at the beginning of the session and negotiation of  cryptographic keys to be used during the session. IPsec is an end-to-end security scheme operating in the Internet Layer of the Internet Protocol Suite. It can be used in protecting data flows between a pair of hosts ( host-tohost ), ), between a pair of security gateways ( network-to-network ), ), or between a security [1] gateway and a host ( network-to-host ). ). Some other Internet security systems in widespread use, such as Secure Sockets Layer (SSL), Transport Layer Security (TLS) and Secure Shell (SSH), operate in the upper layers of the TCP/IP model. Hence, IPsec protects any application traffic across an IP network. Applications do not need to be specifically designed to use IPsec. The use of  TLS/SSL, on the other hand, must be designed into an application to protect the application protocols. IPsec is a successor of the ISO standard Network Layer Security Protocol (NLSP). NLSP was based on the SP3 protocol that was published by NIST, but designed by the Secure Data Network System project of the National Security Agency (NSA).

Security architecture The IPsec suite is an open standard. IPsec uses the following protocols to perform various [3][4] functions:

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Authentication Headers (AH) provide connectionless integrity and data origin [5][6] authentication for IP datagrams and provides protection against replay attacks. Encapsulating Security Payloads (ESP) provide confidentiality, data origin authentication, connectionless integrity, an anti-replay service (a form of partial [1] sequence integrity), and limited traffic flow confidentiality.

Security association The IP security architecture uses the concept of a security association as the basis for building security functions into IP. A security association is simply the bundle of  algorithms and parameters (such as keys) that is being used to encrypt and authenticate a particular flow in one direction. Therefore, in normal bi-directional traffic, the flows are secured by a pair of security associations. Security associations are established using the Internet Security Association and Key Management Protocol (ISAKMP). ISAKMP is implemented by manual configuration with pre-shared secrets, Internet Key Exchange (IKE and IKEv2), Kerberized Internet [11][17][18] Negotiation of Keys (KINK), and the use of IPSECKEY DNS records. In order to decide what protection is to be provided for an outgoing packet, IPsec uses the Security Parameter Index (SPI), an index to the security association database (SADB), along with the destination address in a packet header, which together uniquely identify a security association for that packet. A similar procedure is performed for an incoming packet, where IPsec gathers decryption and verification keys from the security association database.

Modes of operation IPsec can be implemented in a host-to-host transport mode, as well as in a network tunnel mode.

Transport mode In transport mode, only the payload (the data you transfer) of the IP packet is usually encrypted and/or authenticated. The routing is intact, since the IP header is neither modified nor encrypted; however, when the authentication header is used, the IP addresses cannot be translated, as this will invalidate the hash value. The transport and application layers are always secured by hash, so they cannot be modified in any way (for example by translating the port numbers). Transport mode is used for host-to-host communications. A means to encapsulate IPsec messages for NAT traversal has been defined by RFC documents describing the NAT-T mechanism.

Tunnel mode In tunnel mode, the entire IP packet is encrypted and/or authenticated. It is then encapsulated into a new IP packet with a new IP header. Tunnel mode is used to create virtual private networks for network-to-network communications (e.g. between routers to link sites), host-to-network communications (e.g. remote user access), and host-to-host communications (e.g. private chat).

Cryptographic Cryptographic algorithms Cryptographic algorithms defined for use with IPsec include:   

HMAC-SHA1 for integrity protection and authenticity. TripleDES-CBC for confidentiality AES-CBC for confidentiality.

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