Advanced Computer Networks (ICTW485) Security PDF

ADVANCED COMPUTER NETWORKS (ICTW485) Overview Overview of Security Tenets of Network Security Risk, threat and vulnerability Cryptographic Principles, concepts & Terminologies Types of Ciphers What is Security? “The quality or state of being secure—to be free from danger” A successful organization...

ADVANCED COMPUTER NETWORKS (ICTW485) Overview Overview of Security Tenets of Network Security Risk, threat and vulnerability Cryptographic Principles, concepts & Terminologies Types of Ciphers What is Security? “The quality or state of being secure—to be free from danger” A successful organization should have multiple layers of security in place: ◦ Physical security ◦ Personal security ◦ Operations security ◦ Communications security ◦ Network security ◦ Information security NETWORK SECURITY oIs a set of rules and configurations designed to protect the integrity, confidentiality and accessibility of computer networks and data using both software and hardware technologies. oNetwork security protects your network and data from breaches, intrusions and other threats. Model for Network Security  Model for Network Security using this model requires us to: – design a suitable algorithm for the security transformation – generate the secret information (keys) used by the algorithm – develop methods to distribute and share the secret information – specify a protocol enabling the principals to use the transformation and secret information for a security service Network Access Security  Network Access Security using this model requires us to: – select appropriate gatekeeper functions to identify users – implement security controls to ensure only authorised users access designated information or resources trusted computer systems can be used to implement this model BASIC TERMS oVulnerability oThreat oExploit oRisk otrust VULNERABILITY ‘A weakness that may lead to undesirable consequences.’ Typical vulnerabilities include ◦ Hardware Vulnerability ◦ Software Vulnerability ◦ Procedure Vulnerability ◦ External or environmental Vulnerability Cont. THREAT ◦ ‘The danger that a vulnerability will actually be taken advantage of.’ ◦ Describes how the vulnerability would be attacked: ◦ E.g., buffer overflow is the vulnerability, and the threat would be transmission of a TCP/IP packet to cause buffer overflow. ◦ EXPLOIT ◦ An “exploit” is a an attack using known vulnerabilities ◦ “Zero-day” attack refers to attacks taking place before the vulnerability becomes known to software Cont. RISK ‘A potential problem’, consisting of a ◦ Vulnerability ◦ Threat (attack rate) ◦ Extent of the consequences. TRUST ‘A relationship between two entities where one entity allows the other to perform certain actions.’ Tenets of Network Security (also referred to as security goals) Confidentiality It means guarding information from everyone except those with rights to it. Confidentiality is a security feature to assure that information can only be received by eligible communication parties. In modern cryptography, confidentiality is achieved through applying encryption mechanisms. Integrity Integrity is to assure that the information is not tampered with by a noneligible party or through a transmission or storage error. oIntegrity deals with the validity and accuracy of data. oFor some organizations, data and information are intellectual property assets. Examples include copyrights, patents, secret formulas, and customer databases. This information can have great value. oInformation has integrity when it is whole, complete, and uncorrupted. Availability The information created and stored by an organization needs to be available to authorized entities. Services, system, application & data should be accessible when needed and without extra delay. Ensuring timely and reliable access to and use of information. A loss of availability is the disruption of access to or use of information or an information system. BUSINESS EXAMPLE Confidentiality — An employee should not come to know the salary of his manager Integrity — An employee should not be able to modify the employee's own salary Availability — Paychecks should be printed on time as stipulated by law Cryptographic Concepts, Principles & Terminologies Overview of Cryptology  Concepts Cryptology: science of encryption; combines cryptography and cryptanalysis Is the science of secure communication Cryptology: cryptography + cryptanalysis Cryptography: process of making and using codes to secure transmission of information. ◦ The art and science of keeping messages secure. ◦ it is practiced by cryptographers.  Cont. Cryptanalysis: process of obtaining original message from encrypted message without knowing algorithms. the art and science of breaking ciphertext; that is, seeing through the disguise. Cryptanalysts are practitioners of cryptanalysis,  Basic Terminologies Plaintext: original message to be encrypted Cipher-text: the encrypted message Enciphering or encryption: the process of converting plaintext into cipher-text Encryption algorithm: performs encryption Two inputs: a plaintext and a secret key Deciphering or decryption: recovering plaintext from cipher-text OTHER TRADITIONAL CIPHERS SUBSTITUTION CIPHER TRANSPOSITION CIPHER  Substitution Cipher A substitution cipher replaces one symbol with another. It can be categorized as either mono alphabetic ciphers or polyalphabetic ciphers  Monoalphabetic Substitution In monoalphabetic substitution, the relationship between a symbol in the plaintext to a symbol in the ciphertext is always one-to-one.  Monoalphabetic Ciphers Additive ciphers/Shift ciphers Multiplicative Ciphers Affine Cipher  Additive/Shift cipher The simplest monoalphabetic cipher is the additive cipher. This cipher is sometimes called a shift cipher and sometimes a Caesar cipher, but the term additive cipher better reveals its mathematical nature. A shift cipher can also be described as Encryption EK(x) = x + K mod 26 Decryption DK(x) = x - K mod 26 for English alphabet by setting up a correspondence between alphabetic characters and residues modulo 26. K=3 in Caesar Cipher. Additive When the cipher is additive, the plaintext, ciphertext, and key are integers in Z26.  Shift Ciphers replace letters of a message by other distinct letters a fixed distance away Famous shift cipher: Caesar Cipher Shift by 3 letters reputedly used by Julius Caesar (100 – 44 B.C.) Plaintext: I CAME I SAW I CONQUERED Ciphertext: L FDPH L VDZ L FRQTXHUHG Multiplicative Ciphers In a multiplicative cipher, the plaintext and ciphertext are integers in Z26; the key is an integer in Z26*.  Affine Cipher The cipher that we get after combining additive and multiplicative ciphers is called affine cipher. Monoalphabetic Substitution Cipher Because additive, multiplicative, and affine ciphers have small key domains, they are very vulnerable to brute-force attack.  Polyalphabetic Cipher In polyalphabetic substitution, each occurrence of a character may have a different substitute. The relationship between a character in the plaintext to a character in the ciphertext is one- to-many.  Example Auto Key Cipher Assume that Alice and Bob agreed to use an autokey cipher with initial key value k1 = 12. Now Alice wants to send Bob the message “Attack is today”. Enciphering is done character by character. Advantages : Hides the single-letter frequency statistics of the plain-text. Disadvantages: Vulnerable to brute-force attack as additive cipher.  Transposition Ciphers A transposition cipher does not substitute one symbol for another, instead it changes the location of the symbols. Keyless Transposition Ciphers Keyed Transposition Ciphers Combining Two Approaches  Keyless Transposition Simple transposition ciphers, which were used in the past, are keyless. A good example of a keyless cipher using the first method is the rail fence cipher. The ciphertext is created reading the pattern row by row. For example, to send the message “Meet me at the park” to Bob, Alice writes She then creates the ciphertext “MEMATEAKETETHPR”. Cont. Alice and Bob can agree on the number of columns and use the second method. Alice writes the same plaintext, row by row, in a table of four columns. She then creates the ciphertext “MMTAEEHREAEKTTP”. Symmetric-Key Ciphers  Symmetric Encryption Symmetric encryption: uses same “secret key” to encipher and decipher message ◦Encryption methods can be extremely efficient, requiring minimal processing ◦Both sender and receiver must possess encryption key ◦If either copy of key is compromised, an intermediate can decrypt and read messages  General idea of symmetric-key cipher The original message from Alice to Bob is called plaintext; the message that is sent through the channel is called the ciphertext. To create the ciphertext from the plaintext, Alice uses an encryption algorithm and a shared secret key. To create the plaintext from ciphertext, Bob uses a decryption algorithm and the same secret key. Kerckhoff’s Principle Based on Kerckhoff’s principle, one should always assume that the adversary, Eve, knows the encryption/decryption algorithm. The resistance of the cipher to attack must be based only on the secrecy of the key.  Symmetric Encryption There are two requirements for secure use of conventional encryption: We need a strong encryption algorithm. Sender and receiver must have obtained copies of the secret key in a secure fashion and must keep the key secure. If someone can discover the key and knows the algorithm, all communication using this key is readable.  STREAM AND BLOCK CIPHERS The literature divides the symmetric ciphers into two broad categories: stream ciphers and block ciphers. Although the definitions are normally applied to modern ciphers, this categorization also applies to traditional ciphers.  Block Cipher In a block cipher, a group of plaintext are encrypted together creating a group of ciphertext of the same size. A block cipher is a method of encrypting data in blocks to produce ciphertext using a cryptographic key and algorithm. The block cipher processes fixed-size blocks simultaneously, as opposed to a stream cipher, which encrypts data one bit at a time. Most modern block ciphers are designed to encrypt data in fixed-size blocks of either 64 or 128 bits. Block Cipher  Block Cipher A block cipher requires an initialization vector (IV) that is added to the input plaintext in order to increase the keyspace of the cipher and make it more difficult to use brute force to break the key. The IV is derived from a random number generator, which is combined with text in the first block and the key to ensure all subsequent blocks result in ciphertext that does not match that of the first encryption block.  Examples of Block Ciphers DES – Data Encryption Standards AES – Advanced Encryption Standards Blowfish Twofish 3DES ETC.  Stream Ciphers A stream cipher encrypts a continuous string of binary numbers by using time varying transformations on plaintext information. Therefore, this kind of encryption operates bit-by-bit, using keystreams to create ciphertext for arbitrary lengths of plaintext messages. In stream cipher, one byte is encrypted at a time while in block cipher ~128 bits are encrypted at a time. Initially, a key(k) will be supplied as input to pseudorandom bit generator and then it produces a random 8-bit output which is treated as keystream. The resulted keystream will be of size 1 byte, i.e., 8 bits. Stream Cipher follows the sequence of pseudorandom number stream.  Stream Cipher One of the benefits of following stream cipher is to make cryptanalysis more difficult, so the number of bits chosen in the Keystream must be long in order to make cryptanalysis more difficult. By making the key more longer it is also safe against brute force attacks. The longer the key the stronger security is achieved, preventing any attack. Keystream can be designed more efficiently by including more number of 1s and 0s, for making cryptanalysis more difficult. Considerable benefit of a stream cipher is, it requires few lines of code compared to block cipher. Stream Cipher  Examples of Stream Ciphers RC4 – Rivest Cipher Salsa20 SEAL – Software-optimized Encryption Algorithm HC-256 RABBIT Grain etc. ASYMMETRIC KEY CIPHER  Asymmetric Encryption Asymmetric key cryptography uses two separate keys: one private and one public. Locking and unlocking in asymmetric-key cryptosystem General idea of Asymmetric-key cipher  CONT. Plaintext/Ciphertext Unlike in symmetric-key cryptography, plaintext and ciphertext are treated as integers in asymmetric-key cryptography. Encryption/Decryption C = f (Kpublic , P) P = g(Kprivate , C) RSA Cryptosystem The most common public-key algorithm is the RSA cryptosystem, named for its inventors (Rivest, Shamir, and Adleman). Encryption, Decryption and Key Generation in RSA CONT. RSA Encryption RSA Decryption TRIAL QUESTION P and Q are two prime numbers. P=13 and Q=11. Take Public key E=3. if original message is 00111011, then what will be the ciphertext value and private key value according to RSA Algorithm? Calculate the plaintext value from the ciphertext. Thank you