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Subject Name : Cryptography and Network Security Subject Code : IT1352 UNIT I 1. Specify the four categories of security threads? ._Interruption ._Interception ._Modification ._Fabrication 2. Explain active and passive attack with example? Passive attack: Monitoring the message during transmission. Eg: Interception Active attack: It involves the modification of data stream or creation of false data stream. E.g.: Fabrication, Modification, and Interruption 3. Define integrity and nonrepudiation? Integrity: Service that ensures that only authorized person able to modify the message. Nonrepudiation: This service helps to prove that the person who denies the transaction is true or false. 4. Differentiate symmetric and asymmetric encryption? Symmetric Asymmetric It is a form of cryptosystem in which encryption and decryption performed using the same key. It is a form of cryptosystem in which encryption and decryption Performed using two keys. Eg: DES, AES Eg: RS

Introduction Cryptography and Network Security 2 marks What is Active Attack? An intrusion into a computer network which attempts to delete or modify the data stored on the computers which form part of the network. This is one of the most serious forms of attack since many companies' operations critically depend on data. What is Passive attack? An intrusion into a computer network which reads the data passing along some of the transmission lines without modifying it. Differentiate active and passive attack S.No Active Attack Passive Attack 1 An intrusion into a computer network which attempts to delete or modify the data stored on the computers which form part of the network An intrusion into a computer network which reads the data passing along some of the transmission lines without modifying it. 2 Identify the intrusion because of modification and difficult to prevent active attacks,because of wide variety of potential physical ,software and network vulnerabilites. Diff

RSA Algorithm with Example RSA Algorithm was discovered by a group of three scientists namely Ron Rivest,Adi Shamir and Len Adleman and was first published in 1978. The RSA scheme is a block cipher in which the plain text and cipher text are integers between 0 and n-1 for some n. A Typical size of n is 1024 bits or 309 decimal digits. This is a public key encryption scheme. In this scheme two pairs of integers {e, n} and {d, n} are used. First of them i.e. {e.n} is called the RSA public key and the other one i.e. {d, n} is called the RSA secret key. The sender uses the public key and encrypts the message say M into cipher text as – C = M^e mod n. Where C is the cipher text and M is the message or the plane text At the receiving end the receiver accept the cipher text C and decrypt the C into M using secret key {d, n}- M = C^d mod n. Example: Let , e=3, d=7, n=33. Suppose the message is ‘SUN’ and we use the numeric values of the characters according to their serial in alphabets. Plainte