Communication Technology Design for Confidentiality and Quality Monitoring of CV Service - Essay Example

Questions 2 and 3 As evidence of your activity, make a copy of the windows detailed below and paste1 them into your TMA answer document: the New Message window at the equivalent stage to that shown in Figure 7.21 on page 76 of Book E. (This copy should be taken before you make any changes to the message.) the Open Message window at the equivalent stage to that shown in Figure 7.23 on page 77 of Book E. Question 2 (a) Complete Tables A1, A2 and A3 to illustrate the result of the Diffie-Hellman process if both principals in the transaction pick the same starting value from a limited range of possible values, and if both principals in the transaction pick different starting values. Table A1 Values used in the derivation of session key examples Value for the modulus (n1) 257 Value for Chung's secret key (kC) 234 Value for Lilly's secret key (kL) 127 Value of message V1 126 Value of message V2 37 Value of message V3 72 Table A2 Calculation of matching session key Step 1 Chung operates on V3 by exponentiation modulo n1 with kC to give V3 kC mod n1 and sends the results to Lilly. V3 kC mod n1 72234 mod 257 235 mod 257 Step 2 Lilly operates on V3 by exponentiation modulo n1 with kL to give V3 kLkC mod n1 and sends the result to Chung. V3 kL mod n1 72127 mod 257 25 mod 257 Step 3 Chung takes V3 kL mod n1 received from Lilly and operates on it by exponentiation modulo n1 with kC to give V3 kLkC mod n1. He intends to use this as session key ks2C to encrypt his message to a client. Ks2C = V3 kLkC mod n1 = 72(127*234) mod 257 = 35 mod 257 Step 4 Lilly takes V3 kC mod n1 received from Chung and operates on it by exponentiation modulo n1 with kL to give V3 kCkL mod n1. She intends to use this as session key ks2L to attempt to decrypt Chung's message to a client. Ks2L = V3 kCkL mod n1 = 72(234*127) mod 257 = 35 mod 257 Table A3 Calculation of random session key for use with oblivious transfer Step 1 Chung operates on V1 by exponentiation modulo n1 with kC to give V1 kC mod n1 and sends the results to Lilly. V1 kC mod n1 126234 mod 257 89 mod 257 Step 2 Lilly operates on V2 by exponentiation modulo n1 with kL to give V2 kLkC mod n1 and sends the result to Chung. V2 kL mod n1 37127 mod 257 125 mod 257 Step 3 Chung takes V2 kL mod n1 received from Lilly and operates on it by exponentiation modulo n1 with kC to give V2 kLkC mod n1. He intends to use this as session key ks1C to encrypt his message to a client. Ks1C = V2 kLkC mod n1 = 37(127*234) mod 257 = 133 mod 257 Step 4 Lilly takes V1 kC mod n1 received from Chung and operates on it by exponentiation modulo n1 with kL to give V1 kCkL mod n1. She intends to use this as session key ks1L to attempt to decrypt Chung's message to a client. Ks1L = V1 kCkL mod n1 = 126(234*127) mod 257 = 252 mod 257 (b) If Chung and Lilly had both picked the value V4 for their parts of the key exchange using the method illustrated in part (a), the result would be a session key of 192. Complete Table A4 to show how a session key ks = 192 might be encrypted with the client's public key, and then decrypted by the client on receipt. Table A4 Encryption of the session key Step 1 The value for the session key ks supplied in Question 2 Part (b). ks =192 Step 2 The value for the modulus n2 supplied in Question 2 Part (b) n2 =26 Step 3 The value of the session key ks written as text ks expressed in text = one nine two Step 4 A suitable value for Tait's public key KT KT = 15 Step 5 The session key ks encrypted with Tait's public key KT. { ks} KT = C T: {R}ks, {ks}KT = CNINQNIZSC Step 6 __ A suitable value for Tait's private key KT __ KT =7 Step 7 The result of decrypting the encrypted session key __ using Tait's private key KT {{ks}KT}KT = ONENINETWO Question 3 Complete the following unfinished sections in the main body and appendix of the report printed in the appendix to this companion, and referred to in the 'Background for Questions 2 and 3'. Include in your answer the parts shown below. Title Communication Technology Design for Confidentiality and Quality Monitoring of CV Service Section 2 A simplified explanation of encryption Encryption is the conversion of data into a form called ciphertext. Ciphertext is not understandable unless it is decrypted History tells us that even during the time of Julius Ceasar a method of encryption was already being used in military communications to prevent the enemy from discovering battle plans (Mycrypto.net 2008). Today, the encryption process involves altering and rearranging bits of digital data using a systematic procedure that can be converted into a computer program. Encryption is a commonly used method for providing a certain degree of security in technology-based systems. Simple encryption methods include the substitution of letters for numbers, the rotation of letters in the alphabet or the "scrambling" of voice signals by inverting the sideband frequencies. The more complex methods use sophisticated computer algorithms that rearrange the data bits in digital signals. Data is converted into a series of numbers which are then used as input into calculations. The calculated results become the encrypted data (Case Resource). Section 3 Public key encryption In 1976 the idea of public key encryption was introduced to the field of cryptography. The idea revolved around the premise of making the encryption and decryption keys different so that the sender and recipient need not know the same keys. The sender and the recipient will both have their own private key and a public key would be known by anyone. Each encryption or decryption process would require at least one public key and one private key (Mycrypto.net 2008). Public key encryption techniques or asymmetric key systems avoid the need to distribute keys in secret. Symmetric key systems are those which allow the decryption process to be derived from the encryption key. This being the case, the exchange of information about secret keys are highly sensitive issues because revealing a secret key jeopardizes all the transactions carried out using that key (Case Resource). A public key encryption scheme has six components. First, there's the plaintext message to which an algorithm is applied. Then there's the encryption algorithm or the mathematical operations that will conduct substitutions and transformations to the plaintext. Then there's the ciphertext or encrypted message produced by the algorithm. Next is the decryption algorithm that will be applied on the ciphertext to convert it back to plaintext. And finally, there are the public and private keys, where one is used for encryption and the other for decryption (Mycrypto.net 2008). Section 4 The case for session keys Session keys are also called symmetric keys because the same key is used for both encryption and decryption. These are randomly generated to ensure the security of a communication sessions between a user and another computer or between two computers. The key is used to encrypt a message and then sent along with the message to the recipient. The recipient also has a session key which it will use to decrypt the message received. Because much of the security of session keys depends on the length of time they are used, session keys are changed frequently. A different session key is used for each session (Patkos 2004). If a session key is compromised, the breach of security is limited to the period when the session key was in use. If the breach was discovered, the process to remedy the breach is to merely start a new session (Case Resource). Section 5 The Diffie-Hellman process The Diffie-Hellman process was developed by Whitfield Diffie and Martin Hellman in 1976. It was the first system to utilize asymmetric keys. The system overcomes the difficulties of symmetric key systems. Asymmetric key systems use two keys, a private key that the user keeps and a public key that can be shared with everybody which makes it easily distributed. Diffie-Hellman is not a typical encryption system because it is not used to encrypt data, but rather to securely exchange the keys that encrypt data. The process begins when each side of the communication generates a private key. Then, each side generates a public key which is a derivative of the private key. The two systems then exchange their public keys. Each side of the communication now has their own private key and the other system's public key. Since the public key is a derivative of the private key, the two keys are mathematically linked (Palmgren 2006). Appendix 1 Modular arithmetic Modular arithmetic is a branch of mathematics that deals with a system of arithmetic for integers, where numbers "wrap around" after they reach the modulus. This system was introduced by Carl Friedrich Gauss in his book Disquisitiones Arithmeticae, published in 1801. An application of modular arithmetic is the 24-hour clock - the arithmetic of time-keeping. For example, 7:00 in the evening is expressed as 19:00. Eight hours later would be 3:00, not 27:00 because the time "wraps around at the end of the day. This is arithmetic modulo 24(Modular Arithmetic 2008). Modular arithmetic is used in the mathematical operations for encryption and decryption. Works Cited Case Resource. 2008. Mycrypto.net. 2008. Encryption. 10 Aug 2008. Palmgren, K. 2006. Diffie-Hellman Key Exchange - A Non-Mathematician's Explanation. 10 Aug 2008. Patkos, A. 2004. Session Key. 10 Aug 2008. Modular Arithmetic. 2008. 10 Aug 2008. Read More