CIS3360: Security in Computing Homework 5 1. ( 15 points) Knowledge - based Question: a. What are the differences between public/symmetric key cryptography? The advantage and disadvantage of each? Symmetric Cryptography involves 2 people using the same private key to encrypt and decrypt i nformation. While in Public key cryptography there are 2 different keys that are used, a public key for encryption and a private key for decryption. Public Key Cryptography Advantages The public key does not have to be secured that is why it is public. Which anyone can use. It is much more secure than Symmetric Cryptography. Disadvantages It is harder to implement and slower than Symmetric cryptography. Symmetric Key Cryptography Advantages It is much easier to implement , and takes up much less processing power. Disadvantages It is less secure; both parties have to agree on the same private key to use. a. For English alphabet based texts regardless of upper or lower case (i.e., assuming each letter has only 26 possible value), if the length of the key using Vigenere Cipher is 4, how many possible encryption keys exist? (hint: we all know that Caesar cipher has 26 possible encryption keys) 26^4 possible encryption keys. b. What is the usage of a cryptographic hash function? Can two documents have the same hash value? The primary use of cryptographic hash function is for message integrity. Yes it is possible for 2 documents can have the same hash value. 2. (10 points) Determine whether a statement is True or False. If a statement is false, you must explain why. a. Digital signature of a message m is H(m), where H() represent a cryptographic hash function such as MD5 or SHA - 1. TRUE.