Basic Definitions 1. 2. 4. 5. Alice and Bob should at some point have access to a ________ mode of communication. Cryptography is only needed when a message is both _______ and ________. To determine how difficult a cryptosystem is to break, we measure its ________. To determine how quickly a cryptosystem operates, we measure its ________.
Basic Definitions 6. 7. 8. 9. 10. _______ is the science of keeping information secure even though it is transmitted through an insecure medium. _______ is the science of breaking ciphers. A _______ is a matching between two different alphabets. To break a cipher means to determine the ______. A cryptosystem is made up of five parts: plaintext space, ciphertext space, encryption function, decryption function, and __________.
Substitution Cryptosystems 1. 2. 3. 4. 5. A substitution cipher uses this to represent its key. A rotation cipher uses this to represent its key. An affine cipher uses this to represent its key. How many possible keys does a substitution cipher on have? How many possible keys does a rotation cipher on have?
Substitution Cryptosystems How many possible keys does an affine cipher on have? 7. Encrypt using a rotation cipher over with . 8. Encrypt using an affine cipher over with 9. Cipher X consists of a rotation, and then an affine cipher. What type of cipher is X? 10. Cipher Y is a substitution cipher over . Cipher consists of applying Y twenty-four times. What type of cipher is X? Be as specific as possible. 6.
Math Find in . 2. Find in . 3. Find in . 4. Find in . 5. Find . 6. Solve for and . 7. Solve the pair and for and . 8. For what is invertible in ? 9. Find the prime factorization of 142. 10. Find in . 1.
Tricky Questions 1. 2. 3. 4. 5. Which of these is a faster growth rate: or ? Which of these is a faster growth rate: or ? Approximately how many primes are there between 100,000 and 1,000,000? Find a rotation cipher with more keys than a substitution cipher. What is the maximum number of solutions that can have over . ( are constants, is the variable)
Tricky Questions 6. 7. 8. 9. 10. A substitution cipher over has a key sorted by plaintext. During decryption, how many tablelookups are required in the worst case? A substitution cipher over has a key sorted by plaintext. 4 different characters are encrypted. How many table-lookups are required in the worst case? How many possible Vigenere ciphers over are there that can encrypt exactly 3 characters? A one-time-pad is used on a 5 character message. Oscar figured out the keys, but not the order. In the worst case, how many guesses must be try before deciphering the message? How many factors does 1,000,000 have?
Comparing Cryptosystems 1. 2. 3. 4. 5. Among Rotation, Affine, and Autokey, which is most resistant to a known-plaintext attack? Among Affine, Autokey, and Vigenere, which can encrypt the fastest? Among Affine, Autokey, and Vigenere, which can decrypt the fastest? Which has a larger keyspace? Affine over or Vigenere over ? Which has a larger keysize? Substitution over or rotation over
Comparing Cryptosystems Which is more secure? Affine or a Vigenere ciphers? 7. Which is more secure? Vigenere or Hill ciphers? 8. Could a computer with 4 processors perform 200 Rotation encryptions or 100 Autokey encryptions faster? 9. Could a computer with 4 processors perform 200 Rotation encryptions or 100 Affine encryptions faster? 10. Which has a larger keyspace? Hill over or Vigenere over ? 6.
Reference Information Created in the summer of 2013 by Dr. Jeffrey Beyerl for use in a cryptography class. This is just a vanilla PowerPoint, but of course like anything you download from the internet: use at your own risk.