1. CPSC 37301 CPSC 3730 Cryptography Chapter 2 Classical Encryption Techniques

2. CPSC 37302 Fig 2.1 Model of Conventional Encryption

3. CPSC 37303 Brute Force Attack/ Key Search Table 2.2 Average Time Required for Exhaustive Key Search Key Size (bits)Number of Alternative Keys Time required at 1 decryption/µs Time required at 10 6 decryptions/µs 32 2 32 = 4.3  10 9 2 31 µs= 35.8 minutes2.15 milliseconds 56 2 56 = 7.2  10 16 2 55 µs= 1142 years10.01 hours 128 2 128 = 3.4  10 38 2 127 µs= 5.4  10 24 years5.4  10 18 years 168 2 168 = 3.7  10 50 2 167 µs= 5.9  10 36 years5.9  10 30 years 26 characters (permutation) 26! = 4  10 26 2  10 26 µs= 6.4  10 12 years6.4  10 6 years

4. CPSC 37304 Caesar Cipher (substitution technique) Replace each letter of the alphabet with the letter standing three places further down the alphabet. a --> D, b -->E, …, and so on plain: meet me after the party cipher: PHHW PH DIWHU WKH SDUWB

5. CPSC 37305 Caesar Cipher (substitution technique) if we assign a numerical equivalent to each letter (a=0, b=1, …, z=25), the algorithm can be expressed as follows. For each plaintext letter p, the cipher letter c is c=E(p)=(p+3) mod (26)

6. CPSC 37306 Caesar Cipher (substitution technique) Since a shift may be any amount, so the general Caesar algorithm is: c=E k (p)=(p+k) mod (26) The decryption algorithm is: p=D k (p)=(c-k) mod (26) Key (k) is the range from 1 to 25

7. CPSC 37307 English Letter Frequencies

8. CPSC 37308 Row Transposition Ciphers a more complex transposition write letters of message out in rows over a specified number of columns then reorder the columns according to some key before reading off the rows Key: 3 4 2 1 5 6 7 Plaintext: a t t a c k p o s t p o n e d u n t i l t w o a m x y z Ciphertext: TTNAAPTMTSUOAODWCOIXKNLYPETZ

9. CPSC 37309 Row Transposition Ciphers 1 2 3 4 5 6 7 Key: 3 4 2 1 5 6 7 Plaintext: a t t a c k p o s t p o n e d u n t i l t w o a m x y z Ciphertext: TTNAAPTMTSUOAODWCOIXKNLYPETZ Column Permutation: 3 -> 1, 4->2, 2->3, 1-> 4, 5->5, 6->6, 7->7