1. Public Key (RSA) Day 27

2. Objective Students will be able to… …understand how RSA is used for encryption and decryption. …understand some of the challenges of implementing RSA.

3. RSA Named after Rivest, Shamir, and Adleman –1977 –Patent in 1983 –Patent expired in 2000 Clifford Cocks – discoved it in 1973, but this wasn’t released until 1997 (worked for Government Communications Headquarters (GCHQ)

4. RSA – Encryption/Decryption C = P e mod n (Encryption) P = C d mod n (Decryption) e and n are keys to the cipher. n = pq (where p and q are large primes) ed = 1 mod φ(n) (Used for finding d) ed mod (p – 1)(q – 1) = 1

5. RSA – Encryption/Decryption Selecting d –Must be between min(p, q) and (p – 1)(q – 1) –Must be relatively prime to (p – 1)(q – 1)

6. RSA Encryption Example Select to primes, 11 and 23 Let d = 19 Find e. Encrypt the message, “Hi”

7. RSA Encryption Example Select to primes, 11 and 23 Let d = 19 Find e. Decrypt the previous cipher text.

8. RSA Assignment