Unit 11: Cryptography, Public Key Encryption and Digital Signature

Presentation slides

Quiz and solutions

1. The total processing speed of microprocessors (based on clock rate and number of circuits) is doubling roughly every year.  Today a symmetric session key needs to be 100 bits long to be considered strong.  How long will a symmetric session key have to be in 30 years to be considered strong? (Hint: Consider how much longer decryption takes if the key length is increased by a single bit.) Explain.
2. Longer keys are more difficult to crack. Most symmetric keys today are 100 to 300 bits long. Why don’t systems use far longer symmetric keys—say, 1,000 bit keys?
3. How are digital certificates and drivers’ licenses similar, and how are they different?

The total processing speed of microprocessors (based on clock rate and number of circuits) is doubling roughly every year.  Today a symmetric session key needs to be 100 bits long to be considered strong.  How long will a symmetric session key have to be in 30 years to be considered strong? (Hint: Consider how much longer decryption takes if the key length is increased by a single bit.) Explain.

Longer keys are more difficult to crack. Most symmetric keys today are 100 to 300 bits long. Why don’t systems use far longer symmetric keys—say, 1,000 bit keys?

How are digital certificates and drivers’ licenses similar, and how are they different?