Problem 4c: How do we storethe secret keys?

• Modern computers don’t keep secrets well

  • that’s why we need cryptography...

• Usual option: user-selected passphrases

  • but we need 90 bits of “randomness” (see problem 4b)
  • according to Shannon, English text has just over 1 bit per letter of “entropy”. 90 letters is a lot of typing...

• Another option: secure crypto modules

  • smartcards, PCMCIA cards, special chips
  • expensive, and frequently have flaws

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