gistfile1.md

Keys have lifetimes. After encrypting a certain number of bytes, keys should be replaced.

What if instead of encrypting large ammounts of our data with keys, we used a method similar to DHE?

protocol

• given symmetric key (or public key) k
• given message m
• generate a one-time symmetric key k2
• encrypt(k1, k2) -> k2c
• encrypt(k2, m) -> mc
• send k2c || mc

symmetric

given:
  m := message
  k := secret symmetric key
  n := nonce()


c := encrypt2(k, n, m):
  ns := [ H(n), H(H(n)), ... ] 

  k2 := keygen()
  k2c := encrypt(k, ns[1], k2)
  
  c := encrypt(k2, ns[2], m)
  return ns[0] || k2c || c

assymetric

given:
  m := message
  pk := public key
  n := nonce()


c := encrypt2(pk, n, m):
  ns := [ H(n), H(H(n)), ... ] 

  k2 := keygen()
  k2c := encrypt(pk, ns[1], k2)
  
  c := encrypt(k2, ns[2], m)
  return ns[0] || k2c || c