IND-CPA(Chosen Plaintext Attack)

indistinguishable under chosen plain text attack if there is no PPT-bounded adversary with non-negligible advantage of wining the CPA game.

Send Bob stuff to encrypt for us (queries), then send him messages that he can send us back as a challenge (coin flip), and we can use our queries to give us an advantage to determine what message we sent him!

• w/public key cryptography, anyone can encrypt, though only the key holder can DEcrypt.
• like IND-EAV game, except A can send queries(messages) to B, and B responds with it's encryption
• Modeling A as a PPT-bounded adversary means that we limit the number of queries A can make to being polynomial in the security parameter. If the key space is 2^k, we can't get away with saying "suppose the adversary makes 2^k encryption queries," since that's basically assuming unnatural ability to scale resources (i.e., cheating).

Deterministic encryption

• encrypting same text two separate times gives the same text each time

non-deterministic encryption

• gives you a different cipher each time
• needs:
  • a key
  • a plain text
  • a random value
  • the decryption
  • decryption function is structured such that the random value disappears during decryption (and the plain text can be recovered).