Karteikarten
Authenticated Encryption
Karten in diesem Stapel (13)
- 1What is nonce-based authentic encryption?Same as usual but Dec either outputs M or failure
- 2What does authentic encryption provide? Which adversary is better for each?Confidentiality: EUF-CMA
Integrity: IND - 3What is existential forgery?Forging a nonce-ciphertext pair (one that isn't valid) but returns a valid tag
- 4IND for authentication encryption and explanation for freshnessAgain in the real world the message is given, in the ideal it's sampled. If they were able to use the cipher they got from encoding, decoding gives them a valid tag despite the wrong message but ideal always gives invalid
- 5IND-CCA?Adversaries can encrypt and decrypt
- 6Why are nonces good?Defend against replay attacks since they are different each time and give originality to a message.
- 7What is generic composition?Combining non-authenticated encryption with MACs
- 8What's MAC Then Encrypt and it's pros and consYou add a layer of protection to the tag
Mismatch in authenticating plaintext and actual authentication which can lead to ciphertext forgery
The message has to be stored before the tag can be verified since the tag involves the message which could lead to leaked unverified plaintexts
- 9What's Encrypt then Mac and why it's the G.O.A.T?Computation of tag can be pipelined with encryption since encryption doesn't need the tag.
The tag can be verified before decryption since it doesn't use the message.
- 10What is Encrypt & Mac and what are the pros and cons?Can't pipeline tag computation and encryption.
Leads to unverified message being leaked
- 11Where's the nonce for CBC mode?First block of the cipher text
- 12How to combat CTR mode?CTR just generates a keystream and masks the plaintext. Assuming it's 2 blocks:
Mask (XOR) C* with Z to get C so that C /=/ C* and you can use the oracle.
Query with (N*, C) to get M
Simply unmask M by XORING with Z and you get M^ - 13What nonce-ciphertext is a valid forgery for a CTR that doesn't have nonce authentication?Any nonce (N,C*) where N /=/ N* since there's no authentication of nonces
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- Cryptography Karteikarten am Authenticated Encryption, erstellt von Philip Masters am 08/01/2020.
- Erstellt von
- Philip Masters
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