Flashcards
One-Time Cryptosystems
Cards in this deck (13)
- 1What is a one-time pad?Enciphers bitstrings of a fixed length by XOR'ing where K has the same length as M
- 2What is kr-1ca?Only one ciphertext available
- 3What is kr-1kpa?Message and ciphertext available
- 4What is kr-1cpa?Message comes from a distribution
- 5What is ow-pas?Tries to guess message given a cipher
- 6Shannon's Theorem?Let E be an enciphering scheme where K = M, then E is perfectly secure iff. Kg draws uniformally at random and E satisfies that for all message-cipher pairs there's a unique K
- 7Pros and cons of one-time pad?Perfect secrecy but the key can't be re-used and seeing any message pairs makes the key available
- 8What is left-or-right indistinguishabilityThe adversary picks two messages to output a bit to indicate which game it thinks it's playing. Can only be done iff. it can tell encipherings apart
- 9What is random ciphertext indistinguishability?In the real experiment the adversary knows the real enciphering, in ideal the ciphertext is chosen randomly
- 10Reduction steps with 1-CPA and 1-KCA example1CPA is better than 1KPA so create an adversary for 1CPA.
1) Recall what the adversary aims to do: 1CPA wants to return a key based on a C which is an encoded M.
2) Ensure that the adversary simulates the inputs and outputs of the underlying adversary
KPA gives a message to it's oracle and forwards it to CPA. CPA uses it's own oracle to get a ciphertext. CPA gives the message and ciphertext to KPA who outputs K^ and gives this to CPA.
Since reductions are that if KPA is successful then CPA will be, so we assume K^ is correct - 11What is: Authenticity Integrity ConfidentialityAuthenticity: Guarantee that the message originated from sender
Integrity: Message not tampered with
Confidentiality: Peopl can't read it - 12What is Kerckhoff's Principle?Adversaries can see the system but not the key
- 13What is onewayness?The adversary has an oracle that it can feed N, M pairs and it will return the corresponding cipher from the key we chose.
He also has the nonce and in the CCA case the challenge ciphertext. Using this and the oracle he can formulate a guess.
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- Cryptography Flashcards on One-Time Cryptosystems, created by Philip Masters on 04/01/2020.
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- Philip Masters
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