Flashcards
Symmetric Encryption
Cards in this deck (22)
- 1What 3 things do encryption provide?- Confidentiality
- Integrity
- Authenticity - 2What are the 3 primitive encryption types?- Stream cipher
- Block cipher
- Hash function - 3What is the Caesar cipher?Letters are swapped with ones further in the Alphabet by a key K.
Vulnerable to frequency analysis. - 4What is Kerkhoff's Pinciple?A cryptographic system must be secure even if everything about the system is known, with the exception of the secret key
- 5State the 6 attack models- Brute-force
- Ciphertext-only
- Known-plaintext
- Chosen-plaintext
- Chosen-ciphertext
- Related-key attack - 6Describe the only perfect cipherOne-time pad.
New key for every message.
Key length == message length.
Inpractical due to key size and generation. - 7Describe an implementation of the perfect cipherModern stream cipher.
XORs message with a key.
Keys are produced by an infinite pseudorandom keystream. - 8What is a block cipher?Fixed-size plaintext to fixed-size ciphertext. More computationally expensive than stream ciphers.
Vulnerable if changes aren't diffused. - 9Describe an SP NetworkSubstitution-Permutation Network.
Repeats rounds of S/P.
S = swap values using lookup (confusion).
P = shuffle values (diffusion) - 10How many rounds are needed to ensure security?One round susceptible to analysis attacks. More rounds causes more diffusion and makes it harder to analyse / detect patterns.
- 11What is the Luby-Rackoff principle?3 rounds = chosen-plaintext protection.
4 rounds = chosen-plaintext and chosen-ciphertext protection. - 12Describe SP Networks and Key mixingCombining keys with SP networks.
Key XOR Message => SP Network => Key XOR cipher-text => SP Network etc. - 13What is a Feistal Cipher?Technique for chaining multiple rounds. Works with any round function.
- 14Draw the Feistal CipherC = R + L XOR F(R, K)
- 15What is DES?Data Encryption Standard.
64-bit block size,
56-bit key size,
16 rounds.
Feistal cipher. - 16What is AES?Advanced Encryption Standard.
Rijndael SP Network.
128-bit block size,
128/192/256-bit key size,
10/12/14 rounds. - 17What is a Block Cipher Mode?Describes how a cipher is applied to messages larger than the block-size
- 18Name 4 Block Cipher Modes- Electronic Code Book (ECB)
- Cipher Block Chaining (CBC)
- Counter Mode (CTR)
- Galois Counter Mode (GCM) - 19Describe ECBEncrypt each block one after another. Vulnerable to analysis attacks (repeating patterns produce the same cipher blocks)
- 20Describe CBCXOR output of each block with the next input before applying the cipher.
First output is an IV.
Can insert malicious blocks.
Sequential. - 21Describe CTREncrypt a counter and XOR with message block.
Counter is combined with a nonce. Parallelisable. - 22Describe GCMExtension of CTR.
Adds authenticity and integrity.
Combines ciphertext with authentication tag.
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- Bachelors Degree Computer Science (Computer Security) Flashcards on Symmetric Encryption, created by Alex Neves on 21/05/2016.
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- Alex Neves
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