5504115
Beschreibung
Karteikarten von Alex Neves, aktualisiert more than 1 year ago
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Erstellt von Alex Neves
vor mehr als 8 Jahre
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| Frage | Antworten |
| What 3 things do encryption provide? | - Confidentiality - Integrity - Authenticity |
| What are the 3 primitive encryption types? | - Stream cipher - Block cipher - Hash function |
| What is the Caesar cipher? | Letters are swapped with ones further in the Alphabet by a key K. Vulnerable to frequency analysis. |
| What 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 |
| State the 6 attack models | - Brute-force - Ciphertext-only - Known-plaintext - Chosen-plaintext - Chosen-ciphertext - Related-key attack |
| Describe the only perfect cipher | One-time pad. New key for every message. Key length == message length. Inpractical due to key size and generation. |
| Describe an implementation of the perfect cipher | Modern stream cipher. XORs message with a key. Keys are produced by an infinite pseudorandom keystream. |
| What is a block cipher? | Fixed-size plaintext to fixed-size ciphertext. More computationally expensive than stream ciphers. Vulnerable if changes aren't diffused. |
| Describe an SP Network | Substitution-Permutation Network. Repeats rounds of S/P. S = swap values using lookup (confusion). P = shuffle values (diffusion) |
| How 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. |
| What is the Luby-Rackoff principle? | 3 rounds = chosen-plaintext protection. 4 rounds = chosen-plaintext and chosen-ciphertext protection. |
| Describe SP Networks and Key mixing | Combining keys with SP networks. Key XOR Message => SP Network => Key XOR cipher-text => SP Network etc. |
| What is a Feistal Cipher? | Technique for chaining multiple rounds. Works with any round function. |
| Draw the Feistal Cipher | C = R + L XOR F(R, K) |
| What is DES? | Data Encryption Standard. 64-bit block size, 56-bit key size, 16 rounds. Feistal cipher. |
| What is AES? | Advanced Encryption Standard. Rijndael SP Network. 128-bit block size, 128/192/256-bit key size, 10/12/14 rounds. |
| What is a Block Cipher Mode? | Describes how a cipher is applied to messages larger than the block-size |
| Name 4 Block Cipher Modes | - Electronic Code Book (ECB) - Cipher Block Chaining (CBC) - Counter Mode (CTR) - Galois Counter Mode (GCM) |
| Describe ECB | Encrypt each block one after another. Vulnerable to analysis attacks (repeating patterns produce the same cipher blocks) |
| Describe CBC | XOR output of each block with the next input before applying the cipher. First output is an IV. Can insert malicious blocks. Sequential. |
| Describe CTR | Encrypt a counter and XOR with message block. Counter is combined with a nonce. Parallelisable. |
| Describe GCM | Extension of CTR. Adds authenticity and integrity. Combines ciphertext with authentication tag. |
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