Flashcards
1. Introduction to Cryptography
Cards in this deck (22)
- 1What are the five objectives of cryptography?1. Confidentiality - ensuring only authorized individuals have access to the information.
2. Integrity - detecting if a message has been altered.
3. Non-repudiation - Preventing an entity from denying they sent a message.
4. Secret-sharing - methodologies which allow parties to share secret information through an insecure channel.
5. Zero-knowledge proof - The ability to demonstrate possession of information without sharing it. - 2Define "plain-text" and "cipher-text"An unencrypted message and an encrypted message.
- 3Describe the Caesar cipher.This is a symmetric key algorithm
- 4Describe a cryptosystem.
- 5Define a cipher.A cipher is a pair of algorithms used for computing the values of encryption and decryption functions.
- 6Describe the Caesar redux algorithmThis is an asymmetric key algorithm.
- 7Prove that the tuple (P,C,K,E,D), defined as for the Caesar redux algorithm, is a cryptosystem.
- 8What is encoding?Transforming a set of letters and symbols into a set of corresponding numbers.
- 9What is a weakness of the Caesar cipher?The Caesar cipher has a small key space, with only 26 possible decryption keys, one of which leads to a comprehensible plain-text message.
- 10What is a mono-alphabetic substitution cipher? What form does the encryption/decryption key take?A mono-alphabetic substitution cipher allows for an arbitrary permutation of characters within the alphabet. The encryption/decryption is the entire sequence of 26 letters.
- 11How many substitution ciphers are there on the standard English alphabet?26!
(This corresponds to the number of permutations on a set of size 26) - 12What type of attack are mono-alphabetic substitution ciphers susceptible to?Frequency analysis.
- 13What is a bigram?A two letter sequence (like th or sh).
- 14What type of attack is a frequency analysis attack?A cipher-text only attack. (where a cryptanalyst attempts to determine the plain-text using only the cipher-text)
- 15What is a poly-alphabetic substitution cipher?A poly-alphabetic substitution cipher uses a different cipher-text 'alphabet' for each position of the plain-text message.
- 16How was Enigma cracked?Using a known plain-text attack which gave information concerning the encryption key.
- 17What is a symmetric cipher?When knowledge of the encryption key permits easy computation of the decryption key.
- 18Describe the process of asymmetric or public-key cryptography (PKC).A: Generates both an encryption and decryption key (where is difficult to compute the decryption key given only the encryption key).
A: Publishes the encryption key
B: Encrypts a plain-text message using the public encryption key.
A: Only A can decrypt the cipher-ext message using her decryption or private key. - 19What is a downside to public-key cryptosystems?They are typically much slower and require larger keys than their symmetric-key counterparts.
- 20What is PKC used for in practicality?In practice, one uses symmetric-key cryptosystems to encrypt large messages and the keys are then shared via public-key cryptography.
- 21What are the effects of large keys?Larger keys typically produce slower algorithms which require more space.
- 22How many operations are required to add two n-bit numbers?n operations.
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- Cryptography (Topics) Flashcards on 1. Introduction to Cryptography, created by Alice Richens on 25/01/2018.
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- Alice Richens · Jan 2018
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- Feb 4, 2018
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