Flashcards on Introduction to Cryptography and Security
Introduction to Cryptography & Security for Students
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Symmetric Encryption
41 cards
Card 1
Question: What is the purpose of an Initialization Vector (IV) in symmetric encryption?
Answer: To randomize the ciphertext for the same key and plaintext so identical plaintexts encrypt to different ciphertexts (with same key).
Card 2
Question: Does an IV have to be random? What requirement must it meet?
Answer: An IV does not necessarily have to be random, but it must be unique for each encryption with the same key; same IV and key produce the same keystream.
Card 3
Question: In a stream cipher, what happens when the same IV and key are reused?
Answer: The same IV and key produce the same keystream, causing identical encryption output for the same plaintext (security risk).
Card 4
Question: How do stream ciphers process data compared to block ciphers?
Answer: Stream ciphers process data bit-by-bit or byte-by-byte as it arrives, while block ciphers operate on larger fixed-size blocks (e.g., 64b, 128b, 256b).
Card 5
Question: Give two use cases where stream ciphers are especially efficient.
Answer: Hardware implementations and continuous or unknown-size data streams such as audio or video.
Card 6
Question: Why might block ciphers be preferable in software and for known file sizes?
Answer: They are suitable for software implementation, allow parallel processing for efficiency when file size is known, and operate on fixed-size blocks.
Card 7
Question: What drawback can block cipher padding introduce?
Answer: Padding may be needed for incomplete final blocks and can lead to attacks if padding cannot be distinguished from data; typically padding length is wr
Card 8
Question: What are block ciphers conceptually?
Answer: Permutations operating on fixed-size blocks of data (typically 128b or 256b in modern contexts; presentation mentions 128b, 256b).
Card 9
Question: What is DES (Data Encryption Standard) and who developed the original cipher?
Answer: DES is the Data Encryption Algorithm (DEA) standardized by NIST in 1977; it was based on an IBM cipher (Lucifer) developed by H. Feistel for a Lloyd’s
Card 10
Question: What block size and effective key size does DES use?
Answer: DES uses 64-bit input/output blocks and a 56-bit key (often represented as 64 bits including parity bits).