SB 10: Cryptography Variants Flashcards
What is a stream cipher?
An encryption technique that works byte by byte to transform plain text into code that’s unreadable to anyone without the proper key. Stream ciphers are linear, so the same key both encrypts and decrypts messages. Inspired by the one-time-pad.
What is a block cipher?
Enciphers and deciphers multiple bits at once using the same key. Errors in one block usually doesn’t affect others. Identical plaintext block produces identical ciphertext blocks.
What are the security implications of Shor’s algorithm?
It breaks the assumption that it is computationally infeasible to factor a large enough number N onto two primes in polynomial time. Any algorithm relying on a factoring attack being infeasible will no longer be secure once a machine that can implement the algorithm exist.
What are the security implications of Grover’s algorithm?
Can be used for searching through data fast. A brute force attack against symmetric keys will become feasible. The risks can be mitigated by increasing the key length.
What is distributed ledger technology?
Distributed ledger data is typically spread across multiple nodes (computational devices) on a P2P network, where each replicates and saves an identical copy of the ledger data and updates itself independently of other nodes. The primary advantage of this distributed processing pattern is the lack of a central authority, which would constitute a single point of failure.
What are the advantages and disadvantages of a stream cipher?
Advantages
Speed of transformation: Because each symbol is encrypted without regard for any other plaintext symbols, each symbol can be encrypted as soon as it is read. Thus, the time to encrypt a symbol depends only on the encryption algorithm itself, not on the time it takes to receive more plaintext.
Low error propagation:Because each symbol is separately encoded, an error in the encryption process affects only that character.
Disadvantages:
Low diffusion: Each symbol is separately enciphered. Therefore, all the information of that symbol is contained in one symbol of ciphertext.
Susceptibility to malicious insertions and modifications: Because each symbol is separately enciphered, an active interceptor who has broken the code can splice pieces of previous messages and transmit a spurious new message that may look authentic.
What are the advantages and disadvantages of a block cipher?
Advantages:
High diffusion. Information from the plaintext is diffused into several ciphertext symbols. One ciphertext block may depend on several plaintext letters.
Immunity to insertion of symbol. Because blocks of symbols are enciphered, it is impossible to insert a single symbol into one block. The length of the block would then be incorrect, and the decipherment would quickly reveal the insertion.
Disadvantages
Slowness of encryption. The person or machine doing the block ciphering must wait until an entire block of plaintext symbols has been received before starting the encryption process.
Padding. A final short block must be filled with irrelevant data to make a full-sized block.
Error propagation. An error will affect the transformation of all other characters in the same block.
