TI2: Cryptography Quiz
The CAESAR encryption works by cyclically shifting all letters by x positions in the alphabet (1 <= x <= 25). For example, with x=3, A becomes D. If you apply CAESAR twice with different x, is it more secure?
To find a large prime easily, you propose the following: You take all primes until some x, multiply them with each other, and subtract 1, resulting in a prime p. You then get another prime p' by p'=(p+1)p-1, which can be iterated. Does this method work?
Alice wants to send a 1 if her answer is yes, and a 0 if her answer is no. To do so, she chooses a one-time pad of one bit as encryption. Is this method malleable?
Malleability can be prevented by hashing the ciphertext, and sending the hash together with the ciphertext.
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