Cryptography Fundamentals Questions and Answers

Answer: D

The cipher text is TRNIE TZENZ.

Split the plaintext into blocks of five, padding the last with Z: INTER and NETZZ. The key's top row tells which plaintext position goes into each cipher position: the first cipher letter is plaintext letter 3, then 5, 2, 1 and 4.

INTER: letters 3, 5, 2, 1, 4 are T, R, N, I, E, giving TRNIE. NETZZ: letters 3, 5, 2, 1, 4 are T, Z, E, N, Z, giving TZENZ.

The other options are wrong arrangements: (B) simply swaps the two padded blocks, and (A) and (C) do not follow the key's order of positions.

Answer: B

Encryption transforms data into cipher text.

Encryption applies an algorithm and a key to readable plain text, producing unreadable cipher text. Only someone with the right key can reverse it by decryption to recover the plain text. That reversibility with a key is what separates encryption from other transformations.

Plain text is the input to encryption, not its output. Hash values come from hashing, a one-way function with no key that cannot be reversed. Metadata is data about data, such as a file's size or timestamps.

Answer: A

Data encryption techniques are used for protecting data in a data communication system. The data is converted to a form that cannot be read without the key, so it is safe while it travels on the network and from tapping.

Encryption does not reduce the storage space (compression does that), and it does not itself improve or decrease data integrity, which is the task of checks like checksums and hashes. So the other options are wrong.

Answer: C

The false statement is the one about AES key lengths. The Advanced Encryption Standard supports fixed key lengths of 128, 192 and 256 bits, not variable lengths of 56 and 124 bits. The 56-bit key belongs to DES.

The other statements are true: symmetric algorithms use the same key to encrypt and decrypt, DES was widely used in security products, and public key algorithms use a different key for each of encryption and decryption.