Which encryption technique maps each letter to a chosen other letter?

Which encryption technique maps each letter to a chosen other letter?

• A. Caesar Cipher
• B. Encryption
• C. Decryption
• D. Random Substitution Cipher

Answer: (D)

Substitution ciphers replace every letter with another letter according to a mapping. In a random substitution cipher, that mapping is chosen (typically at random) so each letter has a specific, one-to-one partner in the ciphertext alphabet. This directly fits the idea of “maps each letter to a chosen other letter,” since every plaintext letter is tied to a particular ciphertext letter by a preselected mapping. A Caesar cipher is also a substitution, but it uses a fixed shift for all letters rather than a randomly chosen mapping, which is why it isn’t the best match for the description. Encryption and decryption are the processes of turning plaintext into ciphertext and back, not the specific method of how letters are mapped.

Substitution ciphers replace every letter with another letter according to a mapping. In a random substitution cipher, that mapping is chosen (typically at random) so each letter has a specific, one-to-one partner in the ciphertext alphabet. This directly fits the idea of “maps each letter to a chosen other letter,” since every plaintext letter is tied to a particular ciphertext letter by a preselected mapping.

A Caesar cipher is also a substitution, but it uses a fixed shift for all letters rather than a randomly chosen mapping, which is why it isn’t the best match for the description. Encryption and decryption are the processes of turning plaintext into ciphertext and back, not the specific method of how letters are mapped.