What uses a key of the same length as the message where each bit or character from the plaintext is encrypted by a modular addition?

The correct answer is B. One-time pad. A one-time pad (OTP) uses a random key that is exactly the same length as the plaintext message. Each bit or character of the plaintext is combined with the corresponding key bit/character using modular addition (XOR for binary data). When used correctly - with a truly random…

Submitted by mike_84· Apr 18, 2026Cryptography

Question

What uses a key of the same length as the message where each bit or character from the plaintext is encrypted by a modular addition?

Options

ARunning key cipher
BOne-time pad
CSteganography
DCipher block chaining

How the community answered

(41 responses)

A
7% (3)
B
88% (36)
C
2% (1)
D
2% (1)

Explanation

A one-time pad (OTP) uses a random key that is exactly the same length as the plaintext message. Each bit or character of the plaintext is combined with the corresponding key bit/character using modular addition (XOR for binary data). When used correctly - with a truly random key, used only once, and kept secret - the OTP is mathematically proven to be unbreakable. A running key cipher also uses a long key but is derived from text (not truly random), making it weaker. Steganography hides messages rather than encrypting them. CBC is a block cipher mode, not a cipher itself.

Topics

#Cryptography#One-time pad#Encryption#Key length

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