repeating-key cipher

noun
UK /rɪˈpiːtɪŋ kiː ˈsaɪfə/
US /rɪˈpiːtɪŋ kiː ˈsaɪfər/

A repeating-key cipher is a secret code that uses the same short password over and over to hide a message.

The spy used a repeating-key cipher so that the same word kept scrambling each letter in turn.

SYNONYMS

periodic-key ciphercyclic-key cipherrecurrent-key cipherrepeating-password cipher

RELATED WORDS

Vigenère cipherpolyalphabetic cipherencryption keycryptographykeystream

OTHER MEANINGS

2. A classical encryption method in which a keyword is repeated to match the length of the plaintext before combining letters.

In a repeating-key cipher, the keyword LEMON repeats as LEMONLEMON to encrypt the whole message.

3. A cipher whose key cycles through a fixed sequence, making the encryption pattern predictable over long texts.

Cryptanalysts can break a repeating-key cipher by finding the key length through frequency analysis.

4. Any cipher that reuses the same key material periodically rather than generating a fresh keystream.

Unlike a one-time pad, a repeating-key cipher reuses its key and is therefore less secure.