Which of the following is not a DES mode of operation?

The correct answer is C. Input feedback. The standard modes of operation for DES (and block ciphers generally) are: Electronic Code Book (ECB), Cipher Block Chaining (CBC), Cipher Feedback (CFB), Output Feedback (OFB), and Counter (CTR). 'Input Feedback' is not a valid or recognized mode of operation. The mode that…

Submitted by chiamaka_o· Apr 18, 2026Cryptography

Question

Options

ACipher block chaining
BElectronic code book
CInput feedback
DCipher feedback

How the community answered

(47 responses)

A
9% (4)
B
2% (1)
C
87% (41)
D
2% (1)

Explanation

The standard modes of operation for DES (and block ciphers generally) are: Electronic Code Book (ECB), Cipher Block Chaining (CBC), Cipher Feedback (CFB), Output Feedback (OFB), and Counter (CTR). 'Input Feedback' is not a valid or recognized mode of operation. The mode that sounds similar is Output Feedback (OFB), which feeds the cipher's output back into itself. Cipher Feedback (CFB) is also a real mode. 'Input Feedback' appears to be a fabricated distractor.

Topics

#DES#Block Cipher Modes#Symmetric Encryption

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