Final answer:
3DES does not operate in the mode DES-DDD2, which is not a recognized mode. The correct 3DES modes are DES-EEE3, DES-EDE3, and DES-EEE2, each signifying a particular sequence of encryption and decryption steps with a specific number of keys.
Step-by-step explanation:
The mode in which 3DES does NOT work is DES-DDD2. The naming of these modes is determined by how DES (Data Encryption Standard) is applied within the 3DES encryption process. 3DES enhances the security of the original DES by applying the encryption algorithm multiple times with different keys.
Here are the modes listed:
- DES-EEE3: This implies the DES algorithm is used three times for encryption (E) with three different keys.
- DES-EDE3: DES is used three times with three keys, first for encryption (E), then decryption (D), and finally encryption (E) again. Decryption here is meant to increase compatibility with DES.
- DES-DDD2: This is not an existing mode for 3DES. It suggests an incorrect sequence of two operations which is not part of the standardized modes.
- DES-EEE2: Uses two keys and the DES algorithm is applied three times for encryption, using the first key twice and the second key once.
Therefore, the correct answer is C) DES-DDD2, as it is not a real operational mode of 3DES.