Final answer:
Cipher Block Chaining (CBC) is the DES operating mode that can be used for large messages while providing the assurance that an early error won't affect the entire communication. It works by XORing each plaintext block with the previous ciphertext block, providing error isolation.
Step-by-step explanation:
You asked which Data Encryption Standard (DES) operating mode can be used for large messages with the assurance that an error early in the encryption/decryption process won't spoil results throughout the communication. The answer is Cipher Block Chaining (CBC).
Cipher Block Chaining (CBC) is an operating mode that addresses this concern effectively. In CBC mode, each block of plaintext is XORed with the previous ciphertext block before being encrypted. This means that even if there is an error in one block, it does not propagate to affect the subsequent blocks. Thus, CBC can provide error isolation in a way that other modes may not.
Conversely, Electronic Codebook (ECB) mode does not offer this advantage because each block is encrypted independently of the others, making it less desirable for long messages where error propagation could be an issue. Cipher Feedback (CFB) and Output Feedback (OFB) modes, while they provide some level of error propagation protection, still can allow errors to affect the decryption process beyond the erroneous block.