Which encryption mode applies an initialization vector and an incrementing counter value to generate a keystream, making it more efficient than modes that require padding?

The correct answer is CTR (Counter mode) because it utilizes a unique concept of generating a keystream through the combination of an initialization vector (IV) and a counter value. This approach allows the encryption process to be more efficient as it enables the encryption of data in parallel, which is not the case for block cipher modes that require extensive padding.

In CTR mode, the encryption engine increments the counter with each block. This means that the same plaintext blocks do not produce the same ciphertext blocks if the counter is incremented, ensuring that encryption remains secure. The use of the initialization vector helps to ensure that even if the same counter value is reused in different sessions, the ciphertext will still differ as long as the IV is different, preventing potential attacks based on repeated key or counter usage.

The efficiency of CTR mode arises because it does not require padding. Unlike other modes such as CBC or 3DES, which often need additional information appended to the data to fill out the final block, CTR works seamlessly with any size of data, allowing it to be processed in its native format. This is particularly beneficial for applications requiring high-speed processing or where data sizes may not align perfectly with the block size, as padding can introduce delays or overhead.

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