Which mode is used to ensure confidentiality by combining plaintext with a keystream generated from an incrementing counter value?

The chosen answer is based on the operation of CTR (Counter mode) encryption. CTR mode ensures confidentiality by transforming plaintext into ciphertext through a process that involves combining the plaintext with a pseudo-random keystream. This keystream is generated using an incrementing counter value combined with a secret key.

In CTR mode, the encryption process is quite efficient as it allows data to be encrypted in parallel, thus speeding up the encryption and decryption operations. This is particularly useful in scenarios requiring high throughput. Since the counter value changes with each block, the keystream remains unique for each block, ensuring that identical plaintext blocks will result in different ciphertext blocks if they're encrypted at different times.

The fundamental aspect of CTR mode is its use of the counter which, when combined with a secure key, produces a unique keystream for every encryption operation. This approach allows for strong confidentiality, as an attacker cannot derive any information about the plaintext without access to the key, even if they see multiple identical blocks of ciphertext.

The other options do not provide the same methodology for ensuring confidentiality via an incrementing counter. GCM combines CTR with authentication but does not focus solely on the counter aspect. AES, while a encryption standard, does not identify a specific mode