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The Advanced Encryption Standard (AES) is a symmetric encryption algorithm that utilizes a block cipher structure, which means it encrypts data in fixed-size blocks. AES specifically operates on blocks of 128 bits and supports key lengths of 128, 192, or 256 bits. This flexibility in key lengths allows for varying levels of security; longer keys generally provide a higher level of security against brute-force attacks.

AES replaced the older Data Encryption Standard (DES), which had limitations such as the use of shorter keys and vulnerability to exhaustive search attacks due to its smaller key size. The selection of variable key lengths in AES enhances its security while maintaining efficiency in encryption and decryption operations, which is crucial for its adoption in various applications, including securing sensitive data.

The other choices do not accurately reflect the characteristics of AES. While a block cipher is involved, the mention of 64-bit keys aligns with older algorithms like DES, which is not AES. Similarly, describing AES as a stream cipher contradicts its classification as a block cipher. Lastly, while data integrity is essential in cryptography, AES is not a hashing algorithm, which serves a different purpose of verifying data integrity rather than encrypting data for confidentiality.