Which encryption standard is the current U.S. federal government standard for symmetric encryption?

The Advanced Encryption Standard (AES) is the current U.S. federal government standard for symmetric encryption. It was established by the National Institute of Standards and Technology (NIST) in 2001 after a thorough evaluation process to replace the aging Data Encryption Standard (DES). AES is recognized for its strong security, efficiency, and versatility, as it can encrypt data in block sizes of 128 bits using key lengths of 128, 192, or 256 bits.

AES is widely adopted for its robustness against various types of cryptographic attacks and is used in numerous applications, including secure communications, financial transactions, and data protection standards enforced by federal regulations. Its inclusion as the federal standard signifies its trustworthiness and effectiveness as a symmetric encryption algorithm, making it a cornerstone in the field of cybersecurity.

In contrast, the other choices represent different modes of operation (GCM, CBC) or encryption algorithms (ChaCha) that are not designated as the federal standard for symmetric encryption itself, although they may be used in conjunction with standards like AES or for specific use cases in modern cryptography.