Which algorithm is an accepted standard that can utilize a 128-bit key?

The Advanced Encryption Standard (AES) is indeed an accepted standard for encryption that supports a 128-bit key size among others (it also supports 192- and 256-bit key sizes). AES was established by the National Institute of Standards and Technology (NIST) in 2001 after a rigorous evaluation process to secure sensitive information across various applications.

AES is a symmetric-key algorithm, meaning the same key is used for both encryption and decryption. The use of a 128-bit key provides a high level of security, making it a suitable choice for modern encryption needs. The algorithm operates on fixed block sizes and is designed to be efficient in both hardware and software implementations.

Other algorithms mentioned, such as MARS, RC2, and IDEA, have their specific characteristics and use cases, but they do not serve as the accepted standard. MARS did not gain widespread adoption; RC2 is considered less secure than newer alternatives; and IDEA, while important historically, is not as commonly used today in preference for AES. Thus, AES stands out as the go-to standard when it comes to employing a 128-bit key for encryption.