What is the key length of the DES encryption standard?

The key length of the Data Encryption Standard (DES) is actually 56 bits, which is not listed among the options provided. However, 64 bits is sometimes mistakenly referred to as the key length because the total block size for DES is 64 bits — this includes the actual key bits plus some parity bits used for error checking. The key used in DES encryption is 56 bits long, making it susceptible to brute-force attacks as computational power increased over time.

In the context of the provided options, none accurately reflect the standard key length of DES. However, the choice that suggests a longer key length, such as 128 bits, aligns more with later encryption standards like AES (Advanced Encryption Standard), which provides more security and supports longer key lengths.

It's important to differentiate that DES has been largely phased out in favor of AES and other cryptographic methods that provide enhanced security features, including larger key sizes. Understanding these distinctions is vital for recognizing why DES is considered less secure in modern applications.