Which of the following is a false statement regarding DES?

The statement that DES allows for a variable key length is false because DES (Data Encryption Standard) has a fixed key length of 56 bits. This is one of its defining characteristics. Unlike some other encryption algorithms that allow for varying key lengths, DES standardizes on this specific length, which has made it less secure over time.

In the context of symmetric key algorithms, DES shares a common key for both encryption and decryption, which is correctly stated in the first option. The claim that it is considered obsolete for most applications is also accurate, as advances in computational power and the discovery of vulnerabilities, such as brute-force attacks, have rendered it inadequate for securing sensitive data effectively. The comparison to RSA highlights a key distinction between symmetric and asymmetric algorithms; DES generally performs faster in encryption and decryption operations than RSA, a public key algorithm that operates with much larger key sizes.