What would be an appropriate strength for the key-encrypting key (KEK) used to protect an...

The strength of a key-encrypting key (KEK) should be at least equivalent to the strength of the data-encrypting key (DEK) it protects to ensure the overall security of the cryptographic system.​

Option A:Incorrect. DES (Data Encryption Standard) with a 256-bit key length is not a standard configuration, as traditional DES uses a 56-bit key, which is considered weak by modern standards.​

Option B:Incorrect. RSA with a 512-bit key length is considered weak and does not provide sufficient security for protecting AES 128-bit keys.​

Option C:Correct. Using an AES 128-bit key as the KEK to protect an AES 128-bit DEK ensures that both keys have equivalent strength, maintaining the integrity of the encryption system.​

Option D:Incorrect. ROT13 is a simple substitution cipher and does not provide adequate security for encrypting cryptographic keys.​

For detailed guidelines on cryptographic key management, refer toRequirement 3: Protect Stored Account Datain thePCI DSS v4.0.1document.​