Which cryptographic approach uses the same key for encryption and decryption?

Correct answer: Symmetric encryption

Option C is correct because symmetric encryption uses a single shared key for both encrypting and decrypting data, making it fast and efficient for bulk data protection; examples include AES and 3DES. Option A is incorrect because hashing is a one-way function that produces a fixed-length digest and cannot be reversed to recover the original data, so no decryption key is involved. Option B is incorrect because asymmetric encryption uses a mathematically linked key pair, a public key for encryption and a private key for decryption, meaning the two operations use different keys. Option D is incorrect because digital signatures use asymmetric key pairs to provide authentication and integrity, and are not a standalone encryption mechanism that uses one key for both operations.