Final answer:
In symmetric encryption, one key is used for both encrypting and decrypting data, and it needs to be kept secret between the sender and receiver.
Step-by-step explanation:
The number of keys required for symmetric encryption is one. In a symmetric key encryption system, the same key is used for both encryption and decryption of the data.
This means that the sender and the receiver must both have access to the same secret key, and they must keep it confidential. Unlike asymmetric encryption, which uses a public and private key pair, symmetric encryption is more straightforward but requires secure key distribution and management to prevent unauthorized access.