(ISC)2 Certified in Cybersecurity Practice Exam

How many keys are needed for two people using symmetric encryption to have a confidential conversation?

1. 1

2. 3

3. 8

4. None

The correct answer is: 1

In symmetric encryption, the same key is used for both encryption and decryption. This means that when two people want to communicate confidentially, they share a single key that both parties use to encrypt their messages before sending them and to decrypt the messages they receive. Consequently, only one key is required for both individuals to securely exchange messages. This approach simplifies the communication process since both parties can easily encrypt and decrypt their conversations using the same key without needing to establish multiple keys for different interactions or participants. The simplicity of using one key is one of the primary advantages of symmetric encryption compared to asymmetric encryption, which relies on a pair of keys (public and private) for secure communications. In the context of the other options, having three or eight keys would be unnecessary and inefficient for secure communication between just two individuals; it complicates the key management process. Similarly, the idea of needing "none" suggests that no key or encryption is involved, which would not provide confidentiality in their communications. Therefore, the use of a single key is both efficient and sufficient for ensuring confidentiality in a symmetric encryption scenario between two parties.