What is the primary downside of symmetric encryption?

The primary downside of symmetric encryption is that it requires both parties to have the same private key. This key must be exchanged securely before they can communicate, presenting a significant challenge in terms of key distribution. If the key is intercepted during transmission, anyone with access to it can decrypt messages meant for the legitimate parties. Additionally, managing and storing keys securely can become cumbersome, especially as the number of participants in the communication increases.

The other options address different aspects of encryption technology but do not capture the critical limitation associated with symmetric encryption's key management process. For instance, while symmetric encryption may not be the fastest in every scenario, saying it is too slow for real-time applications does not accurately describe its performance, as many applications utilize symmetric encryption efficiently. Furthermore, symmetric encryption is certainly employed in financial transactions, and while it is susceptible to brute-force attacks, with sufficient key length and security practices, its resilience can be greatly improved. Thus, the requirement for a shared private key stands out as the primary concern in symmetric encryption.