Why is it difficult to scale symmetric encryption?

Scaling symmetric encryption presents challenges primarily because both the sender and receiver must manage the same private key. This requirement creates complexity in key distribution and management, especially in environments where there are many users. If each pair of users requires a unique key, the number of keys increases exponentially with the number of users. For instance, if there are n users, each pair would need a separate key, leading to a total of n(n-1)/2 unique keys. This situation can become unwieldy and prone to errors in key distribution, increasing the risk of keys being compromised.

Effective management of symmetric keys also typically involves secure methods of key exchange, which can complicate the infrastructure needed to support communication securely. In contrast, asymmetric encryption allows for a simpler key management process because it does not require pairs of users to share a private key, instead employing a public and private key combination that eases the scaling process.

Therefore, the requirement for both parties to manage the same private key is a significant factor that complicates the scalability of symmetric encryption systems.