There are situations where a single connection (or file) may require additional throughput available. While network bandwidth and CPU cores are available, they cannot be utilised. (Aside from means that are external to the algorithm as is)
- VPN - when encryption is done only on the tunnel connection that internally encapsulates packets of multiple flows.
Typically, it is thought that an encryption algorithm itself is a sequential process, that relies on the previous block or bit(s) in order to accomplish effective cipher strength. This means the algorithms cannot be multi-threaded.
Is this true of all encryption? Does this apply equally to modern common algorithms (block and stream)?
Is there a way to purpose-make an encryption algorithm that works on multiple threads (cores)? Are there any existing algorithms (perhaps not common or academic only) that would work across multiples cores?
Usually, this isn't a problem, because machines may make use of multiple connections (HTTPS), but it means a single connection is limited by the cipher transform speed of a single CPU core. Also, when multiplexing is used (like VPN), this might be a particularly limiting issue.