(Approximately) how many more bits of data must be transferred over the network during an encrypted connection compared to an unencrypted connection?
IIUC, once the TLS handshake has completed, the number of bits transferred is equal to those transferred during an unencrypted connection. Is this accurate?
As a follow up, is transferring a large file over https significantly slower than transferring that file over http, given fast processors and the same (ideal) network conditions?
In 2020, TLS 1.2 and 1.3 are more typical with AES-GCM being a streaming cipher mode with lower overhead.
See https://tools.ietf.org/id/draft-mattsson-uta-tls-overhead-01.xml#rfc.section.3.
Per packet, the overhead for AES-GCM is 29 bytes. The TCP MSS may be as large as 1460 (https://blog.apnic.net/2014/12/15/ip-mtu-and-tcp-mss-missmatch-an-evil-for-network-performance/). So for a large download (where the maximum MSS is used), the overhead would be 29:1431 which is 2.03%.
(Handshake overhead is separate being once-off)
