Daniel S. Sterling Daniel S. Sterling - 2 months ago 35
HTTP Question

How much network overhead does TLS add compared to a non-encrypted connection?

(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?


I've gotten this question a few times, so I decided to write up a small explanation of the overhead with some sample numbers based on common case. You can read it on my blog at http://netsekure.org/2010/03/tls-overhead/.

Summary from blog post:

  • The total overhead to establish a new TLS session comes to about 6.5k bytes on average.
  • The total overhead to resume an existing TLS session comes to about 330 bytes on average.
  • The total overhead of the encrypted data is about 40 bytes.