Does HTTPS use TCP or UDP?

Solution 1:

HTTPS can run over any reliable stream transport protocol. Normally that's TCP, but it could also be SCTP. It is NOT expected to run over UDP, which is an unreliable datagram protocol (in fact, while that's not its official name, that's a good way to remember what it is).

The IANA assignment for UDP is historical; at the time, nearly every protocol was assigned both the TCP and UDP port numbers, even if it was expected that it would only ever use one. There has been discussion of merging the port number registries, and only ever assigning one port to one protocol from here on. That is to make it easier to deploy future transport protocols that would otherwise need their own registries. I'm not aware of how that discussion concluded.

Solution 2:

It uses TCP. It would be difficult to run it on UDP without the guarantee of packets arriving. If the packets don't arrive, the encrypted data will not be decipherable.