This PR extended `parse_tls_serverhello()` in a few ways:
* If the "full" response is to be parsed, then additional checks are performed to verify that `$tls_hello_ascii` contains the entire response
* The extensions field is parsed and the list of extensions found is placed in `$TLS_EXTENSIONS` (if the "full" response is being parsed).
* Initial support for TLS 1.3 is added:
- Accounts for differences between TLS 1.2 ServerHello and TLS 1.3 ServerHello (as outlined in PR #499).
- Recognizes new alerts and handshake message types.
- Allows for server response to include message fragments of type "application data"
I forgot that `parse_tls_serverhello()` is also called by `client_simulation_sockets()`. Since PR #499 changed the input to `parse_tls_serverhello()`, the change needs to be made in `client_simulation_sockets()` as well.
Now that the mapping file is no longer used, `$ADD_RFC_STR` should not be unset just because the mapping file cannot be found.
In addition, since `show_rfc_style()` is now used in `parse_tls_serverhello()`, it cannot return an empty string just because the user set "--mapping no-rfc" on the command line. Instead, `neat_list()` should check the value of `$ADD_RFC_STR` and not call `show_rfc_style()` if it has been unset.
Finally, since `show_rfc_style()` no longer returns strings with extra spaces, there is no need to call `strip_spaces()`
In some cases the server's response to a ClientHello spans more than one packet. If the goal is just to determine whether the connection was successful and to extract a few pieces of information from the ServerHello message, then this is unlikely to be a problem. However, if there is a desire to extract the server's certificate chain (Certificate message) or to determine the type and size of the server's ephemeral public key (ServerKeyExchange message), then the entire response needs to be obtained, even if it spans multiple packets.
This PR adds a new function, `check_tls_serverhellodone()`, that checks whether the entire response has been received (e.g., whether the ServerHelloDone message has been received). If the response indicates that the response is incomplete, then `tls_sockets()` requests more data from the server until the response is complete or until the server doesn't provide any more data in response.
The PR only changes the behavior of `tls_sockets()` if the caller indicates that it wants to extract the ephemeral key or that it wants the entire response to be parsed. Otherwise, only the first packet returned by the server is sent to `parse_tls_serverhello()`. [The value of `$process_full` is not used at the moment, but will be in a subsequent PR that modifies `parse_tls_serverhello()`.]
This PR also changes `tls_sockets()` to send a close_notify to the server if the connection was successfully established.
PR #346 added a test for version tolerance to `run_protocols()`, but I think it may now be more appropriate to remove that test. Draft -16 of TLS 1.3, which was posted on September 22, changed the way that version negotiation is handled for TLS 1.3 and above. The current version tolerance test sends a ClientHello with the version field set to "03, 05", to represent a TLS 1.4 ClientHello. While this was consistent with RFC 5246 and with drafts of TLS 1.3 up to -15, draft -16 changed the version field to `legacy_version` and declared that its value should be "03, 03" for TLS 1.2 and above. (For TLS 1.3 and above a Supported Versions extension is included to inform the server which versions of TLS the client supports.) The change in draft -16 was made as a result of the problems with servers not handling version negotiation correctly.
Since the current draft suggests that a server should never be presented with a ClientHello with a version higher than "03, 03" (even for clients that support TLS versions higher than 1.2), it seems there is no reason to include the version tolerance test anymore.
For servers that do not support TLS 1.2, the additional checks that were added by PR #346 will already detect if the server cannot perform version negotiation correctly.
