SSLEngine weird behavior in 11+21?

Simone Bordet simone.bordet at gmail.com
Wed Jul 11 22:06:43 UTC 2018


Hi,

I can see this (weird) behavior in SSLEngine for TLS 1.3 in JDK 11+21.
It's a simple new connection (no resumption) that performs a TLS 1.3 handshake.
The bytes numbers are those that I get, they may be different for
others depending on certificate size, etc.

1. Client wraps 394 bytes then goes into NEED_UNWRAP.
2. Server unwraps 394 bytes then goes into NEED_TASK and then into NEED_WRAP.
3. Server wraps (in 3 wraps) 160, 6 and 907 bytes then goes into NEED_UNWRAP.
4. Client unwraps 160 bytes then goes into NEED_TASK and then into NEED_WRAP (?)
5. Client wraps 6 bytes, then goes into NEED_UNWRAP.
6. Client unwraps (in 2 unwraps) 6 and 907 bytes, then goes into
NEED_TASK and then into NEED_WRAP.
7. Client wraps 58 bytes and goes into FINISHED (?)
8. Server unwraps (in 2 unwraps) 6 and 58 bytes then goes into NEED_WRAP.
9. Server wraps 72 bytes then goes into FINISHED.
10. Client MUST unwrap those 72 bytes going again into FINISHED (which
already happened at 7).

There are 2 things that I find weird:

A) That at 4, the client goes into NEED_WRAP, even if it has not
finished to unwrap what the server sent. Apparently, it only goes into
NEED_WRAP to generate a CHANGE_CIPHER_SPEC (I am guessing from the
number of bytes generated), but then goes back into NEED_UNWRAP to
finish reading what the server sent. This is also not optimal as it
forces applications to do something with those 6 bytes: either put
them aside (additional data structures that may not be needed) or -
worse - write them to the server causing an additional write (after
all the effort TLS 1.3 put in to have a 1 RTT handshake).
I think that step 4 should go into NEED_UNWRAP, and that step 5 and
step 6 should be switched, so that the client would unwrap the 160, 6
and 907 sent by the server, and only after wrapping the 6 and the 58.
To be clear, the current behavior is (u==unwrap, w=wrap): u160, w6,
u6, u907, w58.
I think it should be: u160, u6, u907, w6, w58.

Is there any reason that the 6 bytes needs to be generated in-between
the processing of the frames sent by the server?

B)That at 7 the client goes into FINISHED, but it is not finished
really: in fact it needs to perform step 10, but there is no
indication from the SSLEngine that it must do so.
Currently, step 7 says the client is finished and there is no clue
that it must unwrap those last 72 bytes.
I think step 7 should go into NEED_UNWRAP instead, and only at 10 go
into FINISHED.

Thanks!

-- 
Simone Bordet
---
Finally, no matter how good the architecture and design are,
to deliver bug-free software with optimal performance and reliability,
the implementation technique must be flawless.   Victoria Livschitz


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