On 6/5/2019 8:25 PM, Anthony Scarpino wrote:
On 6/5/19 7:30 PM, Xuelei Fan wrote:
On 6/5/2019 7:21 PM, Anthony Scarpino wrote:
On Jun 5, 2019, at 5:37 PM, Xuelei Fan <xuelei....@oracle.com> wrote:
On 6/5/2019 4:57 PM, Jamil Nimeh wrote:
I think what it's saying is that what was explicitly called out in
4507 (where there is both the extension_data length bytes AND the
opaque vector length) is not how deployed implementations did it.
It implies that deployed implementations do what you laid out below
where you just have 2 bytes of ID and 2 bytes of length. And I
believe that is compatible with what 5077 specifies.
Hm, I agreed with you.
So the potential problem is if one endpoint or the other happens to
implement 4507 to the letter, extra length bytes and all. But the
authors of 5077 say that no known implementations do this. That's
good for us I think, because in the two-ish years between 4507 and
5077 nobody did straight 4507, or they maybe did and fixed it by
the time 5077 came around.
I may view it differently.
If an implementation encoded per the format:
00 23 Extension type 35
00 02 Length of extension contents
00 00 Length of ticket
Just as your analysis previous, a RFC 5077 server will just ignore
the extension. No real hurt actually.
But if an implementation encoded empty SessionTicket extension per
the format (the known implementation):
00 23 Extension type 35
00 00 Length of extension contents
The server could read it as RFC 5077, and use stateless
implementation. When the ServerHello extension sent back. No matter
the RFC 4057 client accept it or not, there are interop issues.
If the client does not accept it (unlikely), the connection cannot
be established.
If the client accept it, the resumption session will use the
negotiated ticket, and then non-empty SessionTicket extension is
encoded as:
00 23 Ticket Extension type 35
01 02 Length of extension contents
01 00 Length of ticket
FF FF .. .. Actual ticket
The server would have to handle it (RFC 4507 format) if it want the
session resumption works. Here come the interop issues.
That is true, but i believe it is extremely unlikely that the length
would not be in the ST empty extension, but the length would be in
the ST resumption extension.
I did not get the point.
The below two messages I believe are even less likely to occur. 4 byte
ST message ([Ext Type, Ext Len]) with a 6 byte NST message ([Ext Type,
Ext Len, Ticket Len] + Actual ticket) would mean the implementation was
coded up correctly for the ST and incorrectly the NST.
If I read the appendix A of RFC 5077 correctly, the initial handshake
uses (for known implementation, which is the ambiguous part of RFC 4507):
00 23 Extension type 35
00 00 Length of extension contents
Yes, this is 5077, and if 4507 was properly implemented if I understand
the appendix right. But 4507 may also include the length of the ticket
as well as the length of the extension, like you mentioned in the early
message.
I agreed. Both RFC 4507 and RFC 5077 use the above format. And RFC
4507 could use another format as well.
And session resumption uses (which is not ambiguous for RFC 4507):
00 23 Ticket Extension type 35
01 02 Length of extension contents
01 00 Length of ticket
FF FF .. .. Actual ticket
So it is the known format/behavior if RFC 5077 is right.
This is not a valid ticket for 5077,
No, it is not. It is the format of RFC 4507. The problem comes because
it is not a valid ticket for 5077. If it is valid format for RFC 5077,
there is no problem, I guess.
Let me try again.
RFC 4507 client uses the following format for the initial handshake:
00 23 Extension type 35
00 00 Length of extension contents
The RFC 5077 server response with an empty ST in SH.
00 23 Extension type 35
00 00 Length of extension contents
The client could accept the empty ST in SH.
The server send a NST message, and the client could parse it as well.
The RFC 4507 client uses the following format for session resumption:
00 23 Ticket Extension type 35
01 02 Length of extension contents
01 00 Length of ticket
FF FF .. .. Actual ticket
If the RFC 5077 server cannot parse it, it is not possible for session
resumption, fall-back to full-handshake.
I think it will always happen as if the client complies to RFC 4507.
this is the confusion of 4507. It
cannot be interpreted as 5077 because the ticket length will leak into
the actual ticket and corrupt the crypto.
Sure, it is not a RFC 5077 format so it cannot be parsed as RFC 5077.
That's the problem that the appendix A of RFC 5077 is trying to
describe, I think.
Xuelei
When the crypto fails the
code will not proceed with resumption, going into full handshake.
Tony
