I note in draft-21 the following text:
When clients use a PSK obtained externally to send early data, then
the following additional information MUST be provisioned to both
parties:
- The TLS version number for use with this PSK
- The cipher suite for use with this PSK
- The Application-Layer Protocol Negotiation (ALPN) protocol
[RFC7301], if any is to be used
- The Server Name Indication (SNI), if any is to be used
Later it says this:
In order to accept early data, the server MUST have accepted a PSK
cipher suite and selected the first key offered in the client's
"pre_shared_key" extension. In addition, it MUST verify that the
following values are consistent with those negotiated in the
connection during which the ticket was established.
- The TLS version number and cipher suite.
- The selected ALPN [RFC7301] protocol, if any.
The language about "during which the ticket was established" seems to
suggest that the following checks do not apply to an external PSK -
which I don't think is intended. Additionally there does not seem to
be a requirement on the server to check that the SNI is consistent.
So, there is a mandatory requirement for an external PSK to specify
the SNI, but no requirement on the server to check that it is actually
correct. Is this discrepancy intentional?
Matt
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