[TLS] TLS1.2 vs TLS1.0

[Ulrich Herberg <[e-mail]>]

Hi,

I have not followed this WG, so please forgive me if a similar
question has already been discussed.

I am participating in another SDO on a standard for automated Demand
Response, called OpenADR (www.openadr.org), an application for the
smart grid. The application is basically a web service, exchanging XML
over HTTP over public networks, and using TLS (with RSA and ECDSA /
SHA1 ciphers for TLS 1.0 and SHA2 for TLS1.2). Currently, the draft
allows for TLS1.0 and 1.1, but recommends using 1.2 (and requires
vendors to provide a migration plan in case TLS1.0 is obsoleted) .
TLS1.0 and 1.1 RFCs have been obsoleted by the IETF; but I am not sure
about the best current practice. Is it absolutely discouraged to use
them? The argument in the OpenADR alliance is that many libraries and
programming languages do not support TLS1.2, so they recommend to
start the handshake with 1.2 and then downgrade - if required - to
1.0. I read that NIST disallows SHA1 after 2013; which would also
affect TLS1.0, which does not support SHA2.

What would be your recommendation in this case? Mandate TLS1.2 and
disallow TLS1.0? Or just strongly recommend ("SHOULD") to use TLS1.2
and SHA2 ciphers, and otherwise to use TLS1.0?

Best regards
Ulrich