Re: [TLS] Using RSA PSS in TLS

Peter Gutmann <> Mon, 14 October 2013 11:02 UTC

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From: Peter Gutmann <>
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Thread-Topic: [TLS] Using RSA PSS in TLS
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Date: Mon, 14 Oct 2013 10:58:57 +0000
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Subject: Re: [TLS] Using RSA PSS in TLS
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=?UTF-8?B?SGFubm8gQsO2Y2s=?= <> writes:

>legacy compatibility is exactly the point. Implementations must be prepared
>to communicate to servers / clients that do not support the new version.

Never underestimate that amount of weight that carries.  There was an attempt,
some years ago, to mandate RSA-PSS for certificates.  It met with pretty much
universal rejection, to the extent that people would probably ignore the
requirement even if it was made a MUST in the spec (at the time it was
described as "X9.42 all over again", a reference to another MUST that everyone
ignored), and as a result was dropped.

The problem with -PSS is that it doesn't real fix anything in -1.5 (I know
it's *theoretically* better, but unless you do -1.5 really badly there's no
practical weakness that would encourage an upgrade).  Counting against that is
the near-insurmountable cost of a changeover (everyone has to redeploy global
crypto infrastructure from scratch).