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Re: [TLS] PSS and TLS 1.3

Nikos Mavrogiannopoulos <nmav@redhat.com> Mon, 23 January 2017 08:10 UTC

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From: Nikos Mavrogiannopoulos <nmav@redhat.com>
To: Dr Stephen Henson <lists@drh-consultancy.co.uk>, "tls@ietf.org list" <tls@ietf.org>
Date: Mon, 23 Jan 2017 09:05:28 +0100
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Subject: Re: [TLS] PSS and TLS 1.3
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On Fri, 2017-01-20 at 17:43 +0000, Dr Stephen Henson wrote:

> Additionally PSS signatures (see RFC4055) can be used with RSA keys
> (rsaEncryption OID) and RSA-PSS only keys (id-RSASSA-PSS OID). Does
> the RSASSA-PSS mean that both types must be accepted?

That's a quite interesting finding. Although that protocol behavior
seems to ease transition to RSASSA-PSS, it also paves the field for new
cross protocol attacks. A server which can sign with either of RSASSA-
PSS and RSA-PKCS1 and the same key is certainly less secure than a
server which can sign with either of them. The only way to enforce that
a key is restricted is by requiring the id-RSASSA-PSS OID for RSASSA-
PSS.

regards,
Nikos

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