Re: [TLS] TLS 1.3: Deterministic RSA-PSS and ECDSA

Peter Gutmann <pgut001@cs.auckland.ac.nz> Tue, 09 August 2016 08:55 UTC

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From: Peter Gutmann <pgut001@cs.auckland.ac.nz>
To: Tony Arcieri <bascule@gmail.com>, "mrex@sap.com" <mrex@sap.com>
Thread-Topic: [TLS] TLS 1.3: Deterministic RSA-PSS and ECDSA
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Date: Tue, 9 Aug 2016 08:55:30 +0000
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Subject: Re: [TLS] TLS 1.3: Deterministic RSA-PSS and ECDSA
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Tony Arcieri <bascule@gmail.com>; writes:

>Do you think we'll see real-world MitM attacks against RSA-PSS in TLS similar
>to those we've seen with PKCS#1v1.5 signature forgery, such as BERserk?

Not BERserk specifically because that was an attack on the ASN.1, not the
signature format.  OTOH PSS doesn't encode the hash algorithm as 1.5 does, so
here's a much simpler attack: Take a breakable hash function with an output
the same size as the one used in the sig, generate your collision, and paste
the sig onto colliding data, indicating the use of the breakable function not
the one used to generate the original sig.  Done.  Couldn't happen with 1.5
because that encodes the details of the hash function used as part of the
signature.

Peter.