Re: [Curdle] Confirming a change to draft-ietf-curdle-rsa-sha2-12

Peter Gutmann <pgut001@cs.auckland.ac.nz> Tue, 13 March 2018 08:39 UTC

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From: Peter Gutmann <pgut001@cs.auckland.ac.nz>
To: denis bider <denisbider.ietf@gmail.com>
CC: Ron Frederick <ronf@timeheart.net>, "Salz, Rich" <rsalz@akamai.com>, "curdle@ietf.org" <curdle@ietf.org>, "Mark D. Baushke" <mdb@juniper.net>
Thread-Topic: [Curdle] Confirming a change to draft-ietf-curdle-rsa-sha2-12
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Date: Tue, 13 Mar 2018 08:39:25 +0000
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Subject: Re: [Curdle] Confirming a change to draft-ietf-curdle-rsa-sha2-12
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denis bider <denisbider.ietf@gmail.com> writes:

>S is fixed size. It is exactly the size of the modulus.

Ah, I'd never noticed that (the original PKCS #1 hides that detail a lot
better).  However for the most common use, certificates and similar, this
would conflict with the ASN.1 DER requirements, which trump the PKCS #1 ones.

Does anything non-ASN.1 do the fixed-length encoding?  My test code includes
special-case tests for RSA data blocks shorter than the modulus to make sure
it can handle these cases, I know that there are at least some implementations
out there that do this because when I accidentally broke the variable-length
handling I got complaints and included the self-test checks to make sure it
wouldn't happen again.

Peter.