Re: [PATCH 4/8] akcipher: Move the RSA DER encoding to the crypto layer

From	David Howells <dhowells@redhat.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH 4/8] akcipher: Move the RSA DER encoding to the crypto layer
Date	2016-02-26 12:50 +0100
Message-ID	<r6p4f-2AD-21@gated-at.bofh.it> (permalink)
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Andrew Zaborowski <balrogg@googlemail.com> wrote:

> Without overhauling akcipher you could modify pkcs1pad so that sign
> takes the hash as input, adds the DER struct in front of it to build
> the signature, and the verify operation could at most check that the
> DER string matches the hash type and return the hash.  But I think
> RFC2437 suggests that you rather compare the signatures, not the
> hashes.

Whilst that is true about what RFC2437 shows, I wonder how strict it wants to
be about that rather than it just being a convenient way of describing the
algorithm.

The advantage of doing it the way the RFC suggests is that you get to use the
EMSA-PKCS1-V1_5-ENCODE operation twice, thereby saving code and only having
one place for bugs to occur instead of two - but you can argue this either
way.

That said, I would be okay with it returning just the message hash with the
padding stripped off, providing the padding is validated in the crypto layer,
if that's necessary.

David

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Re: [PATCH 4/8] akcipher: Move the RSA DER encoding to the crypto layer Andrew Zaborowski <balrogg@googlemail.com> - 2016-02-23 01:10 +0100
  Re: [PATCH 4/8] akcipher: Move the RSA DER encoding to the crypto layer David Howells <dhowells@redhat.com> - 2016-02-23 12:00 +0100
    Re: [PATCH 4/8] akcipher: Move the RSA DER encoding to the crypto layer Andrew Zaborowski <balrogg@googlemail.com> - 2016-02-23 12:30 +0100
      Re: [PATCH 4/8] akcipher: Move the RSA DER encoding to the crypto layer David Howells <dhowells@redhat.com> - 2016-02-26 12:50 +0100

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