On 19/09/2015 15:34, Michael Heide wrote:
Am Wed, 16 Sep 2015 08:55:51 +0200 schrieb Michael Heide
<[email protected]>:
My question now is: how to (proper) handle it?
Maybe a more sensible way to handle those signatures with OpenSSL is to still
not allow such things but instead return an error indicating success if it
/would/ be allowed to do it this way? The application then can check for this
specific error and translate it into success. (meaning: this specific error is
set if OpenSSL successfully compared both hashes and is - as such - not really
a fatal error.)
This way OpenSSLs default behaviour won't change, it's still an error to not
encapsulate the encryptedDigest in an asn1 structure. But the application
programmer is able to handle it.
see attachment.
(Maybe a callback-function at the place where the error gets generated would be
a better option. But I think that would be a more extensive change in OpenSSL.)
I am in no position to include this, but here are a few
thoughts on improving your patch.
1. The error should not call this "plain", this would lead
to the same misunderstanding I had earlier. Try something
like "RSA_R_PKCS1_1_DIGEST_ONLY_VALID" to indicate that this
is a variant of PKCS#1 v1.x signature formatting (the outer
part with 00|01|FF....|00 is still there), but without the
inner DER encoded ASN.1 structure.
2. Because the hash algorithm OID is not there, something
needs to check that the hash algorithm is the right one for
this RSA public key. This test is really in another layer
(PKCS#7/CMS), but needs to be stronger in this case due to
the lack of an embedded hash algorithm identifier inside the
RSA calculation.
3. It would be really nice if someone in the know would
explain under which conditions this alternative signature
algorithm is used and/or necessary.
Enjoy
Jakob
--
Jakob Bohm, CIO, Partner, WiseMo A/S. http://www.wisemo.com
Transformervej 29, 2860 Søborg, Denmark. Direct +45 31 13 16 10
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