On Wed, Apr 11, 2018 at 11:58 AM, Horia Geantă <horia.gea...@nxp.com> wrote:
> On 4/11/2018 1:36 AM, James Bottomley wrote:
>> On Tue, 2018-04-10 at 23:01 +0100, Martin Townsend wrote:
>>> Using openssl to get the signature in my x509 cert
>>> Signature Algorithm: sha256WithRSAEncryption
>>> So there's an extra 0x00 and the signature is 257 bytes so I guess
>>> this is upsetting CAAM, just need to work out where it's coming from,
>>> or whether it's valid and CAAM should be handling it.
>> A signature is just a bignum so leading zeros are permitted because
>> it's the same numeric value; however, there are normalization
>> procedures that require stripping the leading zeros, say before doing a
>> hash or other operation which would be affected by them.
>> CAAM should definitely handle it on the "be liberal in what you accept"
>> principle. The kernel should probably remove the leading zeros on the
>> "be conservative in what you do" part of the same principle.
> Looking at the generic SW implementation (crypto/rsa.c, rsa_verify()), leading
> zeros are removed:
> s = mpi_read_raw_from_sgl(req->src, req->src_len);
> CAAM implementation of rsa is not doing this (though it is removing leading
> zeros when reading public, private keys).
> It has to be fixed. Thanks for the report.
Do you have any idea when a fix will be available? I'm happy to test
on my setup here.
>>> I notice that in my stack trace I have pkcs1pad_verify which
>>> suggests some sort of padding?
>> Yes, RSA has various forms of padding because the information being
>> encrypted is usually much smaller than the encryption unit; PKCS1 is
>> the most common (although its now deprecated in favour of OAEP because
>> of all the padding oracle problems).
> RSA padding has been intentionally added as a template, wrapping "textbook"
> (raw) RSA primitives.
> For PKCS#1 v1.5, a template instantiation is called pkcs1pad(rsa, hash_alg).
> Currently in kernel the only supported RSA padding scheme is PKCS#1 v1.5.
> When implemented, another scheme - for e.g. OAEP - would be added in a similar
> way, as a template: oaep(rsa, ...).