On Mon, Mar 01, 2021 at 09:54:37PM -0800, Andy Lutomirski wrote:
> On Mon, Mar 1, 2021 at 9:06 PM Tianjia Zhang
> <tianjia.zhang@xxxxxxxxxxxxxxxxx> wrote:
> >
> >
> >
> > On 3/1/21 5:54 PM, Jarkko Sakkinen wrote:
> > > On Mon, Mar 01, 2021 at 01:18:36PM +0800, Tianjia Zhang wrote:
> > >> q2 is not always 384-byte length. Sometimes it only has 383-byte.
> > >
> > > What does determine this?
> > >
> > >> In this case, the valid portion of q2 is reordered reversely for
> > >> little endian order, and the remaining portion is filled with zero.
> > >
> > > I'm presuming that you want to say "In this case, q2 needs to be reversed because...".
> > >
> > > I'm lacking these details:
> > >
> > > 1. Why the length of Q2 can vary?
> > > 2. Why reversing the bytes is the correct measure to counter-measure
> > > this variation?
> > >
> > > /Jarkko
> > >
> >
> > When use openssl to generate a key instead of using the built-in
> > sign_key.pem, there is a probability that will encounter this problem.
> >
> > Here is a problematic key I encountered. The calculated q1 and q2 of
> > this key are both 383 bytes, If the length is not processed, the
> > hardware signature will fail.
>
> Presumably the issue is that some keys have parameters that have
> enough leading 0 bits to be effectively shorter. The openssl API
> (and, sadly, a bunch of the ASN.1 stuff) treats these parameters as
> variable-size integers.
But the test uses a static key. It used to generate a key on fly but
in some of the last versions I replaced key generation with a static
key:
static RSA *gen_sign_key(void)
{
unsigned long sign_key_length;
BIO *bio;
RSA *key;
sign_key_length = (unsigned long)&sign_key_end -
(unsigned long)&sign_key;
bio = BIO_new_mem_buf(&sign_key, sign_key_length);
if (!bio)
return NULL;
key = PEM_read_bio_RSAPrivateKey(bio, NULL, NULL, NULL);
BIO_free(bio);
return key;
}
/Jarkko
