On Thu, 2010-12-09 at 09:38 -0600, Douglas E. Engert wrote: > > On 12/9/2010 8:41 AM, Andre Zepezauer wrote: > > On Thu, 2010-12-09 at 14:31 +0300, Aleksey Samsonov wrote: > >> Hello, > >> > >> 2010/12/9 Martin Paljak<mar...@paljak.pri.ee>: > >>> Hello, > >>> On Dec 9, 2010, at 9:23 AM, webmas...@opensc-project.org wrote: > >>> > >>>> Revision: 4930 > >>>> Author: s > >>>> Date: 2010-12-09 07:23:10 +0000 (Thu, 09 Dec 2010) > >>>> > >>>> Log Message: > >>>> ----------- > >>>> add to r4904: fix calculating of signature size for CKK_GOSTR3410 > >>>> > >>>> - *pLength *= 2; > >>>> + *pLength = (*pLength + 7) / 8 * 2; > >>> > >>> Could you also add a comment? Why not (*pLength + 7) / 4? > >> > >> Yes of course. We need to convert a length in bits to bytes and > >> multiply by two. So if we divide by 4 then we have incorrect rounding > >> result (case (*pLength + 7) % 8>= 4). > > > > Maybe it would be appropriate to define a macro for the conversion. The > > Reason is, that there are a lot of places where the conversion is > > computed as follows: byte_count = bit_count / 8. That is obviously wrong > > in 7 of 8 cases. Also it would improve readability. > > It may comes down to does an algorthim support non-multiple of 8 bits? And > if it can, is it ever used with non multiple of 8 bits? I have never sees an > RSA key that was not a multiple of 8, so it may not be an issue for most of > OpenSC. > > If one is not a multiple of 8, how is it padded?
At least for RSA_PKCS1 the most significant octet is always zero. See PKCS1 01- and 02-padding schema. Therefore the padded signature input is always less than the modulus when compared numerical. _______________________________________________ opensc-devel mailing list opensc-devel@lists.opensc-project.org http://www.opensc-project.org/mailman/listinfo/opensc-devel
