Re: [Ocf-linux-users] Public Key Operation help.

[Nawang C. <naw...@gm...>]

Hi All,
           I am sorry for late mention, I've resolved the issue. Ocf
expects/delivers complete byte string as little endian.

On Fri, Oct 17, 2008 at 12:26 PM, Nawang Chhetan
<naw...@gm...> wrote:
> On Fri, Oct 17, 2008 at 10:17 AM, David McCullough
> <Dav...@se...> wrote:
>>
>> Jivin Nawang Chhetan lays it down ...
>>> Hi David,
>>>              I am trying to perform MODEXP operation through OCF. Device I
>>> am using is "safe". But I am totally lost is middle with issues like:
>>> 1. Endianess: Looking at the cryptoktest program it seems we have to pass
>>> the data to "ocf" in Little Endian format.
>>
>> Thats sounds about right.
>>
>>> 2. Word Length: While converting a byte string into Little Endian format, I
>>> am not sure what is the length of a word(4bytes or 8 bytes).
>>
>> The parameters for OCF MODEXP are byte arrays,  all the code I can see
>> works on bytes.
>>
> Does that mean, if I have a (hex) byte array as BIGNUM input, I need
> to convert it into little
> endian format i.e. if BigNUM=0x1a2b3c4d 5e6f7182 than I should covert
> it to little endian format by reversing the
> complete string to: 0x82716f5e 4d3c2b1a
>
>> The BIGNUM format from openssl however is word based IIRC.
>>
>>> With lack of proper API documentation I am finding it even hard.
>>> Can you give me some pointers where I can clear my above doubts.
>>
>> You might find it easier to look at the openswan patches and how it
>> converts various formats to the OCF version and back.
>>
>> Although both cryptokeytest and openswan convert from BIGNUM to OCF
>> format.  It may help to understand the  BIGNUM format first.  Then you
>> can see how cryptokeytest does the same op using both openssl and
>> it's own modexp,
>>
>
> BIGNUM in openssl library is a structure,
> struct bignum_st
>        {
>        BN_ULONG *d;    /* Pointer to an array of 'BN_BITS2' bit chunks. */
>        int top;        /* Index of last used d +1. */
>        /* The next are internal book keeping for bn_expand. */
>        int dmax;       /* Size of the d array. */
>        int neg;        /* one if the number is negative */
>        int flags;
>        };
>
> BN_BITS2=64,
> when bignum_to_le conversion is done in cryptoktest each BN_BITS2
> words in "bignum_st->d"( not the complete byte string) is converted to
> little endian.
>
> Is this right comprehension ?
> If so then,(to reiterate you) the modexp input data i.e mod, exp and
> base are stored as caddr_t which boils down to char * i.e. modexp data
> in byte string.
>
> Don't you think little endian conversion of entire byte string should
> have been done, instead of each word.
>
>
>> Cheers,
>> Davidm
>>
>> --
>> David McCullough,  dav...@se...,   Ph:+61 734352815
>> Secure Computing - SnapGear  http://www.uCdot.org   http://www.snapgear.com
>>
>
>
>
> --
> Nawang
>



-- 
Nawang Chhetan
Software Engineer
SafeNet India.