SHA patch

17 Dec 2003


      Hello there,

    After some work with the SHS (or is the implementation actually
the SHA?) code listed in _Applied Cryptography_, I have patched it to
allow updates of buffer sizes that are not a multiple of
SHS_BLOCKSIZE. The patched version works for the different groupings
of the test data "abc", e.g.,
        update(abc)
        update(a) + update(bc)
	update(ab) + update(c)

    Since the "abc" case tests only the logic of shsUpdate() [all the
transformation invocations are actually performed by shsFinal()], I
ran the original code and the modified code on several files and
(fortunately) received the same hash values for the two
implementations.

    shsUpdate() follows. You may need to define a bcopy->memcpy macro.

michael

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void
shsUpdate(SHS_INFO *shsInfo, BYTE *buffer, int count)
{
    int	offset, need;

    /* determine if there are left over bytes in the
       shs data. they are handled specially below */
    offset = (int) ((shsInfo->countLo >> 3) & 0x3f);
    need = SHS_BLOCKSIZE - offset;

    /* update bitcount */
    if ((shsInfo->countLo + ((LONG) count << 3)) < shsInfo->countLo)
        shsInfo->countHi++;	/* carry from low to high bitCount */

    shsInfo->countLo += ((LONG) count << 3);
    shsInfo->countHi += ((LONG) count >> 29);

    /* if there were indeed left over data bytes,
       see if the incoming data is sufficient to
       fill to SHS_BLOCKSIZE. if not, copy the
       incoming data and return; otherwise fill
       the block, perform a transformation, and
       continue as usual */
    if (offset)
    {
        if (count < need)
        {
            bcopy(buffer, (BYTE *) shsInfo->data + offset, count);
            return;
        }
        else
        {
            bcopy(buffer, (BYTE *) shsInfo->data + offset, need);
#ifdef LITTLE_ENDIAN
            byteReverse(shsInfo->data, SHS_BLOCKSIZE);
#endif
            shsTransform(shsInfo);
            buffer += need;
            count -= need;
        }
    }

    /* process data in SHS_BLOCKSIZE chunks */
    while (count >= SHS_BLOCKSIZE)
    {
        bcopy(buffer, shsInfo->data, SHS_BLOCKSIZE);
#ifdef LITTLE_ENDIAN
        byteReverse(shsInfo->data, SHS_BLOCKSIZE);
#endif
        shsTransform(shsInfo);
        buffer += SHS_BLOCKSIZE;
        count -= SHS_BLOCKSIZE;
    }

    /* store the left over data */
    bcopy(buffer, shsInfo->data, count);
}

SHA patch

Michael Shiplett