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 =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= 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); }