log.trace("update: " + this.updates + " " + offset + ":" + len);
            log.trace(Hexdump.toHexString(input, offset, Math.min(len, 256)));
        }
        if ( len == 0 ) {
            return; /* CRITICAL */
        }
        this.digest.update(input, offset, len);
        this.updates++;
    }


    /**
     * @return calculated digest
     */
    public byte[] digest () {
        byte[] b;