memset(data + n, 0, sizeof(data) -n);
des_pcbc_encrypt(data, enc, (n + 7) & ~7, sched, ivec, 0);
/* save vector to continue chaining */
memset(data + n, 0, sizeof(data) -n);
des_pcbc_encrypt(data, enc, (n + 7) & ~7, sched, ivec, 0);
/* save vector to continue chaining */