Sorry to take back an old post, but i'm really curious about that thing.
when you say "For 18 words, 1500 years", you mean to just generate ALL possible combinations, right??
if my secret/mnemonic phrase is:
"cat15 cat2 cat3 cat4 cat5 cat6 cat18 cat8 cat9 cat10 cat11 cat12 cat1 cat14 cat7 cat13 cat16 cat17"
and my script generate that exact sequence as the 4th result, is it not the same ??
have i found it in some seconds?
On average, to crack a key, you should assume that you need to exhaust the search space. If you average out every cracking attempt, then you will find that you should only find them when you're nearing the end of the search space and it should follow an exponential distribution. Hence, it is exceeding rare for you to find the actual key within 4 seconds.
and what about the "last" word, you call CHECKSUM, in my case "cat17".
it is not just a word "cat17" ??
It is a word. But that word has to be selected such that it has a relation to the rest of the words. Hence, if you were to swap cat15 and cat2, any software would recognize it as being invalid.