Quote from: simplyred on March 04, 2018, 11:01:29 PM

i got 24 word seed for my ledger nano s. And i split it up on two papers.

21 words on one paper and 3 words on the other one.

Lets say my 21 word paper would be exposed. Would it be hard for the persona that has this 21 word seed to crack the wallet ?

It depends on whether or not the order is known... for instance, if the attacker knew that they had words 1-21 or 4-24 (ie. the first 21 or the last 21 words) and were simply trying to find the missing 3 words... then the number of possible combinations would only be:

2048 * 2048 * 2048 = 8,589,934,592

Which really isn't a lot at all... and a simple script would crack that in minutes.

However, if the attacker had no clue as to the position of the missing words... ie. you'd taken 3 words from position 3, 17 and 23, but there was no indication of position/order of words on the paper (ie. they're not numbered)... then things become a lot more complicated. The number of combinations the attacker would need to test increases by several orders of magnitude and it would require a lot more work. It's possible the time required would extend to hours or days or years. I'm not not sure of the actual math... possibly something like:

(2048 * 24) * (2048 * 24) * (2048 * 24) = 118,747,260,000,000+ combinations (note, I'm very tired, so this math is probably really wrong Tongue

)

Having said that... if you knew that your 21 words had been compromised, you should immediately generate a new seed and move all coins from the old wallet to the new one and then "burn" the old wallet/seed...

Quote from: simplyred on March 05, 2018, 01:53:42 AM

Im just thinking, lets say there are 5000 words, then it would take long time to get these 3 right word in the right order, no ?

There are 2048 words for BIP39 seeds: https://github.com/bitcoin/bips/blob/master/bip-0039/english.txt