Am I safe if 16 words in my 24 word seed are leaked? I use a 24 word seed for my private key. I split the 24 words into 16 words in three pieces of paper, so one needs to have at least two pieces of paper to recover the wallet. However my question is, if someone gets one piece of paper, can they easily brute force the remaining 8 words?
Ideally you shouldn't share any words and brute forcing with one paper in your case may take time but still possible. Also if someone gets one paper he can try social engineering to get another. Below links might help in understanding things involved in brute forcing.
https://medium.com/@johncantrell97/how-i-checked-over-1-trillion-mnemonics-in-30-hours-to-win-a-bitcoin-635fe051a752
https://twitter.com/JohnCantrell97/status/1274024510786883584
TLDR:
With 8 known words there are 2⁴⁰ (~1.1 trillion) possible mnemonics
To test a single mnemonic we have to generate a seed from the mnemonic, master private key from the seed, and an address from the master private key
Usage of GPU for brute forcing
Tx fee is normally high during such attacks
Open source code that was used:
BIP39-Solver-CPU: This is the CPU benchmark tool he wrote in Rust to get an idea of how long it will take do solve on a CPU for certain number of unknown words.
https://github.com/johncantrell97/bip39-solver-cpu
BIP39-Solver-GPU: This is the actual GPU version he ran on each worker GPU to solve this problem.
https://github.com/johncantrell97/bip39-solver-gpu
BIP39-Solver-Server: This is the actual server he ran that handled distributing the work to all the workers.
https://github.com/johncantrell97/bip39-solver-server
It would take the same system that brute forced the last 4 words of his mnemonic 837 quintillion millennium to brute force all possible 12 word mnemonics.