“Smash the phone to pieces. Keep only the handwritten paper.”
I came across a post in the middle of the night telling people to spend 100 yuan on the crummiest secondhand phone they could find on Xianyu, disconnect it from the internet, restore it to factory settings, generate a seed phrase offline, then smash the phone and keep only the handwritten paper.
The logic isn’t wrong: the essence of a cold wallet is being offline.
100 yuan buys you offline access, not security.
I took it apart, and found two things the original post left out:
You don’t know where that secondhand phone came from. A factory reset won’t remove a backdoor installed by flashing the firmware. By the time the seed phrase is generated, there may already be something on the phone recording it.
Paper is a single point of failure. Smash the phone and you’re left with one sheet of paper. If it gets soaked, burned, smudged, or lost during a move, it’s all gone. If you’re really going to do this, make at least two copies and store them separately.
If you’re going to cold-store the little bit of $BTC you have, don’t bet on an old phone of unknown origin.
#ColdWallet
I came across a post in the middle of the night telling people to spend 100 yuan on the crummiest secondhand phone they could find on Xianyu, disconnect it from the internet, restore it to factory settings, generate a seed phrase offline, then smash the phone and keep only the handwritten paper.
The logic isn’t wrong: the essence of a cold wallet is being offline.
100 yuan buys you offline access, not security.
I took it apart, and found two things the original post left out:
You don’t know where that secondhand phone came from. A factory reset won’t remove a backdoor installed by flashing the firmware. By the time the seed phrase is generated, there may already be something on the phone recording it.
Paper is a single point of failure. Smash the phone and you’re left with one sheet of paper. If it gets soaked, burned, smudged, or lost during a move, it’s all gone. If you’re really going to do this, make at least two copies and store them separately.
If you’re going to cold-store the little bit of $BTC you have, don’t bet on an old phone of unknown origin.
#ColdWallet
