A wallet that keeps your keys in your own sock.
ColdSock is a small, Bitcoin-only device. It creates your keys, keeps them offline and signs your payments itself. Your phone shows your balance and prepares payments, but never holds the keys to your savings.
How a payment works
- Prepare on your phone. In the ColdSock app, enter the amount and the address. The app shows the payment as a QR code.
- Scan with ColdSock. The device reads the QR code with its camera. No cable, no Bluetooth, no Wi-Fi.
- Check on the device screen. ColdSock shows the amount, the full address and the fee. You approve on its keypad.
- Scan back and send. ColdSock shows the signed payment as a QR code. Your phone scans it and sends it to the Bitcoin network.
Your keys never leave the device. Even if your phone or computer is infected, nobody can spend your Bitcoin without the device in your hand.
Why it's safe
Offline, always
It talks to your phone only through QR codes. No radio, no data cable.
Bitcoin only
No other coins or tokens. Less code, fewer places to attack.
You check every payment
Amount, address and fee on the device's own screen before you approve.
Signed software only
The device runs only software we have signed, checked every time it starts.
PIN on its own keypad
Typed on the device, never on your phone. Too many wrong tries wipe the keys.
Tamper-evident
Hard plastic case and a sealed box, so you can see if it's been opened.
A backup you can't get wrong
On first use, ColdSock writes an encrypted backup of your keys to a memory card. The device creates the password for that backup, shows it to you once, and you write it on the card in the box.
- Hide the memory card and the password in separate places. The card alone is useless to a thief, and so is the password alone. Together, they give full access to your Bitcoin.
- ColdSock checks straight away that the backup can be read back.
- You can test the backup at any time, and rewrite it if the card gets old.
- If you prefer the standard 24 recovery words, you can use those too.
Lost or broken device? Restore everything on a new one from the backup and its password.
PIN and backup password
Your PIN unlocks the device. You type it on ColdSock's own number keypad, never on your phone or computer. After the first few digits, the device shows two secret words you chose at setup. If they're not your words, stop: that isn't your device. Each wrong PIN makes you wait longer before the next try, and too many wrong tries wipe the keys from the device. Your Bitcoin isn't lost: restore it from your backup.
Your backup password protects the memory card. The device creates it for you as a set of random words, so it can never be a weak password like a birthday. There are so many possible combinations that no computer could ever try them all. The real risk is someone finding the card and the password together, so keep them apart.
Device stolen?
Useless without your PIN, and it wipes itself after too many wrong tries.
Memory card found?
Useless without the backup password, which you keep somewhere else.
The app: The Sock and Pocket
The Sock
Your savings on the ColdSock device. The app shows the balance and history and prepares payments, but holds no keys. Every payment needs the device.
A small spending wallet on your phone, for everyday amounts. Top it up from The Sock when it runs low.
Savings in your sock, spending money in your pocket. Read more in our guide Hot wallet or cold wallet?
Simple hardware
- Black-and-white screen, big enough to show the full address and QR codes.
- Standard AAA battery you can change yourself. Your keys stay safe without power.
- Number keypad for your PIN and for approving payments.
- Camera for reading QR codes.
- Memory card slot for your encrypted backup and for updates.
Built on open standards
We plan to use the standard Bitcoin formats for keys, addresses and QR payments, so ColdSock can also work with well-known wallet apps, not just ours. Before it goes on sale, the device and its software will be checked by independent security experts.