Sweep to Cold Storage

This guide provides step-by-step instructions for securing your Bitcoin in cold storage using hardware wallets. Follow these detailed steps to ensure your Bitcoin is safely transferred from mobile wallets to long-term secure storage.

Table of Contents

• Understanding Cold Storage
• Preparing for the Transfer
• Setting Up Your Hardware Wallet
• Transferring Bitcoin from Mobile Wallets
  • From Flash Wallet
  • From Other Mobile Wallets
• Verifying Your Transfer
• Best Practices for Cold Storage
• Recovery and Backup Procedures
• Advanced Cold Storage Options

Understanding Cold Storage

Cold storage refers to keeping your Bitcoin private keys offline on a dedicated hardware device, dramatically reducing potential attack vectors compared to mobile or online wallets.

Benefits of Hardware Wallets

• Enhanced Security: Private keys never leave the device
• Protection from Malware: Immune to computer viruses and keyloggers
• Physical Verification: Transactions require physical confirmation
• Disaster Recovery: Built-in backup and recovery options
• Long-term Storage: Designed for secure, long-term Bitcoin storage

When to Use Cold Storage

Cold storage is recommended when:

• Your Bitcoin holdings exceed $1,000 in value
• You plan to hold Bitcoin for more than 6 months
• You want maximum protection against remote attacks
• You’re creating a long-term savings plan or inheritance

Preparing for the Transfer

Before beginning the transfer process, prepare the following:

1. Hardware wallet device (Bitkey, ColdCard, or Trezor)
2. Pen and paper for recording recovery phrases
3. Secure location free from cameras or onlookers
4. Mobile wallet with Bitcoin to transfer
5. Small amount for testing (always send a test transaction first)
6. Time without distractions (30-60 minutes for setup)
7. Stable internet connection (for the mobile wallet side)

Setting Up Your Hardware Wallet

Each hardware wallet has a specific setup process. Select your device below.

Bitkey

About Bitkey

Bitkey uses a “two-of-three” multi-signature security model with a mobile app component, hardware component, and recovery key component.

Setting Up Your Bitkey

1. Initial Hardware Setup
   • Unbox your Bitkey hardware device
   • Power on by pressing the circular button
   • Follow on-screen instructions to set up your device PIN
   • Verify the device displays an untampered seal message
2. Install the Bitkey Mobile App
   • Download the Bitkey app from the App Store or Google Play
   • Open the app and select “Set up a new wallet”
   • Follow the pairing instructions to connect to your hardware device
   • Create a secure PIN for the app
3. Create Your Recovery Key
   • When prompted, the app will guide you through creating a recovery key
   • Write down all 12 or 24 seed words IN ORDER on provided recovery cards
   • Verify each word carefully - these words ARE your Bitcoin
   • Store recovery cards in a secure, private location
4. Verify Your Setup
   • Complete the recovery phrase verification test on both devices
   • Ensure both the hardware and mobile components show the same wallet balance
   • Test the approval process for a small transaction

Creating a Receive Address with Bitkey

1. Connect Your Wallet
   • Open the Bitkey mobile app on your smartphone
   • Ensure it’s properly paired with your hardware device
   • Verify both devices are powered on and responsive
2. Generate Address
   • Tap “Receive” in the mobile app
   • The app will generate a new Bitcoin address
   • Your hardware device will display a verification request
3. Verify Address
   • Important: Confirm the address matches on both mobile and hardware devices
   • This verification step protects against address replacement attacks
   • Never use an address you haven’t verified on the hardware device
4. Label the Address (Optional)
   • Add a description like “Flash Transfer - March 2025”
   • This helps track the source of funds later
   • Labels are stored locally and not on the blockchain

ColdCard

About ColdCard

ColdCard is a Bitcoin-only hardware wallet that can operate completely air-gapped and offers advanced security features.

Setting Up Your ColdCard

1. Initial Hardware Setup
   • Unbox your ColdCard
   • Insert a microSD card (optional but recommended)
   • Connect the device using the included USB cable
   • Create a new wallet when prompted
   • Set up a strong PIN with both a prefix and suffix
2. Backup Your Seed Words
   • Carefully write down all 24 seed words in order
   • Double-check each word against the ColdCard screen
   • Consider stamping seed words on metal for fire/water resistance
   • Secure your backup in a safe location
3. Advanced Security Setup
   • Set up a BrickMe PIN (emergency delete function)
   • Configure Duress PIN if desired (shows limited funds)
   • Set up a passphrase for additional security (optional)
   • Test your PINs to ensure they work correctly
4. Install Companion Software
   • For desktop interaction, install Sparrow Wallet
   • Connect your ColdCard via USB or use the microSD card for air-gapped operation
   • Export the wallet public key to Sparrow using the microSD card
   • Verify the wallet appears correctly in Sparrow

Creating a Receive Address with ColdCard

1. Connect Your Wallet
   • Option 1 (USB): Connect ColdCard via USB cable to your computer
   • Option 2 (Air-gapped): Use microSD card for complete isolation
   • Open Sparrow Wallet on your computer
2. Generate Address
   • In Sparrow Wallet, select the “Receive” tab
   • Choose the address type (Native SegWit recommended)
   • Sparrow will display a new Bitcoin address and QR code
3. Verify Address
   • Crucial security step: Verify the address on ColdCard’s screen
   • On ColdCard, navigate to Address Explorer
   • Compare the address shown in Sparrow with the one on ColdCard
   • Only proceed if addresses match exactly
4. Label the Address (Optional)
   • In Sparrow, add a label such as “Flash Transfer - March 2025”
   • This helps you track which deposits came from where
   • Labels are stored in Sparrow, not on the blockchain

Trezor

About Trezor

Trezor offers an intuitive user experience with a simple interface while maintaining strong security.

Setting Up Your Trezor

1. Initial Hardware Setup
   • Unbox your Trezor device
   • Connect it to your computer via USB cable
   • Visit trezor.io/start
   • Follow the on-screen instructions
   • Create a new wallet when prompted
2. Create Device PIN
   • Create a strong PIN following the on-screen instructions
   • The PIN entry uses a randomized keypad for protection
   • Remember this PIN - it protects physical access to your device
3. Backup Recovery Seed
   • Write down all 12 or 24 seed words in exact order
   • Verify the recovery seed when prompted by the setup wizard
   • Store in a secure, private location away from potential threats
   • Consider creating a metal backup for fire/water resistance
4. Setup Trezor Suite
   • Install Trezor Suite on your computer
   • Connect your device and unlock it with your PIN
   • Create a Bitcoin wallet in Trezor Suite
   • Optionally add a passphrase for additional security

Creating a Receive Address with Trezor

1. Connect Your Wallet
   • Connect Trezor to your computer via USB cable
   • Open Trezor Suite on your computer
   • Unlock your device with your PIN
   • Enter passphrase if you’ve set one up
2. Generate Address
   • In Trezor Suite, click on the “Receive” tab
   • Select the account you want to receive to (if multiple)
   • Choose address type (Native SegWit recommended for lower fees)
   • Trezor Suite will generate a new Bitcoin address
3. Verify Address
   • Trezor will prompt you to confirm the address on the device
   • Compare the address on your screen with the one on Trezor
   • Only approve if they match completely
   • This step protects against malware that might try to display fake addresses
4. Label the Address (Optional)
   • Add a descriptive label like “Flash Transfer - March 2025”
   • Trezor Suite will save this label with the address
   • Makes it easier to identify funds and their source later

Transferring Bitcoin from Mobile Wallets

Now you’re ready to send Bitcoin from your mobile wallet to your hardware wallet:

From Flash Wallet

1. Open Flash App
   • Go to the “Wallet” tab
   • Ensure you have sufficient balance
   • Check that your Lightning channels have enough outbound capacity
2. Initiate Transfer
   • Tap “Send” or “Withdraw”
   • Select “On-chain withdrawal”
   • Note that on-chain withdrawals have higher fees than Lightning
3. Enter Details
   • Paste your hardware wallet’s receive address
   • Double-check the address is correct (first and last few characters)
   • Start with a small test amount (e.g., 0.0001 BTC or 10,000 sats)
   • Enter an amount that’s high enough to cover network fees
4. Review and Confirm
   • Check the withdrawal fee (higher fees confirm faster)
   • Prioritize security over saving on fees for cold storage transfers
   • Verify all details are correct one final time
   • Tap “Confirm” to initiate the transfer
5. Initial Test Verification
   • Wait for the test transaction to confirm (10-60 minutes)
   • View the transaction status in the Flash app
   • Verify receipt on your hardware wallet
   • Once confirmed, proceed with transferring larger amounts

From Other Mobile Wallets

1. Open Your Mobile Wallet
   • Access the wallet containing your Bitcoin
   • Navigate to Send/Transfer function
   • Make sure your wallet is updated to the latest version
2. Enter Hardware Wallet Address
   • Paste your verified hardware wallet address
   • Double-check the entire address if possible
   • For large transfers, verify the address through multiple channels
   • Never manually type addresses - always copy and paste
3. Set Transaction Fee
   • Choose an appropriate fee based on urgency
   • For cold storage, medium priority is usually sufficient
   • Check mempool.space for current fee recommendations
   • Consider the tradeoff between confirmation time and cost
4. Send Test Transaction
   • Start with a minimal amount (0.0001 BTC or equivalent)
   • Review all details before confirming
   • Confirm the transaction in your wallet
   • Record the transaction ID/hash for reference
5. Complete the Transfer
   • After confirming receipt of test transaction
   • Send remaining amount in one or multiple transactions
   • Consider privacy implications of transaction patterns
   • Keep transaction IDs for future reference

Security Reminder

Always verify the receiving address on your hardware wallet’s secure screen before sending any funds. A compromised computer could display a different address than the one you intended to use.

Verifying Your Transfer

After sending, verify the transfer was successful:

1. Check Transaction Status

   • Use a block explorer like mempool.space
   • Enter your transaction ID or wallet address
   • Monitor confirmations (6+ is considered extremely secure)

2. Verify on Hardware Wallet

   • Bitkey: Check balance in both mobile app and hardware device
   • ColdCard: Check balance in Sparrow Wallet or via microSD export
   • Trezor: Check balance in Trezor Suite

3. Document the Transfer

   • Record the transaction ID
   • Note the date, amount, and sending address
   • Store this information securely for future reference

Best Practices for Cold Storage

Maximize your security with these best practices:

1. Multiple Hardware Wallets

   • Consider using different brands for diversification
   • Separate wallets for different purposes (spending vs. long-term)

2. Regular Verification

   • Check device functionality every 6-12 months
   • Update firmware when security updates are released
   • Perform test recoveries annually

3. Secure Storage Environment

   • Keep hardware wallets in cool, dry locations
   • Protect from electromagnetic interference
   • Consider a fireproof, waterproof container

4. Physical Security

   • Don’t discuss hardware wallet ownership publicly
   • Consider a home safe or bank safety deposit box
   • Have a “decoy” wallet with small funds if concerned about physical threats

5. Avoid Common Mistakes

   • Never enter seed phrases on a computer or phone
   • Don’t store seed phrases in cloud services or digital formats
   • Don’t share photos of seed phrases or hardware wallets
   • Beware of phishing attempts targeting hardware wallet users

Recovery and Backup Procedures

Prepare for emergencies with proper backup procedures:

1. Seed Phrase Protection

   • Store seed phrases separately from hardware devices
   • Consider metal backup solutions (Cryptosteel, BlockPlate, etc.)
   • Split backups across multiple secure locations

2. Test Recovery Procedure

   • Practice recovery without actual funds
   • Understand the process before an emergency
   • Document steps for heirs or trusted individuals

3. Inheritance Planning

   • Create clear instructions for heirs
   • Consider multi-signature setups for inheritance
   • Establish legal frameworks appropriate to your jurisdiction

Advanced Cold Storage Options

For users seeking maximum security:

1. Multi-Signature Setups

   • Require multiple devices to approve transactions
   • Distribute risk across different security models
   • Popular options: Sparrow Wallet multisig, Caravan

2. Air-Gapped Operations

   • Keep signing device completely offline
   • Transfer transaction data via microSD or QR codes
   • ColdCard and some Trezor models support this workflow

3. Geographic Distribution

   • Store backup components in different physical locations
   • Consider jurisdictional diversification for large holdings
   • Balance security with practical accessibility

Need Help?

If you encounter any issues during the transfer process, reach out to Flash support through the app or visit our community forums for assistance.