Manuel Proquin
Bitcoin Wallet Architecture4.7(90)
Intermediate
Dive into the cryptographic principles that power Bitcoin wallets.
1. Introduction
The Ninja SAFU method is a DIY (Do It Yourself) solution that lets you create a sustainable, secure and discreet backup of your seed phrase (a 12- or 24-word mnemonic phrase defined by the BIP-39 standard). This phrase is essential for restoring a Bitcoin wallet or any other compatible wallet.
Instead of writing down your words on paper - a simple but vulnerable method - you'll engrave them on stainless steel washers, assembled on a bolt. The result is a compact, fire-, corrosion-, water- and shock-resistant backup. Unlike paper, which can be destroyed by flames, humidity or time, stainless steel guarantees long-term preservation, even under extreme conditions (up to 1300°C or 20 tons of pressure).
The Ninja SAFU approach offers several advantages:
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Confidentiality: You're not buying a product identified as being intended for cryptocurrency backup. The components are standard (washers, bolts, metal box), available in hardware stores, which reduces the risk of targeting in the event of a data leak from a specialized vendor.
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Affordability: This solution costs between 15 and 140 EUR, depending on the tools you already have.
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Reliability: Tested since 2020, the method has been tried and tested by safety experts such as Jameson Lopp, who have subjected it to rigorous stress tests (extreme heat, corrosion, mechanical pressure).
This step-by-step guide will show you how to make your own Ninja SAFU backup, to better protect your bitcoins against loss or destruction. If you'd like to learn more about backing up and protecting a seed phrase, please consult the appendices.
2. Hardware
To create a Ninja SAFU backup, you'll need the following components, all available from hardware stores or online.
2.1 Materials required
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Stainless steel washers (M8 recommended):
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Material: Stainless steel (e.g. 304 or V4A for enhanced corrosion resistance)
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Size: M8 (inner diameter 8 mm, outer diameter ~24 mm). M6 washers are too small and difficult to engrave.
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Quantity: 12 or 24 washers for a standard seed sentence, plus optional washers (see section 3.4) and ten or so for tests or errors.
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Stainless steel bolt and nut (M8):
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Specifications: Bolt 2.5 to 5 cm long, depending on number and thickness of washers, diameter 8mm. A wing nut facilitates tool-free opening, but a simple nut can also be used.
- Letter and number punch set (3 mm or 6 mm):
- Specifications: 6 mm high characters facilitate legibility and may be preferable if part of the lettering is degraded. Choose a sturdy set for repeated use.
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Hammer or sledgehammer:
- A sledgehammer is preferable for sufficient and precise stamping force
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Anvil or sturdy surface:
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A thick, hard surface (e.g. 1 kg anvil or 10 cm paving stone) to absorb shocks.
If you don't want to invest in a set of punches, you can also engrave your washers with an engraving pen. This solution is often more economical, but requires greater care to obtain a satisfactory result.
2.2 Optional tools
- Stamping device: Holds the washer and guides the punch, allowing for precise, clean stamping, better orientation and even spacing of letters
- Sealing devices: Sealed pouch or sealing strip
- Hermetically sealed container: For storing the block of washers
2.3 Safety
- Gloves and Safety glasses recommended.
- Pipe wrench into which to slide the punch, so that you hold the punch with the pipe wrench and not with your fingers.
2.4 Quantities and estimated cost
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Quantity for a 24-word backup: 24 washers (minimum), 1 bolt, 1 wing nut, 1 set of punches, 1 hammer/massette, 1 anvil/support.
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Total cost:
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Washers and bolts/nuts: ~ 15 EUR
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Punch set: ~ 45 EUR
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Protective case: ~ 55 EUR
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With all accessories: ~ 140 EUR
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See appendix for sample equipment.
3. Step-by-step instructions
- Getting ready:
- Private location, no cameras (including smartphones)
- Robust, shock-absorbing surface
- Gloves and safety glasses
- Clean all grease and dirt from washers
- Practice on test washers
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Burn mnemonic words :
- Engrave the complete word on one side. Don't limit yourself to the first 4 letters, in case the 4th is damaged.
- Strike firmly with the hammer, holding the punch with a pipe wrench
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Number the washers :
- On the same side, engrave the word position number, essential if the washers come loose.
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Record information (optional and recommended) :
- Engrave the redundant word on the other side of the puck
- Engrave a wallet identifier on an additional washer
- Engrave the derivation path of the account you are using on an additional washer. You can find this information in the settings of your wallet software. For example, for a standard Taproot wallet, the default derivation path will be:
m / 86' / 0' / 0' / - Burn in the PIN code to unlock your Hardware Wallet, or the anti-phishing words if you're using a COLDCARD.
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Do NOT burn passphrase :
- If you use a passphrase, make sure you don't write it down on the same card as your mnemonic. The passphrase is designed to protect your wallet in the event of theft of the mnemonic. More information in the appendix.
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Check legibility :
- Make sure every word and number is clear and legible.
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Assemble the washers :
- Thread the washers onto the bolt in the order of the numbers.
- Optional: add blank washers to the ends.
- Screw on the wing nut to secure the battery.
- Tighten firmly to increase protection against water, fire and mechanical stress.
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Test backup :
- From your new backup, try to recover your wallet
- Sealing the backup (optional and recommended):
- By sealing strips, or in sealed pouches.
- If you use a pouch, make a note of its unique identification number, so that you can check that it's the right pouch and not a decoy replacing the original.
4. Storage
4.1 Choose a suitable location
Store your backup in a discreet location, out of sight and accessible for periodic checks. Choose fireproof and watertight storage, at home or in a place under your exclusive control.
Avoid locations where you are dependent on a third party (bank safe, notary): you will lose autonomous access to your funds, which goes against Bitcoin's principles of sovereignty.
Never reveal that you use a method like Ninja SAFU. Discretion is a layer of security in its own right.
4.2 Redundancy
If required, create several copies and store them in different geographical locations.
Even if the materials chosen for your device are water and fire resistant, you won't be able to access it if it's buried under m3 of rubble in your home, and will be very difficult, if not impossible, to retrieve.
5. Follow-up and maintenance
Even when well stored, your backup needs to be checked regularly:
- Out of sight, inspect the backup once or twice a year.
- In the event of degradation of engravings, recreate a new backup, test it, then destroy the old copy carefully.
- If the backup is in a sealed pouch :
- Check your login
- Check its integrity
- Regularly open the envelope to inspect the condition of the engravings, and if all is well, place the backup in a new pocket
STAY SAFU !
APPENDICES
A.1 Save your recovery phrase
A.2 Understanding the passphrase BIP39
A.3 How Bitcoin wallets work
A.4 Classification of the Ninja SAFU method
According to Jameson Lopp:
A.5 Example of hardware
- Washers for
- Titan
- Washers + nut + protective case (for washers)
- Titan
- TerraSteel
- Punch set
- PlebStyle
- Basis of typing
- PlebStyle
- Tapping device (guide)
- TerraSteel
- Sealing device
- Sealed pouch
- Sealing strips
- Complete kit
- Titan
- TerraSteel
Note: Links to online stores are provided for information purposes only.
No commercial partnership exists between Plan B and the above-mentioned sellers and manufacturers.
Plan B cannot be held responsible for defects, price variations or problems related to the quality or delivery of products. DYOR
A.6 Photo credits
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Author
This tutorial has been written by Manuel Proquin
You can say thanks by tipping the professor.
Discovering Bitcoin hasn't fundamentally changed who I am, but it has considerably amplified my power to act, both on my own scale and for society as a whole. Owning Bitcoin embodies clear vision, critical thinking and strength of character. By safeguarding their finances from inflation and censorship, Bitcoiners strengthen their autonomy and influence, shaping the future according to their values. Despite the challenges, Bitcoin inspires a determined optimism to build a freer, more resilient world of tomorrow. Also a Bitcoin consultant and coach, founder of orangepeel.fr, administrator of the Bitcoin Meetup in Nantes (France) and an avid board sports enthusiast.
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