Seed phrases are a convenient way to back up a wallet while maintaining complete ownership. However, they have significant disadvantages. If a seed phrase is lost or stolen, the funds can be irremediably compromised. Furthermore, planning for inheritance requires entrusting the phrase to a third party, which again places the funds at risk.
Penlock's secret-splitting generates 3 (encrypted) shares. Any two of these shares can be used to recover the original seed phrase, but a single compromised share reveals nothing about it. This 2-of-3 backup allows for off-site recovery, as well as trust-minimized inheritance.
In addition to printing and assembling the components linked below, you will need a pencil, an eraser, a pen, scissors, and the seed phrase to split:
The worksheet is divided into 4 sections: one for the seed phrase, and three for the shares. Each section contains the same number of word, and words are composed of 6 characters: two with a gray background (for the Penlock checksum), and 4 with a white background (for the truncated words). An additional sheet is provided to produce copies of shares 2 and 3.
The wheel is the primary tool for splitting and recovering the seed phrase. To assemble it, proceed with the following steps:
The wheel has 4 distinct sections that will be referred to as follows: the pointer, the outer (character) ring, the inner (character) ring, and the numbered spiral.
This file contains the standard wordlist used by most wallets. Each word has been prefixed with a 2-character checksum (the grayed characters). It helps detect and correct mistakes that might occur during the splitting or recovery process.
These tiles are used to generate random numbers. After printing and cutting, ensure the value on the tiles is identical on both sides. A detailed check of every tile is not required; if the document was misprinted, none of the tiles will be correct.
Before generating your shares, it is advised to create a clear plan for how they will be stored. A good backup strategy is one that suits your needs and technical ability. Moreover, the recovery process must be easy to remember, even after years, and — in the case of inheritance — achievable by your heirs. To help you design this strategy, we provide a generic framework that you can tailor to your needs.
A suggested type of storage is written on each share. The general principle is to force an attacker to execute two different types of attacks to gain access to the seed phrase.
For digital and legal shares, we generally recommend keeping it simple by opting for a service provider you already trust and use. If this is not an option, familiarize yourself with the new service first. Most crucially, always ensure the recovery path is properly configured and well understood ahead of time.
Off-site recovery is an important feature of any backup system. In practice, this requires the ability to access two different shares from outside your primary residence. The social and legal shares typically provide this capability. If you choose not to use a legal share, cloud-syncing the digital share is a viable alternative.
Trust-minimized inheritance is achieved by creating a path that lets your heir access a second, different share in addition to the social share they were already given. There are two ways to do this:
If you generated your seed phrase with Penlock, directly on the worksheet, then you can skip this section.
Use the wordlist to find your words formatted the Penlock way, and copy the first 6 characters on the worksheet under the 'Seedphrase' section, respecting the gray & white backgrounds coding.
The shares are generated sequentially, one character at a time. The first character of each share is produced from the first character of the seed phrase, and so on. Use a pencil for now, as corrections might be needed if a mistake occurs:
Before disposing of the cleartext seed phrase, it is of utmost importance to verify that all shares are correct. This is done by simulating the recovery process in a way that speeds up the verification. As before, we proceed sequentially, one character at a time:
Assuming that 'Share 1' is stored digitally, it requires no further processing. 'Share 2' and 'Share 3', however, need to be traced over in pen, cut out, and possibly copied, depending on your backup strategy. Use the worksheet's extra shares for this purpose, ensuring you copy the data accurately and respect the share numbering.
After cutting out these shares, fill out the back of each one by adding the date, the wallet brand and model, and the owner’s name or pseudonym. This prevents shares from different sets from being mixed up and simplifies the recovery process later.
We recommend storing physical shares in waterproof, sealed containers such as opaque poly mailers. When entrusting a share to another person, ensure clear identifying information is written on the container and explain proper storage practices (e.g., keeping it dry, safe, and confidential).
The legal share — if it is part of an inheritance plan — may be accompanied by the printed recovery guide and the required components, as detailed in that guide. This will simplify the recovery process for the beneficiary.
The digital share must be entered with care and stored with the same identifying information as the other shares. Note that no other shares should ever be digitized, as this would weaken the security of the 2-of-3 backup.