While a 2-of-3 split is a good enough backup strategy, the K-of-M generalization is sometimes needed for sophisticated use cases such as social recovery. With this method, up to 26 shares shares can be generated. A recovery threshold is chosen by the user (the "K" in "K-of-M"); it indicates the number of shares that will be needed to recover the seed phrase, while less than "K" shares won't leak any information. For example, a 3-of-5 split will generate 5 shares and require 3 of them to recover the seed phrase.
It is worth noting that the K-of-M split uses a different algorithm, known as Shamir Secret Sharing Scheme. Compared to the 2-of-3 split, this method takes exponentially longer to perform as K (the number of shares needed for recovery) and M (the total number of shares) grows. However, the recovery time increases linearly.
Tweaking a share consist of replacing its characters by the corresponding tweaked characters:
Recovery can be achieved by deriving the secret (seed phrase + checksum) from the gathered shares. The tweaking factors have to be determined using both K-of-M wheels as explained later.