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Shamir Backup

Shamir Backup

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Crypto Guide
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A Shamir Backup, specifically referring to Shamir’s Secret Sharing (SSS) scheme, is a cryptographic method for splitting a secret into multiple parts, known as shares. This scheme was developed by Adi Shamir, one of the co-inventors of the RSA algorithm.

Purpose of Shamir Backup: The primary purpose of Shamir’s Secret Sharing is to enhance the security and resilience of cryptographic key management by distributing the responsibility for safeguarding a secret among multiple parties. This is particularly useful in scenarios where a single point of failure is undesirable, such as in cryptocurrency custody or data protection.

How Shamir Backup Works: Shamir’s Secret Sharing involves breaking a secret into a specified number of shares (pieces). The secret can only be reconstructed when a minimum threshold of these shares is combined. The process involves the following steps:

  1. Generation of Shares:
    • A secret, often a cryptographic key, is chosen.
    • The secret is then split into a predetermined number of shares using mathematical operations.
  2. Distribution of Shares:
    • Each share is given to a different party or entity, ensuring that no single party possesses the full secret.
  3. Reconstruction:
    • To reconstruct the original secret, a minimum number of shares (the threshold) must be combined using a specific mathematical algorithm. The threshold is set during the initial sharing process.

Key Characteristics:

  • Threshold Security: The original secret can only be reconstructed when the threshold number of shares is combined. This adds a layer of security, as an adversary would need to compromise multiple entities to reconstruct the secret.
  • Flexibility: The scheme allows for flexibility in determining the number of shares and the threshold required for reconstruction.
  • Security against Share Loss: Even if some shares are lost or compromised, as long as the threshold is met, the secret can still be reconstructed.
  • Secure Distribution: The shares can be securely distributed to different physical locations or parties, reducing the risk of a single point of failure.

Use Cases:

  • Cryptocurrency Wallets: Shamir Backup is used to protect private keys by splitting them into multiple shares, enhancing security against single points of failure.
  • Data Protection: It’s used in scenarios where sensitive data needs to be securely distributed among multiple parties or devices.
  • Secure Access Control: In situations where multiple entities need to collaborate to access sensitive information, Shamir’s Secret Sharing provides a secure mechanism.

Shamir’s Secret Sharing provides a robust solution for protecting critical secrets, reducing the risk of unauthorized access, and ensuring the availability of the secret even if some components are compromised or lost.

Additional Resources
BitCoin Magazine1

Why Keystone implemented Shamir Backups2

Trezor – Shamir Backup3
Trezor Guide to Shamir Backup4
Trezor – Move to new wallet5

Trezor – A better way to secure your keys6

Trezor Shamir Backup solution7

Metal Crypto Seed Storage Reviews8

BIP-39 Word list9

  1. https://bitcoinmagazine.com/technical/why-advanced-bitcoiners-should-consider-upgrading-to-a-shamir-backup [↩]
  2. https://blog.keyst.one/why-keystone-implemented-shamir-backups-71e319f972a6 [↩]
  3. https://trezor.io/learn/a/what-is-shamir-backup [↩]
  4. https://blog.trezor.io/shamir-backup-a-new-security-standard-3aa42a6ebb5f [↩]
  5. https://trezor.io/learn/a/move-crypto-to-a-wallet-with-a-new-seed [↩]
  6. https://blog.trezor.io/shamir-backup-the-revolution-of-private-keys-backup-is-here-858687ed7fe7 [↩]
  7. https://www.theblock.co/post/256114/trezor-new-crypto-hardware-wallets-backup-solution [↩]
  8. https://jlopp.github.io/metal-bitcoin-storage-reviews//https://jlopp.github.io/metal-bitcoin-storage-reviews/ [↩]
  9. https://raw.githubusercontent.com/tinyseed-backup/word-lists/main/BIP39_Tinyseed_io.pdf [↩]