Securing Information: Shamir's Secret Sharing Scheme and Bitcoin

Securing Information: Shamir's Secret Sharing Scheme and Bitcoin

Author: Robert Strickland (crypto-journalist)


Securing Information: Shamir's Secret Sharing Scheme and Bitcoin

When it comes to safeguarding bitcoins, the most dependable method is storing them in cold wallets. In such cases, the private key's security is upheld by a 12-word seed phrase. But how far can one go in pursuit of security?


Cryptography and privacy play a significant role in the world of cryptocurrencies, offering users maximum control over their assets without reliance on third parties like banks, governments, or exchanges. They can retain their assets in their personal wallets, with the private key safeguarded by a seed phrase. Possessing this seed phrase grants access to the wallet; however, losing it can result in a permanent loss of funds. Unlike traditional assets, Bitcoin lacks a safety net such as a customer support hotline, legal recourse, or technical assistance in case of a lost seed phrase.

To address this issue without compromising security, Shamir's Secret Sharing Scheme (SSS) comes into play. Adi Shamir, an Israeli cryptographic scientist, made invaluable contributions to the field, particularly with the RSA (Rivest, Shamir, and Adleman) public-key cryptographic algorithm. While Bitcoin doesn't use RSA, it employs the more convenient ECDSA (Elliptic Curve Digital Signature Algorithm). The Fiat-Shamir protocol, another of Shamir's contributions, has limited application and has been deemed insufficiently secure in some studies.

Adi Shamir is an Israeli cryptographic scholar. His contribution to the study of the subject is difficult to overestimate. The public-key cryptographic algorithm RSA (short for Rivest, Shamir, and Adleman) was a milestone in the history of asymmetric encryption methods. The Fiat-Shamir protocol is widely used for zero-disclosure identification. 

Returning to SSS, this algorithm divides a secret into multiple parts, rendering each part useless on its own. To recover the secret, a predetermined number of these parts must be combined, which is known in advance. For instance, if a secret is divided into six parts and it is decided that four are necessary to recover it, even if two parts are lost, the secret can still be retrieved. This concept resembles multi-signature security.

In the context of seed phrase storage, SSS allows for encryption of the private key followed by splitting it into fragments. This theoretically enhances the security of Bitcoin wallet keys. Alternatively, the secret can be distributed among trusted individuals, preventing any single person from independently accessing the funds. Traditional seed phrases face the dilemma of balancing the risk of loss by creating multiple copies (increasing the risk of theft) or reducing the risk of theft with a single copy (increasing the risk of loss). Shamir's Secret Sharing Scheme eliminates both risks by dividing the secret into multiple parts and requiring a predetermined number of parts for wallet recovery.

One interesting application of SSS is inheritance planning, where portions of the secret can be distributed to heirs, granting access to the wallet only when they collaborate. Some hardware cryptocurrency wallets, such as those from Trezor, implement this scheme. However, it's important to note that SSS may not be suitable for everyone.

SSS is typically used in conjunction with hardware wallets, which introduces the risk of malware or compromised firmware intercepting the required parts of the secret. Furthermore, hardware wallets themselves carry risks, including device damage, loss, or firmware issues. While SSS hypothetically reduces the risk of loss, it doesn't eliminate it entirely. For active users requiring constant access to their assets, SSS can limit their mobility.

In summary, while SSS offers enhanced security for Bitcoin wallet keys, it may be considered redundant by some. The traditional seed phrase remains a reliable mechanism and can be strengthened in various ways. Alternatively, using a passphrase or implementing sound security practices, such as securely storing the seed phrase in a hidden, safe location, can also provide robust protection for cryptocurrency assets.


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