Quantum-resistant Bitcoin using Lamport Signatures

This post was first published on Medium.As quantum computing potentially transitions from theory to practice, its implications for cryptographic systems, particularly those underpinning cryptocurrencies like Bitcoin, become increasingly profound. Bitcoin, reliant on the Elliptic Curve Digital Signature Algorithm (ECDSA), faces potential vulnerability in the quantum era.If quantum computers ever become sufficiently powerful, we provide a way to make Bitcoin resistant to its attacks by using Lamport Signatures. The crucial idea is to program Lamport Signatures in smart contracts, and thus no change/”fix” to the base layer is needed. This drastically differs from existing approach of upgrading Bitcoin’s cryptographic algorithms via a fork (softfork or hardfork) to be quantum-resistant, which are currently favored by so-called Bitcoin experts.The truth is that Bitcoin was always quantum resistant.1Whether a quantum attack on Bitcoin is viable, both technically and economically, is outside the scope of this article. For interested readers seeking more in-depth information on the topic, it is recommended to explore additional resources such as [1].Quantum computers and BitcoinQuantum computers operate on the principles of quantum mechanics, allowing them to perform complex calculations at speeds unattainable by classical computers. This capability poses a significant threat to cryptographic algorithms like the elliptic curve digital signature algorithm (ECDSA) used in Bitcoin, which hinges on the infeasibility of deriving private keys from public keys. Quantum algorithms, such as Shor’s algorithm, could theoretically break ECDSA, thereby compromising Bitcoin’s security model.Lamport SignaturesIn response to this looming threat, Lamport signatures, a one-time signature scheme using hash functions, emerge as a quantum-resistant alternative. Contrary to ECDSA’s reliance on number-theoretic assumptions vulnerable to quantum computing, Lamport signatures derive their security from the difficulty of inverting hash functions, which remain robust against known quantum attacks.Here is a concise technical description of how Lamport signatures work:Key GenerationSigningSignature VerificationComparing with Public Key:Lamport signatures are “one time signature” and necessitate a new signing key for each transaction, whose one-time nature aligns with Bitcoin’s single-use address model. The signatures are larger than ECDSA signatures but only at ~16 KB, making them practical today.ImplementationWe have implemented a working example of Lamport signature verification. The code is rather simple. The smart contract exposes a single public method called “unlock,” which allows a redeemer to take the locked bitcoins by providing a valid Lamport signature. On a higher level, this is pretty much the same mechanism as in a standard P2PK(H) transaction.We have successfully made the first transaction using Lamport signatures on Bitcoin:97f055bccb27539604de9ed99f1067f76fb7cae29b00fbc0a7bb744c8e0c74d8The full source code of this contract, along with some tests, can be found on GitHub.DiscussionThere are optimizations to make Lamport signatures more efficient in terms of signature and key size.There are also alternative approaches to using smart contracts to make Bitcoin quantum-resistant without breaking changes, such as addictive hashes.***[1] Bitcoin and Quantum Computing: Craig S Wright 2017Watch: sCrypt applications are proving how powerful Bitcoin is title=”YouTube video player” frameborder=”0″ allow=”accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share” allowfullscreen>New to blockchain? Check out CoinGeek’s Blockchain for Beginners section, the ultimate resource guide to learn more about blockchain technology.