The Quantum Resistant Ledger (QRL) project is a public blockchain ledger designed to be specifically secure against quantum computing (QC) advances. Unlike existing ledgers, such as bitcoin or ethereum, the QRL is specially designed to use a form of post-quantum secure signature for transactions called XMSS. The QRL also uses a low power proof-of-stake (POS) algorithm which again utilises iterative hash-chains and provably secure hash-based pseudo random number functions. The POS algorithm is designed to have zero reliance upon conventional signatures which are vulnerable to a sufficiently powerful QC and allows nodes to run on low power devices such as raspberry PI’s or laptops and passively earn income by staking.
There are several important cryptographic systems which are believed to be quantum-resistant: hash-based cryptography, code-based cryptography, lattice-based cryptography, multivariate-quadratic-equations cryptography and secret-key cryptography. All these schemes are thought to resist both classical and quantum computing attack given sufficiently long key sizes. Forward secure hash-based digital signature schemes exist with minimal security requirements that rely only upon the collision-resistance of a cryptographic hash function. Changing the chosen hash function produces a new hash-based digital signature scheme. Hash-based digital signatures are well studied and represent the primary candidate for post-quantum signatures in the future. As such they are the chosen class of post-quantum signature for the QRL.