The Quantum Resistant Ledger (QRL) project is a public chain ledger designed specifically for the advancement of Quantum Computing (QC). Unlike existing ledgers such as Bitcoin or Ethereum, QRL is specifically designed to use a type of post-quantum secure signature for XMSS transactions.

QRL also uses a low-power proof-of-proof (POS) algorithm, which again uses iterative hash chaining and a verifiable hash-based pseudo-random number function. The POS algorithm is designed to have no dependence on traditional signatures, which are susceptible to sufficiently strong QC, and allows nodes to run on low-power devices (such as Raspberry Pi or laptops) and passively earn income through staking.

There are several important cryptosystems considered to be quantum resistant: hash-based cryptography, code-based cryptography, lattice-based cryptography, multivariate quadratic cryptography, and secret-key cryptography. Given sufficiently long key sizes, all these schemes are considered to resist both classical and quantum computing attacks.

Forward secure hash-based digital signature schemes have minimal security requirements, relying only on the collision resistance of cryptographic hash functions. Changing the chosen hash function results in a new hash-based digital signature scheme. Hash-based digital signatures are well-studied and are prime candidates for future post-quantum signatures. Therefore, they are the chosen class of post-quantum signatures after QRL.