Ripple Moves to Quantum-Proof the XRP Ledger Ahead of ‘Q-Day’

Ripple outlined a four-phase plan to make the XRP Ledger (XRPL) quantum-resistant by 2028, positioning the network for a potential “Q-Day” — the point at which a cryptographically relevant quantum computer could break the public-key cryptography that guards user balances.

The roadmap, published April 20, begins with active testing of post-quantum cryptographic schemes in the first half of 2026 and runs alongside the ledger’s existing signature systems rather than replacing them outright. A contingency layer, the “Quantum-Day” plan, would let users migrate to quantum-safe accounts if current standards collapse before the scheduled transition finishes.

In practice, that means XRPL holders could rotate off vulnerable keys without abandoning their accounts. Ripple contrasts this with Ethereum, where a post-quantum migration would require users to manually move assets to entirely new addresses.

The push comes as quantum risk moves from theoretical to credible. Research from Google Quantum AI, cited by Ripple and Decrypt, concluded that roughly 500,000 physical qubits could crack the elliptic-curve problem underpinning XRPL’s keys, about a 20-fold reduction from earlier estimates. At that scale, Google estimated a quantum machine could derive a private key from an exposed public key in around nine minutes.

A separate line of work pressed the timeline further. On July 28, 2026, Anthropic disclosed that its Claude Mythos Preview model had found a previously unknown structural weakness in HAWK, a post-quantum digital signature candidate under consideration for NIST standardization. The attack recovered signing-equivalent keys from HAWK-256 challenge instances, cutting the scheme’s security from 2^64 to 2^38, a reduction of roughly 67 million.

That part is new. AI-assisted cryptanalysis has not previously surfaced a working key-recovery against a NIST-tracked candidate.

The finding does not mean deployed cryptography is broken. HAWK is a candidate signature scheme, not an in-use standard, and the attack targets a reduced-security variant. But it reframes the question for blockchain developers: the assumption that post-quantum primitives would hold for years while networks migrated is now softer than it looked.

XRPL’s exposure mirrors the broader market’s. Project Eleven estimates that around 6.9 million bitcoin (roughly one-third of the total supply) sits in wallets with permanently exposed public keys, leaving them susceptible to a future quantum attack. Bitcoin developers are weighing multiple responses, including a second Bitcoin Improvement Proposal floated the week of April 14. The Ethereum Foundation has stood up a dedicated post-quantum team, with a roadmap identifying four areas of the network’s cryptography that need hardening.

Ripple is collaborating with Project Eleven on validator testing and early custody prototypes for post-quantum cryptography. The company has said it will design, build, and propose a new amendment to the XRPL to carry the quantum-safe signatures, though no specific amendment name has been disclosed.

XRP was recently trading near $1.43, up less than one percent on the day and roughly seven percent over the week, according to Decrypt.

The XRP Ledger team described the approach as one that “optimizes for preserving XRP Ledger’s current strengths while preparing for contingencies to minimize disruption if Q-Day arrives unexpectedly.” When that day lands is the open question, and the researchers and the engineers, as ever, do not agree.