Is XRP quantum resistant?

Not yet. XRP Ledger accounts sign with secp256k1 or Ed25519, which a large enough quantum computer could break. No such computer exists, and the ledger has no post-quantum signature type or amendment so far.

Which XRP Ledger accounts would be at risk?

Those whose public key is on the ledger, which happens the first time a key signs a transaction. An address that has only ever received payments has not revealed its key.

What should I do about quantum risk now?

Nothing urgent. One hedge is to keep long-term holdings in an address whose key has never signed. Then watch for an amendment that adds a post-quantum key type; a regular key or signer list could move signing to it without changing your address.

Insights

XRPL Quantum Resistance

A large enough quantum computer could work out a private key from its public key and sign in its place. That computer does not exist yet, and the XRP Ledger has no post-quantum signatures yet either. What is exposed, what is not, and how the ledger could change.

What a quantum computer would threaten

XRP Ledger accounts sign with secp256k1 or Ed25519 keys. Both rest on problems that Shor’s algorithm, run on a large quantum computer, would solve: given a public key, it would find the private key. Hash functions are far less affected. Validators sign with the same kinds of keys, and theirs are published, so consensus would need the upgrade too.

Which accounts are exposed

Accounts that have signed. An address is a hash of a public key, and the key itself goes on the ledger the first time it signs a transaction (xrpl.org). Every active account has revealed its key.
Accounts that have only received. An address that has never sent anything has never revealed its key; an attacker would have to break the hash first.
Accounts that sign with a regular key. The master key stays unrevealed if it has never been used; only the regular key is on the ledger.

Where post-quantum signatures stand

NIST published its first post-quantum standards in August 2024, including ML-DSA, from CRYSTALS-Dilithium (FIPS 204), and SLH-DSA, from SPHINCS+. The XRP Ledger’s server software has no post-quantum key type, and no amendment for one has been put to the validators (how amendments work). Post-quantum signatures are also much larger than today’s, which would make every transaction bigger.

How the ledger could move

A new key type would arrive as an amendment, voted on by validators like any other change. Accounts would not need new addresses: the ledger already lets an account hand signing to a different key (a regular key) or to several (a signer list), so an account could move its signing to a post-quantum key and then disable the old one.

Questions

Is XRP quantum resistant?: Not yet. XRP Ledger accounts sign with secp256k1 or Ed25519, which a large enough quantum computer could break. No such computer exists, and the ledger has no post-quantum signature type or amendment so far.
Which XRP Ledger accounts would be at risk?: Those whose public key is on the ledger, which happens the first time a key signs a transaction. An address that has only ever received payments has not revealed its key.
What should I do about quantum risk now?: Nothing urgent. One hedge is to keep long-term holdings in an address whose key has never signed. Then watch for an amendment that adds a post-quantum key type; a regular key or signer list could move signing to it without changing your address.