Ripple aims to modernize cross-border payments with a ledger — but why does Do You Need a Blockchain? (Wüst & Gervais, 2017) say it doesn't remove the trust problem?

Because currencies on Ripple (other than its own XRP) are "issued" by gateways that must be trusted to honour withdrawals — so Ripple shifts the correspondent-banking trust onto gateways rather than eliminating it.

Ripple provides a shared settlement ledger and its native currency XRP, and makes payments atomic (all intermediate hops succeed or none do — unlike the legacy system where a failed hop needs reversals and manual fixes). But only XRP carries no counterparty risk. Every other currency is issued by a gateway: an on-chain "USD" is a claim on that gateway, not a real central-bank dollar, so each issuer effectively mints a parallel currency you must trust to redeem. That reintroduces the trust relationships of correspondent banking, just relocated to the gateways. The paper notes the fix would be central banks acting as gateways (issuing genuine on-chain currency), which would collapse settlement trust back to trusting the central bank — unavoidable anyway.

Go deeper:

• Ripple / XRP Ledger (Wikipedia) — the shared settlement ledger, native XRP, and the gateway-issued IOUs that carry counterparty risk.