Locking and issuing

A blockchain cannot reach into another blockchain. XRP lives on the XRP Ledger and nowhere else. To use its value on a second chain, you need a bridge.

A bridge does not trade one asset for another. The XLS-38 spec offers a good picture: a box with an endless supply of wrapped coins.

• Put a real coin into the box. A wrapped coin comes out on the other chain.
• Put a wrapped coin back. A real coin comes out again.
• There is no other way in or out of the box.

The chain where the real asset lives is the locking chain. The chain that gets the wrapped copy is the issuing chain. For XRP, the XRP Ledger would be the locking chain and a sidechain would be the issuing chain.

A sidechain is its own ledger. It has its own validators, its own rules and its own list of trusted validators. Nodes on one chain know nothing about the other.

Each end of the bridge is a special account called a door account. The door on the locking chain holds the locked assets. The door on the issuing chain issues the wrapped ones.

Since the chains cannot see each other, someone has to carry the news. Witness servers watch both doors. When assets are locked on one side, witnesses sign a statement saying so and deliver it to the other side.

This bridge design is part of the protocol itself, not an app. It is not enabled on mainnet. Validators have been able to vote on it since January 2024.

The XChainBridge amendment (XLS-38) adds three ledger entry types and eight transactions.

A bridge is identified by an XChainBridge object with four fields:

Two bridge types exist:

• XRP-XRP. The issuing chain's door must be its genesis account, which holds all of that chain's XRP.
• IOU-IOU. For a token bridge, the issuing-chain door must be the issuer of the wrapped token.

XChainCreateBridge creates the Bridge entry. Each door account sends it on its own chain. It sets SignatureReward, the total paid to witnesses per transfer, and optionally MinAccountCreateAmount. XChainModifyBridge can change only those two values.

A Bridge entry cannot be removed, so a door account cannot be deleted.

For testing, xrpl.org lists a Sidechain-Devnet. Devnet acts as the locking chain and the sidechain as the issuing chain.

Related: XRPL EVM sidechain, Hooks and Xahau.

Live count: Amendments page.