# Bascule Drawbridge

The Bascule Drawbridge provides an extra layer of security by cross-checking all actions by the Security Consortium before they can be executed. This third-party view of the world is built and controlled by Cubist, to prevent cross-chain bridge hacks in real-time.

The Bascule Drawbridge is a state oracle running its own smart contract. It is unique to Lombard's multi-layered security approach. The drawbridge, operated by Cubist, attests the truth from the Bitcoin network on destination chains independently of the Consortium. This adds additional security to LBTC by providing a secondary and independent attestation on the state of the Bitcoin network. Minting of LBTC, in normal operating conditions, requires a valid signature from both the Consortium and the Bascule Drawbridge.\
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The Reverse Bascule Drawbridge is an off-chain Bascule contract, used for verifying BTC withdrawals, where the on-chain state of LBTC is checked before authorization within CubeSigner.&#x20;

### Overview of Bascule Drawbridge

<figure><img src="https://2727780006-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FshysQ5d1rHU8C0eDQoLF%2Fuploads%2FYclhVfRyeifEXHZExGiQ%2Fimage.png?alt=media&#x26;token=6b83a44b-9302-466e-9d8e-6df207e75df5" alt=""><figcaption></figcaption></figure>

1. A Bitcoin deposit is detected on the Bitcoin network, to a deterministic user deposit address owned and controlled by Lombard Protocol.
2. Cubist wait for 6 block confirmations for security, before writing this information to the Bascule smart contract on a supported blockchain.
3. When attempting to mint on the LBTC contract, both the Bascule attestation and the Security Consortium majority signatures must be provided.

### Overview of Reverse Bascule Drawbridge

<figure><img src="https://2727780006-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FshysQ5d1rHU8C0eDQoLF%2Fuploads%2Fz5Zlx6Bksu8786Kvk9w9%2Fimage.png?alt=media&#x26;token=9d3a081f-b9a3-4774-820e-26d76c1f4863" alt=""><figcaption></figcaption></figure>

1. User calls redeem function on the LBTC smart contract on any supported blockchain. The corresponding LBTC is burned.
2. Cubist listen to the redeem events emitted from the LBTC smart contract, and after a set number of block confirmations for security, will write this state into CubeSigner.
3. CubeSigner checks for receipt of redeem attestation after the Security Consortium have initiated a Bitcoin withdrawal process.

For more information on the Bascule Drawbridge, check out [this blog](https://cubist.dev/blog/introducing-the-bascule-drawbridge-for-bitcoin-bridge-security).
