> For the complete documentation index, see [llms.txt](https://legacy-docs.across.to/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://legacy-docs.across.to/reference/security-model-and-verification.md).

# Security Model and Verification

The Across [smart contracts](/reference/contract-addresses.md) plus the [UMIP](https://github.com/UMAprotocol/UMIPs/blob/master/UMIPs/umip-179.md) provide the fundamental rules of the Across Protocol. The `ACROSS-V2` price in [UMIP-157](https://github.com/UMAprotocol/UMIPs/blob/7b1a046098d3e2583abd0372c5e9c6003b46ad92/UMIPs/umip-157.md) and extended by [UMIP-179](https://github.com/UMAprotocol/UMIPs/blob/master/UMIPs/umip-179.md) precisely define the constraints and rules of the system. Actors in the system (relayer, dataworker) must behave in accordance to these rules. The system is secured by optimistic verification of relayer repayments and rebalance instructions by [UMA's Optimistic Oracle](https://uma.xyz/), requiring only a single honest actor to dispute invalid proposals to keep the system secure. 

Please refer to [UMIP-157](https://github.com/UMAprotocol/UMIPs/blob/7b1a046098d3e2583abd0372c5e9c6003b46ad92/UMIPs/umip-157.md) and [UMIP-179](https://github.com/UMAprotocol/UMIPs/blob/master/UMIPs/umip-179.md) for detailed information about system architecture, security model and verificaiton.