What is an Authorization to Operate (ATO)?

An Authorization to Operate (ATO) is a formal declaration issued by a senior agency official (often the Authorizing Official, or AO) that authorizes an information system to operate in a particular security environment for a certain period of time, based on the implementation and validation of its security controls and the assessment of risk the system poses to the organization's operations and assets.

The ATO process is part of the NIST Risk Management Framework (RMF) used by the U.S. federal government, as well as in other organizations, to ensure that information systems meet security requirements before they go live. It involves several steps:

1. Categorize the information system: Define the system and categorize the information processed, stored, and transmitted based on impact levels (e.g., low, moderate, high).
2. Select security controls: Identify appropriate security controls for the system and document them in the System Security Plan (SSP).
3. Implement security controls: Put the chosen security controls in place.
4. Assess security controls: Evaluate the effectiveness of the security controls to ensure they are functioning correctly and as intended.
5. Authorize the information system: The AO reviews the assessment results and the risks the system might pose to the agency and decides whether the risks are acceptable.
6. Monitor security controls: Continuously monitor the security controls and the state of the system to ensure that risks remain at an acceptable level.

Receiving an ATO indicates that the system has met the necessary security requirements and can be used to process, store, or transmit information while managing risk effectively. However, it does not mean the system is free from security risk. An ATO typically has an expiration date, after which the system must go through the ATO process again to ensure continued compliance with the evolving threat landscape and policy changes.