Differential privacy in Snowflake Data Clean Room¶

How differential privacy works for clean rooms¶

Clean rooms offer their own differential privacy implementation that is different from Snowflake differential privacy, so read this document to understand the different behavior and settings.

Differential privacy protects the privacy of entities in your data. Clean rooms define an entity as a unique value in a column. Clean rooms determine which columns contain data that are likely to be sensitive; for example, a social security number or email address is probably a sensitive entity, but a color is not. When differential privacy is applied, clean rooms might identify one or more entity columns in each table. You cannot configure which columns are designated as entity columns.

Differential privacy in clean rooms also adds noise to numeric results associated with each entity.

Users might try to compare multiple different query results in order to reduce the noise; this is called a differencing attack. In order to mitigate differencing attacks, differential privacy calculates and monitors a privacy budget assigned to an account. Each query has a cost that reflects how much entity privacy is exposed by that query. This cost is determined mathematically, and depends on the query, the data, and the previous queries from that user. If a query cost exceeds the remaining privacy budget limit, the query will fail. Otherwise, the query can continue and the cost is added to the user’s daily privacy budget. The privacy budget is refreshed daily.

Differential privacy in clean rooms does not enforce aggregation constraints on queries, but you can add aggregation constraints on your data or templates independently.

Enable and manage differential privacy in the UI¶

In the clean room UI, providers can set privacy settings at the template level; consumers cannot enable or modify differential privacy settings. Standard Snowflake templates used in the clean rooms UI can have different privacy settings per template.

To use the clean room UI to enable or disable differential privacy for a template:

1. Open the Created` tab of the Clean Rooms page

2. Select Edit or » Edit on the clean room tile (depending on whether the clean room allows you to run an analysis).

3. Select Next until you reach Configure Analysis & Query.

4. At the bottom of the page, expand Privacy Settings. Select or deselect Differential Privacy and provide your settings for that template, including privacy budget for users and query cost. You can also set threshold values to enforce minimum group sizes in this query.

5. To configure settings for a different template, first set values for the current template, then choose a different template in the template selector.

Enable and manage differential privacy in the API¶

In the clean rooms API, either side can enable and configure differential privacy at the collaborator level.

All custom templates use the same differential privacy settings in a clean room. Snowflake-provided templates can be configured with individual privacy settings in the UI.

Use the following procedures to configure differential privacy:

• consumer.enable_templates_for_provider_run - Turn differential privacy off or on with default values for all provider-run analyses.

• consumer.set_privacy_settings - Specify individual differential privacy settings in provider-run analyses involving custom templates.

• provider.set_privacy_settings - Specify individual differential privacy settings in consumer-run analyses involving custom templates.

• provider.add_custom_sql_template - Provide a sensitivity parameter to increase or decrease the epsilon (noise level) for a template above or below the base line epsilon set for the consumer.

• provider.add_consumers - Specify privacy settings per consumer. You can add the same customer multiple times with different privacy settings to change their privacy settings.

• provider.suspend_account_dp_task - Turn off differential privacy budget monitoring for all clean rooms in this account. Differential privacy is no longer enforced.

• provider.resume_account_dp_task - Turn on differential privacy budget monitoring for all clean rooms in this account. Any differential privacy settings will be respected.

Privacy settings for a clean room are stored in SAMOOHA_CLEANROOM_cleanroom_ID.admin.privacy_budget, where APPLICATION_ID is a template name (NULL represents all custom templates) and PARTY_ACCOUNT is the user it is applied to.

Additional privacy functionality¶

cleanroom.addnoise(<val>, <epsilon>, <noiserand>, [<gaussian>], [<delta>])

CALL samooha_by_snowflake_local_db.provider.add_custom_sql_template(
$cleanroom_name,
$template_name,
$$
SELECT
  cleanroom.addNoise(
    count(distinct p.hashed_email),  -- Value
    {{ privacy.epsilon | sqlsafe }}, -- Epsilon
    UNIFORM(0::FLOAT, 1::FLOAT, RANDOM()) -- Noiserand
    ) AS noisy_count
FROM
    IDENTIFIER({{ source_table[0] }}) p
$$);

Managing differential privacy costs¶

Differential privacy incurs costs even when individual users or templates have not enabled differential privacy, because the system checks every query to see whether differential privacy should be applied. If you want to eliminate this cost, you can disable differential privacy for the account:

1. First, turn off differential privacy for all clean rooms using the web app:

   1. Log in to the web app.

   2. Disable differential privacy in all non-failed clean rooms, even if not shared or published:

      1. Select Clean rooms » Created » Edit.

      2. Select Next until you reach Configure Analysis & Query.

      3. At the bottom of the page, expand Privacy Settings. Deselect Differential Privacy if it is selected, then click Next and Finish to save your changes. If it is not selected, just click Cancel and move on to the next clean room.

2. Finally, suspend the differential privacy background task in your account by calling the provider.suspend_account_dp_task procedure in Snowsight.

Some notes and troubleshooting:

• If you forget to disable differential privacy for a clean room and suspend the background task, differential privacy might not function in that clean room for users who have already installed it.

• If differential privacy is enabled within a clean room prior to the clean room being installed, the installation of the clean room fails. In this case, you must disable differential privacy in the clean room or re-enable the task as outlined below.

If you later want to enable differential privacy in your account, either enable differential privacy for any clean room in the account or call the provider.resume_account_dp_task procedure in Snowsight.