Column-level security with masking policies in Snowflake - Step-by-Step Execution

Process Flow - Column-level security with masking policies

User Queries Data

↓

Check Masking Policy on Column

↓

Evaluate User Role

↓

Apply Masking Logic

↓

Return Masked or Original Data

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User Sees Data Based on Permissions

When a user queries a column with a masking policy, Snowflake checks the user's role, applies the masking logic, and returns either masked or original data accordingly.

Execution Sample

Snowflake

CREATE MASKING POLICY ssn_mask AS
  (val STRING) RETURNS STRING ->
  CASE
    WHEN CURRENT_ROLE() IN ('FULL_ACCESS_ROLE') THEN val
    ELSE 'XXX-XX-XXXX'
  END;

ALTER TABLE employees MODIFY COLUMN ssn SET MASKING POLICY ssn_mask;

This code creates a masking policy for the SSN column that shows the real value only to users with FULL_ACCESS_ROLE; others see a masked value.

Process Table

Step	User Role	Column Value	Masking Policy Applied	Returned Value
1	FULL_ACCESS_ROLE	123-45-6789	Check role in policy	123-45-6789
2	READ_ONLY_ROLE	123-45-6789	Check role in policy	XXX-XX-XXXX
3	ANALYST_ROLE	123-45-6789	Check role in policy	XXX-XX-XXXX
4	FULL_ACCESS_ROLE	987-65-4321	Check role in policy	987-65-4321
5	READ_ONLY_ROLE	987-65-4321	Check role in policy	XXX-XX-XXXX
6	ANALYST_ROLE	987-65-4321	Check role in policy	XXX-XX-XXXX
7	No role or unknown	123-45-6789	Check role in policy	XXX-XX-XXXX

💡 Execution stops after returning masked or original data based on user role.

Status Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4	After Step 5	After Step 6	After Step 7
User Role	N/A	FULL_ACCESS_ROLE	READ_ONLY_ROLE	ANALYST_ROLE	FULL_ACCESS_ROLE	READ_ONLY_ROLE	ANALYST_ROLE	No role
Column Value	N/A	123-45-6789	123-45-6789	123-45-6789	987-65-4321	987-65-4321	987-65-4321	123-45-6789
Returned Value	N/A	123-45-6789	XXX-XX-XXXX	XXX-XX-XXXX	987-65-4321	XXX-XX-XXXX	XXX-XX-XXXX	XXX-XX-XXXX

Key Moments - 3 Insights

Why does the returned value change based on user role?

Because the masking policy checks the user's role (see execution_table rows 1 and 2). If the role is allowed, the real data is returned; otherwise, a masked value is returned.

What happens if a user has no role or an unknown role?

The masking policy treats unknown or missing roles as unauthorized and returns the masked value (see execution_table row 7).

Is the original data changed in the database when masking is applied?

No, the original data stays the same. Masking only changes what the user sees at query time (refer to variable_tracker 'Column Value' vs 'Returned Value').

Visual Quiz - 3 Questions

Look at the execution_table, what value does a user with FULL_ACCESS_ROLE see for the SSN '987-65-4321'?

A XXX-XX-XXXX

B NULL

C 987-65-4321

D Access Denied

💡 Hint

Check execution_table row 4 under 'Returned Value'.

At which step does the masking policy return a masked value for the SSN '123-45-6789'?

A Step 2

B Step 1

C Step 4

D Step 7

💡 Hint

Look at execution_table rows with 'READ_ONLY_ROLE' and 'Returned Value'.

If a new role 'HR_ROLE' is added to FULL_ACCESS_ROLE list, how would the returned value change for that role querying '123-45-6789'?

A It would return 'XXX-XX-XXXX'

B It would return '123-45-6789'

C It would return NULL

D It would cause an error

💡 Hint

Refer to the masking policy logic in execution_sample and how roles affect returned value.

Concept Snapshot

Column-level security with masking policies:
- Define a masking policy with CASE logic based on user roles.
- Attach the policy to sensitive columns.
- When queried, Snowflake checks user role.
- Returns original data if authorized, else masked data.
- Original data remains unchanged in storage.

Full Transcript

Column-level security with masking policies in Snowflake works by defining a masking policy that controls what data users see based on their roles. When a user queries a column with a masking policy, Snowflake evaluates the user's role. If the role is authorized, the user sees the original data. Otherwise, the data is masked, for example, replaced with 'XXX-XX-XXXX' for social security numbers. The original data in the database is never changed; masking only affects query results. This ensures sensitive data is protected while allowing authorized users full access.