# SI-19(4)_removal-masking-encryption-hashing-or-replacement-of-direct-

> Remove, mask, encrypt, hash, or replace direct identifiers in a dataset.

- Skill: `cyberstrikeus/si-19-4-removal-masking-encryption-hashing-or-replacement-of` (Agent Skill)
- Install (CLI): `npx skillmds@latest add cyberstrikeus/si-19-4-removal-masking-encryption-hashing-or-replacement-of`
- Raw SKILL.md: https://api.skillmd.com/api/skills/cyberstrikeus/si-19-4-removal-masking-encryption-hashing-or-replacement-of/raw
- Safety review: PASS (external: skill-scanner PASS, skillspector PASS)
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: AI & ML
- Author: cyberstrikeus (https://skillmd.com/u/cyberstrikeus)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/cyberstrikeus/si-19-4-removal-masking-encryption-hashing-or-replacement-of

---


# SI-19(4) Removal, Masking, Encryption, Hashing, or Replacement of Direct Identifiers

> **Enhancement of:** SI-19

## High-Level Description

**Family:** System and Information Integrity (SI)
**Framework:** NIST SP 800-53 Rev 5

There are many possible processes for removing direct identifiers from a dataset. Columns in a dataset that contain a direct identifier can be removed. In masking, the direct identifier is transformed into a repeating character, such as XXXXXX or 999999. Identifiers can be encrypted or hashed so that the linked records remain linked. In the case of encryption or hashing, algorithms are employed that require the use of a key, including the Advanced Encryption Standard or a Hash-based Message Authentication Code. Implementations may use the same key for all identifiers or use a different key for each identifier. Using a different key for each identifier provides a higher degree of security and privacy. Identifiers can alternatively be replaced with a keyword, including transforming "George Washington" to "PATIENT" or replacing it with a surrogate value, such as transforming "George Washington" to "Abraham Polk."

## What to Check

- [ ] Verify SI-19(4) Removal, Masking, Encryption, Hashing, or Replacement of Direct Identifiers is documented in SSP
- [ ] Confirm control is operating effectively
- [ ] Review evidence of continuous monitoring for SI-19(4)
- [ ] Verify enhancement builds upon base control SI-19

## How to Test

### Step 1: Review Documentation

Examine the System Security Plan (SSP) and related artifacts for SI-19(4) implementation details. Verify the organization has documented how this control is satisfied.

### Step 2: Validate Implementation

```
# For cloud environments, use cloud-audit-mcp tools
# For on-premises, review system configurations directly

# Example: Check if account management policies exist
grep -r "account.management\|access.control" /etc/security/ 2>/dev/null
```

### Step 3: Test Operating Effectiveness

Verify the control is actively functioning, not just documented. Check logs, configurations, and operational evidence.

## Tools

| Tool            | Purpose                    | Usage                          |
| --------------- | -------------------------- | ------------------------------ |
| cloud-audit-mcp | Check integrity monitoring | `cloud_audit_monitoring`       |
| AWS CLI         | Review GuardDuty/Inspector | `aws guardduty list-detectors` |

## Remediation Guide

### Control Statement

Remove, mask, encrypt, hash, or replace direct identifiers in a dataset.

### Implementation Guidance

There are many possible processes for removing direct identifiers from a dataset. Columns in a dataset that contain a direct identifier can be removed. In masking, the direct identifier is transformed into a repeating character, such as XXXXXX or 999999. Identifiers can be encrypted or hashed so that the linked records remain linked. In the case of encryption or hashing, algorithms are employed that require the use of a key, including the Advanced Encryption Standard or a Hash-based Message Authentication Code. Implementations may use the same key for all identifiers or use a different key for each identifier. Using a different key for each identifier provides a higher degree of security and privacy. Identifiers can alternatively be replaced with a keyword, including transforming "George Washington" to "PATIENT" or replacing it with a surrogate value, such as transforming "George Washington" to "Abraham Polk."

## Risk Assessment

| Finding                                                                                              | Severity | Impact                                      |
| ---------------------------------------------------------------------------------------------------- | -------- | ------------------------------------------- |
| SI-19(4) Removal, Masking, Encryption, Hashing, or Replacement of Direct Identifiers not implemented | High     | System and Information Integrity            |
| SI-19(4) partially implemented                                                                       | Medium   | Incomplete System and Information Integrity |

## CWE Categories

| CWE ID | Title                     |
| ------ | ------------------------- |
| CWE-20 | Improper Input Validation |

## References

- [NIST SP 800-53 Rev 5 - SI-19(4)](https://csrc.nist.gov/projects/cprt/catalog#/cprt/framework/version/SP_800_53_5_1_1/home?element=si-19.4)
- [NIST SP 800-53A Rev 5 (Assessment Procedures)](https://csrc.nist.gov/pubs/sp/800/53/a/r5/final)
- [NIST SP 800-53 Rev 5 Full Catalog](https://csrc.nist.gov/pubs/sp/800/53/r5/upd1/final)

## Checklist

- [ ] Control documented in SSP
- [ ] Implementation evidence collected
- [ ] Operating effectiveness validated
- [ ] Continuous monitoring in place
- [ ] Related controls (SC-12, SC-13) reviewed