Security and Governance

Defense-in-Depth Security Model

Layered security, each layer provides independent protection:

1. Encryption at rest (TDE) — protects against physical media theft
2. Encryption in transit (TLS/SSL) — protects against network interception
3. Access control (RBAC/ABAC) — enforces least privilege
4. SQL injection prevention — protects against application-layer attacks
5. Audit logging — accountability and forensic capability

Encryption at Rest (TDE)

Encrypts DB files on disk without application changes. Encrypts data pages before writing, decrypts on read into memory. AES 128/256-bit symmetric encryption. Transparent to applications.

Key Hierarchy (SQL Server)

1. Service Master Key (Windows DPAPI) -> 2. Database Master Key -> 3. Certificate -> 4. Database Encryption Key (DEK)

Implementation

-- SQL Server TDE (key hierarchy: Service Master Key -> DB Master Key -> Certificate -> DEK)
CREATE DATABASE ENCRYPTION KEY WITH ALGORITHM = AES_256
    ENCRYPTION BY SERVER CERTIFICATE TDE_Cert;
ALTER DATABASE [YourDB] SET ENCRYPTION ON;
-- PostgreSQL: pgcrypto for column-level, full TDE in v17+ | Oracle: ALTER SYSTEM SET ENCRYPTION KEY

Best Practices

• Back up certificates/keys immediately — loss means unrecoverable data
• Store backups in separate secure location | Implement key rotation policy
• Use customer-managed keys (BYOK) for regulatory compliance
• Monitor performance impact (typically 3-5% overhead)
• TDE does not protect data in memory — use column-level encryption for highly sensitive fields

Encryption in Transit (TLS)

Configuration Checklist

• TLS 1.2+ enforced (disable 1.0/1.1)
• Valid certificates from trusted CA (not self-signed in prod)
• Certificate rotation policy established
• Client cert auth for server-to-server connections
• Connection string enforces SSL (sslmode=require in PostgreSQL)

Access Control

RBAC (Role-Based)

Assign permissions to roles, roles to users. Standard in all major DBs.

-- PostgreSQL RBAC: create roles with specific grants, assign to users
CREATE ROLE app_readonly; GRANT SELECT ON ALL TABLES IN SCHEMA public TO app_readonly;
CREATE ROLE app_readwrite; GRANT SELECT, INSERT, UPDATE ON ALL TABLES IN SCHEMA public TO app_readwrite;
GRANT app_readonly TO reporting_user; GRANT app_readwrite TO application_user;

ABAC (Attribute-Based)

Access decisions based on attributes of user, resource, environment. More flexible than RBAC for complex scenarios (multi-tenant, data classification).

Least Privilege

• Application accounts: DML only (SELECT/INSERT/UPDATE/DELETE)
• Migration accounts: DDL + DML, time-limited
• Admin accounts: full access, MFA required, audit logged
• Reporting accounts: SELECT only on specific schemas/views

SQL Injection Prevention (OWASP)

Parameterized Queries (Primary Defense)

# VULNERABLE - string concatenation (SQL injection risk)
query = f"SELECT * FROM users WHERE name = '{user_input}'"

# SAFE - parameterized (all languages: Python %s, Java ?, C# @param, Node.js $1)
cursor.execute("SELECT * FROM users WHERE id = %s AND status = %s", (user_id, 'active'))

Additional Defenses (OWASP)

Input validation: whitelist allowed chars/formats | Stored procedures: reduce direct SQL exposure | Least privilege: no DDL for app accounts | WAF rules | Never expose DB error messages to end users

Data Governance

Data Lineage

Track data from source through transformations to consumption:

• Technical lineage: Column-level mapping through ETL/ELT pipelines
• Business lineage: Business meaning and ownership
• Tools: Apache Atlas, OpenLineage, Marquez, dbt lineage, AWS Glue, Azure Purview

Purpose: Regulatory compliance (GDPR Article 30) | Impact analysis (downstream schema change effects) | Root cause analysis (bad data origin) | Audit trails

Data Quality Dimensions

Dimension	Definition	Example Check
Accuracy	Correctly represents real-world entities	Email format validation
Completeness	Required fields populated	NOT NULL checks, completeness %
Consistency	Same data across systems agrees	Cross-system reconciliation
Timeliness	Current and available when needed	Freshness SLAs
Uniqueness	No unintended duplicates	Duplicate detection on business keys
Validity	Conforms to defined rules/formats	Range checks, enum validation

Master Data Management (MDM)

Establish single source of truth for core entities (customer, product, location) | Define golden record resolution rules | Implement data stewardship roles | Use MDM platform or reference data services

Compliance Frameworks

GDPR (EU)

• Right to erasure (Art. 17): Hard-delete capability including backups/replicas
• Data portability (Art. 20): Export in machine-readable format (JSON, CSV)
• Consent management: Track per processing purpose with timestamps
• Data minimization: Collect/retain only necessary personal data
• Privacy by design: Pseudonymization, encryption, access controls from initial design
• Breach notification: 72-hour requirement, implement detection/alerting

CCPA (California)

Right to know (disclose collected data) | Right to delete | Right to opt-out of data sale | Non-discrimination regardless of privacy choices

HIPAA (Health Data)

PHI encryption at rest and in transit | Role-based access with minimum necessary standard | Audit all PHI access | Business associate agreements for third-party processors

Implementation Checklist

• Data classification schema (public, internal, confidential, restricted)
• Retention policies per classification
• Deletion procedures (including backups, replicas, caches)
• Consent tracking mechanism
• Audit logging for sensitive data access
• Data processing records (GDPR Art. 30)
• Breach response procedure documented and tested
• Privacy impact assessment for new processing activities

Backup and Recovery

3-2-1 Rule

3 copies of data | 2 different storage types | 1 copy offsite

Backup Types

• Full: Complete DB copy, baseline for recovery
• Incremental: Changed blocks since last backup, fast/small, recovery requires chain
• Differential: Changes since last full, faster recovery than incremental chain
• Transaction log: Enables point-in-time recovery (PITR)

Recovery Validation

Test recovery regularly (monthly minimum) | Document RTO and RPO | Encrypt backup files | Store encryption keys separately from backups