E1-F5: OIB Checksum Validation Service

Epic: E1: User & Profile Management

Size: S (Small)

Problem / Outcome

All OIB entries must be validated using Croatian checksum algorithm.

Scope

In-Scope:

• Utility function/service for OIB checksum validation
• 11-digit format check

Out-of-Scope:

• OIB lookup against government database

Acceptance Criteria

• AC1: Given valid OIB with correct checksum, when validated, then return true
• AC2: Given OIB with invalid checksum, when validated, then return false with error message
• AC3: Given OIB with wrong length, when validated, then return false with "Must be 11 digits"

Technical Details

OIB uses ISO 7064, MOD 11-10 checksum algorithm:

1. Start with initial value 10
2. For each of the first 10 digits:
3. Add digit to current value
4. Take modulo 10 (if result is 0, use 10)
5. Multiply by 2
6. Take modulo 11
7. The 11th digit should equal 11 minus the final value (mod 10)

Data Model Impact

None (utility service)

Permissions/Roles

• Internal service

How to Verify

npm test -- --grep "OIB validation"

Expected: Known valid OIBs pass, invalid OIBs fail.

Dependencies

• None

Implementation Tasks

See E1: User & Profile Tasks

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Last Updated: January 2026