Understanding the Cryptographic Hash Chain

A hash chain is a way of connecting your records together so that if anyone tries to change, delete, or insert a record, the tampering is mathematically detectable.

Think of it like a chain of sealed envelopes. Each envelope contains a record and a fingerprint of the previous envelope. If someone opens and changes any envelope, the fingerprints no longer match — and everyone can tell.

Every presence record you create gets a unique digital fingerprint called a SHA-256 hash. This hash is calculated from the record's data (date, jurisdiction, timestamp, etc.) combined with the hash of your previous record.

This means each record is cryptographically linked to the one before it, forming an unbreakable chain. If any record is modified after creation, the chain breaks — and Borderly (or any third party) can detect it.

For tax residency purposes, the integrity of your records is everything. A hash chain means:

• You cannot accidentally (or intentionally) alter past records without detection.
• An auditor or tax authority can independently verify that your records have not been tampered with.
• Your records are more credible than a simple spreadsheet or calendar.