How can I prove my carbon records were not changed after the fact?

Question

Senseible · Accepted Answer

Fingerprint every source file with a hash such as SHA-256, write each calculation to an append-only log where every entry includes the hash of the one before, and share the latest hash with your auditor or lender at each reporting date. Any later edit then shows up. This proves records were not altered, not that they were true. A SHA-256 hash, defined in NIST FIPS 180-4, turns a file into a 64 character code. Change one character in the invoice PDF and the code changes completely. Store the hash next to every emission line that came from that file, so anyone holding the original can recompute it and compare. Write each emission line, correction and approval as a new entry. Never overwrite. Each entry's hash is computed from its own content plus the previous entry's hash. Editing or deleting an old entry breaks every hash after it, so the change is visible to anyone who checks the chain. A chain kept only by you can, in principle, be rebuilt from scratch. Send the latest hash to your auditor, lender or buyer when you report, or include it in the signed report. Later, they recompute the chain and confirm it still ends in the hash they received. You do not need a blockchain for this. That the invoice itself was genuine or the quantity on it was right. A fake bill hashed on day one stays fake. That nothing was left out. A hash chain shows what was recorded, not what was never uploaded. That the method was correct. Keep the factor source and methodology version with each line so a reviewer can judge that separately.