The integrity seal
The gold seal on the documentation carries the cryptographic fingerprint of the exact document you received. With it, you, your tax advisor, or the tax authority can confirm at any time that the document has not changed since delivery, and that it came from me.
What the seal carries
Outer ring — integrity
The outer ring carries the SHA-256 hash of the document's exact bytes. Re-compute the hash of your file and compare it. If even one character of the document had changed, the hash would not match. This check needs no keys and no special tools.
Inner ring — origin
The inner ring carries an Ed25519 signature over the same bytes, made with my signing key. It verifies against the public key below, and only the holder of the private key could have produced it.
Verify a sealed delivery
Sealed deliveries come with a small signature file (.sig) next to the document. With the document, the signature, and the public key, anyone can check both properties on any machine:
- Download the public key: seal-pubkey.pem
- Hash the document and compare with the seal's outer ring.
- Verify the signature against the public key.
# 1 — integrity: matches the outer ring? sha256sum document.pdf # 2 — origin: signed by ilja.tax? openssl pkeyutl -verify -pubin -inkey seal-pubkey.pem \ -rawin -in document.pdf -sigfile document.sig # → "Signature Verified Successfully"
The public key
MCowBQYDK2VwAyEANobk5gXQp9By8QZtTLdVkcJv4PeO8I9OsF2MPeEVwyQ=
SHA-256 fingerprint
8C1C A86D ACC3 CD2F 2DD5 9291 1E6D AB6E 42E8 6FFA 1208 A48F AC84 4E5A E692 2B59
The same fingerprint is drawn into the two text rings of the ilja.tax logo, so the mark in the navigation carries the same key.
This is a private integrity seal, not a qualified electronic signature under eIDAS, and it has no statutory legal effect. It proves that the bytes are unchanged and that they came from me. The methodology inside the documentation makes the numbers defensible.