An invoice dispute can cost you more than the invoice itself — in time, legal fees, and client relationships. Digital signatures address this problem at the root by creating a cryptographically verifiable record that proves an invoice has not been altered since the moment it was signed.

What Is a Digital Signature?

A digital signature is not an image of a handwritten name. It is a mathematical proof generated using public-key cryptography. When you sign an invoice digitally, the system creates a unique fingerprint (called a hash) of the document's contents and encrypts it with a private key that only you hold.

Anyone with your public key can verify that:

  1. The invoice was signed by you (authentication)
  2. The invoice has not been modified since signing (integrity)
  3. You cannot deny having signed it (non-repudiation)

How RSA-2048 Works in Practice

Facturi uses RSA-2048, a widely accepted encryption standard that is considered secure for at least the next decade by major cryptographic authorities. Here is what happens when you sign an invoice:

  1. The invoice content is hashed using SHA-256, producing a fixed-length digest.
  2. The digest is encrypted with your organization's private RSA key.
  3. The resulting signature is embedded in the invoice PDF and stored in an audit log.
  4. A public verification URL is generated that anyone — including courts and tax authorities — can use to confirm authenticity.

Are Digital Signatures Legally Valid?

In most jurisdictions, yes. Key legislation includes:

  • European Union — eIDAS Regulation (EU) 910/2014 recognizes electronic signatures as legally equivalent to handwritten signatures.
  • United States — ESIGN Act and UETA give electronic signatures full legal standing.
  • Spain — VeriFactu and the Ley Antifraude require electronic invoices to be tamper-proof, which digitally signed invoices satisfy.
  • Most other jurisdictions — UNCITRAL Model Law on Electronic Commerce provides a framework that many countries have adopted.

The Tamper-Proof Chain

Facturi takes security a step further with a blockchain-style hash chain. Each invoice includes a reference to the hash of the previous invoice, linking all documents in a sequence. Altering any single invoice would break the chain and become immediately detectable — even retroactively.

What This Means for Your Business

When a client claims they never received an invoice, or disputes the amount, a digitally signed document with a timestamped audit trail is compelling evidence. It removes ambiguity and shifts the burden of proof firmly in your favor.

For businesses operating in regulated industries or jurisdictions with electronic invoicing mandates, digital signatures are not optional — they are a compliance requirement. For everyone else, they are the difference between a document and a legal record.