The digital signature is a signing method, equivalent to one's handwritten signature, which an individual can use to sign data sent electronically. As with a handwritten signature, the electronic signature is inseparable from the document concerned.

It contains encrypted checksums (hash values). These are used to ascertain the integrity of the data and uncover any change that may have been made to the data. As part of the signing process, an irreversible procedure saves the document in an abbreviated form. The hash value that derives from this is encrypted and the document is sent along with the encrypted hash value.

On an invoice printout, the hash value may appear as a written line, e.g. on the left-hand side of the page.

Invoice printout with digital signature

On a faxed invoice, the digital signature appears as a 2D barcode. This barcode can be inserted into the document in different ways, e.g. along the lower edge of an image, or as a square.

The invoice issuer sends their invoice to their customers via nexMart. In the process, we sign it electronically and save it to the archive. The invoice issuer can use their login to access their invoice whenever they wish. The invoice recipient also saves the invoice that they have received in their archive and they can access it there via their own login whenever they wish. When a new invoice is saved to the archive, the invoice recipient gets an e-mail notification from us. This contains a link that they can use to access their invoice.

The invoices are stored in the archive for 10 years from the start of the following year. The archive complies with GDPdu and GoBS guidelines.

At nexMart, we offer a full invoice data output management service. This means your entire invoicing workflow can be done via nexMart. So, as well as electronically signed invoices, you can also send printed invoices on your own paper with nexMart's customary quality.

To make this process as convenient as possible for you, nexMart gives you—where necessary—an easy-to-install printer driver that processes all your invoice documents via a single channel. Once it has been set up, you just send nexMart all your invoices and nexMart will take care of the rest.

The verification of a digital signature consists of the verification of the signature itself plus the verification done on the validity of the signed invoice.

The process used is to recalculate the encrypted checksums in the electronic signature and then compare them with the original values. If they match, the data is sent to a trust centre that checks whether the invoice and the digital signature comply with legal requirements. If they do, the trust centre issues a verification log. The files are then saved together in the archive, where they can be viewed.