According to today's legal opinion, authenticity is only ensured if the communication, for example the written document, is signed with original signatures by authorized persons who are allowed to make the written declaration of intent. In some cases, the law requires notarization, assessment or certification to determine authenticity.
In terms of information technology, authenticity is about the binding nature of data, documents, information or messages that can be reliably assigned to a specific data terminal or sender. Authenticity must ensure that the origin of such information can be proven beyond doubt. One possibility for proof is the digital signature( DSig).