A digital signature is an encryption of messages on the Internet using a cryptographic process that enables the message to be uniquely assigned to the sender. An asymmetric cryptosystem is used for this purpose, which consists of a secret signature key (private key) and a publicly known verification key (public key). Using the digital signature with the verification key from this key pair, it is later possible to determine perfectly who sent a message.
Types of digital signature
The digital signature can be divided into several types. A simple electronic signature has no legal significance. A typical example is the simple scanning of a signature. A clear assignment to a person is not possible. An advanced electronic signature is secured by authentication using a certificate. The qualified electronic signature offers even greater security. This signature, which is usually digital, is issued with the aid of a signature creation device, for example a smart card, and certified by an independent trust center (certification service provider). In this case, unauthorized access by third parties to the sender’s personal key is not possible.
Legal basis of the digital signature
In Germany, the digital signature is anchored in two legal regulations, the Signature Act (SigG) and the Ordinance to the Signature Act (SigV). These legal regulations not only define the requirements that an electronic signature must meet, but also list possible certification service providers. The German Civil Code (BGB) also contains a list of cases in which a digital signature is required to conclude a legal transaction.
Validity of a digital signature
The encryption algorithms and certificates used to create a digital signature are subject to a relatively short expiration date. Encryption algorithms expire after five years at the latest. They must always be renewed promptly, as it can be assumed that they will be decrypted at some point. Documents that have already been signed and whose encryption algorithm expires can retain their evidential value by re-signing them. Otherwise, this can be challenged at a later date. Certificates usually expire after two to three years, but after five years at the latest. After this period, the trust center blocks the private key. In this case, a digital signature cannot be created again until a new private key is issued.
How a digital signature works
Anyone who wants to create a digital signature has the signature software assign a hash value to the message, which is then secured by a key. Once the recipient has received the message, he or she can decrypt it using the public key. The signature software recalculates the hash value already determined at the beginning. Only if this check value matches the first hash value then the sender and the content are authenticated by the digital signature.
Saving time with the digital signature
The digital signature saves both consumers and the state time and effort when it comes to submitting applications or forms that require an original signature. These can also be processed digitally at the relevant office instead of having to process paper applications. This results in further time savings.
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