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What is a digital siganture?

Illustrative image for digital sigantures

A digital signature is a mathematical scheme for verifying the authenticity of digital messages or documents. A valid digital signature, where the prerequisites are satisfied, gives a recipient very strong reason to believe that the message was created by a known sender (authentication), and that the message was not altered in transit (integrity).

Digital signatures are a standard element of most cryptographic protocol suites, and are commonly used for software distribution, financial transactions, contract management software, and in other cases where it is important to detect forgery or tampering.

How do digital signatures work?

A digital signature scheme typically consists of three algorithms:

  • A key generation algorithm that selects a private key uniformly at random from a set of possible private keys. The algorithm outputs the private key and a corresponding public key.
  • A signing algorithm that, given a message and a private key, produces a signature.
  • A signature verifying algorithm that, given the message, public key and signature, either accepts or rejects the message's claim to authenticity.

In the two videos below it is explained its functioning:

How to sign a document digitally

In order to sign digitally a document, it is necessary to have an electronic ID, which contain the crytographic passwords necessary to sign and to idetnify the signer. They can be obtained arranging an appointment in an official office in which Ids are made or renewed. For example this one in Murcia:

The process of signing a document can be done in two different ways depending on which application the user decides to sign:

  • Downloading an application to sign documents directly on your computer so that tere is no need of internet conexion to sign a document. In Spain, the official application tu use is AutoFirma
  • Signing directly on the Internet. This options is used when you need to sign a form or an application. You only need to download a plug-in offered by VALIDe, which works on the same browser, to sign documents on the Internet.

To know more about these applications click here.

As examples, in these videos in Spanish it can be seen how to sign a document digitally with both programs, witch Adobe Acrobat and how to intall your certificate in a computer:

Futher information