The qualified electronic signature is the type of signature that enjoys the highest legal guarantees and therefore, is the most appropriate for the signing of any contract, document or transaction that requires such guarantees. It can only be done with qualified digital certificates issued by a duly accredited Trust Service Provider. For this reason, the qualified electronic signature is considered by law the equivalent of the handwritten signature. It has full legal value and guarantees the enforceability of a document against third parties. The advanced electronic signature can be made with different technologies, such as biometric signatures or digital certificates. In particular, the use of qualified digital certificates is the safest mechanism for this type of signature, since it directly guarantees the integrity of the signed document in the process. The simple electronic signature is done with the data in electronic format attached to other electronic data or logically associated with them that the signer uses to sign. However, there is no evidence of who the signer has actually been.