## 3 Proposed Model  
The study of the state of the art of blockchain in education, the requirements of the academic organizations in the framework of the GDPR, and previous initiatives, their limitations, and drawbacks, discussed in the previous section, shed some light on the desired properties of novel solutions addressing the challenges identified. Motivated by the findings obtained in the process described above, a novel conceptual design of a system is proposed to issue, store, and verify different types of academic information, both for formal and informal learning, that can be applied to different usage scenarios. We can find in the literature [22; 23; 24; 25; 26; 27], several relevant use cases in the following:  
* Certificate issuance and management of academic information. This application is further discussed below to illustrate the solution proposed. For this use case, an academic institution issues a certificate, transcript, or diploma and records information on the blockchain so it can be verified for authenticity or recovered, even by authorized third parties;
* Registration of learning paths. In this use case, student's achievements are registered by the educational institutions on the blockchain for both formal and informal studies so they can also be verified. Academic data managed in this case extend the certificates and diplomas mentioned in the previous point. * Tracking of competence values. Diplomas and certificates are not the only alternatives to provide evidence about the competences acquired by a student since their grades can be converted into competence values that can be issued by the academic institution to be verified by authorized third parties. * Recording of academic credits. Another application of this solution is to record learners' credits achieved for successfully completed courses. This type of academic information would be generated by the educational organization according to the proposed model. * An indirect use case of the proposed model in this section, as it will be discussed later, corresponds to the enrichment of the academic information managed in the previous use cases with additional public nonsensitive personal data, such as the type of academic information, degree, or category of a certificate. This could be used to anonymously generate statistics, learning analytics data, or trends relevant to the education domain. It is important to remark that the proposed model also protects and keeps data private, complying with the GDPR even in the case that the educational institution disappears. The proposal is scalable and efficiently implementable using currently available technologies, which, in turn, guarantees its potential application and sustainability. According to these characteristics, the solution discussed below is intended to serve as a conceptual framework for the development of final systems addressing the issues identified. To protect personal academic information in this proposal, the provisions in Art. 6 Section 1 of the GDPR and related articles are considered whenever there are no other applicable regulations or laws. Therefore, the designed solution should allow data subjects to control the access to their information, share only a part of it according to their interests, be notified when data are processed, and reclaim and carry away their personal records (Article 20 of the GDPR). It should also support allowing and removing permissions to a specific party (Art. 7 Section 3 of the GDPR). The right to erasure (i.e., the \"right to be forgotten\" in Article 17 of the GDPR) will also be technically considered in the proposed system. In general, the designed solution that will be described in the following sections complies with the Privacy by Design principle (Art. 25 of the GDPR) and would allow educational institutions to tamperproof store heterogeneous types of academic information that can be verified by third parties if holders grant them the necessary authorization.