CDA is Certified Digital Art, it is a ZIP containing a work of art in high resolution digital format accompanied by a certificate attesting to the authorship of the work, the ownership of the buyer and is endorsed by the signature of a gallery that appears on the certificate as the minter of the CDA.
In practice, it is a contract of assignment of rights of use, dissemination and commercialization of the work in favor of the new owner.
You can see more details at FAQ.

The idea was born from the need to create a system that defines and organizes the uniqueness of the artworks in digital format, both of the artist's authorship and ownership by the buyer, recognizing the particular identity of the digital work, different from the physical work.
The CDA as an Art format and the recognition of the digital work as an artistic work are manifested in the terms of the agreement contained in the CDA.
CDAs are unique works of art, with special qualities and new possibilities inherent to digital archives, such as the reproduction in any medium, format and support of the digital artistic work contained in the CDA.
It is a path that in a way humanises digital art, since the agreements required for the CDA certificate involve the collaboration of several people, artistic agents or institutions. Each party represents a commitment because, although its format is digital and its realisation requires technological means, the CDA defines and regulates its use, distribution and commercialisation.